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Food

Carbohydrates 
Fat
Fiber
Protein
Minerals
Vitamin
Water
Other nutrients

Intestinal bacterial flora Balanced diet
Malnutrition
Food guide pyramid
Energy
Obesity and weight control
Pregnancy and lactation
Infancy (0–1 year of age)
Young children (1–6 years)
Adolescents (10–20 years)
Ageing
Illness
Anorexia nervosa and bulimia
Vegetarianism and veganism
Diet selection
How to interpret food labels
Food allergy and food intolerance
Food toxicity
Avoiding food-borne illness
Exercise
Protein
Carbohydrate
Fat
Alcohol
Water
Dietary fibre
Beverages
Cholesterol
Vitamins
Minerals 

Vegetarianism and veganism

People who live on a diet totally devoid of animal products are known as vegans and are rare in the western world. Much more common are those who eat milk, milk products and eggs in addition to plant foods: they are known as lacto-ovovegetarians, or vegetarians for short. Vegetarians are not, of course, a homogeneous group and among them are people who further restrict their diets in various ways. Some of these extra restrictions may be harmless, although they may make it very difficult to devise a nutritionally adequate diet; some of the extra restrictions, on the other hand, can be actually harmful. When considering the health of vegetarians in comparison with the health of the omnivorous general population it needs to be remembered that vegetarians often vary markedly from the general population in their use of alcohol, tobacco and other drugs and in their attitude to a healthy way of life.

Protein

mixtures of plant foods are valuable sources of protein. When eaten together, pulses (beans, peas, lentils) and cereals (wheat, rice, soybeans, rye, barley) provide a protein source as good as animal protein. In addition, eggs, milk and milk products have proteins of high nutritional quality and the amount of protein in hard cheese may equal or exceed that in animal muscle. Nuts and seeds, when puréed, are also useful sources of protein. Thus it is easy for a vegetarian to have an entirely satisfactory protein intake and it is not difficult for a vegan, though the latter has to eat a bulkier meal. The daily protein requirement remains the same for a vegetarian on a good diet as for a person eating all types of animal foods. T

 

Fat

The fat intake of vegetarians is somewhat lower than that of the general population. Currently, for vegetarians it is about 38 per cent of total energy intake, whereas it is about 41 per cent for the average omnivore. The vegetarian diet is higher in polyunsaturated fatty acids than the general diet and is lower in saturated fat so it should thereby convey a health advantage.

Dietary fibre

Vegans have a daily intake of about 50 g of dietary fibre, for vegetarians it is about 40 g and for omnivores it is about 25 g. Although a diet high in fibre is generally beneficial, an intake as high as 50 g per day may at first give a sense of bloating and will certainly produce considerable amounts of colonie gas which may cause discomfort. In addition, the fibre may reduce the intestinal absorption of iron, calcium and zinc and perhaps other minerals. The large quantity of plant material eaten may increase the phytate intake which will also lessen the absorption of iron and calcium. Severe mineral deficiency in vegetarians, however, is rarely seen.

Calcium, zinc and iron

For vegetarians, the dietary supply of calcium is very high because of their intake of milk and cheese, whereas for vegans the calcium intake may be less than desirable, especially in pregnancy, in lactation and in children and adolescents. Furthermore, vegans are likely to absorb calcium poorly because of the very high fibre and phytate in their diet. Many vegans would probably benefit from dietary supplementation with calcium tablets. The zinc intake in vegetarians, as in omnivores, is very variable and their zinc status is uncertain. The large fibre, phytate, oxalate and tannin intakes by vegetarians will tend to limit their absorption of both zinc and iron. The intake of iron by vegetarians and vegans is usually high, but the iron in plants is less easily absorbed than is the iron in animal foods. Nevertheless, most vegetarians and vegans are not iron-deficient. Their high vitamin C intake will aid the uptake of iron by the intestine.

Vitamins

Apart from vitamins B12 and D, vegans and vegetarians can get all the vitamins they need from plant foods. Vitamin A, which is found only in animal foods, can be derived from β-carotene and similar pigments widely spread in plants; of the B-group except B12 are easily obtained from numerous plants; vitamin C is abundant in citrus and other fruits; and vitamins E and K are available in many plants, with vitamin K being synthesized by micro-organisms in the large intestine from where it can be absorbed into the blood. The need for vitamin D can be satisfied by sunning the skin of the face and hands for perhaps an hour or two each day. Further amounts of vitamin D are available for vegetarians from dairy products and for vegans from vitamin D-enriched foods. Vitamin B12 is freely available to vegetarians in eggs, milk and milk  products, but for vegans vitamin B12 has to be obtained from enriched food or by supplementation. Normally available plant foods do not contain vitamin B12. When the intake of this vitamin is high it can be stored in the liver sufficiently well for a 5-year supply to be accumulated.

Vegetarian children

Vegetarian and vegan children can grow and develop normally. It is essential that the mother is well-fed during her pregnancy and lactation and that her mineral and vitamin intakes are high. During infancy most vegetarian children do well because most are breast-fed for at least six months. If bottle-fed, vegan infants can be fed on an infant formula based on soya, enriched with iron, calcium and vitamins. After six months of age, all vegetarian and vegan infants must have supplements of iron and vitamins A, B2, B12, C and D. These supplements may be started at one month, with vegan children getting extra calcium. Once weaning starts it is essential that vegetarian and vegan infants and young children get an adequate energy intake by keeping me fat in the diet higher than would be necessary for omnivore children. This is because the vegetarian diet is bulkier than the omnivore diet and there is the danger that the small stomachs of infants and young children will not be able to accept a sufficient volume of vegetarian food, leading to an energy deficiency. That this is a real problem rather than just a theoretical one is shown by the finding that many vegetarian children are lighter than age-matched omnivore children, although this does not necessarily mean that the vegetarian children are unhealthy. Most vegetarian children do not show signs of dietary deficiency because their parents know how to prepare good vegetarian diets.

General health

Vegetarians are lighter in body weight and have a lower body mass index than omnivores and because of the low incidence of obesity among vegetarians there is a low incidence of late-onset diabetes mellitus. Most life-long vegetarians and vegans have a lower blood pressure than the general population. In addition, coronary heart disease is less common in vegetarians than in omnivores, which may be due to lower body weight, to increased intake of dietary fibre, to lower blood cholesterol levels, to lower saturated fat intake, to higher intake of polyunsaturated fatty acids, to an increased intake of vitamins A, C and E and to a generally healthier life-style. The high fibre diet also seems to reduce the risk of developing some large bowel diseases. Despite all these advantages apparently derived from their diet and general regard for their health, vegetarians do not appear to live longer than non-vegetarians, although they may be healthier while they are alive.