Background: Weight loss may be associated with unfavorable changes in body composition not compensated for by subsequent weight gain.
Objective: We examined the composition of weight change in relation to obesity, previous weight changes, weight-loss attempts, and physical activity.
Design: Part of the Danish MONICA (Monitoring Trends in Cardiovascular Disease) project, this was a longitudinal population study of changes in weight and body composition, with examinations in 1982-1983, 1987-1988, and 1993-1994. A total of 1236 men and 1200 women aged 35, 45, 55, or 65 y in 1987-1988 participated. Changes in fat and fat-free mass were measured by bioelectrical impedance.
Results: Before adjustment for age-related changes, fat-free mass made up 41% of weight lost and 24% of weight gained in men. In women, loss of fat-free mass (35%) was more than double that of gains (15%). After adjustment, the fractions of weight gained as fat-free mass were not significantly different from the fractions lost. These fractions were independent of age, obesity, and weight changes in the previous 5 y; successful weight-loss attempts; and physical activity. Independent of age and degree of obesity, weight changes were associated with greater changes in fat-free mass in men than in women.
Conclusions: These data do not support the theory that weight loss or weight cycling may lead to an unfavorable body composition, nor do they provide a biological explanation for why long-term weight loss is often unsuccessful. However, the metabolic and health consequences of weight change may differ in men and women.