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Is soy a superfood or poison?

(Juan Mabromata /AFP/GettyImages)

HARTFORD — The information on the internet ranges from calling soy products superfoods to calling it a poison.

Soybeans are made up of many active constituents and some in isolation can cause problems and others can bring benefits but when you eat or drink it, you are getting the good and the bad constituents mixed together. It is high in nutrients and fiber and it has a constituent in it that can block some nutrient absorption. It has some components that act a little like estrogen but outside of rodent models where very high soy phytoestrogens were used, the risk of breast cancer does not seem to be impacted. The net effect, soybeans, edamame, soy milk, tofu and miso are neither miracle foods nor poisons.

In a report by a federal Agency for Healthcare Research and Quality Evidence-based Practice Center in 2005, they found that there were only three things that you can say with confidence that soy products do, either good or bad. Here they are, slightly reduce LDL cholesterol and triglycerides, and mildly reduce some menopausal symptoms. Will the effects on LDL cholesterol reduce your risk of heart disease? Possibly but the effects would be slight and the data to date cannot prove it. So if people are pestering you to eat tofu with the promise of immortality, there is no proof that that is true.

In January in the Journal of Clinical Endocrinology and Metabolism, a new potential benefit of soy emerged that is intriguing but requires further research. In a past Ask the Pharmacist segment we discussed how bisphenol A (BPA) is a component of many plastics used in non-beverage bottles and the lining of cans. Virtually everyone has some BPA in their bloodstream right now. Well, BPA can make it harder for some people to conceive a child and bring it to term. In this Harvard study, women with fertility problems undergoing in vitro fertilization who had more BPA in the blood had a harder time conceiving and delivering babies but those who said they regularly ate or drank soy products were more successful. Eating or drinking soy products did not reduce BPA blood concentrations but it seems to have prevented it from hampering fertilization. In rodent studies, something in soy alters the BPA preventing it from interfering with DNA but does not eliminate it from the body. Since this was an observational study, we can’t say for sure that this association is true or how much soy is the right amount but for infertile couples undergoing in vitro fertilization, eating or drinking a normal amount of soy products from time to time might be helpful.

As far as harms go, there is no credible evidence to suggest eating or drinking a normal amount of soy products will yield a good or bad effect on cancer, thyroid function, mental function, or aluminum toxicity. What is a normal amount? Up to a cup of edamame, 2 cups of soy milk, and 6 ounces of tofu. Drinking 2 cups of soy milk, eating a pound of soybeans, drinking a soy protein shake, and having 12 ounces of tofu a day might give you street credibility with the hipsters but it may not be healthy and might cause problems, just like taking too much of any vitamin or any other nutrient would. Remember, even water can kill you if you overdo it, the key is a balanced diet. Soy can be a low-fat protein source for vegetarians, vegans, and people with milk allergies and you don’t have to avoid it because of the potential health risks.

 – Dr. Michael White from the UConn School of Pharmacy