Weighing the evidence

The article, published in the American Journal of Clinical Nutrition, included data from a number of epidemiological studies. The authors described the key differences that have been observed in studies comparing vegetarians with non-vegetarians:

• Obesity is less prevalent in vegetarians (which in turn helps decrease risk of certain diseases, such as cancer, diabetes, and heart disease).
• Vegetarians have less body fat, weigh less, and have lower BMI (body mass index, a measure of overweight and obesity) than non-vegetarians.
• BMI increases as the amount of animal products eaten in the diet increases: vegans have the lowest BMI, those that eat dairy and eggs (lacto-ovo vegetarians) and fish-eating vegetarians have medium BMI, and meat eaters have the highest BMI.

Less is known about vegetarianism in children and adolescents, but the existing data point to similar trends: vegetarian children appear to be leaner, have lower BMI and waist circumference, are less likely to be overweight or obese, and have better lipid profiles. Findings from some studies suggest that meats, dairy products, and eggs are specifically associated with increased risk of overweight, while cereal grains, pulses, and nuts protect against it.

Why do vegetarians weigh less?

The study’s authors proposed the following contributing factors to explain vegetarianism’s protective effects against overweight and obesity:

• Plant-based foods are low in protein, fat, and calories but high in many nutrients, complex carbohydrates, fibre, and water.
• Studies in young adults and children have linked high protein intake with high BMI and increased obesity risk later in life.
• High-fibre meals such as those eaten by vegetarians are more filling and reduce between-meal eating.
• The high polyunsaturated fat to saturated fat ratio of plant-based diets has been shown to increase resting metabolic rate, and there is preliminary evidence that a vegetarian diet might also.

Health considerations for vegetarian children

Although a vegetarian diet can be lower in protein, calcium, zinc, iron, vitamin B12, and vitamin D, experts agree that a well-planned vegetarian diet can provide adequate amounts of both macro- and micronutrients, and can be healthy for children, adolescents, and adults.

“In conclusion, obesity represents a significant threat to the present and future health of children and leads to a wide range of physical and psychological consequences,” the authors of the report state. While the decision to make a long-term change to your child’s diet is one that should be made with careful thought toward supporting your family’s specific health goals and may be served by discussion with your doctor, as the the authors suggest, a “plant-based diet appears to be a sensible approach for the prevention of obesity in children.”

(Am J Clin Nutr 2010;91:1525S–9S)