side effects of vegan diet
With the exception of vitamin B 12 a vegan diet can in principle provide all necessary nutrients. However, in practice, vegans are frequently deficient in calcium , iron , vitamin D , selenium , phosphorous , and zinc . Vitamin B 12 presents a special issue. This vitamin is not provided to any meaningful extent by non-plant foods. (The algae spirulina contains B 12 , but in a non-absorbable form.) Deficiency in B 12 is therefore inevitable among those who follow a strict vegan diet and do not take supplements.