Reducing dietary fat from a meal increases the bioavailability of exogenous carbohydrate without altering plasma glucose concentration.

The primary goal of this study was to determine the acute glycemic and endocrine responses to the reduction of fat content from a meal. On three separate occasions, nine overweight subjects (body mass index = 30 +/- 1 kg/m(2); 5 men, 4 women) consumed 1) a control meal ( approximately 800 kcal; 100 g of carbohydrate, 31 g of fat, and 30 g of protein), 2) a low-fat meal ( approximately 530 kcal; 100 g of carbohydrate, 1 g of fat, and 30 g of protein), or 3) a low-fat meal plus lipid infusion [same meal as low-fat meal, but the total energy provided was the same as control (800 kcal), with the "missing" fat ( approximately 30 g) provided via an intravenous lipid infusion]. All three meals contained [(13)C]glucose (3 mg/kg body wt) to assess the bioavailability of ingested glucose. During the 5-h period after each meal, we measured the recovery of [(13)C]glucose in plasma, plasma glucose, and insulin concentrations. We also measured plasma concentration of the gastrointestinal peptides: glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide-1 (GLP-1), and peptide YY(3-36) (PYY(3-36)). The recovery of the ingested [(13)C]glucose in the hour after ingestion was greater (P < 0.05) after the low-fat than after the control meal [area under the curve (AUC): 1,206 +/- 252 and 687 +/- 161 microM.h, respectively]. However, removing dietary fat from the meal did not affect the plasma concentration of glucose or insulin. Importantly, [(13)C]glucose recovery was not different during the low-fat and lipid infusion trials (AUC: 1,206 +/- 252 and 1,134 +/- 247 microM.h, respectively), indicating that the accelerated delivery of exogenous glucose found after removing fat from the meal is due exclusively to the reduction of fat in the gastrointestinal tract. In parallel with these findings, the reduction in fat calories from the meal reduced plasma concentration of GIP, GLP-1, and PYY(3-36). In summary, these data suggest that removing fat from the diet expedited exogenous glucose delivery into the systemic circulation and reduced the concentration of key gastrointestinal peptides, yet maintained plasma glucose concentration at control levels.