Predicting Weight Gain and Weight Loss Associated With Overeating or Fasting

For obese individuals, losing weight and keeping it off are extremely difficult, whereas some other individuals are thin and report trouble gaining weight. In most weight loss and overfeeding studies there is a large variation in the amount of weight lost or gained, and it is not clear whether an individual s response to an intervention can be predicted. Measurement of the amount of energy an individual uses over 24 hours (24 hour energy expenditure or 24-EE) and the response of 24-EE to overfeeding and fasting may help predict which individuals will have the greatest changes in weight with changes in energy balance. In previous work, 24-EE responses to overfeeding and fasting were related such that individuals with the greatest increase in 24-EE upon overfeeding tended to have the smallest decrease in 24-EE upon fasting ( spendthrift phenotype) and those individuals with less increase in 24-EE during overfeeding had a greater decrease in 24-EE with fasting ( thrifty phenotype). Those with the spendthrift phenotype who had a greater increase in 24-EE in response to overfeeding gained less weight over time. Furthermore, studies have shown that diets with very low protein content may magnify the variability in response to overfeeding. The aim of this study is to determine if a phenotype defined by 24-EE responses to overfeeding and underfeeding is related to weight loss or gain in 4 different under- and overfeeding settings: an inpatient weight loss group for obese individuals who will be administered one of two diets based on a 50% reduction of their daily energy needs for six weeks (standard reduction diet or calorie reduced diet that is still high in protein; 6 week weight reduction, 10 week stay, n=20/standard reduction diet group and n=10/relative high protein diet), and two overfeeding groups for lean, weight gain resistant individuals: a low-protein overfeeding group at 150% of daily energy needs for 6 weeks overfeeding (6% protein, 64% carbohydrate, 30% fat; 10 week stay, n=10), and a normal protein overfeeding group at 150% of daily energy needs for 6 weeks overfeeding (20% protein, 50% carbohydrate, 30% fat; 10 week stay, n=10). We will also examine additional metabolic and behavioral measurements to determine how they relate to weight change and changes in 24-EE. These include sympathetic nervous system activity, behavior, adipose and muscle tissue energy content, and abdominal adipocyte size. The study will evaluate the relationship between the percent increase in 24-EE in response to overfeeding/underfeeding and the amount of weight change over time in each subject. These findings may provide important information for predicting and adapting specific individualized interventions for obesity.