ABSTRACT
Recommended diets for the prevention and treatment of obesity have included a high intake of carbohydrates, fats, or proteins. Outcomes are similar for each of these emphases, except that a high-protein intake helps conserve lean tissue. Water facilitates weight loss by reducing appetite and averting the consumption of sweetened beverages. Weight loss reflects not only loss of body fat but also a depletion of glycogen reserves and associated water, a breakdown of lean tissue, and alterations in mineral balance and thus body water content. Decreases in body mass with dieting are sometimes substantially less than may have been anticipated due to decreases in resting metabolism, decreases in the amount or activity of brown fat, hormonal adjustments, decreases in voluntary leisure activity, decreases in the cost of body displacement, and a failure to adhere to the prescribed diet. Fat use is decreased by recent ingestion of carbohydrate and restriction of blood flow to the active muscles. Losses of lean tissue compromise fat loss, and have negative effects on cardiac and skeletal muscle function. The long-term success rate of dieting is disappointing, although weight maintenance may be enhanced if dieting is supplemented by exercise.
