Soy protein can help address US cardiometabolic health

According to the National Health and Nutrition Examination Survey (NHANES) conducted in 2017-18, only 6.8% of U.S. adults have optimal cardiometabolic health.1 What’s more, there has been a significant downward trend in cardiometabolic health over nearly 20 years.

NHANES defined optimal cardiometabolic health according to five criteria: adiposity, fasting blood glucose, blood lipids, blood pressure, and absence of prior clinical cardiovascular events (Table 1). Among the five criteria, subjects were most likely to score poorly for adiposity. These findings led to calls for clinical and public health strategies that prioritize treatment and prevention of obesity.  The rise in obesity rates among Americans has been well documented.2,3

The trend of rising rates of obesity nationally and globally speaks to the ineffectiveness of public health efforts addressing weight management. No single dietary approach has been shown to work best for weight loss.4,5

However, diets higher in protein may provide some advantages. The protein leverage hypothesis, which was proposed in 2005, maintains that dietary protein is one key to preventing weight gain.6,7 Evidence suggests protein is involved in regulating caloric intake and is more satiating than either carbohydrates or fat.8,9

Protein also protects against muscle loss. Loss of lean tissue, which is common with weight loss, can have adverse health consequences, although it doesn’t outweigh the benefits of weight loss.  A new analysis of multiple weight loss trials involving 207 middle-aged adults overweight or obese who were examined before and during 6 months of caloric restriction, found higher protein intake reduced the loss of muscle tissue.10  Over a 6-month period, participants lost on average about 5% of their body weight. However, those in the high protein group lost half as much lean tissue as those in the low protein group.

For those who eat plant-based diets in particular, soy foods may play a role in weight management. Soybeans are higher in protein than nearly all other legumes,11 and the quality of soy protein is higher than that of nearly all other plant proteins.12

In addition, soy protein may offer additional benefits for cardiometabolic health. For decades, scientists have recognized the cholesterol-lowering properties of soy protein.13-15 Also, many soy foods are sources of polyunsaturated fat, which helps lower blood cholesterol when it replaces saturated fat in the diet.

However, new research suggests that the protein in soy foods might also protect against heart attack or stroke by helping to prevent plaques from rupturing.

Obstructive coronary artery disease, that is, coronary heart disease (CHD), is the gradual narrowing or closing of arteries that supply the heart with blood. This blockage is usually caused by a build-up of plaque (atherosclerosis), and can begin as early as the teenage years, slowly worsening in some people and more quickly in others. If the blockage becomes severe enough, it can limit or block the flow of oxygen-rich blood to the heart muscle. An acute blockage results in a heart attack.

Often, a pivotal step in this process is the rupturing of a plaque, which leads to coronary thrombosis or a blood clot potentially blocking blood flow to the heart. Plaques that are more vulnerable to rupture are distinguished by a large lipid necrotic core and thin fibrous cap. Cardiologists can measure plaque fragility via optical coherence tomography (OCT).

In a small study involving 194 patients with CHD, soy and nut consumption was inversely related to plaque vulnerability, that is, the higher the consumption, the lower the vulnerability. Dietary intake was determined through the use of a semi-quantitative food frequency questionnaire and plaque vulnerability was measured by OCT.16 Patients with vulnerable plaque consumed on average only 6.67 grams daily of nuts and soy, whereas patients without vulnerable plaque consumed 9.99 grams per day. Furthermore, as nut and soy consumption increased, risk of vulnerable plaque decreased in a stepwise fashion. Vitamin C was also shown to reduce risk of plaque vulnerability, possibly decreasing inflammation as shown by its association with lower blood levels of two markers of inflammation, tumor necrosis factor-alpha (TNF-a) and interleukin-6. In contrast to soy and nuts, sodium was found to be a dietary risk factor for plaque vulnerability.

It’s not clear from this study why soy may decrease plaque vulnerability. The evidence didn’t point to a decrease in inflammation, as was the case for vitamin C. However, a recently published statistical analysis of clinical trials found that soy protein, and especially soy protein rich in isoflavones, significantly lowered levels of TNF-a.17 Thus, in addition to decreasing cholesterol levels, soy protein may lower inflammation and, as a result, protect against plaque vulnerability and risk of heart attack.

This article is partially funded by U.S. Soy farmers, their checkoff and the soy value chain.

Mark Messina, Ph.D.

Executive Director

Soy Nutrition Institute

Dr. Mark Messina is a nationally recognized expert on the health effects of soy.