Energy Metabolism and Nutrient Absorption in Lean and Obese Individuals

The prevalence of obesity has risen to epidemic proportions in the world, resulting from both excessive energy intake and low levels of energy expenditure. The effect of nutrient absorption on energy balance, that is, the relative amount of nutrients consumed vs. the amount excreted in stool, has been reported only in small studies in which energy waste in feces and urine between lean and obese individuals was not found to be different. However, these studies were limited by small sample sizes and were not specifically designed to examine whether stool energy loss varied between lean and obese individuals. In addition, little is known about the reproducibility of the measurements of energy loss in stool and urine. We propose to investigate (i) whether there are significant differences in energy loss (as measured in stool and urine) between obese and lean individuals, and (ii) to examine the reproducibility of these measurements. Because the literature suggests a role for enteric bacterial flora in obesity, we will also examine differences in such flora between these groups. We plan to study 25 obese and 25 lean healthy non-smoking Caucasian men age 18 - 45 years old, not taking any medications (including medications for weight loss, antibiotics or probiotics) for the examination of differences in nutrient energy loss. Of these subjects, 10 lean and 10 obese individuals will be invited to repeat the study to test the reproducibility of these measurements. All participants will be admitted to the Clinical Research Unit for 15 days. During their stay, subjects will be fed a weight maintaining diet for 3 days, followed in a random cross-over design by two experimental diets: a 2400 kcal/d or 3400 kcal/d diet for 3 days. Twenty four-hour urine and feces collections will take place each day of the experimental diet period. The energy content of these waste products as well as that of the diet (using duplicate plate analysis) will be measured by bomb calorimetry. Bacterial components in feces will be extracted by repeated fractional centrifugation to obtain bacterial mass and by using 16S rDNA-based oligonucleotide probes to obtain bacterial flora. Primary results will examine the differences in energy loss between lean and obese individuals as well as the reproducibility of the measurements of stool and urine energy content.