Effect of traditional oriental soy products on iron absorption

Article Abstract:

Although soybean products are a good source of protein, the bioavailability of iron from soy is extremely poor. In addition, iron digestion from other foods to which soy has been added is inhibited. The digestibility of iron from identical soy products is quite variable, and the compound in soy which inhibits iron absorption has not yet been identified. Soy products such as tofu and fermented soy foods such as natto, tempeh, miso, and sufu play an important role in traditional Asian cooking, but the iron availability of these foods has not been studied. The methods used to prepare these foods alter the nature of soy protein, and the effect of these methods on iron availability was investigated to allow possible identification of factors affecting iron availability. Soy flour was found to have better iron availability than regular tofu, but worse than silken tofu. One fermented product, sufu, also had worse iron availability than soy flour. Sufu and tofu both had high levels of calcium, the absorption of which is known to compete with, and therefore block, iron absorption. All other fermented soy products had better iron bioavailability than soy flour. Soy miso fermented with rice had a good iron availability, which appears to be due in part to a lack of phytate (which chelates metals, preventing absorption), but also perhaps to a possible promoter of iron absorption. Proteins from the soy products were fractionated into their constituents, but no relationship between protein components and iron availability could be firmly established. Further study of the effects of soy processing on iron availability is needed. (Consumer Summary produced by Reliance Medical Information, Inc.)

Iron, Iron (Metal), Soybean products

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Inorganic zinc and the intestinal absorption of ferrous iron

Article Abstract:

Zinc and iron are both minerals required in human nutrition. Animal studies have shown that zinc and iron are absorbed into the intestines by similar mechanisms. Because they share certain pathways for absorption, the two minerals actually compete to be absorbed. If the dose of one is high, it may block absorption of the other. Previous research established that excess iron can prevent zinc absorption. A study found that in 16 healthy men, excess zinc impaired iron absorption. The degree of competition between the two minerals depended on the ratio of their amounts. The higher the zinc dosage, the less iron was absorbed. This trend needs to be considered when developing vitamin and mineral supplements. Many supplements are currently available that contain iron and zinc in proportions that could diminish absorption of either mineral. Raising the content of zinc to overcome interference by iron is cautioned against, since this would in turn block iron absorption. Instead it is suggested that reducing the quantity of one or both minerals might allow better uptake of both. The dosages tested were similar to those found in commonly available supplements. These results may not apply to people with iron-deficiency or other medical conditions, since the subjects were all healthy.

Case studies, Composition, Dietary supplements, Nutrient interactions, Iron deficiency anemia

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Chronic ethanol feeding and acute ethanol exposure in vitro: effect on intestinal transport of biotin

Article Abstract:

Ethanol has been shown to reduce the intestinal transport and absorption of vitamins and minerals. Studies have shown that alcoholics have lower plasma levels of biotin than nonalcoholics. Biotin is an essential vitamin required for normal cell growth and function. Biotin is transported and absorbed in the intestine by a carrier-mediated process, in which biotin is bound to a protein that allows the biotin to be absorbed. The effects of ethanol on biotin plasma concentrations and intestinal transport were examined. Male rats were maintained on a balanced, six-week diet that included either a 5 percent ethanol solution or a maltose-dextrin solution as a control. The rats receiving the ethanol had lower levels of plasma biotin than the rats on the nonalcohol diet. In addition, ethanol was observed to inhibit the transport of biotin into jejunal sacs prepared from rat small intestine. The extent of the inhibition of biotin transport was directly related to the concentration of ethanol used. A major ethanol metabolite, acetaldehyde, also inhibited biotin transport. The findings indicate that consumption of ethanol inhibits biotin absorption in the small intestine, resulting in reduced plasma levels of biotin. (Consumer Summary produced by Reliance Medical Information, Inc.)

Care and treatment, Measurement, Alcoholism, Alcoholism treatment, Vitamins, Biotin

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