Inositol phosphates with different numbers of phosphate groups influence iron absorption in humans

Area of Science:

• Nutritional Science
• Human Physiology
• Food Chemistry

Background:

• Inositol hexaphosphate (IP(6)) is a known inhibitor of iron absorption.
• The impact of less-phosphorylated inositol phosphates on iron absorption is less understood.

Purpose of the Study:

• To investigate the effects of inositol tri-, tetra-, and pentaphosphates (IP(3), IP(4), IP(5)) on human iron absorption.
• To determine the role of different inositol phosphate forms in iron bioavailability.

Main Methods:

• Human studies measuring iron absorption from single meals using extrinsic labeling with iron isotopes ((55)Fe, (59)Fe).
• Quantified whole-body retention and erythrocyte uptake of iron isotopes.
• Administered meals containing specific concentrations of IP(3), IP(4), and IP(5) added to white-wheat rolls.

Main Results:

• Inositol pentaphosphate (IP(5)) significantly reduced iron absorption by 39%.
• Isolated inositol tri- and tetraphosphates (IP(3), IP(4)) showed no significant effect on iron absorption.
• Combined IP(3) and IP(4) in processed foods led to substantial iron absorption reductions (54-64%).

Conclusions:

• Inositol pentaphosphate (IP(5)) inhibits iron absorption, but IP(3) and IP(4) do not in isolation.
• IP(3) and IP(4) contribute to reduced iron absorption in processed foods, likely through iron binding.
• Degradation of inositol phosphates to forms less phosphorylated than IP(3) may enhance iron absorption from cereals and legumes.