In an age where diet choices are influenced by health, environmental and food safety concerns, vegan and vegetarianism have been gaining in popularity. According to a poll sponsored by the Vegetarian Resource Group, almost one percent of the population of the United States was vegan in 2000.
The latest study is published in the September issue of The American Journal of Medicine (vol 118; No 9; 991-97). In it, researchers from George Washington University School of Medicine write that vegan diets supplemented with vitamin B12, can be "nutritionally adequate for long-term use".
Vitamin B12, found in meat, dairy products and eggs, has a role in the formation of red blood cells and maintenance of a healthy nervous system.
Despite giving the lifestyle a green-flag, they nonetheless advocate that anyone following a prescribed diet should receive counseling as to nutritional adequacy.
The study's lead author, Neal Barnard, MD of George Washington University School of Medicine and the Washington Center for Clinical Research, is also founder of the Physicians Council for Responsible Medicine, an organization that promotes vegetarian and vegan lifestyles and campaigns against the use of animals in research.
As for the low-carbohydrate approach to weight loss, this has been immensely popular in recent years but it is now waning in favor of the low-glycemic approach, whereby foods are given a rating depending on how fast they are absorbed into the blood stream.
The 63 participants in the study were postmenopausal women, all of whom were overweight or obese (BMI of between 26 and 44) and free-living outpatients at the hospital, were randomly assigned to two groups.
Over a 14-week period, one group followed a low-fat, vegan intervention diet consisting of vegetables, fruits, grains and legumes. Ten percent of energy was derived from fat, 15 percent from protein and 75 percent from carbohydrate.
Usually vegans may also include avocados, olives, nuts, nut butters and seeds in their diet but they were proscribed for this study, which was designed to be low in fat.
The other group followed a control diet based on the National Cholesterol Education Program guidelines, of which total fat made up 30 percent or less, saturated fat seven percent or less, protein around 15 percent and carbohydrate more than 55 percent of energy. Cholesterol intake was less than 200mg per day.
There were no limits placed on energy intake for either group, and they were asked to maintain their usual level of exercise. The researchers said that this control on exercise and its possible confounding effects is what sets this study apart from previous research into the effects of such a diet on overweight people.
The researchers found that those on the intervention diets spontaneously decreased their energy intake by more than those on the control diet - although the difference was not significant. However the intervention group's reduction in protein, fat and cholesterol intake was significant, as was their increase in fiber intake. Its carbohydrate intake also increased.
When it came to body weight, those on the intervention diet lost a mean of 5.8 kg, compared to 3.8 kg for the control group - the former being a loss equivalent to weight loss from a reduced calorie (eg 1200 kcal per day) diet, according to the researchers.
BMI and waist circumference reductions were also greater in the intervention group.
"The consumption of a low-fat, vegan diet was associated with significant weight reduction, along with improvements in measures of glucose tolerance and insulin sensitivity," concluded the researchers.
They said that the effect of the vegan diet on the thermic effect of food merits further exploration, and that longer-term trials are necessary to determine how sustainable the intervention diet is, and what the longer-term clinical improvements may be.