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The regulation of energy intake is a complex process involving numerous factors such as genetic, physiological, environmental, and cognitive factors. This thesis, entitled "Food intake meeting energy and reward homeostasis", encompasses the role of hormone and appetite dynamics, in relation to meal pattern, as well as the concept of reward, and hypothalamus pituitary adrenal (HPA) axis activity, infood intake behavior. The research is executed against the background of the current epidemic of overweight and obesity.The search for physiological biomarkers of appetite is currently very active. Previous studies that based their correlation analyses of visual analogue scale (VAS) ratings for appetite with gut hormone and glucose concentration[...]

The regulation of energy intake is a complex process involving numerous factors such as genetic, physiological, environmental, and cognitive factors. This thesis, entitled "Food intake meeting energy and reward homeostasis", encompasses the role of hormone and appetite dynamics, in relation to meal pattern, as well as the concept of reward, and hypothalamus pituitary adrenal (HPA) axis activity, infood intake behavior. The research is executed against the background of the current epidemic of overweight and obesity.The search for physiological biomarkers of appetite is currently very active. Previous studies that based their correlation analyses of visual analogue scale (VAS) ratings for appetite with gut hormone and glucose concentrations, and energy intake, upon the calculated area under the curve or on the measured values per time point, showed a very low explained variation or no correlation atall. For validation of VAS ratings with gut hormone and glucose concentrations and energy intake the factor time needs to be taken into account. Thus, it was investigated whether changes in VAS appetite scores are synchronized with, or lag behind or in front of changes in gut hormone and glucose concentrations (Chapter 2). Results indicate that the mean explained variation of the development of hunger and fullness scores over time by the development of glucagon-like peptide (GLP)-1, peptide tyrosine-tyrosine (PYY), ghrelin, glucose, and insulin concentrations over time is 30-70 %. This figure is too small to use the changes in gut hormone and glucose concentrations as biomarkers for feelings of appetite, at least at the individual level and probably at group level depending on the aim of the study. Furthermore, ghrelin concentrations lag behind VAS hunger scores and insulin concentrations, suggesting a role for insulin as a negative regulator of ghrelin. Regarding the concept of reward, a computer test was developed and validated that measures the rewarding value of food, i.e. "liking and wanting", in a Dutch study population and applicable in different study designs. In addition, we assessed how the rewarding value of a consumed food item possibly affects the rewarding value of any other food item in general (Chapter 3). Subsequently, the computer test was applied in the assessment of the role of dietary restraint in control over "wanting" following consumption of "forbidden" food (Chapter 4). The computer test for measurement of "liking" and "wanting" proved to be sufficiently valid. Application of the computer test shows that eating a highly liked food item induces a more distinct decrease in "wanting" for food items in general and category-specific "liking", than eating a sufficiently liked "neutral" food item. In addition, successfully restrained eaters decrease food "wanting" specifically after consumption of a non-healthy perceived, "delicious" food vs. a nutritional identical, yet healthy perceived, slightly less "delicious" food. A healthy perceived food may thus impose greater risk for control of energy intake in successfully restrained eaters. Thus, eating what you like contributes to less wanting of more food. Eating out has become an important aspect in the development of obesity, and often involves a different meal pattern. The stimulated food intake through the social context of eating out may be facilitated by a slower appearance of satiation signals, or it may take place despite greater appetite control by possibly more sustained satiety signals. The effects of two different meal patterns, i.e. staggered vs. non-staggered meal consumption, on hormone (GLP-1, PYY, and ghrelin) and appetite dynamics, on the concept of reward, and on subsequent adlibitum energy intake, was investigated in a laboratory setting, thus excluding the environmental factors of eating out (Chapter 5). It was shown that staggered vs. non-staggered meal consumption induces greater appetite control, indicated by higher final GLP-1 concentrations and satiety ratings, lower ghrelin concentrations and hunger ratings, and lower subsequent food "wanting". However, this was not translated into a lower energy intake. In addition to meal pattern manipulation, the activity of the HPA axis ("stress") may play a role in excessive energy intake, in relation to the food reward system. It appears that psychosocial stress is associated with greater weight gain among subjects who are overweight or obese, but less among subjects who are normal weight or underweight. In visceral overweight vs. normal weight subjects the effects of acute psychological stress on the rewarding value of food, in terms of "liking" and "wanting", and on food intake in a fasted as well as satiated state were assessed (Chapter 6). Acute stress augments food "wanting" and energy intake in visceral overweight subjects in the absence of hunger. In a stressful situation the food reward system overrules and promotes excessive food intake in visceral overweight subjects.In everyday life where stress is a pervasive factor, the development of functional foods, able to regulate the physiological and psychological stress response, would be helpful to improve or maintain quality of life. Inconsistencies regarding the possible effects of macronutrients on HPA axis activity and on the stress-induced mood response exist in the literature. Therefore it was investigated whether consumption of comparable meals with different macronutrient contents, i.e. high-protein vs. high-carbohydrate, affect the physiological cortisol and psy-chological mood response (Chapter 7). Moreover it was investigated how con-sumption of high-protein vs. high-carbohydrate foods influences the rewarding value of food, i.e. "liking" and "wanting", and food choice and food intake, in an acute stressful situation (Chapter 8). Consumption of meals with different macronutrient contents, i.e. high-protein vs. high-carbohydrate, does not influence the physiological cortisol and psychological mood response differen-tially. A high-protein vs. high-carbohydrate meal induces lower subsequent "wanting" and energy intake in subjects with high disinhibition during rest; this difference disappears under stress. Acute stress overrules the effects of con-sumption of high-protein foods. In conclusion, from the studies described in this thesis it appears that physiologi-cal "biomarkers", such as GLP-1, PYY, ghrelin, glucose, and insulin, cannot replace feelings of appetite, at least at the individual level and probably at group level depending on the aim of the study. Furthermore, increased meal duration by staggered meal consumption can exert greater appetite control. The stimu-lated food intake in a restaurant setting with staggered meal consumption therefore takes place despite greater appetite control. Energy and reward homeostasis both play a role in food intake behavior in the hungry state. However, in the satiated state it is mainly reward homeostasis that plays a role in food intake behavior, and this role becomes even more important in conditions of acute stress. Chronically eating in the absence of hunger, i.e. eating beyond energy homeostasis, may lead to the development of overweight and obesity. With regard to functional foods able to regulate the stress response, high-protein foods are ineffective in regulating the physiological and psychologi-cal stress response, and have limited impact on stress-related eating behavior. Stress dominates the satiating effect of protein.Energy and reward homeostasis act together in the hungry state, while reward homeostasis overrules in the satiated state.