Effect of small intestinal nutrient infusion on appetite, gastrointestinal hormone release, and gastric myoelectrical activity in young and older men.

OBJECTIVE: The mechanisms responsible for the reduction in appetite and slowing of gastric emptying in older persons are poorly understood. The aim of this study was to evaluate the effects of aging on small intestinal regulation of appetite, GI hormone release, and gastric myoelectrical activity. METHODS: Thirteen older (65-84 yr) and 13 young (18-32 yr) healthy men received isovolumetric, intraduodenal (i.d.) infusions of saline (control), lipid, and glucose for 120 min, on separate days. The energy content of the lipid and glucose infusions was identical at 2.86 kcal/min. Immediately after the i.d. infusions, each subject was offered a buffet meal, and ad libitum food intake was quantified. Blood glucose and plasma insulin, glucagon-like peptide 1, and glucose-dependent insulinotropic peptide were measured. Gastric myoelectrical activity was measured by surface electrogastrography (EGG). RESULTS: I.d. lipid suppressed food intake in both the young and older men (p < 0.05), whereas i.d. glucose suppressed food intake only in the older men (p < 0.05). The blood glucose (p < 0.01) and insulin (p < 0.05) responses to i.d. glucose were greater in older than young men. However, there were no differences in glucagon-like peptide 1 or glucose-dependent insulinotropic peptide responses to any of the infusions. There was a greater increase in the EGG power ratio both during and after i.d. glucose infusion in the young (p < 0.05) than the older men, and an attenuation of EGG frequency by nutrient infusions in older, but not young, men. CONCLUSIONS: Our findings indicate that aging is associated with nutrient-specific changes in appetite, hormonal, and gastric myoelectrical (EGG) responses to i.d. nutrients. An enhanced satiating effect of small intestinal carbohydrates may potentially contribute to the anorexia of aging.

Effects of glucose supplementation on gastric emptying, blood glucose homeostasis, and appetite in the elderly.

The aims of this study were to evaluate the effects of dietary glucose supplementation on gastric emptying (GE) of both glucose and fat, postprandial blood glucose homeostasis, and appetite in eight older subjects (4 males, 4 females, aged 65--84 yr). GE of a drink (15 ml olive oil and 33 g glucose dissolved in 185 ml water), blood glucose, insulin, gastric inhibitory polypeptide (GIP) and glucagon-like peptide-1 (GLP-1), and appetite (diet diaries, visual analog scales, and food intake at a buffet meal consumed after the GE study) were evaluated twice, after 10 days on a standard or a glucose-supplemented diet (70 g glucose 3 times a day). Glucose supplementation accelerated GE of glucose (P < 0.05), but not oil; there was a trend for an increase in GIP (at 15 min, P = 0.06), no change in GLP-1, an earlier insulin peak (P < 0.01), and a subsequent reduction in blood glucose (at 75 min, P < 0.01). Glucose supplementation had no effect on food intake during each diet so that energy intake was greater (P < 0.001) during the glucose-supplemented diet. Appetite ratings and energy intake at the buffet meal were not different. We conclude that, in older subjects, glucose supplementation 1) accelerates GE of glucose, but not fat; 2) modifies postprandial blood glucose homeostasis; and 3) increases energy intake.

Effects of age on proximal gastric motor and sensory function.

BACKGROUND: Healthy aging is associated with a reduction in appetite and food intake, which may predispose to pathologic weight loss and malnutrition. Changes in intragastric mechanisms mediating satiation in the elderly have not been studied. The aim of this study was to evaluate the effects of aging on i) fasting gastric compliance and the perception of gastric distension, and ii) food intake and gastric accommodation to a meal. METHODS: Five healthy older (aged 68-73 years) and five healthy young (aged 22-27 years) men, matched for body mass index, were each studied on three occasions after an overnight fast. On one day ('barostat day'), isovolumetric and isobaric distensions of the proximal stomach were performed, and meal-induced changes in intrabag volume were measured with an electronic barostat. On another day ('tube-only day') subjects were intubated with a nasogastric tube without an intragastric bag before the meal. On the 3rd day (control day) subjects were given the meal without intubation. Energy intake from the buffet meal was quantified, and perceptions assessed using visual analogue questionnaires. RESULTS: During both isobaric and isovolumetric distensions the pressure-volume relationship did not differ significantly between older and young subjects. During gastric distensions perceptions of fullness (P < 0.01), abdominal discomfort (P < 0.05), and bloating (P < 0.05) were less in older than young subjects, whereas the perception of hunger (P < 0.05) was less in the young than in older subjects. There was no difference in energy intake (P = 0.44) between young and older subjects. Food intake was less on the barostat day (P < 0.01) and the tube-only day (P < 0.01) than on the control day in young subjects but was not affected by the different study conditions in the older subjects. After the meal the maximum intrabag volume occurred later in the older than in the young subjects (105 +/- 4 min versus 36 +/- 8 min; P < 0.05), and the intrabag volume change was greater (P = 0.05) in the older than the young subjects later in the postprandial period. CONCLUSIONS: Healthy aging is associated with decreased perception of gastric distension without any change in fasting gastric compliance and with reduced gastric tone late in the postprandial period when compared with the young. Control of food intake is less sensitive to external stimuli in older than in young subjects.