Enhanced dietary fat clearance in postobese women

The objective of this study was to examine the postprandial response to an exogenous fat source in eight weight-stable postobese subjects (2-3 years a fter gastric bypass) and eight matched control women, using a stable isotop e, [C-13]oleate. After a high fat breakfast meal (1,062 cal, 67% fat), [C-1 3]oleate in triglyceride (TG)-rich lipoproteins (S-f >400 and S-f 20-400) a nd nonesterified fatty acids (NEFA), and C-13 in breath CO2, were monitored over 8 h, There were no differences in resting energy expenditure, thermic effect of food, carbohydrate/fat oxidation ratio, breath (CO2)-C-13 enrich ment, or fecal fat content between postobese and control subjects, Postpran dially, there was no difference in S-f 20-400 TG or NEFA, but postobese sub jects had lower S-f >400 incremental area under the curve (AUC) (-33%, P < 0.0025) and glucose [P < 0.01 by repeated measures analysis of variance (RM ANOVA)], Post-prandial C-13 in S-f >400 TG returned to fasting levels 4 h earlier in postobese subjects and was lower than in control subjects at 4 a nd 6 h (P < 0.05 by RM ANOVA), The greatest difference was in the [C-13]NEF A profiles. In control subjects [C-13]NEFA increased markedly over 8 h; pos tobese subject [C-13]NEFA remained close to fasting nonenriched values, and was strikingly lower than in control subjects (72% lower by AUC, P < 0.000 1 by RM ANOVA), Finally, postobese subjects tended to have lower postprandi al insulin (P < 0.01, 4 h), lower postprandial acylation-stimulating protei n, and lower fasting leptin (-46%, P < 0.02). This study demonstrates clear metabolic differences in exogenous dietary fat partitioning in postobese w omen. These findings are compatible with an increased efficiency of dietary fat storage and suggest one possible mechanism for promotion of weight reg ain in postobese individuals.