Overeating and Overweight
Authors: Zhaoping Li, David Heber
Journal: JAMA (2012)

OVERWEIGHT AND OBESITY AFFECT 65% OF THE US public and the US government spends in excess of $200 billion per year on obesityassociated conditions and diseases. For the first time in human history, there are more overweight people (2.1 billion) in the world than underweight individuals. Forecasts suggest that the prevalence of obesity will double worldwide in the next 30 years, with the epicenter of the epidemic in China and India as persons in these countries assume Western eating habits. In this issue of JAMA, Bray and colleagues in a randomized controlled trial evaluated the effects of overconsumption of low, normal, and high protein diets on weight gain, energy expenditure, and body composition. They found that body fat increased in proportion to excess calories but overall weight gain was less with low protein relative to normal or high protein diets. These findings have important ramifications because the Western diet tends to be high in fat and carbohydrates and low in protein. The study results also suggest that body weight may underestimate the true hazards of overnutrition. Obesity results from accumulation of excess body fat. Obesity is not simply excess body weight because overweight can occur from either muscle or fat deposition. Body weight and body mass index are useful in population studies in which excess weight represents excess body fat. However, on an individual level, sex, ethnicity, age, and as Bray et al showed, diet composition can affect the relationship between total body fat and body weight. Accumulation of excess fat is associated with obesity-related medical conditions, whereas increased muscle mass is beneficial because of its positive effect on metabolism. Excess abdominal fat and ectopic fat in the liver, pancreas, and heart can affect inflammation and increase the risk of a number of common obesity-associated disorders. Humans are better adapted to starvation with subsequent maintenance of lean body mass than they are to overfeeding, which results in body fat accumulation. Animal studies and some human studies have suggested a teleological adaptation to ingestion of foods having incorrect amounts of nutrients by burning off excess calories with dietinduced thermogenesis. In animals, brown fat creates heat and the animal is capable of burning off excess calories. Animals can eat foods with incorrect amounts of nutrients and not become fat because of this physiological adaptation. Adult humans have little brown fat. Nevertheless, it has been hypothesized that similar mechanisms could occur in humans, which led Bray et al to perform their study. Bray et al confined healthy human volunteers to an in-house environment in which they were deliberately overfed approximately 1000 calories daily (40% more energy than required for weight maintenance) with diets of varying protein content for 8 weeks. Overeating produced significantly less weight gain in the low protein group (approximately 3 kg) compared with the normal or high protein groups (approximately 6 kg). Total body fat measured by dual-energy x-ray absorptiometry increased similarly in all 3 groups and represented 50% to more than 90% of the excess stored calories. Resting energy expenditure and body protein increased significantly only with the normal and high protein diets but not with the low protein diet. This study demonstrates how low protein foods with hidden sugars or fats may be contributing to the obesity epidemic. Sugars such as sucrose, fructose, and high fructose corn syrup are converted efficiently to fat with calorie excess. Carbohydrates and protein elicit different signaling pathways for muscle and fat cells. Therefore, when individuals consume excess carbohydrates out of proportion to protein, the body may gain less weight than when protein is consumed in adequate amounts. The study by Bray et al demonstrated that the lesser added weight consists largely of fat mass rather than lean body mass when excess calories were the same. Moreover, added fat calories (including hidden fat in processed foods) consumed in excess will also lead to weight gain contributing to the obesity epidemic. A large and well-accepted body of scientific evidence indicates that protein is the most satiating of the macronutrients. High protein diets providing 25% of total energy com-