IRON BIOAVAILABILITY

IRON BIOAVAILABILITY is the proportion of ingested iron which is absorbed from the intestines and transferred into the circulation.

Haem iron:   iron as haemoglobin found in red meat, poultry and fish, is approximately 20% or more absorbed when assessed as a single food.

Non haem iron:   ferrous or ferric iron salts as found in non-animal sources including plant foods and supplements, is absorbed at the rate of 5% or less.

Ascorbic acid can enhance non-haem iron absorption by 2 to 3 times when the dose is kept well below 1,000 mg daily and the variety of foods within the meal is minimal.

The muscle proteins in meat enhance the absorption of non-haem iron by up to 3 times.   Alcohol, lactic, tartaric and citric acids have been reported to increase absorption.

Phytate is a potent inhibitor which can decrease non-haem iron absorption by 50 to 80%.   It is found particularly in cereals, (highest content in those unrefined), legumes and nuts.   A wholemeal bread roll contains 300 mg of phytate, a white roll has 25 mg, cornflakes 40mg/100gram, shredded wheat cereals 950 mg/100 gram and high bran cereals 3,000 mg/100 gram.   Therefore, take ascorbic acid if your diet is high in phytate.

Polyphenols inhibit non-haem iron absorption, they are found in tea, (250 ml cup of black tea reduces absorption by 50%), coffee and some vegetables.   Therefore I recommend tea and coffee be consumed only between meals.

Calcium from dairy foods and supplements has been shown to inhibit both haem and non-haem absorption in a single meal, overall dietary link not clear.   Iron and Calcium do compete with each other for absorption.

Soy products have low IRON BIOAVAILABILITY, except when processed ie miso, tofu.

Breast milk has high IRON BIOAVAILABILITY, cow’s milk iron is plentiful but poorly absorbed and soy milk iron is least readily absorbed.

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