The effect of viscosity on ad libitum food intake.

Background:Energy-yielding liquids elicit weak suppressive appetite responses and weak compensatory responses, suggesting that liquid calories might lead to a positive energy balance. However, data is often derived from foods differing in many characteristics other than viscosity.Objective:To investigate the effect of viscosity on ad libitum food intake in real-life setting and to investigate whether a difference in ad libitum intake is related to eating rate and/or eating effort.Design:In real-life setting 108 nonrestrained subjects (26+/-7 years, BMI 22.7+/-2.4 kg m(-2)) received a chocolate flavored liquid, semi-liquid and semi-solid milk-based product, similar in palatability, macronutrient composition and energy density. In laboratory setting 49 nonrestrained subjects (24+/-6 years, BMI 22.2+/-2.3 kg m(-2)) received the liquid or semi-solid product. Effort and eating rate were controlled by means of a peristaltic pump.Results:In real-life setting the intake of the liquid (809+/-396 g) was respectively 14 and 30% higher compared to the semi-liquid (699+/-391 g) and semi-solid product (566+/-311 g; P<0.0001). In laboratory setting, removing eating effort, resulted in a 29% (P<0.0001) intake difference between liquid (319+/-176 g) and semi-solid (226+/-122 g). Standardizing eating rate resulted in 12% difference between liquid (200+/-106 g) and semi-solid (176+/-88 g; P=0.24). If not controlled, the difference in intake between liquid (419+/-216 g) and semi-solid (277+/-130 g) was comparable to the real-life setting (34%; P