Modulation of the gut microbiota by dietary interventions to prevent cardiometabolic diseases

Modulation of the gut microbiota by dietary interventions to prevent cardiometabolic diseases

OVERVIEW

  • In a study of 307 participants, the Mediterranean-style diet was associated with a composition of the gut microbiota conducive to good cardiometabolic health.
  • In another study, intermittent fasting altered the gut microbiota and prevented the development of hypertension in rats that spontaneously became hypertensive as they aged.
  • The metabolism of bile acids modulated by the microbiota has been identified as a regulator of blood pressure.
  • Dietary interventions aimed at modifying the gut microbiota could be a viable non-pharmacological approach to prevent and treat high blood pressure and other conditions.

Cardiometabolic diseases including type 2 diabetes and cardiovascular disease are on the rise in Canada and around the world. These diseases, which reduce the quality of life and life expectancy of those affected and generate significant costs for society, can be prevented by maintaining good lifestyle habits, including a healthy diet and regular exercise.

Recent studies have linked microbial metabolism and immune interactions in the gut and the risk of cardiometabolic disease (see our articles on the subject herehere and here). Two new studies show that the type of diet and the frequency of meals have effects on the risk of metabolic disease, which are in part due to alterations in the gut microbiota. The results of these new studies suggest that modulation of the gut microbiota by dietary interventions could be a new preventive and therapeutic approach.

US researchers analyzed the microbiome data of 307 male participants in the Health Professionals Follow-up Study as well as their eating habits and biomarkers of blood glucose regulation, lipid metabolism and inflammation. The Mediterranean-style diet (consisting mainly of vegetables, legumes, fruits, nuts, olive oil, and some wine and red meat) was associated with a composition of the gut microbiota conducive to good cardiometabolic health. The positive association between the Mediterranean-style diet and a lower risk of cardiometabolic disease was particularly strong among participants whose microbiota contained little Prevotella copri bacteria. Researchers do not yet understand why the Mediterranean diet is less effective in people whose microbiota contains the bacterium Prevotella copri, however, they make several hypotheses that will need to be verified in future studies. In any case, it can be envisaged that prevention approaches may one day be personalized according to the intestinal microbial profile of each person.

Benefits of intermittent fasting for hypertension
Intermittent fasting involves compressing the time during which one eats over a short period (6-8 h) and “fasting” the rest of the day (16-18 h). Intermittent fasting has positive effects on weight and body fat loss, chronic inflammation, metabolism, and cardiovascular health (see our articles on the subject here and here). The main metabolic benefits of intermittent fasting are reduced blood LDL cholesterol levels, increased insulin sensitivity and better blood glucose control in diabetics, reduced oxidative stress and inflammation. On the one hand, we know that an imbalance in the intestinal microbiota (intestinal dysbiosis) contributes to the development of hypertension. On the other hand, studies in recent years have shown that fasting and caloric restriction significantly reduce blood pressure, both in animal models and in hypertensive patients.

A recent study shows that the beneficial effects of intermittent fasting on blood pressure are attributable, at least in part, to the modulation of the gut microbiota. The researchers used an animal model commonly used in hypertension research: spontaneously hypertensive stroke-prone (SHRSP) rats, a unique genetic model of severe hypertension and stroke. Hypertensive SHRSP rats and normotensive Wistar-Kyoto (WKY) rats were subjected for 8 weeks to one or the other of the following diets: 1) ad libitum throughout the study (control groups) or 2) a diet alternating a day with food at will and a day without access to food (intermittent fasting). Hypertensive (SHRSP) and normotensive (WKY) rats in the control groups ingested the same amount of food. In contrast, the rats subjected to intermittent fasting ate more on days with food at will than those in the control groups, presumably to compensate for the fasting day. Despite this, the total amount of food ingested during the study was significantly lower in hypertensive (-27%) and normotensive (-35%) rats subjected to intermittent fasting, compared to animals in the respective control groups that had access to food at will. Despite a similar food intake, the hypertensive rats in the control group gained significantly less weight than the normotensive rats.

As expected, the blood pressure of hypertensive rats measured weekly was significantly higher than that of normotensive rats. In contrast, intermittent fasting significantly reduced blood pressure in hypertensive rats by an average of about 40 mmHg by the end of the study, compared to hypertensive rats who had access to food at will. This significant decrease brought the blood pressure of hypertensive rats to levels comparable to those of normotensive rats.

Role of the gut microbiota in the regulation of blood pressure
Animal models allow experiments on the role of the gut microbiota that could not be done in humans. In order to find out whether the gut microbiota plays a role in the effect of intermittent fasting, the researchers continued their studies by “transplanting” the microbiota from hypertensive and normotensive rats into “germ-free” rats, i.e. rats reproduced under special conditions in such a way that they do not contain any microorganisms.

Germ-free rats that received microbiota from hypertensive rats had significantly higher blood pressure than those that received microbiota from normotensive rats when subjected to the control diet (ad libitum). In contrast, intermittent fasting reduced the blood pressure of germ-free rats that received microbiota from hypertensive rats to levels comparable to those of rats that received microbiota from normotensive rats. These results demonstrate that the alterations in the microbiota of hypertensive rats caused by intermittent fasting are sufficient to cause a reduction in blood pressure. Analysis of the microbiota by whole-genome shotgun sequencing has enabled researchers to identify bile acid metabolism as a potential mediator of blood pressure regulation. Subsequent analyses revealed that the blood levels of 11 bile acids (out of 18) in hypertensive SHRSP rats were significantly lower than those in normotensive rats. In support of the hypothesis, the addition of cholic acid (a precursor of bile acids) in the food or the activation of the bile acid receptor (TGR5) significantly reduced the blood pressure (by 18 mmHg) of hypertensive rats.

In summary, the quality of food and frequency with which we eat has a significant impact on the microorganisms in our microbiota, cardiometabolic risk factors and, ultimately, our overall health. By changing the diet and the frequency of meals, it may be possible to significantly improve the condition of people with chronic diseases.

The benefits of extra virgin olive oil on cardiovascular health

The benefits of extra virgin olive oil on cardiovascular health

OVERVIEW

  • In addition to being an excellent source of monounsaturated fat, olive oil is the only vegetable oil that contains a significant amount of phenolic compounds with antioxidant and anti-inflammatory properties.
  • These molecules are found in much larger quantities in extra virgin quality oils compared to refined olive oils.
  • Several studies indicate that the presence of these phenolic compounds contributes to the many positive effects of extra virgin olive oil on cardiovascular health.

The traditional Mediterranean diet has several positive effects on cardiovascular health by improving the lipid profile (cholesterol, triglycerides) and by reducing chronic inflammation, blood pressure, blood sugar and the risk of diabetes. Several studies have clearly established that these effects result in a significant reduction in the risk of cardiovascular disease.

The Mediterranean diet is characterized by the abundant consumption of plant-based foods (fruits, vegetables, whole-grain cereals, legumes, nuts, herbs), a moderate intake of fermented dairy products (yogurt, cheese), fish, seafood and red wine as well as a low consumption of red meat and added sugars. It is therefore an exemplary diet, in which complex plant sugars are the main sources of carbohydrates and where the proteins come mainly from fish and legumes instead of red meat.

Another important feature of the Mediterranean diet is the daily use of large amounts (60–80 mL) of olive oil as the main source of fat for cooking. Several studies have reported that countries that are heavy consumers of olive oil have a much lower incidence of cardiovascular disease than those that consume mainly animal fats, suggesting a positive role of olive oil in this protective effect. Traditionally, these beneficial properties of olive oil have been attributed to its very high content (around 80%) of oleic acid, a monounsaturated fatty acid that contributes to its antioxidant properties. However, and unlike most vegetable oils, olive oil also contains a host of minor compounds (1–3% of the oil) that also play very important roles in its positive effects on cardiovascular health (see below). This is particularly the case for several phenolic compounds found exclusively in olive oil, including phenolic alcohols such as hydroxytyrosol and tyrosol and polyphenols of the secoiridoid family such as oleuropein, ligstroside, oleacein and oleocanthal (Figure 1).

 

Figure 1. Molecular structures of the main phenolic compounds of olive oil.


One fruit, several types of oils
Most vegetable oils come from seeds that have been extracted with an organic solvent (e.g. hexane) and subsequently heated to a high temperature to evaporate this solvent and remove impurities that give them an undesirable smell and flavour. These drastic procedures are not necessary for olive oil as the olives are simply pressed and the oil in the pulp is extracted by mechanical pressure, without using chemical processes or excessive heat.

Olive oils are classified according to the quality of the oil that is obtained by the pressing procedure (Figure 2). Good quality oils, i.e. those with low acidity (<2% free oleic acid) and that meet certain taste, bitterness and spiciness criteria are called “virgin” olive oils or, if their acidity is less than 0.8%, “extra virgin” olive oils. These oils contain the majority of the polyphenols in the starting olives and, after centrifugation and filtration, can be consumed as is.

On the other hand, some olive varieties give an inferior quality oil due to too high acidity (> 2%) and/or an unpleasant smell and taste that does not meet the established criteria. These oils, which are unfit for consumption, are called “lampantes” (a name which comes from their ancient use as fuel in oil lamps) and must be refined as is done for other vegetable oils, i.e. using different physicochemical procedures (neutralization with soda, high temperature bleaching and deodorization, hexane extraction, etc.). These steps remove the compounds responsible for the excess acidity and the unpleasant taste of the oil and produce a “neutral” olive oil that has lost its acidity and its flaws, but that is now devoid of the smell, flavour, colour and most of the phenolic components of the starting virgin olive oil. To stabilize these oils and improve their taste, a certain proportion (15–20%) of virgin olive oil is subsequently added and the final product, which is a mixture of refined olive oil and virgin olive oil, is what is sold in grocery stores as “pure olive oil” or simply “olive oil”.

In short, there are three main types of olive oil on the market: virgin olive oil (VOO), extra virgin olive oil (EVOO), and regular olive oil (OO).

Figure 2. The different types of olive oil. From Gorzynik-Debicka et al. (2018).

 

These manufacturing differences obviously have a huge impact on the amount of polyphenols present in virgin, extra virgin, and refined oils (Table 1). For OO-type olive oils (which contain refined oils), the polyphenols come exclusively from virgin olive oil that has been added to restore a minimum of taste and colour (from yellow to greenish) to the chemically treated oil. The amount of these polyphenols is therefore necessarily less than in VOO and EVOO and, as a general rule, does not exceed 25–30% of the content of these two oils. This difference is particularly striking for certain polyphenols of the secoiridoid family (oleuropein, oleocanthal, oleacein and ligstroside) whose concentrations are 3 to 6 times greater in EVOO than in OO (Table 1). It should be noted, however, that these values ​​can vary greatly depending on the origin and cultivar of the olives; for example, some extra virgin olive oils have been found to contain up to 10 times more hydroxytyrosol and tyrosol than regular olive oils. The same goes for other polyphenols like oleocanthal: an analysis of 175 distinct extra virgin olive oils from Greece and California revealed dramatic variations between the different oils, with concentrations of the molecule ranging from 0 to 355 mg/kg.

It should also be mentioned that even if the quantities of phenolic compounds in regular olive oil are lower than those found in virgin and extra virgin oils, they nevertheless largely exceed those present in other vegetable oils (sunflower, peanut, canola, soy), which contain very little or none at all.

FamilyMoleculesOO (mg/kg)VOO (mg/kg)EVOO (mg/kg)
Secoiridoidsoleocanthal38.95 ± 9.2971.47 ± 61.85142.77 ± 73.17
oleacein57.37 ± 27.0477.83 ± 256.09251.60 ± 263.24
oleuropein (aglycone)10.90 ± 0.0095.00 ± 116.0172.20 ± 64.00
ligstroside (aglycone)15.20 ± 0.0069.00 ± 69.0038.04 ± 17.23
Phenolic alcoholshydroxytyrosol6.77 ± 8.263.53 ± 10.197.72 ± 8.81
tyrosol4.11 ± 2.245.34 ± 6.9811.32 ± 8.53
Flavonoidsluteolin1.17 ± 0.721.29 ± 1.933.60 ± 2.32
apigenin0.30 ± 0.170.97 ± 0.7111.68 ± 12.78
Phenolic acidsp-coumaric -0.24 ± 0.810.92 ± 1.03
ferulic -0.19 ± 0.500.19 ± 0.19
cinnamic - -0.17 ± 0.14
caffeic -0.21 ± 0.630.19 ± 0.45
protocatechuic -1.47 ± 0.56 -
Table 1. Comparison of the content of phenolic compounds in olive oil (OO), virgin olive oil (VOO) and extra virgin olive oil (EVOO). Please note that the large standard deviations of the mean values reflect the huge variations in polyphenol content depending on the region, cultivar, degree of fruit ripeness, and olive oil manufacturing process. Adapted from Lopes de Souza et al. (2017).

 

Anti-inflammatory spiciness
The amounts of polyphenols contained in a bottle of olive oil are not indicated on its label, but it is possible to detect their presence simply by tasting the oil. The polyphenols in olive oil are indeed essential to the organoleptic sensations so characteristic of this oil, in particular the sensation of tickling or stinging in the throat caused by good quality extra virgin oils, what connoisseurs call “ardour”. Far from being a defect, this ardour is considered by experts as a sign of a superior quality oil and, in tasting competitions, the “spiciest” oils are often those that receive the highest honours.

It is interesting to note that it is by tasting different olive oils that a scientist succeeded, by coincidence, in identifying the molecule responsible for the sensation of spiciness caused by extra virgin olive oil (see box).

Plant ibuprofen

Chance often plays a role in scientific discoveries, and this is especially true when it comes to the discovery of the molecule responsible for the typical irritation caused by olive oil. On a trip to Sicily (Italy) to attend a conference on the organoleptic properties of different foods, Dr. Gary Beauchamp and his colleagues were invited by the organizers of the event to a meal where guests were encouraged to taste extra virgin olive oil from olive trees cultivated on their estate. Even though it was the first time he had tasted this type of olive oil, Dr. Beauchamp was immediately struck by the tingling sensation in his throat, which was similar in every way to that caused by ibuprofen, and that he had experienced multiple times as part of his work to replace acetaminophen (paracetamol) with ibuprofen in cough syrups. Suspecting that olive oil contained a similar anti-inflammatory drug, Dr. Beauchamp and his team subsequently managed to isolate the molecule responsible for this irritation, a polyphenol they called “oleocanthal”. They subsequently discovered that oleocanthal had, like ibuprofen, a powerful anti-inflammatory action and that regular consumption of extra virgin olive oil, rich in oleocanthal, provided an intake equivalent to about 10 mg of ibuprofen and therefore may contribute to the well-documented anti-inflammatory effects of the Mediterranean diet. 

But why is the stinging sensation of olive oil only felt in the throat? According to work carried out by the same group, this exclusive localization is due to a specific interaction of oleocanthal (and ibuprofen, for that matter) with a subtype of heat-sensitive receptor (TRPA1). Unlike other types of heat receptors, which are evenly distributed throughout the oral cavity (the TRPV1 receptor activated by the capsaicin of chili peppers, for example, and which causes the burning sensation of some particularly hot dishes), the TRPA1 receptor is located only in the pharynx and its activation by oleocanthal causes a nerve impulse signalling the presence of an irritant only in this region. In short, the more an olive oil stings in the back of the throat, the more oleocanthal it contains and the more anti-inflammatory properties it has. As a general rule, extra virgin olive oils contain more oleocanthal (and polyphenols in general) than virgin olive oils (see Table 1) and are therefore considered superior, both in terms of taste and their positive effects on health.

The superiority of extra virgin olive oil
Several studies have shown that the higher polyphenol content in extra virgin olive oil is correlated with a greater positive effect on several parameters of cardiovascular health than that observed for regular olive oil (see Table 2). For example, epidemiological studies carried out in Spain have reported a decrease of about 10–14% in the risk of cardiovascular disease among regular consumers of extra virgin olive oil, while regular consumption of olive oil had no significant effect. A role of phenolic compounds is also suggested by the EUROLIVE study where the effect of daily ingestion, over a period of 3 weeks, of 25 mL of olive oils containing small (2.7 mg/kg), medium (164 mg/kg), or high (366 mg/kg) amounts of polyphenols was compared. The results show that an increased intake of polyphenols is associated with an improvement in two important risk factors for cardiovascular disease: an increase in the concentration of HDL cholesterol and a decrease in oxidized LDL cholesterol levels. Collectively, the data gathered from the intervention studies indicate that the polyphenols found in extra virgin olive oil play an extremely important role in olive oil’s positive effects on cardiovascular health.

Measured parameterResultsSources
Incidence of cardiovascular disease10% reduction in risk for every 10 g/day of EVOO. No effect of regular OO.Guasch-Ferré et al. (2014)
14% reduction in risk for each 10 g/day of EVOO. No effect of regular OO.Buckland et al. (2012)
Lipid profileLinear increase in HDL cholesterol as a function of the amount of polyphenols.Covas et al. (2006)
Increase in HDL cholesterol only observed with EVOO.Estruch et al. (2006)
Blood glucoseEVOO improves postprandial glycemic profile (decrease in glucose levels and increased insulin).Violo et al. (2015)
Polyphenol-rich EVOO reduces fasting blood glucose and glycated hemoglobin (HbA1c) levels in diabetic patients.Santagelo et al. (2016)
InflammationEVOO, but not OO, induces a decrease in inflammatory markers (TXB(2) and LTB(4)).Bogani et al. (2017)
EVOO, but not OO, induces a decrease in IL-6 and CRP.Fitó et al. (2007)
EVOO, but not OO, decreases the expression of several inflammatory genes.Camargo et al. (2010)
EVOO, but not OO, decreases levels of inflammatory markers sICAM-1 and sVCAM-1.Pacheco et al. (2007)
Oxidative stressStrong in vitro antioxidant activity of phenolic compounds of olive oil.Owen et al. (2000)
Linear decrease in oxidized LDL levels as a function of the amount of polyphenols.Covas et al. (2006)
Lower levels of oxidized LDL after ingestion of EVOO compared to OO.Ramirez-Tortosa et al. (1999)
EVOO phenolic compounds bind to LDL particles and protect them from oxidation.de la Torre-Carbot et al. (2010)
EVOO induces the production of neutralizing antibodies against oxidized LDL.Castañer et al. (2011)
EVOO decreases urinary levels of 8-isoprostane, a marker of oxidative stress.Visioli et al. (2000)
EVOO positively influences the oxidative/antioxidant status of blood plasma.Weinbrenner et al. (2004)
Blood pressureEVOO causes a decrease in systolic and diastolic pressures in hypertensive women.Ruíz-Gutiérrez et al. (1996)
EVOO, but not OO, causes a decrease in systolic pressure in hypertensive coronary patients.Fitó et al. (2005)
EVOO improves postprandial endothelial dilation.Ruano et al. (2005)
EVOO increases the NO vasodilator and decreases systolic and diastolic pressures.Medina-Remón et al. (2015)
EVOO, but not OO, improves vessel dilation in pre-diabetic patients.Njike et al. (2021)
EVOO, but not OO, decreases systolic pressure by 2.5 mmHg in healthy volunteers.Sarapis et al. (2020)
Table 2. Examples of studies comparing the effect of EVOO and OO on several cardiovascular health parameters.

 

In addition to its multiple direct actions on the heart and vessels, it should also be noted that extra virgin olive oil could also exert an indirect beneficial effect, by blocking the formation of the metabolite trimethylamine N-oxide (TMAO) by intestinal bacteria. Several studies have shown that TMAO accelerates the development of atherosclerosis in animal models and is associated with an increased risk of cardiovascular events in clinical studies. Extra virgin olive oils (but not regular olive oils) contain 3,3-dimethyl-1-butanol (DMB), a molecule that blocks a key enzyme involved in TMAO production and prevents development of atherosclerosis in animal models fed a diet rich in animal protein. Taken together, these observations show that there are only advantages to favouring the use of extra virgin olive oil, both for its superior taste and its positive effects on cardiovascular health.

Some people may dislike the slightly peppery taste that extra virgin olive oil leaves in the back of the throat, but interestingly, this irritation is greatly reduced when the oil is mixed with other foods. According to a recent study, this attenuation of the pungent taste is due to the interaction of the polyphenols in the oil with the proteins in food, which blocks the activation of the heat receptors that are normally activated by these polyphenols. People who hesitate to use extra virgin olive oil because of its irritant side can therefore get around this problem and still enjoy the benefits of these oils simply by using it as the main fat when preparing a meal.

Why do the Japanese have the highest life expectancy in the world?

Why do the Japanese have the highest life expectancy in the world?

OVERVIEW

  • The Japanese have the highest life expectancy at birth among the G7 countries.
  • The higher life expectancy of the Japanese is mainly due to fewer deaths from ischemic heart disease, including myocardial infarction, and cancer (especially breast and prostate).
  • This exceptional longevity is explained by a low rate of obesity and a unique diet, characterized by a low consumption of red meat and a high consumption of fish and plant foods such as soybeans and tea.

Several diets are conducive to the maintenance of good health and to the prevention of cardiovascular disease, for example, the Mediterranean diet, the DASH diet (Dietary Approaches to Stop Hypertension), the vegetarian diet, and the Japanese diet. We often refer to the Mediterranean Diet in these pages, because it is well established scientifically that this diet is particularly beneficial for cardiovascular health. Knowing that the Japanese have the highest life expectancy among the G7 countries, the special diet in Japan has also captured the attention of experts and an informed public in recent years.

Japanese life expectancy
Among the G7 countries, Japan has the highest life expectancy at birth according to 2016 OECD data, particularly for women. Japanese men have a slightly higher life expectancy (81.1 years) than that of Canadian men (80.9 years), while the life expectancy of Japanese women (87.1 years) is significantly higher (2.4 years) than that of Canadian women (84.7 years). The healthy life expectancy of the Japanese, 74.8 years, is also higher than in Canada (73.2 years).

The higher life expectancy of Japanese people is mainly due to fewer deaths from ischemic heart disease and cancers, particularly breast and prostate cancer. This low mortality is mainly attributable to a low rate of obesity, low consumption of red meat, and high consumption of fish and plant foods such as soybeans and tea. In Japan, the obesity rate is low (4.8% for men and 3.7% for women). By comparison, in Canada 24.6% of adult men and 26.2% of adult women were obese (BMI ≥ 30) in 2016. Obesity is an important risk factor for both ischemic heart disease and several types of cancers.

Yet in the early 1960s, Japanese life expectancy was the lowest of any G7 country, mainly due to high mortality from cerebrovascular disease and stomach cancer. The decrease in salt and salty food intake is partly responsible for the decrease in mortality from cerebrovascular disease and stomach cancer. The Japanese consumed an average of 14.5 g of salt/day in 1973 and probably more before that. They eat less salt these days (9.5 g/day in 2017), but it’s still too much. Canadians now consume on average about 7 g of salt/day (2.76 g of sodium/day), almost double the intake recommended by Health Canada.

The Japanese diet
Compared to Canadians, the French, Italians and Americans, the Japanese consume much less meat (especially beef), dairy products, sugar and sweeteners, fruits and potatoes, but much more fish and seafood, rice, soybeans and tea (Table 1). In 2017, the Japanese consumed an average of 2,697 kilocalories per day according to the FAO, significantly less than in Canada (3492 kcal per day), France (3558 kcal per day), Italy (3522 kcal per day), and the United States (3766 kcal per day).

Table 1. Food supply quantity (kg/capita/year) in selected countries in 2013a.

              aAdapted from Tsugane, 2020. FAO data: FAOSTAT (Food and agriculture data) (http://www.fao.org/).

Less red meat, more fish and seafood
The Japanese eat on average almost half as much meat as Canadians (46% less), but twice as much fish and seafood. This considerable difference translates into a reduced dietary intake of saturated fatty acids, which is associated with a lower risk of ischemic heart disease, but an increased risk of stroke. On the contrary, dietary intake of omega-3 fatty acids found in fish and seafood is associated with a reduced risk of ischemic heart disease. The lower consumption of red meat and higher consumption of fish and seafood by the Japanese could therefore explain the lower mortality from ischemic heart disease and the higher mortality from cerebrovascular disease in Japan. Experts believe that the decline in death from cerebrovascular disease is associated with changes in the Japanese diet, specifically increased consumption of animal products and dairy products, and consequently of saturated fat and calcium (a consumption which remains moderate), combined with a decrease in salt consumption. Indeed, contrary to what is observed in the West, the consumption of saturated fat in Japan is associated with a reduction in the risk of hemorrhagic stroke and to a lesser extent of ischemic stroke, according to a meta-analysis of prospective studies. The cause of this difference is not known, but it could be attributable to genetic susceptibility or confounding factors according to the authors of the meta-analysis.

Soybeans
Soy is a food mainly consumed in Asia, including Japan where it is consumed as is after cooking (edamame) and especially in processed form, by fermentation (soy sauce, miso paste, nattō) or by coagulation of soy milk (tofu). It is an important source of isoflavones, molecules that have anticancer properties and are beneficial for good cardiovascular health. Consumption of isoflavones by Asians has been linked to a lower risk of breast and prostate cancer (see our article on the subject).

Sugar
The Japanese consume relatively few sugars and starches, which partly explains the low prevalence of obesity-associated diseases such as ischemic heart disease and breast cancer.

Green tea
The Japanese generally consume green tea with no added sugar. Prospective studies from Japan show that green tea consumption is associated with a lower risk of all-cause mortality and cardiac death.

Westernization of Japanese eating habits
The westernization of the Japanese diet after World War II allowed the inhabitants of this country to be healthier and to reduce mortality caused by infectious diseases, pneumonia and cerebrovascular diseases, thereby considerably increasing their life expectancy. A survey of the eating habits of 88,527 Japanese from 2003 to 2015 indicates that this westernization continues. Based on the daily consumption of 31 food groups, the researchers identified three main types of eating habits:

1- Plant foods and fish
High intakes of vegetables, fruits, legumes, potatoes, mushrooms, seaweed, pickled vegetables, rice, fish, sugar, salt-based seasonings and tea.

2- Bread and dairy
High intakes of bread, dairy products, fruits and sugar. Low intake of rice.

3- Animal foods and oils
High intakes of red and processed meat, eggs, vegetable oils.

A downward trend in the “plant foods and fish” group (the staple of the traditional Japanese diet or washoku) was observed in all age groups. An increase in the “bread and dairy” group was observed in the 50–64 and ≥65 years age groups, but not among the youngest. For the “animal foods and oils” group, an increasing trend was observed during the thirteen years of the study in all age groups except the youngest (20–34 years). The Japanese are eating more and more like Westerners. Will this have an adverse effect on their health and life expectancy? It is too early to know, only the next few decades will tell.

Contribution of genes and lifestyle to the health of the Japanese
Some risk factors for cardiovascular disease and cancer are hereditary, while others are associated with lifestyle (diet, smoking, exercise, etc.). At the turn of the 20th century, there was significant Japanese immigration to the United States (especially California and Hawaii) and South America (Brazil, Peru). After a few generations, the descendants of Japanese migrants adopted the way of life of the host countries. While Japan has one of the lowest incidences of cardiovascular disease in the world, this incidence doubled among the Japanese who migrated to Hawaii and quadrupled among those who chose to live in California according to a 1975 study. What is surprising is that this increase has been observed regardless of blood pressure or cholesterol levels, and seems rather directly related to the abandonment of the traditional Japanese way of life by migrants.

Since the 1970s, the average cholesterol level of the Japanese has nonetheless increased, but despite this and the high rate of smoking in this country, the incidence of coronary heart disease remains substantially lower in Japan than in the West. To better understand these differences, a 2003 study compared the risk factors and diets of Japanese living in Japan with third- and fourth-generation Japanese migrants living in Hawaii in the United States. Men’s blood pressure was significantly higher among Japanese than among Japanese-Americans, while there was no significant difference for women. Far fewer Japanese were treated for hypertension than in Hawaii. More Japanese people (especially men) smoked than Japanese-Americans. Body mass index, blood levels of LDL cholesterol, total cholesterol, glycated hemoglobin (an indicator for diabetes), and fibrinogen (a marker of inflammation) were significantly lower in Japan than in Hawaii. HDL cholesterol (the “good” cholesterol) was higher in the Japanese than in the Japanese-Americans. The dietary intake of total fat and saturated fatty acids (harmful to cardiovascular health) was lower in Japan than in Hawaii. In contrast, the intake of polyunsaturated fatty acids and omega-3 fatty acids (beneficial for good cardiovascular health) was higher in Japan than in Hawaii. These differences may partly explain the lower incidence of coronary heart disease in Japan than in Western industrialized countries.

In other words, even if these migrants have the same basic risk as their compatriots who have remained in the country of origin (age, sex and heredity), the simple fact of adopting the lifestyle of their host country is enough to significantly increase their risk of cardiovascular disease.

Although the Japanese diet is different from those of Western countries, it has similar characteristics to the Mediterranean diet. Why not prepare delicious Japanese soy dishes from time to time (for example, tofu, edamame, miso soup), drink green tea, eat less meat, sugar and starch and more fish? Not only will your meals be more varied, but you could enjoy the health benefits of the Japanese diet.

Reducing calorie intake by eating more plants

Reducing calorie intake by eating more plants

OVERVIEW

  • Twenty volunteers were fed a low-fat or low-carbohydrate diet in turn for two weeks.
  • Participants on the low-fat diet consumed an average of nearly 700 fewer calories per day than with the low-carbohydrate diet, a decrease correlated with a greater loss of body fat.
  • Compared to the low-carbohydrate diet, the low-fat diet also led to lower cholesterol levels, reduced chronic inflammation, and lowered heart rate and blood pressure.
  • Overall, these results suggest that a diet mainly composed of plants and low in fat is optimal for cardiovascular health, both for its superiority in reducing calorie intake and for its positive impact on several risk factors for cardiovascular disease.

It is estimated that there are currently around 2 billion overweight people in the world, including 600 million who are obese. These statistics are truly alarming because it is clearly established that excess fat promotes the development of several diseases that decrease healthy life expectancy, including cardiovascular disease, type 2 diabetes, and several types of cancer. Identifying the factors responsible for this high prevalence of overweight and the possible ways to reverse this trend as quickly as possible is therefore essential to improve the health of the population and avoid unsustainable pressures on public health systems in the near future.

Energy imbalance
The root cause of overweight, and obesity in particular, is a calorie intake that exceeds the body’s energy needs. To lose weight, therefore, it is essentially a matter of restoring the balance between the calories ingested and the calories expended.

It might seem simple in theory, but in practice most people find it extremely difficult to lose weight. On the one hand, it is much easier to gain weight than to lose weight. During evolution, we have had to deal with periods of prolonged food shortages (and even starvation, in some cases) and our metabolism has adapted to these deficiencies by becoming extremely efficient at accumulating and conserving energy in the form of fat. On the other hand, the environment in which we currently live strongly encourages overconsumption of food. We are literally overwhelmed by an endless variety of attractive food products, which are often inexpensive, easily accessible, and promoted by very aggressive marketing that encourages their consumption. The current epidemic of overweight and obesity thus reflects our biological predisposition to accumulate reserves in the form of fat, a predisposition that is exacerbated by the obesogenic environment that surrounds us.

Eating less to restore balance
The body’s innate tendency to keep energy stored in reserve as fat makes it extremely difficult to lose weight by “burning” those excess calories by increasing the level of physical activity. For example, a person who eats a simple piece of sugar pie (400 calories) will have to walk about 6.5 km to completely burn off those calories, which, of course, is difficult to do on a daily basis. This does not mean that exercise is completely useless for weight loss. Research in recent years shows that exercise can specifically target certain fat stores, especially in the abdominal area. Studies also show that regular physical activity is very important for long-term maintenance of the weight lost from a low-calorie diet. However, there is no doubt that it is first and foremost the calories consumed that are the determining factors in weight gain. Moreover, contrary to what one might think, levels of physical activity have hardly changed for the last thirty years in industrialized countries, and the phenomenal increase in the number of overweight people is therefore mainly a consequence of overconsumption of food. Exercise is essential for the prevention of all chronic diseases and for the maintenance of general good health, but its role in weight loss is relatively minor. For overweight people, the only realistic way to lose weight significantly, and especially to maintain these losses over prolonged periods, is thus to reduce calorie intake.

Less sugar or less fat?
How do we get there? First, it’s important to realize that the surge in the number of overweight people has coincided with a greater availability of foods high in sugar or fat (and sometimes both). All countries in the world, without exception, that have adopted this type of diet have seen their overweight rates skyrocket, so it is likely that this change in eating habits plays a major role in the current obesity epidemic.

However, the respective contributions of sugar and fat to this increase in caloric intake and overweight are still the subjectof vigorous debate:

1) On the one hand, it has been proposed that foods high in fat are particularly obesogenic, since fats are twice as high in calories as carbohydrates, are less effective in causing a feeling of satiety, and improve the organoleptic properties of foods, which generally encourages (often unconscious) overconsumption of food. Therefore, the best way to avoid overeating and becoming overweight would be to reduce the total fat intake (especially saturated fat due to its negative impact on LDL-cholesterol levels) and replace it with complex carbohydrates (vegetables, legumes, whole-grain cereals). This is colloquially called the low-fat approach, advocated for example by the Ornish diet.

2) On the other hand, the exact opposite is proposed, i.e. that it would be mainly carbohydrates that would contribute to overconsumption of food and to the increase in the incidence of obesity. According to this model, carbohydrates in foods in the form of free sugars or refined flours cause insulin levels to rise markedly, causing massive energy storage in adipose tissue. As a result, fewer calories remain available in the circulation for use by the rest of the body, causing increased appetite and overeating to compensate for this lack. In other words, it wouldn’t be because we eat too much that we get fat, but rather because we are too fat we eat too much.

3) By preventing excessive fluctuations in insulin levels, a diet low in carbohydrates would thus limit the anabolic effect of this hormone and, therefore, prevent overeating and the accumulation of excess fat.

Less fat on the menu, fewer calories ingested
To compare the impact of low-carb and low-fat diets on calorie intake, Dr. Kevin Hall’s group (NIH) recruited 20 volunteers who were fed each of these diets in turn for two weeks. The strength of this type of cross-study is that each participant consumes both types of diets and that their effects can therefore be compared directly on the same person.

As shown in Figure 1, the two diets studied were completely opposite of each other, with 75% of the calories in the low-fat (LF) diet coming from carbohydrates versus only 10% from fat, while in the low-carb (LC) diet, 75% of calories were in the form of fat, compared to only 10% from carbohydrates. The LF diet under study consisted exclusively of foods of plant origin (fruits, vegetables, legumes, root vegetables, soy products, whole grains, etc.), while the LC diet contained mainly (82%) animal foods (meat, poultry, fish, eggs, dairy products).

Figure 1. Comparison of the amounts of carbohydrates, fats and proteins present in the low-carbohydrate (LC) and low-fat (LF) diets consumed by study participants. Adapted from Hall et al. (2021).

The study shows that there is indeed a big difference between the two types of diets in the number of calories consumed by participants (Figure 2). Over a two-week period, participants who ate an LF (low-fat) diet consumed an average of nearly 700 calories (kcal) per day less than an LC (low-carbohydrate) diet. This difference in calorie intake is observed for all meals, both at breakfast (240 calories less for the LF diet), at lunch (143 calories less), at dinner (195 calories less), and during snacks taken between meals (128 calories less). This decrease is not caused by a difference in the appreciation of the two diets by the participants, as parallel analyses did not find any difference in the level of appetite of the participants, nor in the degree of satiety and satisfaction generated by the consumption of either diet. However, the LF diet was composed exclusively of plant-based foods and therefore much richer in non-digestible fibres (60 g per day compared to only 20 g for the LC diet), which greatly reduce the energy density of meals (quantity of calories per g of food) compared to the high-fat LC diet. It is therefore very likely that this difference in energy density contributes to the lower calorie intake observed for the low-fat diet.

Overall, these results indicate that a diet consisting of plants, and thus low in fat and high in complex carbohydrates, is more effective than a diet consisting mainly of animal products, high in fat and low in carbohydrates, to limit calorie intake.

Figure 2. Comparison of the daily calorie intake of participants on a low-carbohydrate (LC) or low-fat (LF) diet. From Hall et al. (2021).

Weight loss
Despite the significant difference in calorie intake observed between the two diets, their respective impact on short-term weight loss is more nuanced. At first glance, the LC diet appeared to be more effective than the LF diet in causing rapid weight loss, with about 1 kg lost on average in the first week and almost 2 kg after two weeks, compared to only 1 kg after two weeks of the LF diet (Figure 3). However, further analysis revealed that the weight loss caused by the LC diet was mainly in the form of lean mass (protein, water, glycogen), while this diet had no significant impact on fat loss during this period. Conversely, the LF diet had no effect on this lean body mass, but did cause a significant decrease in body fat, to around 1 kg after two weeks. In other words, only the LF diet caused a loss of body fat during the study period, which strongly suggests that the decrease in calorie intake made possible by this type of diet may facilitate the maintenance of astable body weight and could even promote weight loss in overweight people.

Figure 3. Comparison of changes in body weight (top), lean mass (middle), and body fat (bottom) caused by low-carbohydrate and low-fat diets. From Hall et al. (2021).

Cardiovascular risk factors
In addition to promoting lower calorie intake and fat loss, the LF diet also appears to be superior to the LC diet in terms of its impact on several cardiovascular risk factors (Table 1):

Cholesterol. It is well established that LDL cholesterol levels increase in response to a high intake of saturated fat (see our article on the issue). It is therefore not surprising that the LF diet, which contains only 2% of all calories as saturated fat, causes a significant decrease in cholesterol, both in terms of total cholesterol and LDL cholesterol. At first glance, the high-fat LC diet (containing 30% of the daily calorie intake as saturated fat) does not appear to have a major effect on LDL cholesterol; however, it should be noted that this diet significantly modifies the distribution of LDL cholesterol particles, in particular with a significant increase in small and dense LDL particles. Several studies have reported that these small, dense LDL particles infiltrate artery walls more easily and also appear to oxidize more easily, two key events in the development and progression of atherosclerosis. In sum, just two weeks of a high-fat LC diet was enough to significantly (and negatively) alter the atherogenic profile of participants, which may raise doubts about the long-term effects of this type of diet on cardiovascular health.

Table 1. Variations in certain risk factors for cardiovascular disease following a diet low in carbohydrates or low in fat. From Hall et al. (2021).

Branched-chain amino acids. Several recent studies have shown a very clear association between blood levels of branched-chain amino acids (leucine, isoleucine and valine) and an increased risk of metabolic syndrome and type 2 diabetes, two very important risk factors for cardiovascular diseases. In this sense, it is very interesting to note that the levels of these amino acids are almost twice as high after two weeks of the LC diet compared to the LF diet, suggesting a positive effect of a diet rich in plants and poor in fats in the prevention of these disorders.

Inflammation. Chronic inflammation is actively involved in the formation and progression of plaques that form on the lining of the arteries and can lead to the development of cardiovascular events such as myocardial infarction and stroke. Clinically, this level of inflammation is often determined by measuring levels of high-sensitivity C-reactive protein (hsCRP), a protein made by the liver and released into the blood in response to inflammatory conditions. As shown in Table 1, the LF diet significantly decreases the levels of this inflammatory marker, another positive effect that argues in favour of a plant-rich diet for the prevention of cardiovascular disease.

In addition to these laboratory data, the researchers noted that participants who were fed the LF diet had a slower heart rate (73 vs. 77 beats/min) as well as lower blood pressure (112/67 vs. 116/69 mm Hg) than observed following the LC diet. In the latter case, this difference could be related, at least in part, to the much higher sodium consumption in the LC diet compared to the LF diet (5938 vs. 3725 mg/day).

All of these results confirm the superiority of a diet mainly composed of plants on all the factors involved in cardiovascular health, whether in terms of lipid profile, chronic inflammation, or adequate control of calorie intake necessary to maintain body weight.

Control of inflammation through diet

Control of inflammation through diet

OVERVIEW

  • Chronic inflammation is actively involved in the formation and progression of plaques that form on the lining of the arteries, which can lead to the development of cardiovascular events such as myocardial infarction and stroke.
  • Two studies show that people whose diet is anti-inflammatory due to a high intake of plants (vegetables, fruits, whole grains), beverages rich in antioxidants (tea, coffee, red wine) or nuts have a significantly lower risk of being affected by cardiovascular disease.
  • This type of anti-inflammatory diet can be easily replicated by adopting the Mediterranean diet, rich in fruits, vegetables, legumes, nuts and whole grains and which has repeatedly been associated with a lower risk of cardiovascular events.

Clinically, the risk of having a coronary event is usually estimated based on age, family history, smoking and physical inactivity as well as a series of measures such as cholesterol levels, blood sugar level and blood pressure. The combination of these factors helps to establish a cardiovascular disease risk “score”, i.e. the likelihood that the patient will develop heart disease over the next ten years. When this score is moderate (10 to 20%) or high (20% and more), one or more specific drugs are generally prescribed in addition to recommending lifestyle changes in order to reduce the risk of cardiovascular events.

These estimates are useful, but they do not take into account other factors known to play an important role in the development of cardiovascular disease. This is especially true for chronic inflammation, a process that actively participates in the formation and progression of plaques that form on the lining of the arteries and can lead to cardiovascular events such as myocardial infarction and stroke.

The clinical significance of this chronic inflammation is well illustrated by studies of patients who have had a heart attack and are treated with a statin to lower their LDL cholesterol levels. Studies show that a high proportion (about 40%) of these people have excessively high blood levels of inflammatory proteins, and it is likely that this residual inflammatory risk contributes to the high rate of cardiovascular mortality (nearly 30%) that affects these patients within two years of starting treatment, despite a significant reduction in LDL cholesterol. In this sense, it is interesting to note that the canakinumab antibody, which neutralizes an inflammatory protein (interleukin-1 β), causes a slight but significant decrease in major cardiovascular events in coronary patients. Statins, used to lower LDL cholesterol levels, are also believed to have an anti-inflammatory effect (reduction in C-reactive protein levels) that would contribute to reducing the risk of cardiovascular events. One of the roles of inflammation is also demonstrated by the work of Dr. Jean-Claude Tardif of the Montreal Heart Institute, which shows that the anti-inflammatory drug colchicine significantly reduces the risk of recurrence of cardiovascular events.

Reducing chronic inflammation is therefore a very promising approach for decreasing the risk of cardiovascular disease, both in people who have already had a heart attack and are at a very high risk of recurrence and in healthy people who are at high risk of cardiovascular disease.

Anti-inflammatory diet
Two studies published in the Journal of the American College of Cardiology suggest that the nature of the diet can greatly influence the degree of chronic inflammation and, in turn, the risk of cardiovascular disease. In the first of these two articles, researchers analyzed the link between diet-induced inflammation and the risk of cardiovascular disease in 166,000 women and 44,000 men followed for 24 to 30 years. The inflammatory potential of the participants’ diet was estimated using an index based on the known effect of various foods on the blood levels of 3 inflammatory markers (interleukin-6, TNFα-R2, and C-reactive protein or CRP). For example, consumption of red meat, deli meats and ultra-processed industrial products is associated with an increase in these markers, while that of vegetables, fruits, whole grains and beverages rich in antioxidants (tea, coffee, red wine) is on the contrary associated with a decrease in their blood levels. People who regularly eat pro-inflammatory foods therefore have a higher inflammatory food index, while those whose diet is rich in anti-inflammatory foods have a lower index.

Using this approach, the researchers observed that a higher dietary inflammatory index was associated with an increased risk of cardiovascular disease, with a 40% increase in risk in those with the highest index (Figure 1). This increased risk associated with inflammation is particularly pronounced for coronary heart disease (acute coronary syndromes including myocardial infarction) with an increased risk of 46%, but seems less pronounced for cerebrovascular accidents (stroke) (28% increase in risk). The study shows that a higher dietary inflammation index was also associated with two risk markers for cardiovascular disease, higher circulating triglyceride levels as well as lower HDL cholesterol. These results therefore indicate that there is a link between the degree of chronic inflammation generated by diet and the risk of long-term cardiovascular disease, in agreement with data from a recent meta-analysis of 14 epidemiological studies that have explored this association.

Figure 1. Change in the risk of cardiovascular disease depending on the inflammatory potential of the diet. From Li et al. (2020). The dotted lines indicate the 95% confidence interval.

Anti-inflammatory nuts
A second study by a group of Spanish researchers investigated the anti-inflammatory potential of walnuts. Several epidemiological studies have reported that regular consumption of nuts is associated with a marked decrease in the risk of cardiovascular disease. For example, a recent meta-analysis of 19 prospective studies shows that people who consume the most nuts (28 g per day) have a lower risk of developing coronary artery disease (18%) or of dying from these diseases (23%). These reductions in the risk of cardiovascular disease may be explained in part by the decrease in LDL cholesterol (4%) and triglyceride (5%) levels observed following the consumption of nuts in intervention studies. However, this decrease remains relatively modest and cannot alone explain the marked reduction in the risk of cardiovascular disease observed in the studies.

The results of the Spanish study strongly suggest that a reduction in inflammation could greatly contribute to the preventative effect of nuts. In this study, 708 people aged 63 to 79 were divided into two groups, a control group whose diet was completely nut free and an intervention group, in which participants consumed about 15% of their calories daily in the form of walnuts (30–60 g/day). After a period of 2 years, the researchers observed large variations in the blood levels of several inflammatory markers between the two groups (Figure 2), in particular for GM-CSF (a cytokine that promotes the production of inflammatory cells) and interleukin-1 β (a highly inflammatory cytokine whose blood levels are correlated with an increased risk of death during a heart attack). This reduction in IL-1 β levels is particularly interesting because, as mentioned earlier, a randomized clinical study (CANTOS) has shown that an antibody neutralizing this cytokine leads to a reduction in the risk of myocardial infarction in coronary heart patients.

Figure 2. Reduction in blood levels of several inflammatory markers by a diet enriched with nuts. From Cofán et al. (2020). GM-CSF: granulocyte-monocyte colony stimulating factor; hs-CRP: high-sensitivity C-reactive protein; IFN: interferon; IL: interleukin; SAA: serum amyloid A; sE-sel: soluble E-selectin; sVCAM: soluble vascular cell adhesion molecule; TNF: tumour necrosis factor.

Taken together, these studies therefore confirm that an anti-inflammatory diet provides concrete benefits in terms of preventing cardiovascular disease. This preventative potential remains largely unexploited, as Canadians consume about half of all their calories in the form of ultra-processed pro-inflammatory foods, while less than a third of the population eats the recommended minimum of five daily servings of fruits and vegetables and less than 5% of the recommended three servings of whole grains. This imbalance causes most people’s diets to be pro-inflammatory, contributes to the development of cardiovascular diseases as well as other chronic diseases, including certain common cancers such as colon cancer, and reduces the life expectancy.

The easiest way to restore this balance and reduce inflammation is to eat a diet rich in plants while reducing the intake of industrial products. The Mediterranean diet, for example, is an exemplary anti-inflammatory diet due to its abundance of fruits, vegetables, legumes, nuts and whole grains, and its positive impact will be all the greater if regular consumption of these foods reduces that of pro-inflammatory foods such as red meat, deli meats and ultra-processed products. Not to mention that this diet is also associated with a high intake of fibre, which allows the production of anti-inflammatory short-chain fatty acids by the intestinal microbiota, and of phytochemicals such as polyphenols, which have antioxidant and anti-inflammatory properties.

In summary, these recent studies demonstrate once again the important role of diet in preventing chronic disease and improving healthy life expectancy.

Do houseplants have beneficial effects on health?

Do houseplants have beneficial effects on health?

OVERVIEW

Having and caring for houseplants can:

  • Reduce psychological and physiological stress.
  • Improve recovery after surgery.
  • Increase attention and concentration.
  • Increase creativity and productivity.

In our modern societies, where everything seems to go faster and faster, many feel the harmful effects of stress and anxiety; however, this appears to have increased since the start of the COVID-19 pandemic. During spring and summer 2020, many Quebecers took advantage of the beautiful weather to recharge their batteries in nature, either by visiting a park, camping, walking in the forest, or renting a cottage in the countryside. As winter approaches, contact with greenery becomes scarce and travel to regions with warmer climates is risky and strongly discouraged by Public Health. Apart from hiking in our beautiful coniferous forests, one of the only possible contacts with greenery during this long winter will be the green plants we take care of in our homes. Houseplants decorate and bring a natural touch to our homes, but do they have proven beneficial effects on our physical and mental health.

Stress reduction
A systematic review in 2019 identified some 50 studies on the psychological benefits of houseplants, most of these studies being of average quality. The most noticeable positive effects of houseplants on participants are an increase in positive emotions and a decrease in negative emotions, followed by a reduction in physical discomfort.

In a randomized, controlled crossover study of young adults, participants saw their mood improve more after transplanting an indoor plant than after performing a task on the computer. In addition, participants’ diastolic blood pressure and sympathetic nervous system activity (physiological response to stress) were significantly lower after transplanting a plant than after performing a computer task. These results indicate that interaction with houseplants can reduce psychological and physiological stress compared to mental tasks.

Plants in the office
In 2020, a Japanese team carried out a study on the effects of plants in the workplace on the level of psychological and physiological stress of workers. In the first phase of the study (1 week), workers worked at their desks without a plant, while in the intervention phase (4 weeks), participants could see and care for an indoor plant that they were able to choose from six different types (bonsai, Tillandsia, echeveria, cactus, leafy plant, kokedama). Participants were instructed to take a three-minute break when feeling tired and to take their pulse before and after the break. During these 3-minute breaks, workers had to look at their desks (with or without an indoor plant). Researchers measured psychological stress with the State-Trait Anxiety Inventory (STAI). The participants’ involvement was therefore both passive (looking at the plant) and active (watering and maintaining the plant).

The psychological stress assessed by STAI was significantly, albeit moderately, lower during the intervention in the presence of an indoor plant than during the period without the plant. The heart rate of the majority of patients (89%) was not significantly different before and after the procedure, while it decreased in 4.8% of participants and increased in 6.3% of patients. It must be concluded that the intervention had no effect on heart rate, which is an indicator of physiological stress, although it slightly reduced psychological stress.

A study of 444 employees in India and the United States indicates that office environments that include natural elements such as indoor plants and exposure to natural light positively influence job satisfaction and engagement. These natural elements seem to act as “buffers” against the effects of stress and anxiety generated by work.

Recovery after surgery
It appears that houseplants help patients recover after surgery, according to a study in a hospital in Korea. Eighty women recovering from thyroidectomy were randomly assigned to a room without plants or to a room with indoor plants (foliage and flowering). Data collected for each patient included length of hospital stay, use of analgesics to control pain, vital signs, intensity of perceived pain, anxiety and fatigue, STAI index (psychological stress), and other questionnaires. Patients who were hospitalized in rooms with indoor plants and flowers had shorter hospital stays, took fewer painkillers, experienced less pain, anxiety, and fatigue, and they had more positive emotions and greater satisfaction with their room than patients who recovered from their operation in a room without plants. The same researchers performed a similar study in patients recovering after an appendectomy. Again, patients who had plants and flowers in their rooms recovered better from their surgery than those who did not have plants in their rooms.

Improved attention and concentration
Twenty-three elementary school students (ages 11–13) participated in a study where they were put in a room with either an artificial plant, a real plant, a photograph of a plant, or no plant at all. The participants wore a wireless electroencephalography device during the three minutes of exposure to the different stimuli. Children who were put in the presence of a real plant were more attentive and better able to concentrate than those in the other groups. In addition, the presence of a real plant was associated with a better mood in general.

Productivity
A cross-sectional study of 385 office workers in Norway found a significant, albeit very modest, association between the number of plants in their office and the number of sick days and productivity. Workers who had more plants in their office took slightly fewer sick days and were a bit more productive on the job. In another study, American students were asked to perform computer tasks, with or without houseplants, in windowless rooms. In the presence of plants, participants were more productive (12% faster in performing tasks) and less stressed since their blood pressure was lower than in the absence of houseplants.

What about air quality?
Do plants purify the air in our homes? This is an interesting question since we spend a lot of time in increasingly airtight homes, and materials and our activity (e.g. cooking) emit pollutants such as volatile organic compounds (VOCs), oxidizing compounds (e.g. ozone), and fine particles. A NASA study showed that plants and associated microorganisms in the soil could reduce the level of pollutants in a small, sealed experimental chamber. Are these favourable results obtained in a laboratory also observable in our homes, schools and offices? Some studies (this one for example) conclude that plants decrease the concentrations of CO2, VOCs and fine particles (PM10). However, these results have been called into question by researchers (see this study) who question the methodology used in previous studies and who believe that plants are ineffective in improving the indoor air quality of our buildings. According to these researchers, it would be better to focus research efforts on other air-cleaning technologies as well as on the beneficial effects of plants on human health.

Conclusion
Indoor plants can provide health benefits by reducing psychological and physiological stress. Owning and maintaining plants can improve mood and increase attention and concentration. New, more powerful and better controlled studies will be needed to better identify and understand the effects of plants on human health.