Ascorbic acid prevents the dose-dependent inhibitory effect of polyphenols and phytates on non-heme-iron absorption

Department of Medicine, University of Witwatersrand, Johannesburg, South Africa.
American Journal of Clinical Nutrition (Impact Factor: 6.77). 03/1991; 53(2):537-41.
Source: PubMed


The effects of maize-bran phytate and of a polyphenol (tannic acid) on iron absorption from a white-bread meal were tested in 199 subjects. The phytate content was varied by adding different concentrations of phytate-free and ordinary maize bran. Iron absorption decreased progressively when maize bran containing increasing amounts of phytate phosphorous (phytate P) (from 10 to 58 mg) was given. The inhibitory effect was overcome by 30 mg ascorbic acid. The inhibitory effects of tannic acid (from 12 to 55 mg) were also dose dependent. Studies suggested that greater than or equal to 50 mg ascorbic acid would be required to overcome the inhibitory effects on iron absorption of any meal containing greater than 100 mg tannic acid. Our findings indicate that it may be possible to predict the bioavailability of iron in a diet if due account is taken of the relative content in the diet of the major promoters and inhibitors of iron absorption.

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    • "In plant-based diets, phytate (myo-inositol hexakisphosphate) is the main inhibitor of iron absorption.[23] The negative effect of phytate on iron absorption has been shown to be dose dependent and starts at very low concentrations of 2-10 mg/meal.[3746] The molar ratio of phytate to iron can be used to estimate the effect on absorption. "
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    • "The combination of fermentation for 2 h and baking at 220°C for 15 min was the only processing method which completely degraded phytate and significantly increased iron absorption in that study. Other constituents of food, either exogenous or endogenous, such as ascorbic acid (Gillooly et al., 1983; Siegenberg et al., 1991) and β–carotene (provitamin A) (Garcia-Casal et al., 2000, 2006), have been reported to promote iron absorption in the presence of phytate. However, roasting ingredients in the open-pans used in cereallegume blends formulations (Table 3) and further cooking of the reconstituted blend as porridge would totally degrade the endogenous ascorbic acid (Teucher et al., 2004). "
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