Lessons for vegetarians and vegans from the EPIC-Oxford study
by Paul Appleby
Traduzione a cura di Luciana Baroni -- (testo tradotto in italiano)
The European Prospective Investigation into Cancer and Nutrition (EPIC) is the largest ever 'cohort' study of diet and health. Co-ordinated by the International Agency for Cancer Research (IARC, part of the World Health Organisation), the study includes 520,000 people in 10 European countries (Denmark, France, Germany, Greece, Italy, The Netherlands, Norway, Spain, Sweden and the United Kingdom). The aim of the EPIC study is to investigate the relationships between diet, lifestyle and environmental factors and the incidence of cancer and other chronic diseases.
EPIC-Oxford is one of 23 EPIC centres. Recruitment to EPIC-Oxford was carried out between 1993 and 1999. Participants were recruited from throughout the UK both through participating GPs and by post, the aim of the postal recruitment being to recruit as many vegetarians and vegans as possible. Nearly 65,500 people were recruited to EPIC-Oxford, of whom 57,500 completed a detailed lifestyle and food frequency questionnaire (FFQ), 31,100 completed a 7-day food diary, 19,700 provided a blood sample, and 38,000 completed a follow-up questionnaire some five years after recruitment.
All EPIC-Oxford participants were asked the following four questions: "Do you eat meat?", "Do you eat fish?", "Do you eat dairy products?", "Do you eat eggs?". From the answers to these questions we were able to divide participants into one of four diet groups as shown in Table 1, these groups forming the basis for many analyses.
The main findings from the EPIC-Oxford study to date will be presented under the following headings:
1. Lifestyle characteristics and nutrient intakes
2. Diet and body mass index
3. Hypertension and blood pressure
4. Hormones and diet
5. Diet and mortality
Many nutrient intakes and lifestyle characteristics differ markedly between the four diet groups, with meat eaters and vegans often at the extremes and fish eaters and vegetarians usually having similar and intermediate values. Average nutrient intakes in the cohort as a whole are close to those currently recommended for good health. The wide variation in nutrient intakes should enhance our ability to detect associations of diet with major cancers and causes of death.
Selected lifestyle characteristics of the participants are shown in Table 2. It can be seen that the non-meat eaters are, on average, younger than the meat eaters, that the participants are generally well educated with a low prevalence of smoking, and that many take vitamins or other dietary supplements.
Vegans generally consume more fruits and vegetables than vegetarians and fish eaters who, in turn, consume more than meat eaters. On average, each of the diet groups consume at least half a kilogram of fruits and vegetables daily, suggesting that most participants eat at least five portions of fruits and vegetables daily in line with healthy eating recommendations.
Table 3 shows mean (average) daily nutrient intakes, estimated from the FFQ, by sex and diet group. The table also shows the UK Dietary Reference Value (DRV) for each nutrient as a guide to how closely the participants are following recommended guidelines for healthy eating. It should be noted that the figures are derived solely from foods and drinks and do not take intakes of vitamins and minerals from dietary supplements into account. However, the table shows some clear differences in nutrient intakes between the diet groups that probably reflect real differences in intake. Thus, compared with meat eaters, vegans generally consume more carbohydrate, less protein, less saturated fat, more polyunsaturated fat, and more dietary fibre. Vegetarians and fish eaters generally have similar intakes of these macronutrients at levels that are intermediate between the meat eaters and the vegans. In terms of macronutrient intakes, the vegans would appear to be at an advantage over the meat eaters and, to a lesser extent, the fish eaters and the vegetarians, although all four diet groups comply well with dietary guidelines. However, the low mean intakes of vitamin B12 and calcium among the vegans (each well below the DRV for both women and men) are a cause for concern.
Body mass index (BMI) is a measure of obesity obtained by dividing your weight in kilograms by the square of your height in metres. For example, a person weighing 70 kilograms of height 180 centimetres (1.80 metres) has a BMI of 70 / (1.80 x 1.80) = 21.6 kg/m2 (kilograms per metre squared). A BMI of 20-25 kg/m2 is considered to be in the normal range, whereas a person with a BMI greater than 25 kg/m2 is considered to be overweight and someone with a BMI greater than 30 kg/m2 is considered to be obese. Obesity increases the risk of several chronic diseases including diabetes, coronary heart disease and some cancers.
We compared BMI in the four diet groups, controlling for age. Fish eaters, vegetarians, and especially vegans had significantly lower BMI than meat eaters, by 1-2 kg/m2 on average. Differences in macronutrient intakes (energy, protein, fat, carbohydrate, fibre, sugars, alcohol) accounted for about half the age-adjusted difference in mean BMI between vegans and meat eaters. High protein and low fibre intakes were the factors most strongly associated with increasing BMI.
We compared the prevalence of self-reported hypertension and mean systolic and diastolic blood pressures in the four diet groups. Non-meat eaters, especially vegans, had a lower prevalence of hypertension and lower mean systolic and diastolic blood pressures than meat eaters. The differences were largely attributable to differences in body mass index, which is positively correlated with blood pressure. Table 4 shows mean systolic blood pressure by sex and diet, first controlling for age alone, then controlling for age and BMI, and finally controlling for age, BMI, non-dietary factors and nutrient intakes. Controlling for age alone, the difference in mean systolic blood pressure between meat eaters and vegans was 2.5 mm Hg for women and 4.2 mm Hg for men. However, these differences disappeared after controlling for BMI, non-dietary factors and nutrient intakes as well as age, so that differences in these factors account for most of the variation in blood pressure between the diet groups.
Insulin-like growth factor-I (IGF-I) is a hormone that stimulates cell proliferation. It has been associated with increased risks for prostate cancer in men and breast cancer in women. We compared mean IGF-I concentrations in meat-eaters, vegetarians and vegans for both men and women. Mean IGF-I was similar in the vegetarians and meat eaters, but was 9% lower in the vegan men and 13% lower in the vegan women. These results suggest that vegans may be at lower risk for hormone-related cancers such as those of the breast and prostate.
In a preliminary analysis we compared mortality (death rate) in vegetarians (including vegans) and non-vegetarians. Overall mortality in the two groups was similar although mortality from ischaemic heart disease (heart attack) was 25% lower in the vegetarians. The results were similar to those found in previous studies. Mortality for both the vegetarians and the non-vegetarians in EPIC-Oxford is low compared with national rates.
In the first analysis of data from the follow-up questionnaire, we compared self-reported bowel movement frequency by various factors including diet group. Being vegetarian and especially vegan was strongly associated with a higher frequency of bowel movements, which might confer a lower risk for colorectal cancer. There were also significant positive associations between bowel movement frequency and body mass index, and intakes of dietary fibre and non-alcoholic fluids.
EPIC-Oxford is the largest single study of Western vegetarians and vegans to date, and presents a unique opportunity to study the long-term health of people who do not eat meat. Results from the study suggest that vegetarians and vegans follow diets that generally correspond well with guidelines for healthy eating and confer some benefits in terms of avoiding overweight/obesity and high blood pressure. Whether these benefits will translate into lower mortality and morbidity compared with the 'health conscious' non-vegetarians in the study remains to be seen.
I would like to thank my colleagues at the Cancer Research UK Epidemiology Unit in Oxford and all of the participants in the EPIC-Oxford study, without whose collaboration none of findings reported above would have been possible. EPIC-Oxford is supported by Cancer Research UK, the Medical Research Council, and the European Community.
Paul Appleby, June 2004
Numbers of participants by sex and diet group (Numbers are rounded to the nearest 100)
|Meat eaters||7.800||26.100||33.900 (52%)|
|Fish eaters||1.700||8.400||10.100 (15%)|
Selected lifestyle characteristics by sex and diet group
|Current smoker (%)||11||8||8||10||10||10||9||8|
|Sedentary occupation (%)||51||54||53||48||58||57||59||51|
|University degree (%)||35||47||44||45||50||61||55||49|
|Ever used the pill (%)||70||79||79||70||-||-||-||-|
|Take dietary supplements (%)||59||68||61||56||43||50||45||43|
Mean daily intakes of selected nutrients by sex and diet group
|Total fat (%E)||31.5||30.7||30.4||27.8||31.9||31.1||31.1||28.2||33|
|Saturated fat (%E)||10.4||9.3||9.3||5.1||10.7||9.4||9.4||5.0||10|
|Dietary fibre (g NSP)||18.9||21.6||21.8||26.4||18.7||22.1||22.7||27.7||18|
|Vitamin B12 (mcg)||7.0||4.9||2.5||0.5||7.3||5.0||2.6||0.4||1.5|
(%E indicates that the nutrient is expressed as a percentage of energy; PUFA denotes polyunsaturated fat; NSP denotes non-starch polysaccharide. The DRVs refer to women: values are identical for men except for energy (10.6 MJ/day) and iron (8.7 mg/day).)
Mean systolic blood pressure by sex and diet group
|Factors controlled for||Women||Men|
|Age and BMI||119.7||119.4||120.2||118.4||126.0||125.4||125.8||123.5|
a Age, BMI, non-dietary factors and nutrient intakes.