| Summary: | To examine the mechanism of weight loss following ileogastrostomy, 16 morbidly obese subjects (36±2 years, 45.6±1.1 kg.m ²⁻¹ body mass index (BMI), 48.2±1.0% body fat(BF) (mean±SEM)) were selected and tested prior to and after this procedure. Due to various reasons, complete data were not obtained from any one subject although a total of 16 bypass patients participated in the study. Therefore, the number of subjects in each part of the study varied from six to ten. Body composition was determined using the isotope dilution space (IDS) method and bioelectrical impedanceanalysis (BIA), which were compared with dual energy x-ray absorptiometry (DEXA) measurements in a subgroup of
the participants. Gas exchange analysis was used to measure the changes in basal energy expenditure (BEE) and thermic effect of food (TEF). Total energy expenditure (TEE) was determined during 6-8 weeks after surgery using the doubly labeled water (DLW) method. Weighed food records were used to assess the changes in energy intake during the study period. A group of normal-weight women (48±1 years, 23.4±0.5 kg.m ²⁻¹ BMI, 32.8±1.3
%BF (mean±SEM)) was selected to supplement the overall research.
Average body weight (111.1±3.2 kg, n=7) of the subjects completing the 3-month
measurement decreased by 5.2, 4.2 and 7.8 kg during each of the three months. There was a significant decline (p<O.0001) in fat-free mass (FFM) and fat mass (FM) measured by both IDS and BIA methods. The percentage ofFFM and FM determined by IDS method was not significantly changed during the study period. Presurgical total body mass (125.6±4.5 kg) determined by DEXA was significantly different (p0.044) from that (130.3±6.3 kg) obtained by scale, but postsurgical data did not demonstrate this difference. The results raised an important question about the validity of DEXA in the assessment of body composition in the morbidly obese subjects. With the decrease of body
weight induced by ileogastrostomy, body mass assessment by DEXA was not different from that obtained from scale. There was a close agreement in fat mass (FM) and percentage of body fat (%BF) obtained byIDS method and DEXA postsurgically, however, BIA showed a significant difference from the TBW method or DEXA (p<O.OS). Furthermore, the reduction of LBM and FM determined by IDS method and DEXA were found to be smaller than those obtained by BIA.
Ileogastrostomy did not significantly influence BEE levels but significantly affected TEF (p=0.001). A very high percentage (44%) of energy expended for physical activity was found at the second month after surgery. Because TEE was not measured presurgery, we were unable to assess the changes in TEE. However, our findings did show that TEE was closely correlated with the weight loss induced by ileogastrostomy (r=0.719, p=0.0l9, n= 10). A almost significant relationship between weight loss and fecal energy (r=0. 808, p=0.052, n=6) but not urinary energy loss (r=0.01 1, p=0.983, n=6) was observed in this
study. Surprisingly, energy intake as assessed by weighed food records was not related to weight loss during the short-term energy balance study. Energy intake was insignificantly correlated with energy expenditure (r=0.628, p=0.168) and fecal energy (r=0.732, p=0.084). Results of the validation of reported energy intake showed a large discrepancy between reported energy intake (El) and expenditure (EE) in both obese (1429±271 kcal.d⁻¹ EI vs 2933±239 kcal.d⁻¹ EE, respectively) and normal-weight groups (1653±76 kcal.d⁻¹ EI vs 2215±102 kcal.d⁻¹ EE, respectively). Underestimation, defined as [(EE-EI)IEEx 1001, was
42.0% in the obese group and 20.5% in the normal-weight group after correcting for the changes in body energy stores. The degree of underestimation was not associated with body weight in the normal-weight group, however, a close relationship (r=0.868, p=0.025) between underestimation and body weight was observed in obese group. From these findings it is concluded that ileogastrostomy can significantly reduce body weight, reflected in the decline of LBM and FM. However, the percentage of LBM and FM during 3-month postsurgical measurements was not significantly different from that
presurgery. Isotope dilution method and DEXA appeared to be accurate in assessing the reduction in body composition after intestinal bypass surgery although measurement of total LBM and FM compartments by the methods presently used did not agree very well for these morbidly obese subjects. Factorial energy expenditure results showed that BEE was unchanged but TEF declined significantly. Total energy expenditure and fecal energy loss play very important roles in the weight loss following ileogastrostomy but energy intake was not associated with this weight loss.
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