Phytate (also called phytic acid and inositol hexakisphosphate (IP6)) is a plant source of phosphate that has the ability to form complexes with proteins and metal irons. These complexes are pH dependent, and binding between metal iron and phytate likely reduced the bioavailability of that metal iron in humans. Studies have demonstrated the ability of dietary phytate to lower the bioavailability of divalent metal ion in human nutrition, including iron. However, controversy exists regarding the role of phytic acid in non-haem iron bioavailability because many studies have tested iron absorption after a single meal containing high amounts of phytate, something that does not represent the real world situation of human eating patterns. In addition, other studies using longer timescales have show reduction in the absorption of non-haem iron with high phytate diets but have often had to manipulate other factors such as the vitamin C and protein content of the diet, in order to see effects.
Humans may adapt to high fibre diets over time, such that the phytic acid levels of the diets may not affect non-haem iron absorption. This may reflect increases in iron absorption rates, or decreases in iron excretion rates.
A recent study published in the Journal of nutrition fed healthy, but iron deficient subjects, a diet containing a high (1190 mg/d phytic acid) or low (385 mg/d phytic acid) phytic acid content for 8 weeks. Following the 8 week diet, the subject consumed a test meal that contained 350 mg of phytic acid. The non-heam iron absorption was then assessed following this meal. The results of the study showed that in the high phytate group, there was an increase in non-haem absorption between the baseline and following 8 weeks of high phytate consumption. However, for the low phytate group there was no change between the baseline and following 8 weeks. Therefore, there may be some adaptation to high phytate diets over time, and as such they may not affect iron bioavailability in the long-term. However, the best source of iron remains haem iron from animal tissue, as it is less affected by gastrointestinal factors such as phytate levels. Iron deficiency remains the most common nutritional deficiency worldwide.
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