The body mass of vegetarians in general, and vegans in particular, is closer to the desirable level than the body mass of non-vegetarians.37 People with a body mass 20% above optimal are considered to be at a significantly greater risk of mortality or morbidity (contracting a degenerative disease) than people with normal, or slightly under normal weights.38 The level of obesity can also be assessed by measuring the waistline. A measure of more than 35 inches (78,9 cm) for women and 40 inches (101,6 cm) for men indicates obesity. As percentage overweight is not the easiest parameter to work with, and waistline measurements can be arbitrary, obesity is usually expressed in terms of body mass index (BMI). Clinical obesity is defined as a BMI which is greater than 30. Desirable BMI would be in the range 20 -25. BMI can be calculated as follows:
Obesity is on the increase in affluent societies, and can be ascribed to changes in lifestyle. The reasons for obesity are multifactorial, but increased consumption of fatty foods, overeating and more sedentary lifestyles are the main reasons sited for this phenomenon. Since the last world war, the British population has shown an increase of 3 BMI units in weight and the average adult is now 10 kg heavier at an equivalent height than five decades ago. Since the mid 1980’s, the number of clinically obese people has doubled in the UK,39 and figures for the USA are similar, with 33.4% of the adult population being obese and one in ten 12- to 19-year olds are significantly overweight.40,41 The changes fat consumption relative to carbohydrate consumption in the UK are presented in figure 5.3.)
Figure 5.3. Changes in carbohydrate and fat incorporation in the diet over time in the UK. (From references 39).
Studies have shown, that a high fat-carbohydrate ratio in the diet is associated with obesity.42 The old notion that overweight people should cut down on carbohydrates is thus not true, they should cut down on fat in the diet. In fact, data compiled from over 11 600 Scottish men and women showed that the groups consuming the most sugar had the lowest level of obesity, and this can be ascribed to the lower fat intake associated with a high carbohydrate intake.39 However, not all people on a high fat diet become obese, and there must be other reasons as well as to why some are more prone than others to becoming obese. Nevertheless, a reduction in fat consumption can lead to the desired weight loss in obese people without undue restrictions in the amount of food consumed. It the change in the ratio of fats to carbohydrates that induces the weight loss. Studies on the effect of reduced fat diets have shown that if the percentage fat in the diet is reduced to between 15% and 20% then weight loss follows in obese people even if their overall consumption remains the same.39
Obese people are up to three times more likely to die prematurely than lean people, and the most likely conditions from which they may suffer are heart attacks, strokes, and some forms of cancer. Many studies have shown that obesity is associated with increased risk of hypertension, insulin resistance and diabetes, hypertriglyceridaemia reduction in the levels of HDL-cholesterol and increases in the levels of LDL-cholesterol as well as other diseases such as gout, gallstones, renal failure, infertility and degenerative joint diseases such as arthritis. Moreover, Obese individuals also tend to suffer more frequently from
psychological problems and depression. Obese women are at a greater risk of contracting endometrial cancer, whereas in obese men the risk of prostate cancer is increased.38 In fact the risk of cancer in general is increased, and the incidence of breast, colon, rectum, kidney, cervix, ovary, thyroid and gallbladder cancer is higher in obese than in normal people.43 The issue is however complex, as fat intake and detrimental habits such as smoking and drinking cloud the issue. A study on 750 000 men and women showed that the effect of obesity seems to differ between the sexes. Men who are within 10% of their ideal body mass had the lowest risk of contracting colon, prostate and kidney cancers, whereas women who were 10-20% below the average weight for age and height had lower incidences of colon, breast, uterus, gallbladder, ovary, cervix and kidney cancer.44
The distribution of body fat is also significant in determining the level of risk. Abdominal obesity is more dangerous than gluteal-femoral (upper thigh and buttocks or pear-shaped) obesity. In women the effect of an increased Waist-to-hip ratio (commonly referred to as apple-shaped) has been positively linked to cancer. Increased levels of upper body or abdominal fat have also been related to hypertension and diabetes. Moreover, in some cases it seems probable that the distribution of body fat is of greater significance in increasing the risk of disease, than is the degree of obesity.38
Adipose tissue increases the levels of oestrogens, and increased levels of these hormones have been associated with cancer, particularly of the breast. Pre-menopausal women who are vegans or are on a low-fat vegetarian diet, have lower levels of oestrogens and their menstrual cycles are also shorter by 1-2 days.45 Western diets lead to raised levels of oestrogen in general and this has been associated with cancer. Breast cancer rates are lower in countries where vegetarian diets are commonly consumed.28 The issue is complex, and the causes of cancer are multifactorial. Nevertheless, it has been established that a vegetarian diet offers protection against specific cancers, and colon cancer rates in vegetarians are lower than in non-vegetarians.46 Secondary bile acids have been linked to intestinal tumour formation, and here again vegan vegetarians have the lowest ratio of secondary to primary bile acids.47 Furthermore, cell proliferation, a factor correlated with tumour growths and development,48 is lowest in the colon of vegetarians.28