Rating changes over the course of meals: what do they tell us about motivation to eat?

Detailed analysis of the pattern of change in rated appetite within a meal have proved a useful technique through which to explore appetite control. Variability in individual ratings, and technical difficulties in achieving ratings at equivalent stages of a meal, have lead to the use of curve-fitting techniques to model changes in rated appetite across a meal. These changes could best be described by a quadratic function, in which the three parameters (intercept, linear and quadratic coefficients) represented distinct influences on meal size. In normal subjects, manipulations of palatability and opioid receptor blockade and preloads of alcohol all modified the linear component of this function only, while preloading with maltodextrin reduced appetite at the start of eating (the intercept) but not the pattern of change in ratings within that meal. Thus the linear coefficient appears to measure the degree of stimulation of appetite by the sensory characteristics of the food, while the intercept reflects baseline appetite at the start of a meal. These results suggest that microstructural analyses of rating changes allow some dissociation of the factors underlying motivation to eat, and provide a novel methodology for future experimentation.