ENERGY
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).
FATS
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
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).
VITAMINS
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.
MINERALS
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.