Exclusion of any food group from the diet can increase the risk of nutritional deficiencies.
Vegetarianism can exclude several food groups including meat, fish and alternatives and milk and dairy products.
Other foods may also be avoided if they have come into contact with animal products e.g. vegetables cooked in meat stock or other foods cooked in the same place as meats, depending on the individual.
This can create significant difficulties when trying to achieve a healthy balanced diet which meets all the recommended nutrient intakes.
Nutrients that should be carefully monitored include:
Vegetarians tend to have similar energy intakes to non-vegetarians in the adult population, although the energy content of vegan diets is often lower.
Although meat and dairy products tend to be excluded, energy intakes are usually maintained through consumption of energy dense foods such as vegetable oils, nuts, seeds and foods prepared with vegetable oils, such as pastries, cakes and biscuits.
Protein is essential for growth and repair as well as the synthesis of enzymes and hormones.
Meat and dairy products are excellent providers of “high biological value” protein which generally contains a full range of the essential amino acids that can only be provided by the diet.
Most vegetable proteins are lacking in at least one essential amino acid and are often described as “low or lower biological value” proteins.
Exclusion of meat and dairy products could therefore compromise essential amino acid intake, however a person consuming a wide range and variety of vegetable proteins should be able to obtain all the amino acids they need.
Vegetarians very often have fat intakes similar or slightly less than meat eaters as they can obtain the fat they require from food such as vegetable fats, nuts, cakes, chocolate and other processed foods.
Lacto-ovo-vegetarians and vegans very often have a much lower fat intake - but one which is closer to the Department of Health recommendations for fat intake (30-35% of overall energy intake).
In both vegetarian and vegan groups, saturated fat intake is often found to be lower than in meat eaters, which is associated with health benefits.
The carbohydrate intake from most vegetarian diets is usually similar or slightly higher to that of mixed or “omnivorous” diets.
Vegetarians and vegans have a consistently higher fibre intake, primarily due to the consumption of unrefined cereals and a greater intake of fruit, vegetables and pulses.
Although a high fibre intake has many health benefits, excessive consumption may inhibit the absorption of certain micronutrients such as iron, zinc and calcium. This is because high fibre foods often contain substances such as phytates and oxalates which can prevent absorption of nutrients. In addition, high fibre diets increase the speed in which food passes through the gut and can reduce the amount of time available for absorption of nutrients into the blood.
Fat soluble vitamins
Vitamin A is found primarily in animal foods and fortified foods such as fat-spreads, however it can also be made in the body from provitamin A e.g. beta-carotene found in red and orange fruits and vegetables and therefore deficiency is rare amongst vegetarians provided adequate amounts are consumed.
Vitamin D status does not differ greatly amongst vegetarians and omnivores since it can be made within the body after exposure to sunlight and therefore dietary sources are of less importance.
However, vegetarians who do not receive adequate sunlight e.g. certain vegetarian ethnic groups who cover their skin, may require supplements.
Vitamin E intakes are generally adequate and are frequently higher in vegetarians than omnivores as they eat more vegetable oils, wholegrain products and nuts which are providers of this vitamin.
Vitamin K status is usually good in vegetarians, due to high intakes of foods containing vitamin K such as green leafy vegetables - for example broccoli, cabbage and lettuce.
Water soluble vitamins
The intake of water soluble vitamins from a vegetarian diet is generally much higher than that of an omnivorous diet as the intake of foods containing these such as fruit, vegetables, pulses, nuts and wholegrains is generally higher.
Vitamin C, folate and thiamin intakes are generally higher in vegetarians and vegans than omnivores due to high intakes of foods such as fruits, vegetables and cereals.
Riboflavin intake may pose a potential problem since dairy products and meat are among the main providers of this vitamin and therefore supplements may be required if sufficient dietary intake is not possible.
Vitamin B12 is also not found in any significant amount in plant foods and consequently vegetarians and vegans may suffer from vitamin B12 deficiency.
Milk is a good provider of vitamin B12 therefore if consumption of milk is permitted they should not experience problems.
Vegans and others, who avoid all animal foods, must include foods containing vitamin B12 in their diet as the body’s requirement will not be met otherwise.
It can be obtained from supplements or fortified foods (yeast extract, fortified soya drinks or fortified breakfast cereal).
The intake of minerals depends very often on the foods consumed. Although higher intakes of iron, copper, potassium and magnesium have been observed in vegan subjects, lower intakes of selenium, calcium and iodine have also been noted. Zinc intakes may also be lower, particularly in female vegetarians.
Meat is a good provider of “haem” iron which is easily absorbed from the gut into the blood. Vegetables providing iron or “non haem” iron are less easily absorbed and this often means that poor iron status is a possible problem in vegetarians and vegans.
A diet high in cereals and grains also contains high levels of phytates which bind iron and reduce its absorption, while adequate vitamin C intake promotes iron absorption.
Female vegetarians in particular, should incorporate other foods containing iron into their diet, such as, fortified breakfast cereals, bread, pulses (e.g. soya beans), green vegetables, dried fruits (e.g. apricots), nuts and plain chocolate, so as to avoid the possibility of iron deficiency or anaemia. This is because females in general have higher iron requirements due to iron losses that occur during menstruation, and exclusion of iron containing foods will increase the difficulty of meeting dietary iron requirements.
Zinc has many functions in the body including growth, repair and health of the immune system.
Meat is a good provider of zinc and although other providers include dairy, bread, cereals, pulses, nuts and seeds, these plant foods also contain phytic acid which inhibits zinc absorption and may cause poor zinc status.
Male vegetarians and male omnivores generally have the same zinc intake, but intakes amongst female vegetarians are generally lower.
The calcium intake of vegetarians and omnivores is similar, and may actually be greater in lacto-ovo-vegetarians.
Vegans however have lower calcium intakes as dairy products are omitted from the diet.
They should ensure an adequate calcium intake by consuming plant providers of calcium e.g. beans, pulses, broccoli and green leafy vegetables (low in factors such as oxalate which inhibit calcium absorption) and calcium-fortified foods such as certain fruit juices.
Supplements may also be needed at some stage. Speak to your healthcare professional for advice.
Selenium is an important part of a number of body enzymes and is found in a number of foodstuffs such as meat and meat products, nuts, seeds and grains.
Vegetarians in the UK tend to have lower selenium intakes than omnivores. This pattern has emerged particularly since selenium levels in bread making flour were reduced in the late 1970’s.
Vegetarians and vegans may be at risk of selenium deficiency, and the addition of good providers of selenium to the diet is advisable such as nuts (and eggs if vegetarian).
Iodine is an essential trace element needed for normal mental and physical growth and development.
While lacto-ovo-vegetarians usually do not suffer from iodine deficiency due to the consumption of milk which is a rich source of iodine, vegans may be at risk of deficiency.
Similar to the impact of foods containing phytates on the availability of other minerals such as iron, zinc and calcium, iodine bioavailability can be inhibited by “goitrogenic” compounds although these are generally destroyed with cooking.
Goitrogenic compounds are found in nuts, cruciferous vegetables, millet, sweet potatoes and soya products - all of which are commonly consumed by vegans and may cause poor iodine status if not thoroughly cooked.
Vegans should be encouraged to use iodine supplements to prevent deficiency.
Potassium is essential for the proper functioning of cells including nerves.
Vegetarian diets often provide more potassium than omnivorous diets as vegetarians consume a wider variety of potassium containing foods, such as fruit (bananas), potatoes, vegetables and juices.