Diets high in bran decrease iron absorption by over 90%

This study was published in the American Journal of Clinical Nutrition 1989 Mar;49(3):542-5

Study title and authors:
Iron absorption: no intestinal adaptation to a high-phytate diet.

Brune M, Rossander L, Hallberg L.
Department of Medicine II, University of Göteborg, Sweden.

This study can be accessed at: http://www.ncbi.nlm.nih.gov/pubmed/2538051

Brune notes that several studies have shown that bran (and its high phytate content) inhibits the absorption of iron in man.

The present study examined the possibility that a high bran and phytate intake over a long period would induce adaption in the intestines or its microflora leading to a reduction of the inhibitory effect of dietary phytates on iron absorption. Such changes might occur in vegetarians and populations in developing countries with a usually very high dietary intake of phytates. The study included 13 dedicated vegetarians or vegans who had had a high phytate intake for around 25 years who were compared with six subjects who had a normal unrestricted diet.

The effect of bran on iron absorption was studied by comparing iron absorption from wheat rolls (i) with bran and (ii) without bran in both the vegetarian and non-vegetarian groups.

The study found:
(a) The bran rolls had a large inhibitory effect on iron absorption in both vegetarians and non-vegetarians.
(b) The effect was almost identical in both groups (93% inhibition in the vegetarian group and 92% in the non-vegetarian group) even though the vegetarians had had a very high phytate intake for a long time and the non-vegetarians had a much lower phytate intake.
(c) It can be concluded that no adaption could be observed among the vegetarians despite their high phytate intake.

The study concludes that the fact their is no intestinal adaptation to a high phytate intake has wide nutritional implications, and that a diet with a high phytate content must always be considered to impair iron absorption even if phytate intake has been high for several years.