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Base foodLow concern
Wholegrain
In plain words
The short version
Carries phytates in the bran, which bind iron, zinc and calcium and reduce how much is absorbed.
Why it's green
It's widely considered safe at the amounts used in food, so we mark it green. The Safety section below has the details.
Safety profile
Phytic acid, concentrated in the bran layer, binds iron, zinc and calcium into compounds humans cannot break down. This is why iron from porridge is absorbed far less readily than iron from meat. Soaking, fermenting and leavening all reduce phytate — sourdough bread noticeably more than unleavened.
The detail
Grains with the bran and germ intact: oats, wholemeal wheat, brown rice, rye.
Not an argument against wholegrains, which bring fibre and minerals of their own. It is an argument for vitamin C alongside them if the meal is meant to supply iron.
Sources
- EFSA NDA Panel — Scientific opinion on the tolerable upper intake level for iron (EFSA Journal 2024;22:e8819) — European Food Safety Authority (EFSA), 2024. phytate inhibits non-haem iron absorption
- EFSA NDA Panel — Scientific Opinion on Dietary Reference Values for zinc (EFSA Journal 2014;12(10):3844) — European Food Safety Authority (EFSA), 2014. phytate reduces zinc absorption
- Reduction of phytic acid and enhancement of bioavailable micronutrients in food grains (Journal of Food Science and Technology, 2015;52(2):676–684) — Springer / Association of Food Scientists & Technologists (India), 2015. phytate binds iron, zinc and calcium; humans lack phytase; soaking and fermentation lower it
- Influence of Sourdough Fermentation-Induced Dephytinization on Iron Absorption from Whole Grain Rye Bread–Double-Isotope Crossover and Single-Blind Absorption Studies (Nutrients, 2025;17(24):3891) — MDPI (Nutrients), 2025. sourdough dephytinization raises iron absorption from wholegrain bread
Checked against these sources on .
Educational information only. Not medical, dietary or veterinary advice. Spotted an error? Tell us.