Overweight and Obesity in Women: Health Risks and Consequences

Frank B. Hu, M.D., Ph.D.

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In This Article

Diet and Lifestyle Modification: The Key to Weight Loss and Disease Prevention

Because body weight is primarily determined by the critical balance between energy intake and energy expenditure, an obese person's energy balance over 24 hours has to be negative in order to lose weight. This can be achieved by decreasing total energy intake or increasing physical activity or both. Thus, diet and lifestyle modification is widely considered the primary means to control weight. It is also the most important approach for diabetes prevention. Three clinical trials have demonstrated the beneficial effects of diet and lifestyle intervention on weight loss and diabetes prevention. Among 577 subjects with IGT in Da Qing, China,[64] exercise dietary (or both) interventions resulted in a 42%-46% decrease in the progression from IGT to diabetes in 6 years of follow-up. In the Finnish Diabetes Prevention Program, lifestyle modification reduced the incidence of type 2 diabetes by 58% in people with IGT.[65] The intervention program included a modest weight loss of <10 pounds combined with a healthy diet with less saturated fat and increased fiber intake and regular moderate exercise. In the Diabetes Prevention Project (DPP),[66] 3234 nondiabetic persons with IGT were randomly assigned to placebo, metformin (850 mg twice daily), or a lifestyle modification program with the goals of at least a 7% weight loss and at least 150 minutes of physical activity per week. In this study, 50% of the participants in the lifestyle intervention group had achieved the goal of weight loss of _7% by the end of the curriculum (at 24 weeks), and 38% had a weight loss of at least 7% at the time of the most recent visit. The proportion of participants who met the goal of at least 150 minutes of physical activity per week was 74% at 24 weeks and 58% at the most recent visit. In 2.8 years of follow-up, the lifestyle intervention reduced the incidence of diabetes by 58% (95% CI, 48-66), and metformin reduced its incidence by 31% (95% CI, 17-43), compared with placebo. Lifestyle intervention was equally effective in both men and women and in different ethnic groups.

Despite the success of these trials, several important questions remain. In the DPP, many participants regained the initial weight loss during the follow-up period. Although this is a typical phenomenon in weight loss trials, it raises a question of the long-term effectiveness of the intervention. A detailed analysis on predictors of weight regain would be helpful for improving long-term maintenance of weight loss. In addition, the dietary intervention in the DPP focused on low-fat, low-calorie diets. Although reduction in the percentage of calories from dietary fat intake is commonly recommended for weight loss, long-term clinical trials have provided no convincing evidence that reducing dietary fat per se can lead to substantial weight loss.[67,68] A hypocaloric moderate-fat diet, which allows for a great variety in choosing foods and does not make people feel deprived, can have better long-term compliance and has led to better weight maintenance than a typical low-fat diet.[69] In addition, evidence from recent experimental studies suggests a potential role for a diet high in carbohydrates, especially those with high glycemic index (GI), in the development of obesity.[70,71] In animal studies,[72] high-GI diets, as compared with isocaloric low-GI diets, induce an increase in fat synthesis even when the total body weight remains constant. A recent review suggested that consumption of low-GI foods/liquids was directly associated with reduction in subsequent hunger and increased satiety in most of the short-term feeding studies in humans (lasting for a single meal or a single day).[71] In addition, voluntary energy intake increased after consumption of high-GI meals as compared with consumption of low-GI meals.[71] These observations suggest that long-term consumption of high-GI diets may promote excess energy consumption and thus contribute to weight gain or to the maintenance of excess body weight, especially among susceptible individuals (e.g., sedentary or overweight subjects).[70] However, to date, no long-term studies have tested the effects of GI on weight control.

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