Because The Ingredients Are Not Properly Balanced.

Such diet may produce anaemia, from lack of meat or other animal food; scurvy, from preponderance of salt meat and fish and lack of fresh fruits and vegetables; rickets and marasmus, from errors in infant feeding, such as excess of amylaceous and lack of animal food, necessary salts, etc.; acne, or eczema, from food too rich in fats; constipation, from a too nutritious and concentrated diet; gout from various dietetic errors.

The belief is held by some authorities that a diet of coarse cereals and vegetables favours the development of chronic arteritis. (See Vegetarianism, p. 35).