Influence of vegetable protein sources on trace element and mineral bioavailability

Abstract

Vegetable protein sources are often mixed with cereals for complementary feeding. Both contain high levels of phytic acid, which can inhibit trace element and mineral absorption. In adults, phytic acid has been reported to inhibit the absorption of iron, zinc, calcium and manganese but not copper. There are far fewer studies in infants. Phytic acid is a strong inhibitor of iron absorption in both infants and adults, but its influence on zinc absorption in infants seems to be modest and perhaps most important in children recovering from infection. The influence of phytic acid on calcium and magnesium absorption would seem of minor importance. Because iron and zinc deficiencies are widespread in infants and young children in developing countries, the bioavailability of iron and zinc from complementary food is a major concern. Iron absorption may be as low as 2-3% from porridge based on whole-grain cereals and legumes (phytic acid ∼1 g/100 g) even in iron-deficient subjects. Decreasing phytic acid by 90% (∼100 mg/100 g dried product) would be expected to increase absorption about twofold and complete degradation perhaps fivefold or more. More modest reductions in phytic acid content may not usefully improve iron absorption. Complete enzymatic degradation of phytic acid is recommended. If this is not possible, it is recommended that the molar ratio of phytic acid to iron in an iron-fortified food be <1, preferably <0.5. At these low levels of phytic acid (20-30 mg/100 g dried product), zinc absorption should be satisfactory.