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.

Insufficient dietary fibre intake harms the gut microbiota and the immune system’s balance

Insufficient dietary fibre intake harms the gut microbiota and the immune system’s balance

OVERVIEW

  • The typical diet in Western countries does not contain enough fibre.
  • This insufficient fibre intake adversely affects the bacteria in the gut microbiota and therefore the immunity and health of the host.
  • An abundant and varied consumption of dietary fibre helps maintain a diverse and healthy microbiota, which produces metabolites that contribute to human physiology and health.

Dietary fibre is made up of complex sugars that cannot be digested by human digestive enzymes, but is an important source of energy for gut bacteria, which have the ability to break it down. This fibre comes mainly from plants, but is also found in animal tissues (meat, offal), fungi (mushrooms, yeasts, moulds), and foodborne microorganisms. The main fibres are cellulose, lignins, pectin, inulin, starches and dextrins resistant to amylases, chitins, beta-glucans and other oligosaccharides. However, not all dietary fibre can be used by the intestinal microbiota (cellulose for example), so researchers are more particularly interested in “microbiota-accessible carbohydrates” or MAC, which are found in legumes, wheat and oats, for example.

Resurgence of allergies and inflammatory and autoimmune diseases
Non-communicable diseases, such as allergies and inflammatory and autoimmune diseases have been on the rise in Western countries over the past century. Although we do not know all the causes of these increases, it is quite plausible that they have an environmental component. The transition from the traditional diet to the Western diet that occurred after the Industrial Revolution is often called into question. The typical Western diet consists primarily of processed foods high in sugar and fat, but low in minerals, vitamins, and fibre. The recommended daily intake of dietary fibre is at least 30 grams (1 ounce), while followers of the Western diet consume only 15 grams on average. In addition, people living in traditional societies consume up to 50–120 g/day of fibre and have a much more diverse gut microbiota than Westerners. A diverse microbiota is associated with good health in general, while a poorly diversified microbiota has been associated with chronic diseases common in Western countries, such as type 2 diabetes, obesity, inflammatory bowel disease (ulcerative colitis, Crohn’s disease), colorectal cancer, rheumatoid arthritis and asthma.

Metabolites of the gut microbiota
The gut microbiota contributes to human physiology by producing a multitude of metabolites. The most studied are short-chain fatty acids (SCFAs), which are organic compounds such as acetate, propionate and butyrate that together constitute ≥95% of SCFAs. These metabolites are absorbed and find their way into the bloodstream via the portal vein and act on the liver and then, via the peripheral blood circulation, on other organs of the human body. SCFAs play key roles in the regulation of human metabolism, the immune system, and cell proliferation. SCFAs are metabolites produced by microorganisms in the intestinal microbiota from dietary fibres, which are complex sugars. The microbiota produces other metabolites from amino acids derived from dietary protein, including indole and its derivatives, tryptamine, serotonin, histamine, dopamine, p-cresol, phenylacetylglutamine, and phenylacetylglycine.

A lack of dietary fibre leads to the generation of toxic metabolites by the microbiota
Insufficient fibre intake not only leads to reduced microbiota diversity and a reduction in the amount of SCFAs produced, but also causes a shift in the metabolism of microorganisms towards the use of substrates less favourable for human health. Among these alternative substrates, amino acids from food proteins are fermented by the microbiota into branched-chain fatty acids, ammonia, amines, N-nitroso compounds, phenolic compounds such as p-cresol, sulphides, and indole compounds. These metabolites are either cytotoxic and/or pro-inflammatory and they contribute to the development of chronic diseases, particularly colorectal cancer.

Effects on mucus production that protects the intestinal lining
The main substrates used by the microbiota when fibre intake is low are mucins, glycoproteins contained in the mucus that cover and protect the epithelium of the intestinal lining. Maintaining this layer of mucus is very important to prevent infections; however, a diet low in fibre alters the composition of the gut microbiota and leads to a significant deterioration of the mucus layer, which can increase the susceptibility to infections and chronic inflammatory diseases (see figure, below). Transcriptomic analyses have revealed that when there is a lack of MAC-type fibres, the enzymes that break down the mucus are expressed in greater quantities in the microorganisms of the microbiota. The consequences of the deterioration and thinning of the mucus layer are a dysfunction of the intestinal barrier, i.e. increased permeability, which increases susceptibility to infection by pathogenic bacteria. A diet rich in fibre has the opposite effect: the microbiota is diverse and the abundant production of SCFA metabolites stimulates the production and secretion of mucus by specialized epithelial cells, known as goblet cells.

Figure. Effect of a high- or low-fibre diet on the composition and diversity of the gut microbiota and the impact on human physiology. MAC: microbiota-accessible carbohydrates. From Makki et al., 2018.

Immune system
A healthy gut microbiota contributes to the maturation and development of the immune system (see this review article). For example, short-chain fatty acids (SCFAs) produced by the microbiota stimulate the production of regulatory T-cells. SCFAs have many effects on the function and hematopoiesis of dendritic cells as well as on neutrophils, which are the first leukocytes to be mobilized by the immune system in the presence of a pathogen.

Inflammation and colon cancer
The incidence of inflammatory bowel disease has increased dramatically in the West over the past few decades. A diet low in fibre has been correlated with an increased incidence of Crohn’s disease. On the contrary, a sufficient intake of dietary fibre seems to protect against the development of ulcerative colitis, an effect which has been associated with a decrease in SCFAs produced by the microbiota, butyrate in particular, which has anti-inflammatory properties. Inflammatory bowel disease can lead to the development of colon cancer. Additionally, reduced dietary fibre intake has been linked to an increased incidence of colorectal cancer.

Dietary fibre plays a much more complex role than was believed a short time ago, when it was thought that it had a purely mechanical role in intestinal transit, by an increase in the volume of the alimentary bolus and by its emollient properties. Adequate dietary fibre intake helps maintain a diverse and healthy gut microbiota, which can prevent the development of allergies as well as inflammatory and autoimmune diseases. The gut microbiota is the subject of intense research efforts, as evidenced by the numerous scientific articles published each month, and it certainly has not revealed all of its secrets!

Time-restricted feeding: A tool to lose weight and improve cardiometabolic health

Time-restricted feeding: A tool to lose weight and improve cardiometabolic health

OVERVIEW

  • The two most popular forms of time-restricted feeding (intermittent fasting), limiting eating to 4 hours or 6 hours a day, were tested in obese people.
  • Both diets produced the same body weight loss (–3.2%) at the end of the two-month study.
  • Both diets reduced caloric intake by ∼550 kcal/day, without participants having to control the number of calories consumed.
  • Similar reductions in insulin resistance and oxidative stress were observed for both types of diet.

Intermittent fasting has grown in popularity in recent years, as several clinical studies have shown that it can help lose weight and prevent metabolic disease (see also our article: “Intermittent fasting: A new approach to weight loss?”).

There are three different types of diets that are part of intermittent fasting:

  • Alternate-day fasting where you alternate between a day of “fasting” when you consume very few calories (0–800 calories) followed by a day where you eat normally.
  • The 5:2 diet is a modified version of alternate-day fasting that includes two days of fasting per week (<600 calories), followed by five days of normal eating.
  • Time-restricted feeding recommends limiting the period during which food is consumed. The two most popular forms of this diet are the Warrior Diet, where you limit eating to a period of 4 hours a day, and the 18:6 diet, where you fast for 18 hours and eat over a period of 6 hours.

In a randomized controlled study recently published in Cell Metabolism, nutrition researchers wanted to answer the following question: does restricting feeding to a 6-hour window (18:6 diet) produce the same effects on body weight and metabolic risk factors as a 4-hour restriction (Warrior Diet or 20:4 diet)? The researchers hypothesized that compared to a diet limited to a 6-hour period, a diet limited to 4 hours would lead to greater weight loss, a greater drop in blood pressure, better blood glucose control, and more pronounced effects on oxidative stress.

The 58 obese participants (BMI: 30–50 kg/m2) in the 8-week study were divided into three groups:

  • A control group who could eat normally and without time restrictions.
  • A group that had to eat between 3 p.m. and 7 p.m., a restriction over a 4-hour
  • A group that had to eat between 1 p.m. and 7 p.m., a restriction over a 6-hour

There were no restrictions on the amount or type of food consumed and participants were not required to control their calorie intake. During the fasting period, participants were encouraged to drink plenty of water and were allowed to consume calorie-free drinks such as black tea, coffee (without sugar or milk), or diet soda.

After 8 weeks, the two groups that limited their diet to 4-hour and 6-hour periods both lost 3.2% ± 0.4% body weight, while the control group did not significantly lose weight (0.1% ± 0.4%). The 4-hour limited diet therefore did not lead to more weight loss than over a 6-hour period, contrary to the initial hypothesis.

Fasting blood glucose levels were not significantly different between the three groups, eight weeks after the start of the study. In contrast, fasting insulinemia, insulin resistance, and oxidative stress were reduced in both intervention groups, compared to the control group, with no significant difference between the two intervention groups (4 hours vs. 6 hours).

Several parameters, including blood pressure, LDL cholesterol, HDL cholesterol and triglyceride levels were not altered by the time-restricted diet, both for the 4-hour and the 6-hour limitation. These latest results are at odds with previous studies where significant reductions in these parameters were observed. The authors cannot explain these differences, but they suggest that their study may not have had enough participants to be able to observe significant effects on these secondary endpoints of the study.

Summary of key findings from previous studies on intermittent fasting
The effects of alternate-day fasting and the 5:2 diet (2 days of fasting and 5 days of normal eating) on the risk of metabolic disease have been the subject of more than a dozen studies in humans to date. Alternate-day fasting produces 5–7% body weight loss over a short period of time (less than six months). It also provides several metabolic benefits such as reduced blood pressure, LDL cholesterol, triglycerides, fasting insulinemia, insulin resistance, inflammation and oxidative stress. The effects of the 5:2 diet are similar to alternate-day fasting.

Time-restricted feeding has been the subject of fewer studies. There have been six clinical studies in humans to date, and only three of these studies have examined the effects of this diet on body weight loss. According to these few studies, the time-restricted diet produces a loss of body weight of around 2.6 to 3.6% and a reduction in calorie intake of 8 to 20% in 12 to 16 weeks. This type of intermittent fasting has significant effects on metabolic health: marked drop in fasting blood sugar, insulinemia, and insulin resistance. A drop in blood pressure has been observed in several studies, even without loss of body weight. The effects on blood lipid levels are less clear. A few studies of time-restricted feeding report lower triglycerides and LDL cholesterol, but most studies have found no effect on these same lipids.

Conclusion
Although the weight loss seen in this new study is moderate, the authors believe that time-restricted feeding is a promising intervention for those who wish to lose weight. Limiting feeding to a 6-hour period is easier to practice than a 4-hour restriction since someone can, for example, not eat breakfast and have the two meals of the day at relatively normal times (1 p.m. and 6:30 p.m., for example). This study indicates that the 18:6 diet will have as many health benefits as the Warrior Diet (20:4).

Plant-based meat substitutes reduce certain cardiovascular risk factors

Plant-based meat substitutes reduce certain cardiovascular risk factors

OVERVIEW

  • Participants in a study were divided into two groups, for eight weeks, one consumed two daily servings of plant-based meat substitutes (Beyond Meat products: burger, mock beef, sausage, mock chicken), while the other group ate the same amount of real meat (beef, pork, chicken).
  • Participants who ate plant-based meat substitutes lost some weight and had significantly lower blood levels of trimethylamine oxide (TMAO) and LDL cholesterol than those who consumed meat during the same period.
  • Plant-based meat substitutes appear to be beneficial for health compared to meat since high levels of TMAO and LDL cholesterol are two risk factors for cardiovascular disease.

In an article published in these pages in 2019, we discussed the merits and drawbacks of new food products that mimic the taste and texture of meat, such as Beyond Meat and Impossible Burger. These products are certainly more environmentally friendly than red meat (beef and pork in particular), which requires a lot of resources that tax the global environment. On the other hand, they are ultra-processed products that contain significant amounts of saturated fat and salt.

To determine whether plant-based meat substitutes could be healthier than meat, the Beyond Meat company funded Dr. Christopher D. Gardner, an independent and renowned researcher at Stanford University School of Medicine in California, to conduct a randomized controlled study. One must be extremely careful with studies funded by the food industry, since publishing only the results that will support the sale of their products is to their advantage. On the other hand, in the case of this study, all precautions seem to have been taken so that there is no influence on the results: study design (randomized and controlled with a crossover design), statistical analyses conducted by a third party who was not involved in the design of the study and data collection. Beyond Meat was not involved in the design of the study, the conduct of the study, or the analysis of the data. In addition, Dr. Gardner stated that he has already completed six food industry-sponsored studies with null findings from the original hypothesis.

The 36 study participants were randomly divided into two groups. During the first eight weeks, one group of participants were assigned to eat two servings/day of plant-based meat substitutes (Beyond Meat products: burger, mock beef, sausages, mock chicken), while the other group consumed two servings/day of meat (beef, pork, chicken). The two groups then switched their diet for the next eight weeks (crossover study design). Fasting levels of lipids, glucose, insulin, and trimethylamine oxide (TMAO) were measured before the start of the study and every two weeks during both phases of the study.

The main endpoint of the study was the blood level of TMAO, an emerging risk factor associated with atherosclerosis and other cardiovascular diseases. The group that consumed meat during the first eight weeks had a significantly higher TMAO mean level than the group that consumed plant-based meat substitutes (4.7 vs. 2.7 µM), as well as a higher LDL cholesterol (the “bad cholesterol”) mean level (121 vs. 110 mg/dL), while the mean HDL cholesterol (the “good cholesterol”) level was not significantly different.

A surprise awaited the researchers: Participants who first consumed plant-based products during the first eight weeks did not see their TMAO levels increase when they ate meat during the second part of the study. Researchers were unable to identify any changes in the microbiome (gut flora) that could have explained this difference. However, it appears that making the participants “vegetarian” for eight weeks caused them to lose the ability to produce TMAO from meat. This effect of a vegetarian diet on the microbiome has already been demonstrated by Dr. Stanley L. Hazen’s team at the Cleveland Clinic. After a few weeks of returning to a carnivorous diet, the microbiome begins to produce TMAO again from red meat and eggs.

TMAO is a metabolite produced by the gut microbiome from carnitine and choline, two compounds found in large quantities in red meat such as beef and pork. High concentrations of TMAO can promote atherosclerosis and thrombosis. Indeed, numerous observational studies and animal models have shown that there is an association between TMAO and cardiovascular risk, and that it is beneficial to reduce the levels of TMAO. It should be noted, however, that a causal link between TMAO and cardiovascular disease has not been established and that it is possible that it is a marker rather than a causal agent of these diseases.

In addition to the favourable effect on TMAO, participants who ate plant-based meat substitutes lost weight (1 kg on average) and had significantly lower LDL-cholesterol levels than those who ate meat (110 vs. 121 mg/dL). These differences were observed regardless of the order in which participants followed the two diets.

Beyond Meat probably hopes that these results will allow them to respond to criticisms about their products, which areultra-processed and contain a lot of salt and almost as much saturated fat as meat. Many people want to reduce their consumption of red meat, but do not like classic vegetarian dishes. It seems to us that if these meat substitutes appeal to consumers concerned about maintaining good health and allow them to reduce their meat consumption, this will be beneficial for them and may encourage them to cook veggie burgers and other plant-based meat substitutes themselves. Who knows, maybe these products will lead to significant changes in diet in the future. Considerably reducing our meat consumption can only be beneficial to our health and that of the planet.

 

The cardiovascular benefits of soy

The cardiovascular benefits of soy

OVERVIEW

  • Asians have a much lower incidence of cardiovascular disease than North Americans, a difference that has been attributed, at least in part, to their high consumption of soybeans.
  • This protection is due to soy’s high content of isoflavones, a class of polyphenols that have several positive effects on the cardiovascular system.
  • A recent study carried out among 210,700 Americans (168,474 women and 42,226 men) has just confirmed this reduction in the risk of coronary heart disease associated with the consumption of soybeans, illustrating how this legume is an attractive alternative to meat as a source of protein.

It has been known for several years that people in Asian countries have a much lower incidence of cardiovascular disease than in the West. The study of migrant populations has shown that this difference is not due to genetic factors. For example, an analysis carried out in the 1970s revealed that the Japanese who had emigrated to California had twice the incidence of coronary heart disease than that of their compatriots who remained in Japan. It should be mentioned that these Asia-America differences are also observed for several types of cancer, in particular breast cancer. Asian women (China, Japan, Korea) have one of the lowest incidences of breast cancer in the world, but this cancer can become up to 4 times more common as a result of their migration to America, and its incidence even becomes similar to that of third generation Americans. The rapid rise in cardiovascular disease or cancer following migration to the West therefore suggests that abandoning the traditional lifestyle of Asians for the one in vogue in North America greatly favours the development of these diseases.

One of the differences between the Asian and North American lifestyles that has long interested researchers is the huge gap in soy consumption. While an average of 20 to 30 g of soy protein is consumed daily in Japan and Korea, this consumption barely reaches 1 g per day in the United States (Figure 1). It is proposed that this difference could contribute to the higher incidence of cardiovascular disease in the West for two main reasons:

  • Like all members of the legume family (lentils, peas, etc.), soy is an excellent source of fibre, vitamins, minerals, and polyunsaturated fats, nutrients known to be beneficial to heart and vessel health;
  • Soybeans are an exceptional source of isoflavones, a class of polyphenols found almost exclusively in this legume. The main isoflavones in soybeans are genistein, daidzein and glycitein (Figure 2), these molecules being present in varying amounts depending on the degree of processing of soybeans.

Figure 1. Comparison of the amounts of soybeans consumed daily by people in different countries. From Pabich and Materska (2019).

 


Figure 2. Molecular structures of the main isoflavones.
Note that equol is not present in soy products, but is rather generated by the gut microbiome following their ingestion.

The highest concentrations of isoflavones are found in the starting beans (edamame) and foods derived from fermented beans (natto, tempeh, miso), while foods from the pressing of beans (tofu, soy milk) contain slightly less (Table 1). These foods are commonly consumed by Asians and allow them to obtain isoflavone intakes varying from 8 to 50 mg per day, depending on the region, quantities clearly greater than those of the inhabitants of Europe and America (less than 1 mg per day). It should be noted, however, that soy is gradually becoming more and more popular in the West as an alternative to meat and that isoflavone intake can reach levels similar to Asians (18–21 mg per day) in certain groups of health-conscious people.


Table 1. The isoflavone content of various foods.
Source: United States Department of Agriculture, Nutrient Data Laboratory.

FoodIsoflavone content
(mg/100 g)
Natto82.3
Tempeh
60.6
Soybeans (edamame)49.0
Miso41.5
Tofu22.1
Soy milk10.7

The importance of a high intake of isoflavones comes from the multiple biological properties of this class of molecules. In addition to their antioxidant and anti-inflammatory activities, common to many polyphenols, a unique feature of isoflavones is their structural resemblance to estrogens, the female sex hormones, and it is for this reason that these molecules are often referred to as phytoestrogens. This estrogenic action has so far been mainly studied in relation to the development of hormone-dependent breast cancers. Since the growth of these cancers is stimulated by estrogens, the presence of phytoestrogens creates a competition that attenuates the biological effects associated with these hormones, especially the excessive growth of breast tissue (this mode of action is comparable to that of tamoxifen, a drug prescribed for several years against breast cancer). It is also important to note that, contrary to a very widespread misconception, the consumption of soybeans should not be discouraged for women who have survived breast cancer. On the contrary, many studies conducted in recent years clearly show that regular soy consumption by these women is absolutely safe and is even associated with a significant decrease in the risk of recurrence and mortality from this disease. It should be mentioned that despite the similarity of isoflavones to estrogens, studies indicate that soy does not interfere with the effectiveness of tamoxifen or anastrozole, two drugs frequently used to treat hormone-dependent breast cancers. Consequently, for people who have been affected by breast cancer, there are only benefits to incorporating soy into their diet.

Several data suggest that the positive effect of isoflavones on health is not limited to their anticancer action, and that the combination of the antioxidant, anti-inflammatory and estrogenic activities of these molecules may also contribute to the cardiovascular benefits of soy (Table 2).


Table 2. Main properties of isoflavones involved in reducing the risk of cardiovascular disease associated with soy consumption.

Cardiovascular effectsProposed mechanisms
Vasodilation of blood vesselsIsoflavones interact with a subtype of estrogen receptor present in the coronary arteries (Erβ), leading to the production of nitrous oxide (NO), a gas that induces vasodilation of blood vessels.
Lower cholesterol levels
Accelerated elimination of LDL and VLDL in the liver.
Isoflavones reduce LDL-cholesterol oxidation in diabetic patients.
AntioxydantEquol, a metabolite of daidzein formed by the intestinal microbiome, has a strong antioxidant activity.
Anti-inflammatoryIsoflavones promote the establishment of an intestinal microbiome enriched with bacteria that produce anti-inflammatory molecules (Bifidobacterium spp., for example).

A cardioprotective effect associated with soy consumption is also suggested by the results of an epidemiological study recently published in Circulation. By examining the eating habits of 210,700 Americans (168,474 women and 42,226 men), the researchers found that people with the highest isoflavone intake (about 2 mg per day on average) had a risk of coronary heart disease decreased by 13% compared to those with minimal intake (0.15 mg per day on average). A protective effect is also observed for tofu, with an 18% reduction in the risk of coronary heart disease for people who consume it once or more per week compared to those who ate it very rarely (less than once per month). Regular consumption of soy milk (once or more per week) is also associated with a slight decrease in risk, but this decrease is not statistically significant.

These reductions may seem modest, but it should be noted that the amounts of soybeans consumed by participants in this study are relatively small, well below what is commonly measured in Japan. For example, in a Japanese study that reported a 45% decrease in the risk of myocardial infarction in women who consumed the most soy, the isoflavone intake of these people was on average around 40 mg/day, i.e. 20 times more than in the American study (2 mg/day). It is therefore likely that the reductions in the risk of coronary heart disease observed in the United States represent a minimum and could probably be greater as a result of higher soy intake.

An interesting aspect of the decreased risk of coronary heart disease associated with tofu is that it is observed as much in younger women before menopause as in postmenopausal women, but only if they are not using hormone therapy (Figure 3). According to the authors, it is possible that after menopause, the estrogenic action of isoflavones compensates for the drop in estrogen levels and may mimic the cardioprotective effect of these hormones. In the presence of synthetic hormones, on the other hand, isoflavones are “masked” by excess hormones and therefore cannot exert their beneficial effects. For younger women, it is likely that the higher expression of the estrogen receptor before menopause promotes a greater interaction with isoflavones and allows these molecules to positively influence the function of blood vessels.

Figure 3. Association between risk of coronary heart disease and tofu consumption by hormonal status.
From Ma et al. (2020).

Taken together, these observations suggest that soy products have a positive effect on cardiovascular health and therefore represent an excellent alternative to meat as a source of protein. A recent study reports that these cardiovascular benefits can be even more pronounced following the consumption of fermented soy products such as natto, which is very rich in isoflavones, but given its texture (sticky, gooey), its strong smell (reminiscent of a well-made cheese), and its low availability in grocery stores, this food is foreign to our food culture and unlikely to be adopted by the North American population. Tofu is probably the most accessible soy-derived food given its neutral taste that allows it to be used in a wide variety of dishes, Asian-style or not. Soy milk is a less attractive alternative, not only because its consumption is not associated with a significant decrease in the risk of coronary heart disease, but also because these products often contain significant amounts of sugar.