Effect of drinking compared with eating sugars or whey protein on short-term appetite and food intake

Background: It is hypothesized that a solid form of food or food components suppresses subjective appetite and short-term food intake (FI) more than a liquid form. Objective: To compare the effect of eating solid vs drinking liquid forms of gelatin, sucrose and its component mixtures, and whey protein, on subjective appetite and FI in young men. Design and subjects: A randomized crossover design was used in three experiments in which the subjects were healthy males of normal weight. Solid and liquid forms of gelatin (6 g) (experiment 1, n = 14), sucrose (75 g) and a mixture of 50% glucose/ 50% fructose (G50:F50) (experiment 2, n = 15), and acid and sweet whey protein (50 g) (experiment 3, n = 14) were compared. The controls were water (experiments 1 and 3) and calorie-free sweetened water with gelatin (sweet gelatin, experiment 1) or calorie-free sweetened water (sweet control, experiment 2). Subjective average appetite was measured by visual analog scales over 1 h and ad libitum FI was measured 1 h after treatment consumption. Results: Average appetite area under the curve was not different between solid and liquid forms of sugars, but was larger, indicating greater satiety for solid compared with liquid forms of gelatin and sweet, but not acid whey protein. The FI was not different from that of control because of solid or liquid sugars or gelatin treatments. However, both solid and liquid forms of whey protein, with no difference among them, suppressed FI compared with control (P < 0.05). Conclusion: Macronutrient composition is more important than physical state of foods in determining subjective appetite and FI. International Journal of Obesity (2011) 35, 562-569; doi: 10.1038/ijo.2010.163; published online 24 August 2010