Interviews with Vegetarian/Vegan Activists
June 2007

Vegetarian Diets and a Healthy Weight

Here is an interview with Stephen Walsh - www.ivu.org/members/council/stephen-walsh.html - author of ‘Plant Based Nutrition and Health’.

Can you please briefly describe a couple studies which suggest that a vegetarian diet may help people attain a healthy weight?

The most usual studies compare vegetarians with non-vegetarians. Pretty consistently the vegetarians are a couple of kilograms lighter, and the vegans a couple of kilograms lighter again. A recent example of this type of study was a paper (International Journal of Obesity, 2003; 27, 728–734) from the European Prospective Investigation of Cancer (EPIC) study group in Oxford. A follow up study of the same group (International Journal of Obesity, 2006; 30: 1389-1396) looked at change in weight over five years and found that while all dietary groups gained weight with age, the average weight gain for meat-eaters was 2.1 kg while vegans gained just 1.5 kg. People who changed their diet over the five years to include more Animal products gained 2.3 kg while those who moved towards a vegan diet gained just 1.2 kg.

What aspects of vegetarian diets might explain the beneficial effect that vegetarian food might have on weight?

In the EPIC study high protein and low fibre intake were both linked with higher weight. Many other studies have supported a role of higher fibre intake from whole plant foods in avoiding both excess weight and the associated health complications such as insulin resistance and diabetes.

Is it possible that the relatively higher water content of fruits and vegetables might help people eat less because the water content decreases appetite?

It seems unlikely that the water content directly accounts for the benefit as soft drinks are associated with weight gain. However, the lower calorie density of some plant foods (calories for a given weight/ volume/ amount of fibre) may play a part in reducing calorie intake: it's easier to overeat doughnuts than apples.

Being vegetarian is no guarantee that people will attain a healthy weight. What are the other factors involved in achieving a healthy weight, and what is the relative importance of each of those factors?

The most important factor is physical activity. In the EPIC study, very active individuals (exercising for at least an hour a day) showed a weight gain of 1.5 kg while those who were inactive gained 2.4 kg. A combination of a relatively unprocessed vegetarian or vegan diet and an active lifestyle provides a sound strategy for avoiding excessive weight gain in young to middle-aged adults.

Is there ongoing research into the link between vegetarianism and weight? If so, what research questions are being investigated?

The observed differences in weight between vegetarians and meat eaters are pretty well established now. What is still in dispute is why these differences occur and what specific factors linked to a vegetarian diet affect weight. Part of the difference may simply be that vegetarians can't always lay their hands on convenient high calorie snack foods when they feel the urge. Part may simply be that vegetarians are more controlled about their food choices in general and are more health conscious. Part, however, is likely to be the relatively high fibre and moderate fat and protein content of typical vegetarian diets. Ongoing research aims to clarify the relative importance of these and other factors.

Is lower weight always better?

Anyone with a body mass index (weight in kg divided by height in metres squared) below 19 would probably be better off being a bit heavier. The statistics tend to favour a BMI of about 20-25 as best on average. Lightly built people may be better on the low end of this while heavier built people may be better on the high end. A substantial "spare tyre" of fat around the stomach is always a bad sign but so is being scrawny: "size zero" is far from ideal for health.

We should also be aware that in the elderly weight loss can be a bigger threat than weight gain. Older adults should be careful to ensure that they consume sufficient food and should emphasise protein-rich foods such as oats, soya products, beans, peas and lentils to ensure a good protein intake as calorie intake declines.