Obesity: Nutritional Considerations

Although genetic factors contribute to obesity, the increased prevalence of this condition during the last century confirms that obesity is the result of gene/environment interactions.⁷ The Western diet, which provides highly palatable, energy–dense foods rich in fat and sugar, is conducive to weight gain. These foods activate reward systems in the brain, up–regulate the expression of hunger signals, and blunt the response to satiety signals, promoting overconsumption.⁸

Common short–term restrictive diets that limit portion sizes tend not to produce long–term weight loss. A better approach is a permanent change in the type of foods individuals select and in physical activity. Individuals who consume foods lower in energy density and higher in water and fiber (eg, salads, soups, vegetables, and fruits) instead of foods high in energy density experience early satiety and spontaneously decrease food intake. This strategy has produced weight loss in several clinical studies.⁹ Because it allows for the intake of larger portions that provide satiety,^10,11 it fosters continued adherence.

The following steps reduce the energy density of the diet and promote weight control:

Reducing dietary fat. Aside from holding over twice as many calories per gram as protein and carbohydrate (9 calories per gram of fat, compared with 4 for protein or carbohydrate), dietary fat promotes passive overconsumption of energy, and the addition of fats to meals results in fat storage rather than fat oxidation. These mechanisms may explain why the prevalence of overweight worldwide is directly related to the percentage of fat in the diet, and why low–fat diets have been consistently shown to promote moderate weight loss.¹² Common sources of fat are meats, dairy products, fried foods, and added oils.

Choosing foods high in complex carbohydrates and fiber. Populations in Asia, Africa, and elsewhere with diets high in complex carbohydrates tend to have a low incidence of obesity. The whole grains and legumes in these diets also provide fiber. Fiber is filling, but contributes little to overall calorie intake. Studies show that fiber intake is inversely associated with body weight and body fat.¹³

Following low–fat, vegetarian diets. Several studies have found that vegetarians tend to be slimmer than omnivores, which is not surprising given that grains, legumes, vegetables, and fruits are low in fat and high in complex carbohydrates and fiber.¹⁴ Randomized trials show that low–fat vegan diets promote greater weight loss than typical low–fat diets, and they also improve  plasma lipids, insulin sensitivity, and other measures.¹⁰ A study of a vegetarian diet in heart patients, used in combination with exercise and stress management, showed sustained weight loss over a 5–year period.15

Minimizing sugars. Sucrose, high–fructose corn syrup, and other sugars add calories without producing satiety. Increased intake of sweetened beverages is associated with a rise in obesity.¹⁶

Low–carbohydrate diets have been popular, but they have not been found superior to either low–fat, high–carbohydrate, or calorie–controlled diets over a 12–month period.¹⁷ Such diets icrease plasma low–density lipoprotein concentrations, sometimes severely, in approximately one third of users. They also cause a sustained increase in urinary calcium losses.¹⁸

Orders

See Basic Diet Orders.

Vegetarian diet, nondairy, low–fat

What to Tell the Family

Obesity contributes to many chronic illnesses, but it may be prevented and successfully treated in most individuals through a diet low in fat and sugar, and high in fiber, along with regular physical activity. Well–planned, low–fat vegan and vegetarian diets are particularly healthful and effective.