Main results from the Oxford Vegetarian Study
The Oxford Vegetarian Study is a nationwide long-term study of the health of
6000 persons who do not eat meat (mostly vegetarians, but including some persons
who eat fish) and 5000 meat-eating controls. Vegetarian subjects were recruited
with the help of The Vegetarian Society, through vegetarian and health food
magazines, and via the media. The control group consists of meat-eating friends
and relatives of the non-meat eaters, matched on age and gender. Recruitment
to the study took place between September 1980 and January 1984.
Volunteers were sent an initial questionnaire requesting information about their
diet, lifestyle (smoking, drinking, work and exercise) and previous medical
history. Later, volunteers under the age of 70 were asked to provide a blood
sample, and in 1985-86 all participants were sent a dietary record form which
they were asked to complete on two weekdays and both weekend days. As a result,
blood cholesterol measurements are available for nearly 3800 participants and
detailed dietary intake data are available for over 5000 participants.
Diet and serum cholesterol concentration
Total, low density lipoprotein (LDL) and high density lipoprotein (HDL) cholesterol
levels were compared in each of four diet groups (vegans, vegetarians, fish
eaters and meat eaters) in a paper published in 1987. Total and LDL cholesterol
concentrations were both significantly lower in the vegans than in the meat
eaters with the vegetarians and fish eaters having intermediate and similar
values. HDL cholesterol concentration was similar in all four diet groups. The
differences suggested that the incidence of coronary heart disease may be 24%
lower in lifelong vegetarians and 57% lower in lifelong vegans than in meat
eaters. A subsequent analysis of the diets of a sample of 208 participants (52
from each diet group) showed that the nature rather than the quantity of dietary
fat is an important determinant of cholesterol concentration, with health-conscious
individuals selecting a fat-modified rather than a low fat diet.
Plasma lipids and lipoprotein cholesterol concentrations in people with different
diets in Britain. Thorogood M, Carter R, Benfield L, McPherson K, Mann JI. British
Medical Journal 1987;295:351-353.
Dietary intake and plasma lipid levels: lessons from a study of the diet of
health conscious groups. Thorogood M, Roe L, McPherson K, Mann J. British Medical
Journal 1990;300:1297-1301.
Diet and mortality
A comparison of the mortality (death rate) of meat eaters and non-meat eaters
after 12 years of follow-up was published in the British Medical Journal on
25 June 1994. The results show that after adjusting for smoking habits, body
mass index (a measure of obesity) and social class (three factors known to influence
mortality), the non-meat eaters experienced lower death rates for all causes
of death combined, ischaemic heart disease and all cancers combined, the differences
being statistically significant (meaning that they were unlikely to have arisen
by chance) for all causes and all cancers combined. Only time will tell whether
these differences are real or a manifestation of the 'healthy volunteer effect'
(the vegetarian volunteers may have been better motivated and therefore healthier
than their non-vegetarian controls). If real, it will be interesting to see
whether the lower mortality for all cancers combined applies 'across the board'
or only to certain cancers which other studies have suggested vegetarians may
be less likely to suffer from. Eventually, it may even be possible to determine
which features of the vegetarian diet account for the lower mortality.
Risk of death from cancer and ischaemic heart disease in meat and non-meat eaters.
Thorogood M, Mann J, Appleby P, McPherson K. British Medical Journal 1994;308:1667-1671.
Emergency appendicectomy and meat eating
Rates of reported emergency appendicectomies (indicating acute appendicitis)
were compared according to participants' history of meat consumption in a paper
published in the Journal of Epidemiology and Community Health. Participants
were grouped according to whether they had always eaten meat, never eaten meat
or stopped eating meat. The percentage who reported an emergency appendicectomy
was higher among the lifelong meat eaters (10.7%) than either the lifelong non-meat
eaters (7.8%) or the former meat eaters (8.0%); and the operations were performed
at an earlier age in the first group (average age at operation 18.9, 26.0 and
19.6 years respectively). The overall age-adjusted emergency appendicectomy
rate ratio comparing participants who did not eat meat with those who did was
0.47, suggesting that vegetarians have a 50% lower risk of requiring an emergency
appendicectomy than non-vegetarians.
Emergency appendicectomy and meat consumption in the UK. Appleby P, Thorogood
M, McPherson K, Mann J. Journal of Epidemiology and Community Health 1995;49:594-596.
Effects of diet, lifestyle and physical characteristics on cholesterol concentration
The effects of dietary, lifestyle and physical factors on participants' concentration
of total and high density lipoprotein (HDL) cholesterol in the blood was investigated
in a paper published in the Journal of Human Nutrition and Dietetics. High total
cholesterol concentration is associated with an increased risk of coronary heart
disease, whereas HDL cholesterol is thought to have a protective effect against
heart disease. After adjusting for age there was a progressive decrease in total
cholesterol concentration from meat eaters to vegans for both male and female
participants, with vegetarians having intermediate values. In contrast, HDL
cholesterol concentrations were similar in all diet groups for both men and
women. When the effects of specific dietary and lifestyle factors were considered
meat and cheese consumption were found to increase total cholesterol, whereas
a high intake of dietary fibre was associated with a reduction in total cholesterol
for both men and women. In accordance with results from other studies, body
mass index (a measure of obestity) and alcohol consumption were associated with
a decrease and increase respectively in HDL cholesterol concentration in both
men and women. The results provide further evidence of the cholesterol-lowering
effect of a vegetarian diet with a high dietary fibre content and limited use
of cheese. Excluding meat from the diet might be expected to result in a 15-25%
reduction in the risk of coronary heart disease, with a similar beneficial effect
if cheese is also excluded.
Associations between plasma lipid concentrations and dietary, lifestyle and
physical factors in the Oxford Vegetarian Study. Appleby PN, Thorogood M, McPherson
K, Mann JI. Journal of Human Nutrition and Dietetics 1995;8:305-314.
Diet and ischaemic heart disease
Ischaemic heart disease is the most common cause of death in the UK and in many
other developed countries. A previous analysis of data from the study showed
that non-meat eaters had a 28% lower risk of death from ischaemic heart disease
before age 80 than meat eaters after adjusting for differences in smoking habits,
body mass index and social class. However, it was unclear which dietary factors
might account for this difference. Therefore, the effects of various dietary
factors on mortality from ischaemic heart disease were examined in a recent
analysis. Participants were grouped not just according to their diet (meat eater,
semi-vegetarian, vegetarian/vegan), but also by their consumption of various
foods and alcohol according to the answers provided on the recruitment questionnaire.
Participants were also divided into thirds of estimated intake of total fat,
saturated fat and dietary cholesterol from land animal sources, and into thirds
of estimated dietary fibre intake from their reported consumption of fibre-rich
foods. The main analysis was restricted to participants with no history of cardiovascular
disease or diabetes at recruitment, of whom 392 died before age 80, including
64 deaths from ischaemic heart disease. After adjusting for differences in age,
sex, smoking habits and social class, vegetarians and vegans had a 17% lower
risk of death from ischaemic heart disease than meat eaters (defined as participants
eating meat at least once a week) although the result was not statistically
significant. The most striking results from the analysis were the strong positive
and highly significant associations between increasing consumption of animal
fats and ischaemic heart disease mortality, the death rates being roughly three
times greater among participants in the highest third of intake compared with
the lowest third of intake for each of total animal fat, saturated animal fat,
and dietary cholesterol. Consumption of eggs and cheese were also positively
associated with ischaemic heart disease mortality, but no protective effects
were noted for dietary fibre, fish or alcohol consumption, as might have been
expected from findings in other studies.
Dietary determinants of ischaemic heart disease in health conscious individuals.
Mann JI, Appleby PN, Key TJ, Thorogood M. Heart 1997;78:450-455.
Diet and body mass index
Body mass index (BMI - a measure of an individual's relative weight calculated
by dividing their weight in kilograms by the square of their height in metres)
was calculated for 1914 male and 3378 female non-smokers aged 20-89 at recruitment
to the study. Answers to the food frequency questionnaire completed by all participants
were used to classify them as either meat eaters or non-meat eaters, and to
estimate intakes of animal fat and dietary fibre. Participants were further
classified according to their alcohol consumption, exercise level, social class,
past smoking habits and parity (whether or not a woman has had children). Mean
(average) BMI was lower in non-meat eaters than in meat eaters in all age groups
for both men and women. Overall mean BMIs in kg/m2, adjusted for differences
in age between the two groups, were 23.18 and 22.05 for male meat eaters and
non-meat eaters respectively and 22.32 and 21.32 for female meat eaters and
non-meat eaters respectively, differences of about one kg/m2 which were massively
statistically significant, indicating that they were very unlikely to have occurred
by chance. In addition to meat consumption, dietary fibre intake, animal fat
intake, social class, past smoking habits, alcohol consumption in men only and
parity in women were all independently associated with BMI. However, these factors
accounted for only about one-third of the difference in mean BMI between meat
eaters and non-meat eaters in both men and women. It was concluded that non-meat
eaters are thinner than meat eaters, and that this may be partly due to a higher
intake of dietary fibre, a lower intake of animal fat, and in men only a lower
intake of alcohol.
Low body mass index in non-meat eaters: the possible roles of animal fat, dietary
fibre and alcohol. Appleby PN, Thorogood M, Mann JI, Key TJ. International Journal
of Obesity 1998;22:454-460.
A summary of the published papers up to and including 1997 may be found in the
following reference:
The Oxford Vegetarian Study: an overview. Appleby PN, Thorogood M, Mann JI,
Key TJ. American Journal of Clinical Nutrition 1999; 70(suppl): 525S-531S.
(Paul Appleby, July 1994, April 1996 and July 1998)
[Note that there is no formal link between Oxford Vegetarians and the Oxford
Vegetarian Study, although some past and present members of Oxford Vegetarians
are participants in the study.]