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Iron deficiency is common among human vegetarians, so how do herbivores cope?

• Vegetarians have dietary difficulties because they force their omnivorous physiology to cope with a herbivorous diet, mineral imbalances being only one of the consequences.

Herbivores survive in good health partly because some are not as vegan as we might imagine. They eagerly eat animal dung, old bones, incidental insects and the like. They are also not too proud to eat dirt wherever they find a salt lick. Also, practically all herbivores rely on a partnership with gut flora to supply micronutrients or improve digestion.

Then again, they need to eat huge volumes of vegetation to ensure they absorb sufficient quantities of minerals from the minute concentrations in plants. After all, plants contain a little iron and manganese as well as macronutrients such as magnesium because these are needed for photosynthesis.

Humans trying to match the performance of specialist herbivores would need bellies like proboscis monkeys, and would be eating 18 hours a day just to keep up; never mind the consequent activity at the nether end, nor the tooth wear that, as herbivores, humans would suffer.

Jon Richfield, Somerset West, South Africa