Nutrition Hotline
By Reed Mangels, PhD, RD
QUESTION: Is a child who is raised without ever eating meat, poultry, or fish at risk of never developing the digestive enzymes (chymotrypsin, trypsin, pepsin, etc.) for these foods?
LA, Massachusetts
ANSWER: The enzymes of the stomach and small intestine which digest large protein molecules into smaller parts, like dipeptides and amino acids, do not differentiate among protein from meat, fish, and poultry, protein from dairy products and eggs, and protein from plant sources. The enzymes simply digest protein. Thus, a child who eats protein, regardless of its source, has enzymes present which can digest protein.
QUESTION: Is it true that soybeans contain phytic acid (phytates) that block the body's uptake of essential minerals like calcium, iron, and zinc, and that they are very resistant to phytate-reducing techniques such as long, slow cooking? If so, is this a reason to avoid soy products?
AG, Kentucky
ANSWER: Soybeans and products made from soybeans contain phytates, the storage form of phosphorus found in whole grains and beans. Phytates interfere with the absorption of minerals, but do not completely prevent us from absorbing minerals like calcium and iron. The presence of phytates is not a good reason for avoiding soy products. Whole grains and other dried beans also contain phytates.
Should we eliminate all of these foods? Let's look at each mineral. Soy products contain significant amounts of iron, so even though iron is not well absorbed from soy, a relatively good amount can still be absorbed. Even more iron can be absorbed if foods rich in vitamin C are eaten along with soy products. Calcium absorption from soy is reasonably good despite the presence of phytic acid. Soy products are not especially high in zinc, and the phytates found in soy products interfere with zinc absorption. However, this is not a reason to avoid soy, since there are other zinc sources for vegetarians. Fermented soy products, including tempeh and miso, have a lower phytate content so that zinc from these foods is better absorbed than from unfermented soy products like tofu and soymilk.
QUESTION: I've seen graphs showing that the higher your intake of animal protein is, the greater your risk of bone fracture. Someone told me that this is not true. What do you think?
JD, Illinois
ANSWER: The problem with this sort of analysis is that it is much too simplistic. Many factors are associated with animal protein intake (higher standard of living, possibly less exercise, maybe more alcohol use), so just targeting animal protein as the culprit in high fracture rate is not accurate. If we look at this issue world-wide, it appears that there are genetic factors which affect fracture rate in some areas where we would expect protein intake to be low. For example, the length of the hip axis of Asian and African women (a genetically determined factor) makes these women less likely to break their hips. Other factors that reduce risk of fracture in Asian women may include more efficient calcium absorption, more weight bearing exercise, greater flexibility, and better balance.
