Q: I’ve been drinking two eight-ounce glasses of soy milk daily. Recently I read that soy might not be as beneficial as was once thought. Am I overdoing it?
Answer provided by Terese Scollard, MBA, R.D., L.D., regional clinical nutrition manager for Providence Nutrition Services, and Kimra Hawk, R.D., L.D., outpatient dietitian: No, two servings a day isn’t too much. A good rule of thumb is to limit your soy intake to two or three servings a day, which is about the amount in the average Japanese diet.
If I could talk with you in person, I would ask, “Why are you drinking soy?” When clients bring up soy, I always want to know the goals and concerns that drew them to soy. Common comments I've heard are: “I hear soy is good for me.” “I want to reduce my hot flashes.” “I want to prevent breast cancer.” “I want to improve bone density.” “I don't like the taste of milk.” “I'm lactose intolerant.” Since I don’t know what your reasons are for including soy in your diet, I’ll address all of these.
Care for some isoflavones with that? No doubt about it, soy has a lot going for it. It's high in desirable polyunsaturated fats, low in unhealthy saturated fat and is cholesterol-free. It is a good source of fiber, protein and minerals. Soy comes in many forms besides soy milk: tofu, tempeh, soy butter, soy nuts, edamame, soy-based burgers, soy cheese, soy yogurt and more. These are great replacements for meats and full-fat dairy products that are high in saturated fat.
But much of the interest in soy stems from its being a source of isoflavones, a type of phytoestrogen. Phytoestrogens are plant compounds that exert weak, estrogen-like effects in the body. A serving of tofu (just under 3 ounces) includes 25 mg of isoflavones, for example. An 8-ounce glass of soy milk has about 9 mg to 43 mg of isoflavones, depending on whether the milk is fortified or not.
Some scientists have theorized that isoflavones have a positive effect on cardiac health, hot flashes associated with menopause, cancer prevention and bone strength. For a time, the American Heart Association recommended including 25 grams of soy products in the daily diet. Not any more.
In January 2006, the Nutrition Committee of the American Heart Association announced the results of its analysis of 22 clinical trials related to isoflavones and large amounts of soy (about 50 mg daily — half of a typical person’s daily protein consumption).
The committee’s bottom line: It found no evidence that these generous amounts of soy reduced the risk of cardiovascular disease. Moreover, the long-term effects of high consumption of soy (and isoflavones) are not known. Without finding clear benefits, the committee nixed the recommendation of loading up on soy with a soy isoflavone supplement.
However, the committee does endorse eating moderate amounts of soy foods, which are often a healthy choice.
Soy and disease prevention Here's a summary of what the Nutrition Committee found:
An average of 50 mg of soy per day didn't lower blood pressure, improve triglycerides or increase HDL (good) cholesterol. It did lower LDL (bad) cholesterol levels by an average of 3 percent. This decline, however, while helpful, was slight enough to disappoint the committee, considering the amount of soy involved.
Research did not demonstrate that soy protein or isoflavones cooled off hot flashes.
Studies gave mixed messages — maybe yes, maybe no — on soy's usefulness in slowing post-menopausal bone loss.
Evidence that soy protein could prevent or treat breast, prostate or endometrial cancers was meager and, in fact, sometimes threw a red flag to a possible negative effect. (A possible exception, identified in a Dutch review of literature in 2003, found that women who had higher intakes of soy foods during adolescence might experience a decreased risk of breast cancer as adults.)
The Nutrition Committee is not closing the books on soy. The American Heart Association will keep on an eye on soy-related research and will update its advice as needed.
Hold the potato chips This cooling of enthusiasm for large amounts of soy does not mean that you may as well toss the soy nuts and grab the potato chips. Soy isn’t a bad thing — it just may not be quite the super-food it was once thought to be.
If you drink soy milk as a substitute for dairy milk — whether due to lactose intolerance or just a dislike of milk — there’s no reason to stop. Our greatest concern about your soy milk is that it be fortified with calcium and vitamin D. As you probably know, some brands of soy milk are fortified and others are not. We are learning more and more about the important role vitamin D plays in our health, so please be sure to choose only soy milk that is vitamin-D-fortified. (Similarly, if you take a calcium supplement, take one that includes vitamin D.)
Feel free to eat soy foods or drink fortified soy milk as part of a well-rounded diet that includes whole grains, at least five daily servings of vegetables and fruits, low-fat dairy products and lean protein. (Remember to stick to three or fewer servings of soy a day.) But don’t turn to powdered soy protein supplements as a way to erase your dietary sins. They won’t — and they may not be a good idea in general.
If you order a soy burger while everyone else at the table orders a bacon burger, yes, you are making a better choice. But this research says you should feel equally good about ordering the turkey or chicken burger — or having a glass of low-fat milk instead of soy milk.
When we read about the AHA’s revised position, we both thought, “That’s what we've been saying all along.” Research continues to reaffirm the dietitian’s mantra: Eat a varied diet that doesn't go overboard with any single food.
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