Since 1999, food manufacturers have been allowed to make heart health claims for foods containing soy protein. This was based on the idea that soy protein might lower LDL cholesterol, which in turn should reduce the risk of heart attacks.
About-Face on Health Claims for Soy Protein:
Now, the FDA is getting ready to do a U-turn on such health claims for soy. It is not that soy protein is thought to be harmful, but the agency has seen a number of studies with inconclusive or contradictory results.
According to the FDA,
“While some evidence continues to suggest a relationship between soy protein and a reduced risk of heart disease…the totality of currently available scientific evidence calls into question the certainty of this relationship…Our review of that evidence has led us to conclude that the relationship between soy protein and heart disease does not meet the rigorous standard for an FDA-authorized health claim.”
What Is the Evidence on Soy Protein and Heart Disease?
We can get a sense of why the FDA may be back-tracking on these health claims by looking at recent research reports. In one recent study, scientists found that Japanese people had no different cardiovascular mortality regardless of how much soy protein they consumed (Nagata et al, American Journal of Clinical Nutrition, Feb. 2017). People who ate more natto, a fermented soy product, were less likely to die of stroke or heart disease, however. Soy and natto are both traditional items in the Japanese diet. Research in another Asian population, Chinese people in Singapore, also found no link between soy protein in the diet and the risk of death from heart disease (Talaei et al, Journal of Nutrition, June 2014).
What would this mean for North American populations who are less accustomed to eating miso, natto, tempeh or tofu? A Canadian pilot study found that people with metabolic syndrome got better results with supplements containing soy, pea and whey proteins than with diet alone (Dahlberg et al, Canadian Journal of Physiology and Pharmacology, Aug. 11, 2017). The low-glycemic load diet should have benefits on its own.
Mediterranean Diet vs. Metabolic Syndrome:
Previous research highlighted a Mediterranean diet that uses olive oil instead of animal fats like butter and is rich in whole grains, vegetables and fruits as a way of combating heart disease. Greek researchers discovered that it can reduce the likelihood of metabolic syndrome (Journal of the American College of Cardiology, online, March 7, 2011).
This constellation of risk factors, including high triglycerides, a big belly, low HDL cholesterol, high blood pressure elevated blood sugar is linked to the development of diabetes and cardiovascular disease. The meta-analysis involving 50 studies and over 500,000 subjects suggests that a Mediterranean diet might lower the risk of developing metabolic syndrome by nearly one third.
Soy protein is not a prominent part of the Mediterranean diet. Scientists hypothesize, however, that the Med diet might be healthful because it has more plant protein and less meat.
As you can see, the evidence is not all pointing in the same direction. We think it makes sense for the FDA to take stock of the research before it issues new guidelines on whether we should all be eating more soy protein.