Dr Ryde's Casebook - January 1999
I've heard that the iron in plant foods is less well absorbed than the iron in meat. Are vegetarians at greater risk of iron deficiency?
Iron is present in food in two forms: haem iron, which is found in meat; and non-haem iron, which is found in plant foods such as cereals, nuts, pulses and vegetables. Only a small proportion of dietary iron is absorbed by the body, the amount depending on the individual. However, it is generally agreed that 20 to 30 per cent of haem iron is absorbed, whereas only about 5 per cent of non-haem iron is absorbed, but this may be increased or decreased by other dietary and physiological factors.
The absorption of non-haem iron is inhibited by phytates, oxalates and phenols, which are present in plant foods, and by the tannin in tea. However, dietary fibre does not affect iron absorption, which is just as well because wholegrain cereals are a major source of iron in the vegetarian diet. The good news for vegetarians is that vitamin C (present in most fruits and vegetables) can significantly enhance the absorption of non-haem iron. For example, 75 mg vitamin C (equivalent to that found in 200 ml pure orange juice) can increase the absorption of non-haem iron by three to four times if consumed at the same meal as the iron-bearing foods. There is also evidence to suggest that the body is able to absorb more iron when body stores are depleted and, conversely, to reduce iron absorption when there is a danger of overload (like many nutrients, iron is toxic in excess).
Studies of vegetarians have generally found that their iron intake is similar to or even higher than that of omnivores. Although haemoglobin concentrations in vegetarians are generally within the normal range, some studies have found significantly lower serum ferritin levels (a measure of the amount of iron stored in the body) in vegetarians compared to omnivores, probably because of the lower absorption of non-haem iron noted above. This may actually be an advantage since recent studies have linked high iron reserves with an increased risk of heart disease and non-insulin dependent diabetes.
In summary, a well-planned vegetarian or vegan diet (dairy products are a poor source of iron) which contains plenty of fruits and vegetables, along with wholegrain cereals, nuts, pulses and seeds is likely to provide adequate iron. Rich sources of iron for vegetarians include bran cereals, fortified breakfast cereals, lentils, figs, cashew nuts, and sesame and sunflower seeds. Other good sources include wholemeal bread and low-oxalate green leafy vegetables (sorry Popeye, but the high oxalate content of spinach limits its value as a source of iron). The use of cast iron cooking utensils can also boost iron intake. Therefore, there is no reason why a well-nourished vegetarian or vegan should be at greater risk of iron deficiency. Indeed, in twenty years of meeting or consulting hundreds of vegetarians I cannot recall a single case of iron-deficiency anaemia.
Dr David Ryde