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Iron, zinc, and calcium bioavailability influenced by dietary phytate content

Posted:  Monday, May 30, 2016

Dietary phytate content hampers mineral bioavailability

Deficiency of essential minerals in pregnant women may result in adverse birth outcomes. Micronutrient intake among pregnant women from resource-poor settings is usually inadequate. This deficiency is further exacerbated by the presence of dietary components such as phytates, which reduce the bioavailability of micronutrients.

A new study, published in the journal BMC Nutrition, looked at the influence of dietary phytate content on the mineral bioavailability in pregnant women from rural Bangladesh. Al Hasan and his colleagues used the multiple pass recall approach with a detailed interview covering 24-hour dietary recall among 717 pregnant women during their second and third trimesters.

The study indicated that the mean daily phytate intake was 695.1 mg, whereas the mean daily intakes of calcium, iron, and zinc were found to be 192.2, 5.1, and 5.7 mg, respectively. The mean molar ratios of phytate to calcium, iron, and zinc were 0.27, 12.8, and 11.2, respectively. Phytate in the diet inhibited iron absorption in all pregnant women, calcium absorption in 52% of pregnant women, and zinc absorption in 12% of pregnant women.

The molar ratios were significantly higher among the highest phytate intake group compared to the other groups. For every 100 mg increment in daily phytate intake, the molar ratios of phytate to calcium, to iron, and to zinc would be expected to be 0.05, 2.48, and 1.96 points higher, respectively. The variance in phytate to mineral molar ratios was significantly predicted by the phytate intake, inadequate micronutrient intake, gestational age, and energy intake. Phytate was the strongest inhibitory predictor of calcium, iron, and zinc bioavailability.

The study has significant limitations. The dietary assessment was obtained after a single 24-hour dietary recall, which failed to take into account the daily variation in nutrient intake. Moreover, the seasonal variation in the micronutrient intake of women was not assessed by the study, as it was conducted at a single time point. The absence of biochemical data on the serum concentrations of calcium, iron, and zinc precluded the correlation of molar ratios with biochemical deficiencies of the minerals.

In conclusion, the study highlights the problem of poor mineral bioavailability in the diet of rural pregnant women of Bangladesh due to high phytate intake. Supplementation and/or fortification of food may not meet the increasing needs of the pregnant women due to phytate-rich diets.

News Source: Al Hasan SM, Hassan M, Saha S, Islam M, Billah M, Islam S. Dietary phytate intake inhibits the bioavailability of iron and calcium in the diets of pregnant women in rural Bangladesh: a cross-sectional study. BMC Nutrition. 2016 Apr 21;2(1):1.

Links: http://bmcnutr.biomedcentral.com/articles/10.1186/s40795-016-0064-8