Energy intakes of vegetarians and vegans meet UK recommended levels (Thorogood, 1990; Draper, 1993) and are in line with World Health Organisation recommendations for adults engaged in light to moderate activities (WHO, 1985). They are also similar to recorded energy intakes for meat-eaters (Gregory, 1990).
Accepted dietary recommendations are that most adults in the UK should reduce their total dietary fat intake.
The 1991 UK Dietary Reference Values; (DRV's) recommend that total fat intake for the population should be no more than 33 per cent of dietary energy (including alcohol) or 35 per cent of energy derived from food. Saturated fatty acids should provide no more than 11 per cent of food energy. The Government policy document The Health of the Nation (Department of Health, 1992) endorsed these targets.
The 1992 National Food Survey (MAFF, 1993) found that fat supplied over 41 per cent of food energy, with over 16 per cent coming from saturated fatty acids.
In general, vegetarians have a lower intake of fat than non-vegetarians (Taber and Cook, 1980). However, the percentage of food energy supplied by fats may still be higher than is desirable. Draper (1993) found 37 per cent of food energy came from fat among vegetarians. This was not significantly different from the 38 per cent among meat-eaters (Gregory, 1990). Vegan diets came closer to the ideal, with 34 per cent of food energy coming from fat.
Vegetarians must ensure that they do not simply substitute high-fat dairy products or convenience vegetarian foods for meat and meat products.
While total fat intake may not always differ significantly between vegetarians and non-vegetarians, vegetarians have consistently been shown to have a lower intake of saturated fat, a higher intake of polyunsaturated fat, and a higher polyunsaturated to saturated fat (P:S) ratio. This may play a part in vegetarians' lower incidence of cardiovascular disease.
ESSENTIAL FATTY ACIDS
Two polyunsaturated fatty acids must be present in the diet as the body
is unable to synthesise them. These essential fatty acids are linoleic acid
and alpha-linolenic acid. Linoleic acid is present at high levels in many vegetables,
fruits, nuts, cereals and plant oils; alpha-linolenic acid is less abundant
but is present in linseed, soyabean and rapeseed oils at high levels, as well
as in pulses, walnuts, broccoli and leafy green vegetables.
Alpha-linolenic acid is converted to eicosapentaenoic acid (EPA) in the body, which is in turn converted to docosahexanoic acid (DHA). DHA is required for retinal and brain function and is important for foetal and infant development.
Vegan diets are devoid of EPA and DHA while vegetarian diets provide small
amounts in dairy products. Vegetarian and vegan women should ensure their diets
include sources of alpha-linolenic acid during pregnancy and breast feeding.
Sanders (1992) has suggested vegans should use plant oils with a low ratio of
linoleic acid to alpha-linolenic acid, eg soya bean or rapeseed oil, as a high
ratio may inhibit conversion of alpha-linolenic acid to DHA. It is important
that the diet has the correct balance of linoleic acid to alpha-linolenic acid
and this can be achieved on a vegetarian diet.
CARBOHYDRATES AND DIETARY FIBRE
Dietary advice is to increase consumption of complex carbohydrates and dietary fibre (non-starch polysaccharides, or NSP) by increasing the consumption of plant foods. Compared with non-vegetarians, vegetarians typically have diets higher in both complex carbohydrate and fibre (Davies, 1985: Wiseman, 1987; Thorogood, 1990). Fibre consumption by vegetarians invariably exceed the DRV of 1.8g/day for adults, tending to range from 33g/day upwards.
There has been some concern over the possibility that diets excessively high in fibre may reduce the bioavailability of certain minerals, including calcium, iron and zinc. However, populations habitually consuming high fibre diets are not characterised by mineral deficiencies.
Protein intakes of vegetarians are generally lower than those of non-vegetarians but still meet UK dietary recommendations. Jackson (1993) calculated the average intake of protein by vegetarians in the UK to be 57g/day, compared with 75g/day for non-vegetarians. Draper (1993) found protein intake in vegetarians to be 66g/day for men and 56g/day for women. UK recommendations are 55g/day for men and 45g/day for women.
Vegetarians eating a balanced diet obtain protein from a variety of food sources. This means essential amino acid requirements can be met by plant foods. The idea of combining proteins from different plant sources to provide all of the necessary essential amino acids is known as protein complementing. Previous emphasis on protein complementing has been overstated and it is now widely accepted that it is not something vegetarians eating a balanced diet need consider.
In fact, the lower protein intake of vegetarians may be beneficial as there is concern that high protein intake may be associated with health risks. Poor or failing kidney function may be aggravated and the loss of calcium from bones increased by excessive dietary protein. In both instances, animal protein appears to be more harmful than plant protein. A high intake of animal protein may also play a contributory role in raised blood pressure (Bursztyn, 1985).
A lower animal protein intake almost inevitably results in a lower fat intake, especially saturated fat, as foods high in animal protein also tend to be high in fat. Dietary advice is to increase the proportion of protein from plant sources (NACNE, 1983).
A balanced vegetarian diet supplies all the vitamins the body requires. Surveys have shown the vitamin status of vegetarian populations to be satisfactory (Shultz, 1983; Helman, 1987). Draper (1993) found intakes of most vitamins for adult vegetarians in the UK to be adequate and in many cases higher than the national average.
Certain vitamins, such as vitamin B12 and vitamin D, are primarily found in animal foods and so concerns over the vitamin status of vegetarians and vegans tend to focus on these.
The only reliable unfortified sources of vitamin B12 are animal foods. Research into possible plant food sources of B12 have found that either no significant amount of B12 is present or that any B12 present is a structurally similar analogue that cannot be utilised by the body.
Vegetarians generally obtain adequate B12 from dairy products. Draper (1993) found mean intake of vitamin B12 in vegetarians to be 181 per cent of the RNI in men and 121 per cent in women.
Vegans tend to have lower vitamin B12 intakes which may or may not reach recommended levels. Vegans should be advised to ensure their diet includes foods that are fortified with vitamin B12. A range of vitamin B12 fortified foods is available, including yeast extracts, vegetable stocks, vegetable burger mixes, soya milks, margarines, breakfast cereals and herbal soft drinks.
Vitamin D is present in vegetarian diets in dairy products. Vegans tend to have low vitamin D intakes, fortified margarines being the main dietary source. However, it is assumed that sufficient amounts of the vitamin can be obtained by dermal synthesis due to the action of sunlight on exposed skin.
Vegans or vegetarians consuming limited dairy products and who are not exposed to sunlight may be advised to take supplementary vitamin D. Groups at risk of insufficient vitamin D include infants and elderly persons confined indoors.
Riboflavin (vitamin B2) may also be low on vegan diets, the main dietary source being milk and milk products. Vegans should ensure their diet includes other sources of riboflavin. such as fortified breakfast cereals, yeast extract and mushrooms.
Vegetarians have adequate mineral intakes and a balanced vegetarian diet
does not lead to mineral deficiencies (Abdulla, 1984; Freeland-Graves, 1988).
Studies of the mineral status of vegetarians have concentrated on iron and zinc, meat and meat products being a major source for both of these minerals.
Vegetarians appear to be at no greater risk of iron deficiency than non-vegetarians and have an adequate intake of iron from plant food sources (Anderson, 1981; Levin, 1986b). Praper (1993) showed mean iron intakes of both vegetarians and vegans met the UK DRVs and indeed exceeded the mean intake of comparative non-vegetarian adults from a nationwide survey.
Non-haem iron from plant foods is less readily absorbed by the body than
haem iron from meat and meat products. However, vitamin C greatly improves non-haem
iron absorption and vegetarian diets are generally rich in vitamin C. It is
recommended that plant food sources of iron are consumed at the same time as
vitamin C rich foods or drinks to facilitate absorption. Good sources of iron
for vegetarians include leafy green vegetables, pulses (including baked beans),
dried fruit, wholemeal bread and fortified breakfast cereals.
There is some suggestion that vegetarians may adapt to their diet by an increased ability to absorb iron (Anderson, 1981). For this reason, new vegetarians may be at a greater risk of iron deficiency than long-term vegetarians (Helman, 1987).
Zinc status among vegetarians also appears to be adequate (Levin, 1986b; Draper, 1993). Freeland-Graves (1980) found no significant differences in mean zinc intakes between vegetarians and non-vegetarians. However, some vegetarian women had low zinc intakes and this was attributed to limited consumption of zinc-rich foods such as pulses and wholegrains. Low zinc intake reflects poor food choices rather than inadequate food sources.
The bioavailability of both iron and zinc is reduced by fibre, phytates and other dietary factors present in plant foods. However, Anderson (1981) found the iron and zinc status of vegetarian women was normal despite high fibre and phytate intake while other studies have confirmed that a high fibre intake does not appear to affect mineral utilisation by vegetarians (Rattan, 1986; Kelsay 1988).
Due to their avoidance of dairy products it has been suggested that vegans may be at risk of calcium deficiency. However, studies have indicated that vegan populations receive adequate calcium from plant foods (Abdulla, 1981, Draper, 1993). Vegetarians have calcium intakes similar to or exceeding those of non-vegetarians.
There is also evidence to suggest vegans may be at risk of iodine deficiency, milk and milk products being the main dietary source (Key, 1992; Draper, 1993). However, many vegans consume edible seaweeds which are good sources. Cereals and vegetables can also contain available amounts, depending on iodine levels in the soil in which they are grown.