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.

The effects of berries on cardiovascular health

The effects of berries on cardiovascular health

Berries are becoming increasingly popular in our diet, whether consumed fresh, frozen, dried or canned, and in related products such as jams, jellies, yogurts, juices and wines. Berries provide significant health benefits because of their high content of phenolic compounds, antioxidants, vitamins, minerals and fibres. Recognizing these health benefits has recently led to a 21% increase in world berry production.

The generic term “berries” is sometimes used to refer to small fruits, but from a botanical point of view, if some berries are genuineberries (blueberries, bilberries, cranberries, currants, lingonberries, elderberries), others are polydrupes (raspberries, blackberries), and the strawberry is a “false fruit” since the achenes (the small seeds on the outer surface of the strawberry) are the actual fruits of the strawberry. Berry fruits are rich in phenolic compounds such as phenolic acids, stilbenes, flavonoids, lignans and tannins (see the classification and structure of these compounds in Figure 1). Berries are particularly rich in anthocyanidins, pigments that give the skin and flesh of these fruits their distinctive red, blue or purple colour (Table 1).


Figure 1. Classification and chemical structure of phenolic compounds contained in berries. Adapted from Parades-López et al., 2010 and Nile & Park, 2014.

Like most flavonoids, anthocyanidins are found in nature as glycosides (compounds made of a sugar and another molecule) called anthocyanins. These anthocyanins can be absorbed in their whole form (linked to different sugars) both in the stomach and in the intestine. Anthocyanins that reach the large intestine can be metabolized by the microbiota (intestinal flora). The maximum concentration of anthocyanins in the bloodstream is reached from 30 minutes to 2 hours after eating berries. However, the maximum plasma concentration (1–100 nmol/L) of anthocyanins is much lower than what is measured in intestinal tissues, indicating that these compounds are metabolized extensively before entering the systemic circulation as metabolites. After administering a radiolabelled anthocyanin to humans, 35 metabolites were identified, 17 in blood, 31 in urine and 28 in feces. Thus, it is likely that these metabolites, rather than the intact molecule, are responsible for the health benefits associated with anthocyanins.

Table 1. Content of phenolic compounds, flavonoids, and anthocyanins of different berries.  Adapted from Parades-López et al., 2010 and Nile & Park, 2014

Berries (genus and species)Phenolic compoundsFlavonoidsAnthocyanins
(mg/100 g fresh fruit)(mg/100 g fresh fruit)(mg/100 g fresh fruit)
Raspberry (Rubus ideaous)121699
Blackberry (Rubus fruticosus)48627682–326
Strawberry (Fragaria x. ananassa)31354
Blueberry (Vaccinium corymbosum)261–5855025–495
Bilberry (Vaccinium myrtillus )52544300
Cranberry (Vaccinium macrocarpon)31515767–140
Redcurrant (Ribes rubrum)1400922
Blackcurrant (Ribes nigrum)29-604644
Elderberry (Sambucus nigra)1044245-791
Red cranberry (Vitis vitis-idea)6527477

Biological activities of berries
Data from in vitro and animal experimental models indicate that the phenolic compounds in berries may produce their beneficial effects through their antioxidant, anti-inflammatory, antihypertensive, and lipid-lowering activities, which could prevent or mitigate atherosclerosis. Perhaps the best-known of the biological activities of phenolic compounds is their antioxidant activity, which helps protect the body’s cells from damage caused by free radicals and counteract certain chronic diseases associated with aging. According to several studies using in vitro and animal models, berries also have anti-cancer properties involving several complementary mechanisms such as induction of metabolic enzymes, modulation of the expression of specific genes and their effects on cell proliferation, apoptosis (programmed cell death, an unsettled process in cancer cells), and signalling pathways inside the cell.

Population studies
In a prospective study conducted in China with 512,891 participants, daily consumption of fruit (all types of fruit) was associated with an average decrease in systolic blood pressure of 4.0 mmHg on average, a decrease of 0.5 mmol/L of blood glucose concentration, a 34% reduction in the risk of major coronary events and a 40% reduction in the risk of cardiovascular mortality. These results were obtained by comparing participants who ate fruits daily to those who did not consume them at all or very rarely. In this study, there was a strong dose-response correlation between the incidence of cardiovascular events or cardiovascular mortality and the amount of fruit consumed. Studies suggest that among the constituents of fruit, it is the flavonoids, and especially the anthocyanins, that are responsible for these protective effects.

A number of prospective and cross-sectional studies have examined the association between the consumption of anthocyanins and cardiovascular risk factors (see this review). In four out of five studies that examined the risks of coronary heart disease or nonfatal myocardial infarction, anthocyanin consumption was associatedwith a reduction in coronary artery disease risk from 12% to 32%. The impact of anthocyanins on the risk of stroke was investigated in 5 studies, but no evidence of a protective effect was found in this case.

With respect to cardiovascular risk factors, studies indicate that higher consumption of anthocyanins is associated with decreased arterial stiffness, arterial pressure, and insulinemia. The decrease in blood pressure associated with the consumption of anthocyanins, -4 mmHg, is similar to that seen in a person after quitting smoking. The effect of anthocyanins on insulin concentration, an average reduction of 0.7 mIU/L, is similar to the effects of a low-fat diet or a one-hour walk per day. A decrease in inflammation has been associated with the consumption of anthocyanins and flavonols, a mechanism that may underlie the reduction of cardiovascular risk and other chronic diseases.

Randomized controlled trials
A systematic review and meta-analysis of 22 randomized controlled trials, representing 1,251 people, report that berry consumption significantly reduces several cardiovascular risk factors, such as blood LDL cholesterol [-0.21 mmol/L on average], systolic blood pressure [-2.72 mmHg on average], fasting glucose concentration [-0.10 mmol/L on average], body mass index [-0.36 kg/m2on average], glycated haemoglobin [HbA1c, -0.20% on average], and tumour necrosis factor alpha [TNF-alpha, 0.99 pg/mL on average], a cytokine involved in systemic inflammation. In contrast, no significant changes were observed for the other markers of cardiovascular disease that were tested: total cholesterol, HDL cholesterol, triglycerides, diastolic blood pressure, ApoAI, ApoB, Ox-LDL, IL-6, CRP, sICAM-1,and sICAM-2.

Another systematic review published in 2018 evaluated randomized controlled trials [RCTs] on the effects of berry consumption on cardiovascular health. Among the 17 high-quality RCTs, 12 reported a beneficial effect of berry consumption on cardiovascular and metabolic health markers. Four out of eleven RCTs reported a reduction in systolic and/or diastolic blood pressure; 3/7 studies reported a favourable effect on endothelial function; 2/3 studies reported an improvement in arterial stiffness; 7/17 studies reported beneficial effects for the lipid balance; and 3/6 studies reported an improvement in the glycemic profile.

Berries and cognitive decline
Greater consumption of blueberries and strawberries was associated with a slowdown in cognitive decline in a prospective study of 16,010 participants in the Nurses’ Health Study aged 70 or older. Consumption of berries was associated with delayed cognitive decline of approximately 2.5 years. In addition, nurses who had consumed more anthocyanidins and total flavonoids had a slower cognitive decline than participants who consumed less.

The exceptional content of phenolic compounds in berries and their positive effects on health remind us that the quality of food is not just about nutrients: proteins, carbohydrates, lipids, vitamins and minerals; a wide variety of other molecules found in plants are absorbed from the intestines and routed through the bloodstream to all cells in the body. While not essential nutrients, phytochemicals such as flavonoids can contribute to better cardiovascular health and healthier aging.

The effects of coffee on cardiovascular disease

The effects of coffee on cardiovascular disease

Updated on July 13, 2018

A recent study published in Nature Medicine suggests that coffee consumption may protect the heart and blood vessels due to the anti-inflammatory effect of caffeine. As we age, a slowing metabolism, combined with increased oxidative stress, causes the body to accumulate several inactive metabolites that are considered toxic to the immune system and activate the inflammatory response. Chronic inflammation is very harmful to the cardiovascular system, as it promotes the progression of several phenomena that damage the heart and blood vessels, such as atherosclerosis, hypertension and insulin resistance. Researchers have observed that people who regularly consume caffeinated drinks, particularly coffee, produce less of these inflammatory metabolites, have more elastic blood vessels, and are on average healthier.

These results are in line with several epidemiological studies showing that regular coffee consumption is associated with the reduced risk of cardiovascular disease and mortality in general. For example, a meta-analysis of studies involving 1,279,804 participants found that people who consumed a moderate amount of coffee (3 to 5 cups per day) were about 15% less likely to be affected by cardiovascular disease (coronary heart disease and stroke) than people who never drank coffee.

Several studies have also shown that coffee consumption is safe for people with established coronary heart disease. For example, a randomized clinical trial involving patients who had suffered a heart attack with acute ST-segment elevation (STEMI) showed that coffee consumption (4 to 5 cups per day, for a caffeine intake of 353 mg) did not cause arrhythmia and was not associated with any cardiovascular disorder. These observations are consistent with other studies showing that coffee consumption is not associated with the development of arrhythmias such as atrial fibrillation, and may even be associated with a decreased risk of such events.

Coffee also does not seem to have any major effects on blood pressure, although caffeine is known to stimulate the sympathetic nervous system. Studies show that, in individuals who never drink coffee, caffeine can indeed cause a short-term increase in blood pressure (by about 10 mm Hg), but the effect is transient and disappears completely in regular drinkers due to the phenomenon of tolerance. The absence of the long-term hypertensive effect of coffee was confirmed by a study involving 155,594 women showing that the regular consumption of coffee, even in high amounts (6 cups per day), is not associated with an increased risk of hypertension. However, the same study reported that the consumption of other sources of caffeine such as soft drinks (regular and diet) is associated with an increased risk of high blood pressure, suggesting that there are other compounds in coffee that may offset the effect of caffeine on blood pressure. Indeed, it is interesting to note that the intravenous administration of caffeine increases blood pressure even among regular coffee drinkers, while the consumption of the beverage itself has no impact. Overall, this data suggests that the neutral effect of coffee on blood pressure is due to the presence of molecules that reduce caffeine’s stimulation of the sympathetic nervous system. This is not surprising considering that coffee is not merely a source of caffeine, but rather a highly complex beverage containing more than a thousand distinct compounds, including several antioxidant and anti-inflammatory molecules.

Studies show that some of these molecules, such as chlorogenic acids and lignans, may also contribute to improving sugar metabolism and thus prevent type 2 diabetes. For example, an analysis of a dozen studies on the relationship between coffee consumption and the risk of type 2 diabetes shows that people who drank 4–6 cups a day were about 30% less likely to develop the disease compared to those who drank it very little or never. A prospective study involving 88,000 women aged 26 to 46 suggests that the protective effect of coffee may be even greater, and can be observed for smaller amounts of coffee, with a 13% and 42% reduction in risk for a daily consumption of 1 cup and 2–3 cups, respectively. These reductions are also observed for decaffeinated coffee, suggesting that, beyond caffeine, the molecules contained in this beverage can help maintain normal blood sugar levels.

Several recent studies also indicate that regular coffee consumption is associated with a decreased risk of neurodegenerative diseases such as Alzheimer’s and Parkinson’s disease, several types of cancer, particularly liver cancer, a decreased risk of recurrence in people who have been affected by hormone-dependent breast and colon cancer, a decreased risk of end-stage renal disease, and a decreased risk of premature death. Coffee’s long-standing reputation as unhealthy is therefore irrelevant. While it is notably appreciated for its stimulating properties, coffee is a drink that has many positive effects, not only for preventing cardiovascular disease but also on health in general.

Dark chocolate is good for the heart!

Dark chocolate is good for the heart!

Updated on February 11, 2019

Not only are plants important sources of vitamins, fibres and minerals but they also contain phytochemicals such as polyphenols that play a very important role in the positive effects of these foods on cardiovascular health. Among the thousands of distinct polyphenols found in nature, the family of flavonoids has received special attention in recent years because of its presence in a large number of plants (fruits, vegetables, nuts, legumes) and beverages (tea, coffee, red wine) that are part of our daily diet. The impact of these molecules on health appears to be particularly important, as population studies indicate that people with the highest flavonoid intake have a lower risk of stroke or coronary artery disease, effects that are accompanied by a decrease in cardiovascular mortality and overall mortality.

Cocoa and its by-products, especially dark chocolate, are exceptional sources of polyphenols (Table 1), in particular flavonoids, suggesting that regular consumption of cocoa products could be very positive for cardiovascular health.

Table 1. Polyphenol content of some foods and beverages. Adapted from Pérez-Jiménez et al. (2010).

FoodPolyphenol content
(mg/100 g or 100 mL)
Cocoa powder3448
Dark chocolate1664
Flax seeds1528
Blueberries836
Black olives569
Pecans493
Coffee (filter)214
Red wine101
Green tea89
Tofu42

The first clue to this positive effect comes from Marjorie McCullough’s observations on the Kuna Indians of the San Blass Islands, an archipelago off Panama. These people are very large consumers of cocoa, which they use to prepare a beverage according to the traditional method of pre-Colombian civilizations. The Kuna drink about five cups of cocoa a day, which translates into a polyphenol intake of around 1800 mg per day, almost 10 times more than North Americans. These people are also distinguished for their very low blood pressure  (110/70 mmHg even at over 60 years old), despite a very high salt diet, and their low incidence of myocardial infarction and stroke. These characteristics are not of genetic origin, because the individuals who have left the island to live on the mainland see their blood pressure quickly increase. Among the lifestyle factors that may explain this difference, the most plausible is the drastic decrease in continental cocoa consumption, which is 10 times lower than among islanders. Therefore, it seems that cocoa polyphenols can have a real impact on cardiovascular health by lowering blood pressure and, at the same time, the risk of ischemic events such as heart attack or stroke that result from hypertension.

Several epidemiological studies have confirmed that high cocoa intake is indeed associated with a decrease in blood pressure and a reduction in the risk of cardiovascular disease and premature mortality. For example, a 15-year Dutch study of 500 people over the age of 65 found that those who consumed the most cocoa-based products had an average systolic pressure of 3.7 mm Hg and a marked reduction (50%) in the risk of cardiovascular mortality. These results have been confirmed by several randomized clinical trials where the consumption of dark chocolate, cocoa or cocoa-derived polyphenols is associated with a decrease in blood pressure and an improvement in endothelial function and insulin sensitivity. These vascular effects are largely due to an increase in the formation of nitric oxide (NO), a powerful vasodilator, by some cocoa flavonoids. A beneficial effect of cocoa consumption on the lipid profile (triglycerides, LDL and HDL cholesterol) and on the reduction of chronic inflammation has also been reported and could contribute to the benefits of dark chocolate for cardiovascular health.

These beneficial effects are also suggested by the results of a meta-analysis of 14 prospective studies conducted with a total of 508,705 participants, followed for a period of 5 to 16 years. The authors observed that people who consumed the most cocoa had a lower risk of coronary heart disease (10% decrease), stroke (16% decrease), and diabetes (18% decrease).

The most recent meta-analysis, which included 23 prospective studies with 405,304 participants, indicates that chocolate consumption is associated with a reduced risk of cardiovascular disease (CVD), if consumption is limited to less than 100 g/week. Those who consumed more chocolate had a 12% lower risk of CVD in general (stroke: -16.3%, myocardial infarction: -16.2%) than those who consumed little. However, the dose-response analysis (Figure 1) shows that at more than 100 g/week there is no longer any protective effect and that the risk of CVD increases at higher doses, which could be attributable to the harmful effect of consuming too much sugar. According to the authors of this meta-analysis, the best dose of chocolate to reduce the risk of CVD is 45 g/week (about half of a 100 g chocolate bar, a common size sold in grocery stores).

Figure 1. Dose-effect association between the consumption of chocolate and the risks of cardiovascular events. From Ren et al., Heart, 2019.

It is now clearly established that several risk factors for cardiovascular disease (hypertension, inflammation, insulin resistance, metabolic syndrome) also increase the risk of cognitive decline and dementia. Conversely, recognized factors to protect cardiovascular health, such as physical exercise or the Mediterranean diet, are associated with a significant decrease in the risk of cognitive disorders. In other words, what is good for the heart is also good for the brain, which raises the interesting possibility that the regular consumption of cocoa-based products can also result in benefits for cognitive function. Studies conducted to date support this, as a high intake of flavonoid-rich foods such as tea, red wine and chocolate is associated with reduced risk of cognitive decline and improved brain performance. In a study of people aged 65 to 82 who showed clinical signs of early cognitive decline, daily consumption of a beverage made with chocolate high in polyphenols was associated with significant improvement of cognitive functions.

More recently, a randomized clinical study showed that dark chocolate consumption was associated with a significant improvement in visual acuity and contrast sensitivity a few hours after intake, a positive impact possibly related to an improvement in blood circulation in the richly vascularized retina. Milk chocolate, which contains less polyphenols, has no effect, suggesting that flavonoids in cocoa are responsible for this improvement in vision.