Phytates/phytic acid are the storage form of phosphorus bound to inositol in the fiber of raw whole grains, legumes, seeds, and nuts. Although these foods have a high phosphorus content, the phosphates in phytates are not released through the digestive process. Phytates, particularly in such raw foods as bran, are a concern because they can bind a portion of the iron, zinc, and calcium in foods, making the minerals unavailable for absorption.
Phytic acid occurs in unsprouted grains, seeds, and legumes, and is particularly rich in the bran. Although these foods have a high phosphate content, the phosphate in phytates is not released by digestion. When bread is leavened by yeast, enzymes degrade phytic acid and phytates pose no problem. Phytic acid is also destroyed during baking and food processing.
Enzymes, called phytases, destroy phytates during certain food processes such as: the yeast-raising of dough, the sprouting of seeds, grains, legumes, the roasting of nuts, presoaking beans, cooking, fermentation as in tempeh, miso, and natto, combining acidic foods with zinc-rich foods, etc.
Not everyone believes that phytates are a bad thing. Although phytates do bind with minerals, they may actually be preventing the formation of free radicals, thereby keeping the minerals at safe levels in the body. Phytates also have a role to play in cell growth and can move excess minerals out of the body. Stephen Holt, MD, a gastroenterologist and author of The Soy Revolution: The Food of the Next Millennium (M. Evans and Company, 1998), says phytates shield us from dangerously high levels of minerals such as iron. Some animal studies have suggested that phytates stop the growth of cancerous tumors. In Earl Mindell's Soy Miracle, he writes that phytates can bind with minerals that may feed tumors.
Phytates are generally found in foods high in fiber. Since fiber-rich foods protect against colon and breast cancers, it is now thought that they are the protective agent in the fiber. It appears that, by binding minerals in the intestines, phytates inhibit the cancer process, especially when it comes to iron. Iron generates free radicals, and phytates may be keeping the mineral balance at a safe level within the body. Phytates act as an antioxidant. Scientists are beginning to express concern over excess iron in the body for this reason. Excessive iron is also known to increase the risk of heart disease. Even a small amount of phytates in food can reduce iron absorption by half, but the effect is less marked if a meal is supplemented with ascorbic acid, which can also help the absorption of zinc and calcium.
Phytates are also known to help prevent cancer by enhancing the immune system. Phytates may increase the activity of natural killer cells which attack and destroy cancer cells and tumors. By working directly to control cell growth, phytates may be an ideal protective agent against a wide range of cancers, carrying excess minerals out of the body, thereby protecting it from a potential overload. Fiber, along with its associated phytates, also provides benefits by regulating the absorption of glucose from starch.
Soybeans contain high levels of phytates; some researchers say more than other beans. Additionally, soy's phytates are so stable that many survive phytate-reducing techniques such as cooking. (The phytates in whole grains can be deactivated simply by soaking or fermenting.)
It is possible that only long periods of soaking and fermenting – as are used in making miso, natto, shoyu, tamari, and tempeh (but not tofu, soymilk, texturized soy protein, or soy protein isolate) – significantly reduce the phytate content of soybeans. It has also been reported that tempeh has lower phytate levels than unfermented soyfoods [Anderson and Wolf, Journal of Nutrition, 1995]. Eating too much unfermented soy may lead to a shortage of crucial minerals.
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