Vegetarianism is associated with health benefits such as reduced risk of age-related disease. It is also associated with carrying less of the visceral fat shown to cause harm to long-term health - which on balance probably means a lower calorie intake. As we all know by now, calorie intake has a disproportionate effect on measures of health. So that would seem to be a more plausible mechanism than, say, reduced dietary intake of AGEs or lower levels of methionine.
Here, however, researchers are claiming that differences in body mass index - a not-so-great proxy measure for the amount of body fat - between vegetarians and non-vegetarians are not terribly important in comparison to blood pressure and cholesterol measures. That is not a particularly intuitive result:
The risk of hospitalisation or death from heart disease is 32% lower in vegetarians than people who eat meat and fish, according to a new study. "Most of the difference in risk is probably caused by effects on cholesterol and blood pressure, and shows the important role of diet in the prevention of heart disease."
This is the largest study ever conducted in the UK comparing rates of heart disease between vegetarians and non-vegetarians. The analysis looked at almost 45,000 volunteers from England and Scotland enrolled in the European Prospective Investigation into Cancer and Nutrition (EPIC)-Oxford study, of whom 34% were vegetarian. Such a significant representation of vegetarians is rare in studies of this type, and allowed researchers to make more precise estimates of the relative risks between the two groups.
The Oxford researchers arrived at the figure of 32% risk reduction after accounting for factors such as age, smoking, alcohol intake, physical activity, educational level and socioeconomic background.
Participants were recruited to the study throughout the 1990s, and completed questionnaires regarding their health and lifestyle when they joined. These included detailed questions on diet and exercise as well as other factors affecting health such as smoking and alcohol consumption. Almost 20,000 participants also had their blood pressures recorded, and gave blood samples for cholesterol testing. The volunteers were tracked until 2009, during which time researchers identified 1235 cases of heart disease. This comprised 169 deaths and 1066 hospital diagnoses, identified through linkage with hospital records and death certificates.
The researchers found that vegetarians had lower blood pressures and cholesterol levels than non-vegetarians, which is thought to be the main reason behind their reduced risk of heart disease. Vegetarians typically had lower body mass indices (BMI) and fewer cases of diabetes as a result of their diets, although these were not found to significantly affect the results. If the results are adjusted to exclude the effects of BMI, vegetarians remain 28% less likely to develop heart disease.