Dose-dependent effects of beverage protein content upon short-term intake

Protein is considered to be more satiating than carbohydrate, quantified by energy adjustment and subjective appetite. However, the effect of increasing protein content upon short-term energy adjustment in beverage contexts is unclear. This study used a repeated-measures, cross-over design. 28 male volunteers (18-35 years) ate a standard breakfast in the laboratory and 210 min later consumed one of four preloads 30 min prior to an ad libitum pasta meal. Three of the preloads were isocaloric ( approximately 1155 kJ) mixed composition dairy fruit drinks (300 g) of low (13% protein energy/87% carbohydrate energy), medium (25% protein energy/75% carbohydrate energy) and high (50% protein energy/50% carbohydrate energy) protein content. The control drink was a low energy (328 kJ) alternative. Results indicated a dose response effect of preload protein level on intake (g) at the ad libitum meal. Ad libitum intake was: control (637.6g+/-39.7), low (596.9 g+/-40.5), medium (546.9 g+/-34.7), and high protein (533.6g+/-42.3). 100% compensation was not achieved; however total energy intake after the medium and high protein drinks did not differ significantly from control. There were no significant differences in hunger and fullness ratings. Our findings support the view that increasing the protein composition of beverages relative to carbohydrate proportionally affects short-term subsequent intake in controlled conditions.