Effects of small-intestinal fat and carbohydrate infusions on appetite andfood intake in obese and nonobese men

To determine whether the satiating effects of nutrients in the small intest ine are lower in obese than in nonobese people, 9 healthy, obese men [age: 18-33 y; body mass index (BMI; in kg/m(2)) 30.4-40.8] and 11 healthy, nonob ese men (age: 18-33 y; BMI: 19.1-26.4) received an intraduodenal infusion o f saline (control), lipid (11.97 kJ/min, or 2.86 kcal/min), or glucose (11. 97 kJ/min) for 120 min on separate days. Fullness, hunger, and nausea were assessed by visual analogue scales. After the infusions, a meal was offered and food intake was quantified. There was no difference in appetite rating s between the obese and nonobese subjects during the infusions, in the amou nt or macronutrient composition of food eaten after the infusions, or in th e time taken to eat the meals. Both the lipid and glucose infusions were as sociated with greater fullness than the control infusion. The energy conten t of the food eaten was less after the lipid infusion than after either the control or glucose infusion (P < 0.01); lipid infusion suppressed energy i ntake by 22% compared with the control infusion and by 15% compared with th e glucose infusion. Suppression of energy intake after intraduodenal nutrie nt infusions was due to slower eating (P < 0.01). Intraduodenal infusions o f fat suppressed appetite and food intake mon than did equienergetic infusi ons of carbohydrate in both obese and nonobese young men, and the responses to intraduodenal fat and glucose were not affected by obesity. The latter observation suggests that established obesity is not associated with reduce d small-intestinal responses to dietary fat or carbohydrate.