The prevalence of extreme obesity has increased three-fold over the past four decades, that is, having a body mass index (BMI;kg/[m.sup.2]) > 40. Obese persons with these BMI often have a long history of excess weight, of repeated failures with traditional weight-loss methods, or both, and gastric bypass surgery is one option as a useful treatment for achieving sustainable weight loss.

Relatively little is known about the long-term effects of weight loss induced by gastric bypass surgery on energy requirements or about the reasons observed for the substantial variability in weight loss between patients. One other question is whether it is possible to identify pre-surgical predictors of weight loss that could help identify those patients that are likely to obtain the maximum benefit from gastric bypass surgery. The potential predictors of weight loss are total energy expenditure (TEE), resting energy expenditure (REE) and leptin, which have been suggested to predict weight loss in several previous studies. Therefore, a group of researchers from Tufts University set out to determine changes in energy expenditure and body composition with weight loss induced by gastric bypass surgery and to examine the utility of several baseline variables, including TEE and REE, for predicting body weight and fat loss in these individuals.

Thirty extremely obese adults who underwent gastric bypass surgery at the Tufts-New England Medical Center Hospital participated in this study. All subjects were initially tested before gastric bypass surgery and then after weight loss and weight restabilization. TEE, REE, fasting leptin levels, body composition, and the thermic effect of food (TEF) were measured at baseline and follow-up. TEE was measured using the doubly labeled water methods and REE through indirect calorimetry. Body composition was evaluated by the Siri 3-compartment model at baseline and follow-up.

Subject characteristics at baseline are summarized in Table 1. The mean duration of weight loss after gastric bypass surgery was 14 + 2 months. Subjects lost 53.2 + 22.2 kg body weight and had significant decreases in REE and TEE. Gastric bypass surgery resulted in a substantial mean weight loss of 38% of initial weight. There were large and significant changes in all body-composition variables and, on an average, weight loss was 79% fat and 21% FFM. The changes in REE were predicted by changes in FFM and fat mass. Weight loss was predicted by baseline fat mass and BMI but not by any energy expenditure variable or leptin. Measured REE at follow-up was not significantly different from predicted REE. In addition, there were no significant changes in TEF, fasting RQ, or PPRQ.

This study showed that both TEE and REE decreased by 25% on an average after massive weight loss and weight restabilization after gastric bypass surgery. The results also indicated, in contrast with several previous reports, that the change in REE was explained by losses of both FFM and fat mass. In addition, the authors observed that mean REE after weight loss was not significantly different from REE predicted wit the use of standard equations developed for non-obese persons. Therefore, these results suggest no energetic adaptation of REE toward increased efficiency after massive weight loss induced by gastric bypass surgery. The data from this study are helpful but further research is needed to examine other potential explanations for the variability in weight loss between patients after gastric bypass surgery, including psychological or behavioral factors that may affect food intake.

Subject characteristics

                              Women (n=24)   Men (n=6)

Age (years)                   38.9+9         9.2+12.7
Height (cm)                   163+7          183+5.4
Baseline weight (kg)          127.4+24.7     187.9+29.5
Baseline BMI (kg/[m.sup.2])   49.3+8.2       57.3+10.4
Baseline waist-to-hip ratio   0.92+0.12      0.94+0.05

Sai Krupa Das, Susan B Roberts, Megan A McCrory, et al., Long-term changes in energy expenditure and body composition after massive weight loss induced by gastric bypass surgery, Am J Clin Nutr 78: 22-30 (July 2003) [Address reprint requests to SB Roberts, Energy Metabolism Laboratory, Room 608, Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University, 711 Washington Street, Boston, MA 02111. E-mail: susan.Roberts@tufts.edu]

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