The Short-Term Effect of Whey Compared with Pea Protein on Appetite, Food Intake, and Energy Expenditure in Young and Older Men

Abstract

Diets higher in protein have been reported to improve age-related changes in body composition via increased energy expenditure, shifts in substrate oxidation, and decreased appetite. However, how protein source (e.g., animal versus plant protein) impacts energy expenditure, appetite and food intake as we age is unknown. The objective of this study was to evaluate the effect of protein source as part of a high protein breakfast on appetite, food intake, energy expenditure, and fat oxidation in young men compared to older men. This study used a randomized, single-blinded crossover design, with a one-week washout period between testing days. Fifteen young (YM; 25.2 ± 2.8 years) and fifteen older (OM; 67.7 ± 4.5 years) healthy, adult men participated in the study. Participants arrived fasted and consumed an isocaloric, volume-matched, high-protein (40 g) test beverage made with either an animal (whey protein isolate; WPI) or plant (pea protein isolate; PPI) protein isolate source. Markers of appetite and energy expenditure were determined at baseline and over four hours postprandial. There was a significant effect of time, age, and protein source on appetite (P < 0.05). There was no effect of protein source on plasma markers of appetite, food intake, energy expenditure, and substrate oxidation. After controlling for body weight OM had decreased energy expenditure (P < 0.05) and lower fat oxidation (P < 0.001) compared to YM. This study indicates that a high protein breakfast containing WPI or PPI exerts comparable effects on appetite, energy expenditure, and 24-hour energy intake in both young and older healthy adult men. This trial was registered at clinicaltrials.gov as NCT03399812.