Dietary fiber zinc absorption

The behavior of minerals is often influenced by the presence of other food constituents. The recent interest in the beneficial effect of dietary fiber has led to studies of the role fiber plays in the absorption of minerals. It has been shown (Toma and Curtis 1986) that mineral absorption is decreased by fiber. A study of the behavior of iron, zinc, and calcium showed that interactions occur with phytate, which is present in fiber. Phytates can form insoluble complexes with iron and zinc and may interfere with the... 

Unlike phytates, the effect of fiber on zinc absorption remains more uncertain. The information recently compiled (Table IX) by Kelsay (15) underscores this. The uncertainty may, in part, be attributed to (a) differences in preexperimental dietary regimen of test subjects, (b) differences in the level of fiber intake,... 

This book is based on the symposium that was designed to assess the current perspective and future direction of research on the nutritional bioavailability of zinc. Inhibitors suspected of interfering with the absorption of zinc are some factors that infiuence bioavailability. Phytates, dietary fibers, proteins, nonenzymatic browning products, and certain micronutrients are among these substances. These inhibitors are covered in various chapters. 

Dietary fiber and phytate. Dietary fiber and phytate are known as potential inhibitors of the absorption of divalent cations however, the literature regarding the effect of dietary fiber and phytate on the bioavailability of minerals is contradictory. Data by Yannai and Sachs (1993) indicate that phytate does not affect methylmercury absorption. Yannai and Sachs (1993) compared the absorption by rats of mercury found intrinsically in experimental fish meal with and without added phytate and found no significant differences in the absorption of Hg (93 5%) between 2 experimental fish meal diets (containing 1.4 mol Hg/kg diet), with or without added sodium phytate. The authors speculated that phytate might be preferentially bound to zinc, iron, and copper, which were present at much higher concentrations in the diet. 

In human diets, leavening of bread and exposure of cereals to wet heat lower the phytate content, increasing zinc avahability. Other factors, such as dietary fiber and a constituent of beans, can also lower zinc intestinal absorption but to a lesser extent. Iron at supplemental dosages (up to 65 mg/day) may decrease zinc absorption so that pregnant and lactating women taking iron may require zinc supplementation, ... 

Evidence that dietary fiber interfered with absorption of bivalent metals by the intestine was first ob -tained in connection with studies of human zinc deficiency in Iran. Human subjects who consumed purified phytate exhibited smaller feeal losses of zinc and calcium than they did when they ate equivalent amounts of phytate in the form of unleavened wheaten whole meal flat breads that are the staple food in rural Iran... 

Wheat bran and whole wheat cereals quantitatively contain high amounts of manganese and are often listed as particularly valuable sources of manganese. However, zinc also is contained in appreciable amounts in wheat bran and whole wheat products but is poorly absorbed by the human from these sources. This has been attributed to either the phytate or the fiber contents of these products or a combination of these two dietary factors. These same factors may also affect the absorption of manganese. 

Fiber components can bind zinc and other minerals, possibly rendering the minerals unavailable for absorption by the animal body (1, 2,. The effect of fiber on zinc balance of human subjects was reviewed previously (4) and appears to be related to level and kind of fiber, level of zinc, other components of the diet, and length of study period. One of the dietary components which may affect zinc availability is oxalic acid. 

I he RDA for zinc is 15 mg. With mixed diets containing phytate and fiber, about 30% of dietary zinc Is absorbed. The efficiency of absorption increases with diets containing very little zinc. Dietary zinc must replace the obligatory losses, which, at the minimum, are about 0.7 mg/day. The RDA for copper has not been determined. The National Research Council recommends 1.5 to 3.0 mg per day as a safe and adequate range of dietary copper intake for adults. The usual dietary intake of copper in the United States is about 1 mg/day. This amount is sufficient to... 

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