Fariba K. Roughead

"Attention shoppers! You can now find soy in the dairy case, the meat case, the cereal aisle, the snack aisle, the produce section, ..."

The soy bean, once grown merely for its oil and as animal feed, has taken center stage in nutrition science circles as well as the supermarket. The Food and Drug Administration recently approved a health claim stating that eating about 25 grams of soy protein daily as part of a low-fat diet will decrease the risk of heart disease.

In addition to its effects on the cardiovascular system, soy may also have beneficial effects on bone. Soy contains a group of compounds called phytoestrogens that may act like estrogen in the body. These compounds are being investigated as an alternative to hormone replacement therapy in the prevention and treatment of osteoporosis.

So, how much soy do you have to eat to get 25 grams of soy protein? To give you an idea, a soy burger has about 10 grams of soy protein, 3 ounces of tofu has about 8 grams, and 8 fluid ounces of soy milk has 8 grams.

With all the hype about the "joy of soy," one may wonder if there is a downside to soy? While it is fairly convincing that soy improves heart health, its possible negative effects on mineral absorption have not been as carefully investigated. Soybeans have compounds, called phytates and oxalates, that inhibit the absorption of important minerals like calcium, zinc and iron.

Many soy products on the market are meat substitutes: soy burgers, soy "chicken" patties, soy breakfast links, etc. So soy often replaces meat, which is an excellent source of dietary zinc and iron. And we don’t fully understand how the habitual replacement of meat with soy affects mineral nutrition. A negative effect may be overcome by fortifying the products with minerals, but research in this area is practically nonexistent.

At the Grand Forks Human Nutrition Research Center, we want to know how daily replacement of meat with soy protein affects the absorption of dietary calcium and the health of our bones. We’re inviting 18 healthy postmenopausal women between the ages of 51 and 75 to participate in a controlled feeding study. That means they will eat only the food we give them; we do all the cooking and the dishes, too.

Findings from studies like this are not only useful in giving the public sound advice about soy protein products, they will also help food manufacturers design soy foods with improved mineral bioavailability (how absorbable the mineral is from the food). The information from this study will also help clarify the healthful place of meat and soy in a varied, balanced diet.

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