Soy & Vitamin Absorption In Body

Soybeans, like other legumes, are high in phytates, often referred to as antinutrients because they may inhibit the absorption of some nutrients. This has initiated concerns about the health effects of soy, especially in vegetarians, vegans or those who frequently replace animal proteins or dairy foods with soy products.

Inhibitors

Phytates and its salt, phytic acid, is a phosphorus-based compound found in soy. It has the ability to bind minerals, proteins and starch, and reduce their absorption. Phytic acid can block the availability of essential nutrients, such as zinc, iodine and iron, and to a lesser extent, calcium, magnesium and copper in the small intestine. Soy foods also contain protease inhibitors, called trypsin. It reduces the efficiency of protein digestion in raw soybeans or tofu, which are often used in smoothies or desserts. Trypsin is inactivated by heat, so foods that are processed or cooked are not affected.

Calcium

The reduction of absorption from phytate binding to soy and soy isolates may vary, depending on the calcium content of the food. Studies at the University of Kebangsaan in Malaysia in 2010 assessed the bioavailability of calcium from tempeh, a traditional fermented soy product, and milk. A group of 20 postmenopausal Malay women drank one 114-gram glass of milk or ate a 206-gram serving of tempeh, each containing 130 mg of calcium. The "International Journal of Food Sciences and Nutrition" published the conclusions, which suggested that absorption of calcium from tempeh was similar to milk but four 206-gram servings of tempeh were required for the same amount of calcium absorption as one 114-gram glass of milk. Soy milk contains isoflavones, which may influence calcium absorption. According to Soya, isoflavones may stimulate estrogen receptors in the intestine and increase calcium absorption.

Iron

Soy may inhibit iron absorption, which is most serious for vegetarians, children and menstruating women, who require adequate sources of iron. The Nestlé Research Centre in Lausanne, Switzerland, conducted a study that evaluated the effect of phytate in soy on iron absorption. It found that when phytic acid was reduced, iron absorption increased fourfold to fivefold. However, after the removal of all phytic acid, iron absorption from the soy protein was still only half that of the egg white control. Conclusions, published in the "American Journal of Clinical Nutrition," suggested that phytic acid is a major inhibitory factor of iron absorption in soy isolates.

Zinc

Soy may contribute to a lower absorption rate of zinc, especially in nonmeat eaters and people with higher zinc requirements. The Washington University School of Medicine in St. Louis tested the effects of various quantities of phytates on zinc absorption in 23 Malawian children. Studies found that the reduction of phytate resulted in higher absorption of total zinc for 14 children recovering from tuberculosis but no effect in well children was noted. Results of the trial, published in the "Journal of Nutrition" suggested that phytate reduction may be beneficial in improving zinc bioavailability in those with increased zinc requirements.

Solution

Fermentation neutralizes phytic acid in soy. To benefit from the nutrients in soy, consume only fermented soy products, which include organic miso, such as mugi barley and genmai miso, organic tempeh, soy sauce or tamari and natto. Avoid unfermented soy products, including tofu, bean curd, soy milk, soy protein powders and soy meat alternatives made from hydrolyzed soy powder. Fermented soy helps form beneficial bacteria in the large intestine, which allows for greater assimilation of foods and nutrients.