Lesser suppression of energy intake by orally ingested whey protein in healthy older men compared with young controls

Abstract

Protein-rich supplements are used widely for the management of malnutrition in young and older people. Protein is the most satiating of the macronutrients in young. It is not known how the effects of oral protein ingestion on energy intake, appetite and gastric emptying are modified by age. The aim of the study was to determine the suppression of energy intake by protein compared with control and underlying gastric-emptying and appetite responses of oral whey protein drinks in 8 healthy older men (69-80y) compared to 8 young male controls (18-34y). Subjects were studied on 3 occasions to determine the effects of protein loads of 30g/120kcal and 70g/280kcal compared to a flavored water control-drink (0g whey-protein) on energy intake (ad libitum buffet-meal), and gastric emptying (3D-ultrasonography) and appetite (0-180min) in a randomized, double-blind, cross-over design. Energy intake was suppressed by the protein compared with control (P=0.034). Suppression of energy intake by protein was less in older men (1±5%) than young controls (15±2%; P=0.008). Cumulative energy intake (meal+drink) during the protein days compared with the control day increased more in older (18±6%) men than young (1±3%) controls (P=0.008). Gastric emptying of all three drinks was slower in older men (50% gastric-emptying time: 68±5min) than young controls (36±5min; P=0.007). Appetite decreased in young, whilst it increased in older (P<0.05). In summary, despite having slower gastric emptying, elderly men exhibited blunted protein-induced suppression of energy intake by whey protein compared with young controls, so that in the elderly protein ingestion increased overall energy intake more.