A vegetarian diet confers a wide range of health benefits. Research has proven that vegetarians suffer less from many of the dieases linked to a modern Western diet: obesity, coronary heart disease, hypertension, type II diabetes, diet-related cancers, diverticular disease, constipation and gall stones (British Medical Association,1986; Dwyer, 1988).

MORTALITY
Epidemiological studies provide clear evidence that vegetarians have a reduced general and cause-specific mortality (McMichael, 1992).
In an 11-year study of 1,900 vegetarians in Germany, Chang-Claude (1992) found mortality from all causes was reduced by one-half compared with the general population. This was mainly attributable to reduced cardiovascular disease in both men and women. A longer duration of vegetarianism was associated with a lower risk, pointing to a real protective effect of the lifestyle (Chang-Claude, 1993).
A 12-year follow-up study of 6,115 British vegetarians and 5,015 meat-eaters found all cause premature mortality to be 20 per cent lower among the vegetarians after adjusting for the confounding effects of smoking, body mass index and socioeconomic status (Thorogood, 1994). Cancer mortality was 39 per cent lower and ischaemic heart disease 28 per cent lower among the vegetarians.
A 21-year study of Californian Seventh-Day Adventists also revealed a significant association between meat consumption and all causes of mortality (Kahn, 1984).
While other factors influencing health such as socioeconomic differences, smoking and physical activity may play a confounding role in these studies, there is sufficient evidence to suggest that a reduced risk of mortality is directly linked to a vegetarian diet.
CARDIOVASCULAR DISEASE

Cardiovascular disease is the main cause of premature mortality in Britain, with most deaths being caused by coronary heart disease.
Vegetarians have a significantly lower incidence of coronary heart disease than meat-eaters. Burr and Butland (1988) found mortality from heart disease was 29 per cent lower in a study of more than 6,000 British vegetarians compared with a control group of health-conscious meat-eaters.
A study of more than 25,000 Seventh-Day Adventists noted a definite dose-related link between meat consumption and heart disease (Snowdon, 1984). Among men aged 45 to 64, those who ate meat daily were three times more likely to die from heart disease than those who did not eat meat.

The degenerative processes leading to heart disease can begin at an early age. Atherosclerosis, the forming of fibrous plaques on arterial walls and one of the first stages in the development of cardiovascular disease, has been observed in young children and adolescents. The Coronary Artery Risk Development in Young Adults (CARDIA) study examined the relationship between diet and health in more than 5,000 young adults aged 18 to 30 (Slattery 1991). Vegetarians were found to have a greatly improved cardiovascular fitness and a lower risk of heart disease.
One way that a vegetarian diet is thought to protect against heart disease is the lower cholesterol levels seen in vegetarians. Raised cholesterol is widely recognised as a primary risk factor for heart disease and studies have consistently demonstrated serum cholesterol levels in vegetarians as being around 10 per cent lower than in non-vegetarians (Burr, 1981; Knuiman and West, 1982; Thorogood, 1990). This figure may result in a 20 to 50 per cent reduction in the incidence of heart disease (Law, 1994). The lower serum cholesterol levels in vegetarians is largely due to lowered low-density-lipoprotein (LDL) cholesterol. This is the cholesterol fraction associated with heart disease.
Healthy eating advice aimed at reducing the risk of heart disease often encourages the use of lean meat cuts. However, in a comparison between a vegetarian diet and a lean meat diet (Kestin, 1989), the vegetarian diet was shown to lower cholesterol more effectively and so lessen the risk of cardiovascular disease.
The California Lifestyle Heart Trial indicated that a low-fat vegetarian diet together with other lifestyle changes such as increased exercise and stress management can actually reverse the progress of heart disease by reducing cholesterol plaques in arteries (Ornish, 1990). Barnard (1992) has shown a low-fat vegetarian diet can achieve high levels of compliance and acceptability among patients with heart disease.
OBESITY

Obesity is a major health problem in the UK and its incidence is increasing in both adults and children. Around 12 per cent of women and 8 per cent of men are clinically obese (Gregory, 1990) and many more are overweight.
Obesity predisposes sufferers to a range of conditions including cardiovascular disease, type II diabetes, and hormone-dependent cancers such as breast cancer. Vegetarians are typically leaner than meat-eaters and obesity is less common in vegetarian populations. Body mass index (BMI) for vegetarians is lower than in meat-eaters and closer to desirable levels (Thorogood, 1989). Levin (1986a) found the prevalence of obesity to be 5.4 per cent in a vegetarian group compared with 19.5 per cent in non-vegetarians. This may be due to vegetarians' lower energy intake overall, with a lower proportion of energy being supplied by fat.

HYPERTENSION
Hypertension, or high blood pressure, can contribute to heart disease, strokes and kidney failure. Both cross sectional populaton studies (Armstrong, 1977; Rouse, 1983) and controlled trials in hypertensive subjects (Margetts, 1986) provide evidence that vegetarians have lower blood pressure than non-vegetarians.
The reason for this is unclear. Studies suggest that the effect is not due to changes in any specific nutrient intake but the overall effect of combined nutrient change (Beilin, 1990).
DIABETES
Around one million people in the UK suffer from diabetes. Of these, about 75 per cent have type II diabetes (non-insulin dependent).
Snowdon (1985) found vegetarians had a substantially lower risk of type II diabetes than non-vegetarians. The link between meat consumption and incidence of diabetes remained after contributory factors such as weight, physical activity and other dietary factors were accounted for.
Dietary recommendations for diabetics encourage a high intake of complex carbohydrates and fibre and low consumption of total and saturated fat (British Diabetic Association, 1982). Vegetarian diets tend to match these recommendations more closely.
The relative leanness of vegetarians also protects against diabetes, obesity being a major risk factor.
GALL STONES
Gall stones are composed af cholesterol, bile pigments and calcium salts. They form in the gall bladder and can cause severe pain.
A study of more than 750 women found that non-vegetarians were almost twice as likely to develop gall stones as vegetarians (Pixley, 1985).
DIVERTICULAR DISEASE AND BOWEL FUNCTION
Diverticular disease is widespread in the UK. Symptoms include abdominal pain and a disturbed bowel habit, usually constipation but sometimes diarrhoea. Gear (1979) found it to be significantly less frequent among vegetarians, probably due to the higher fibre content of vegetarian diets.
The high fibre content of vegetarian diets has also been linked with decreased incidence of constipation, appendicitis, irritable bowel syndrome, haemorrhoids and varicose veins (Dickerson, 1985).
CANCER

Cancer is second only to coronary heart disease as a cause of death in Britain. Accounting for around 25 per cent of all premature deaths with lung, breast and colo-rectal cancers being the most common.
It is estimated that at least one third all cancers are directly related to diet. Research has indicated that vegetarian diets may offer protection against diet-related cancer. PLANT FOODS AND CANCER

Plant foods contain a number of substances which are believed to protect against cancer. Indoles, lignans, isoflavones, protease inhibitors and others have all been shown to be potent anti-carcinogens and may play an important role in the lower cancer incidence among vegetarians.
In contrast, cooked meat and fish contains carcinogens known as heterocyclic amines (HA's). These are present at high levels in the urine of people consuming cooked meats and have been shown to be metabolically active in humans. Evidence suggests meat-derived HA's may play a role in breast, colon and pancreatic cancer (Snyderwine 1994).

COLON AND RECTAL CANCERS
Vegetarians have significantly lower rates of colon cancer than non-vegetarians (Phillips, 1975; Chang-Claude, 1992) and incidence of both colon cancer and rectal cancer has been strongly linked to meat consumption (Willett, 1990; Bidoli, 1992).
The protective effect of a vegetarian diet against colon and rectal cancer is probably due to increased fibre intake and increased consumption of fruit and vegetables together with a lower intake of both saturated and total fat.
Vegetarians have lower levels of colonic bile acids and other faecal mutagens that can promote colon carcinogenesis (Johansson, 1992; de Kok, 1992).
Certain dietary components which are present at increased levels in plant-based diets such as folate, phytosterols and protease inhibitors, have been shown to inhibit colon carcinogenesis and may play an important role in its lower incidence among vegetarians (Troll, 1991; Rao, 1992; Giovannucci, 1993a).
Vegetarian diets also usually include high levels of antioxidant nutrients, the main ones being beta-carotene, vitamin C, and vitamin E. Antioxidants protect the body against damage from highly reactive molecules known as free radicals, generated naturally as a result of oxygen metabolism. Environmental pollutants, cigarette smoke and processed foods can all increase levels to which the body is exposed. Mounting evidence suggests antioxidants exert a considerable protective effect against both cancer and heart disease (Diplock, 1993).
BREAST CANCER
Breast cancer accounts for around 15,000 deaths each year in the UK. Known risk factors include age, obesity, early menarche, late menopause and family history.
Some studies have suggested a casual relationship between dietary fat intake and breast cancer, populations with diets high in animal fat and animal protein having the highest breast cancer mortality rates. However, other studies have found little or no relationship between fat intake and breast cancer, though it has been suggested that this may be due to insufficient between-person variations in fat intake within populations as well as methodological limitations (Rose, 1990; Hankin, 1993).
Evidence suggesting vegetarian women are at lower risk than non-vegetarian women is limited as differences in the incidence of breast cancer between vegetarian and non-vegetarian women are inconsistent. Mills (1989a) found no difference during a six-year study. However, among women with a relatively early menopause (48 years of age or younger) meat consumption and risk of breast cancer were linked (Mills, 1988).
Certain of the known risk factors for breast cancer may be lessened on a vegetarian diet. Obesity is less common and age of menarche may be delayed (Sabate, 1992). Vegetarian women also have altered sex hormone profiles with lower levels of circulating oestrogens (Goldin, 1982; Bennett, 1990). Adlercreutz (1992) has suggested that lignans and isoflavonoid phytoestrogens, present at high levels on vegetarian diets, may affect sex hormone metabolism and so protect against breast cancer. It is also believed that dietary fibre may play a protective role (Baghurst, 1994).
PROSTATE CANCER
Prostate cancer has been strongly linked to meat consumption. In a study of nearly 48,000 men aged between 40 and 75, those eating red meat five or more times a week were 2.6 times more likely to suffer from prostate cancer than those who ate it once a week or less (Giovannucci, 1993b). Mills (1989b) also noted a link between meat consumption and prostate cancer risk.
LUNG CANCER
Vegetarian populations show lower mortality rates from lung cancer compared with non-vegetarian populations. This is largely due to the fact that vegetarians tend to be non-smokers but dietary factors may also play a role. A high level of fruit and vegetable consumption has been shown to be protective against lung cancer (Marchand, 1989; Fraser, 1991). Goodman (1992) suggested that smokers who also had a high intake of animal fat and animal protein had a greater risk of developing lung cancer than other smokers.
OSTEOPOROSIS
Osteoporosis is a condition in which bone mass decreases, making bones more susceptible to fracture. It is a major cause of bone fractures in post-menopausal women and older people in general and is a considerable public health problem. It is linked a number of risk factors, including diet.
Cross-cultural studies have suggested osteoporosis and associated hip fracture may be related to high animal protein intake (Abelow, 1992). Dietary protein has been shown to increase the loss of calcium from bones and urinary calcium excretion. Calcium loss is greater on a diet high in animal protein (Breslau, 1988). Animal protein has a higher sulphur content than vegetable protein and this is believed to lead to raised metabolic acid production and so increase bone calcium loss.
Marsh (1980) found vegetarian women aged between 50 and 89 years lost 18 per cent of bone mass while a control group of non-vegetarian women had a 35 per cent bone loss and suggested a vegetarian diet may be beneficial in protecting against postmenopausal osteoporosis.
Other studies have found no difference in bone density and bone mineral content between vegetarians and non-vegetarians (Hunt, 1989; Tesar, 1992).