Effects of intraduodenal protein on appetite, energy intake, and antropyloroduodenal motility in healthy older compared with young men in a randomized trial

Background: Protein-rich supplements are used widely for the prevention and management of undernutrition in older people. The use of protein supplements in older people could, however, be counterproductive by reducing appetite and overall energy intake. Objective: The objective was to determine whether aging influences the effects of protein loads, administered directly into the small intestine, on energy intake, antropyloroduodenal motility, and appetite. Design: Intraduodenal infusions (240 mL, 60 min) of saline (0 kcal, control) and protein (hydrolyzed whey) loads of 30, 90, and 180 kcal were followed by an ad libitum buffet meal in 10 young (19-29 y) and 10 healthy older (68-81 y) men. Suppression of energy intake (kcal) at the meal by protein infusion compared with control was calculated. Results: In young subjects, a dose-responsive suppression (+/- SEM) of energy intake was found at the buffet meal by protein (suppression at 30 kcal: 7 +/- 8%, P = 0.189; 90 kcal: 17 +/- 8%, P = 0.054; 180 kcal: 33 +/- 7%, P = 0.002), whereas suppression was observed only after the 180-kcal load in older subjects (30 kcal: 7 +/- 4% increase, P = 0.126; 90 kcal: 6 +/- 7% increase, P = 0.291; 180 kcal: 17 +/- 6% suppression, P = 0.016). Suppression of energy intake by protein was less in older than in young subjects (P < 0.005). In young subjects, total energy intake (meal + infusion) on the 180-kcal protein-infusion day was lower than that on the control day (P = 0.041), whereas in older subjects it was greater on the 30-kcal (P = 0.033) and 90-kcal (P = 0.016) infusion days. Energy intake was inversely related to isolated pyloric pressure waves (r = -0.32, P = 0.013) and positively related to antral (r = 0.30, P = 0.021) and duodenal (r = 0.35, P = 0.006) pressure waves. Suppression of energy intake by protein was inversely related to the change in isolated pyloric pressure waves (r = 0.35, P = 0.027) and positively related to duodenal pressure waves (r = 0.32, P = 0.044). Conclusions: Intraduodenal protein suppresses appetite and energy intake less in healthy older than in young adults. In older subjects, intraduodenal protein at low doses increased overall energy intake, which supports the use of protein supplements in undernourished older people. This trial was registered at www.anzctr.org.au as 12612000906853.