Effects of small intestinal nutrient infusion on appetite and pyloric motility are modified by age

The mechanisms responsible for the reduction in appetite and slowing of gastric emptying in older persons are unknown. The aims of this study were to evaluate the effects of aging on small intestinal regulation of appetite and pyloric motility. Eight healthy older (age 65-75 yr) and seven healthy young (age 20-34 yr) male subjects received isocaloric (2.9 kcal/min) intraduodenal infusions of lipid and glucose for 120 min, each on separate days. During the intraduodenal infusions, perceptions of hunger, desire to eat, and fullness were assessed by visual analog scales. Pyloric motility (isolated pyloric pressure waves and tonic pyloric pressure) was measured by manometry during the intraduodenal lipid infusion. On each day, after completion of the intraduodenal nutrient infusion the subject was offered a buffet meal and food intake was quantified. Before intraduodenal nutrient infusions, sensations of hunger (P < 0.01) and desire to eat (P < 0.05) were less in the older compared with the young subjects. In the young, intraduodenal lipid suppressed hunger to a greater extent than intraduodenal glucose (P < 0.05). In older persons, neither intraduodenal nutrient infusion suppressed hunger. Intraduodenal lipid and glucose increased fullness in both age groups (P < 0.05 for both), with no significant difference between the two nutrients. There was no significant difference in food intake from the buffet meal between the elderly and young subjects. Intraduodenal lipid infusion stimulated phasic pyloric pressure waves in both age groups (P < 0.01 for both), and this response was greater (P < 0.05) in older persons. There was an increase (P < 0.01) in tonic pyloric pressure during intraduodenal lipid infusion that was not significantly different between the two age groups. We conclude that the effect of small intestinal lipid infusion on hunger is attenuated, and the stimulation of phasic pyloric pressure waves increased in healthy older persons compared with healthy young males. Increased feedback from small intestinal nutrients does not appear to be responsible for the physiological anorexia of aging.