The study of feeding behavior, and in particular the study of subjective hedonic experience and objective measures of motivation, are central to understanding how appetite regulation can be compromised in certain individuals. Furthermore, with an integrated picture of physiological and behavioral changes that can occur as a result of energy deprivation what emerges is a better understanding of how palatable food can disrupt attempts at regulating body weight at lower levels of body energy stores. In Article I, the genetic association study examining a potential role for a dopamine-related polymorphism in weight loss, it was shown that contrary to the main hypothesis there was no association between TaqIA polymorphism and the amount of body weight loss. In Article II, it was shown that palatability and olfaction ratings increased as a result of a 24 hour fast and females demonstrated larger improvements in overall olfactory performance. Initial body weight was positively related to improved odor detection threshold and total odour score (TDI). Using the same population sample as Article II, Article III highlights that higher sensitivity to reward and disinhibition scores correlated with responding for palatable snack food stimuli in the relative-reinforcing value of food (RRV) task, further indicating that RRV has strong ties with impulsivity. There was a demonstrable lack of negative alliesthesia under the fasted condition where, after a 75% increase in ad libitum energy intake (EI) relative to the fed condition, this greater amount of food consumed was still rated as being more palatable than the lesser amounts consumed under the fed condition. In Article IV it was shown that an equicaloric (-25%) energy deficit by diet alone was a greater challenge to appetite regulation and resulted in greater compensatory increases in EI than deprivation by exercise alone. Independent of deprivation modality there were significant improvements in odour threshold scores. TDI score increased only under diet alone; furthermore, the noted increase in mean TDI score was positively related to increased ad libitum EI. The picture that emerges is that, acutely, a complete fast has more pronounced effects on appetite and ad libitum EI than dieting alone, which in turn had greater effects than exercise alone or controls. Also, TDI improved under all three methods of energy deprivation, but moreso under conditions of deprivation by diet alone.

A number of strategies to lose weight are available. However, a high inter-individual variability is commonly observed in terms of weight loss and its maintenance in individuals enrolled in different interventions. This high variability is mainly explained by individual differences in the activation of compensatory mechanisms triggered by energy deficits. Increases in appetite ratings as well as the rewarding effects of foods are some of the consequences commonly observed from weight loss induced by caloric restriction. On the other side of the energy balance equation, resting energy expenditure (REE) was also found to decrease as consequence of weight loss. Numbers might in fact decrease beyond what could be expected from changes in body weight and composition, highlighting an adaptation in thermogenesis in some individuals. These changes were previously found to be associated with the magnitude of weight loss. However, it is not clear whether different rates of weight loss have a different impact on the compensatory mechanisms described above. Moreover, other questions regarding weight loss maintenance deserve further investigations. For example, the role of exercise, more specifically resistance training (RT), on weight loss maintenance needs additional attention. Accordingly, the present thesis aimed to investigate the effects of caloric restriction on compensatory mechanisms that occur during and after weight loss. We first aimed to determine whether the rate of weight loss differently influence physiological and psychological variables related to energy balance. Secondly, we aimed to elucidate whether early changes in the above mentioned adaptations in energy expenditure (EE) and energy intake (EI) variables predict final outcomes (fat mass - FM and weight loss). Finally, we aimed to determine whether RT promoted greater weight loss maintenance. In Article I and II, we investigated whether different rates of weight loss play a role in EI and EE related-variables. We noted significant increases in fasting appetite measures, as well as increases in satiety measures. REE decreased over time, as did the relative reinforcing value of fruit. No significant group interaction was observed illustrating that different rates of weight loss has no impact on the magnitude of adaptations in EI and EE after weight loss. In article III we demonstrated that early changes in fasting and postprandial appetite measures in response to caloric restriction were associated with greater body weight and FM loss in women. Indeed, greater increases in fasting appetite were associated with greater FM loss, contrary to our hypothesis. However, increases in postprandial appetite were associated with greater FM and body weight loss, independently of changes in eating behaviours. Taken together, articles I and III demonstrated that caloric restriction has a significant impact on increases in appetite and reduction in REE as soon as the in the first week of intervention. Those changes remain significant until the end of the program. In article IV it was shown that 1-year of resistance training (2x/ week) after 6-month of caloric restriction was not sufficient to promote better weight and FM loss in post-menopausal women. Furthermore, the results demonstrated that RT did not improve the differences between measured and predicted measures in REE observed as consequence of weight loss. The picture that emerges is that, increases in appetite and decreases in REE can be observed since the first week of caloric restriction and remain significant until the end of the program, independently of the rate of weight loss. Feeding-related variables such as fasting and postprandial appetite and RRV of a snack food are better predictors of final FM loss, even after adjusting for changes in eating behaviours. In addition, our study demonstrated that different rates of weight loss do not have an independent aspect on either physiological or psychological aspects related to energy balance.

The study of feeding behavior, and in particular the study of subjective hedonic experience and objective measures of motivation, are central to understanding how appetite regulation can be compromised in certain individuals. Furthermore, with an integrated picture of physiological and behavioral changes that can occur as a result of energy deprivation what emerges is a better understanding of how palatable food can disrupt attempts at regulating body weight at lower levels of body energy stores. In Article I, the genetic association study examining a potential role for a dopamine-related polymorphism in weight loss, it was shown that contrary to the main hypothesis there was no association between TaqIA polymorphism and the amount of body weight loss. In Article II, it was shown that palatability and olfaction ratings increased as a result of a 24 hour fast and females demonstrated larger improvements in overall olfactory performance. Initial body weight was positively related to improved odor detection threshold and total odour score (TDI). Using the same population sample as Article II, Article III highlights that higher sensitivity to reward and disinhibition scores correlated with responding for palatable snack food stimuli in the relative-reinforcing value of food (RRV) task, further indicating that RRV has strong ties with impulsivity. There was a demonstrable lack of negative alliesthesia under the fasted condition where, after a 75% increase in ad libitum energy intake (EI) relative to the fed condition, this greater amount of food consumed was still rated as being more palatable than the lesser amounts consumed under the fed condition. In Article IV it was shown that an equicaloric (-25%) energy deficit by diet alone was a greater challenge to appetite regulation and resulted in greater compensatory increases in EI than deprivation by exercise alone. Independent of deprivation modality there were significant improvements in odour threshold scores. TDI score increased only under diet alone; furthermore, the noted increase in mean TDI score was positively related to increased ad libitum EI. The picture that emerges is that, acutely, a complete fast has more pronounced effects on appetite and ad libitum EI than dieting alone, which in turn had greater effects than exercise alone or controls. Also, TDI improved under all three methods of energy deprivation, but moreso under conditions of deprivation by diet alone.

Background: Roux-en-y gastric bypass (RYGB) surgery produces significant weight loss, however a number of patients experience some and/or complete recidivism of weight years after surgery. Limited research has investigated why patients are experiencing weight regain after surgical interventions. Our objective was to identify appetite-related measures associated with weight regain after RYGB surgery. Methods: Using a cross-sectional design, 29 participants (49.6 ± 9.1 years of age; 29-62 months post-RYGB) were divided into three weight categories; (weight maintainers, n = 9; low weight regainers, n = 10; and high weight regainers, n = 10). Appetite, smell function, eating behaviours and food reward were measured in response to a standardized meal. Results: Weight regain increased significantly in association with time after surgery (rs = 0.768, p = 0.016). High regainers gained on average 8.6 kg/year, compared to low regainers and maintainers, 3.8 ± 0.9 kg/year and 0.9 ± 0.9 kg/year, respectively (p < 0.001). Dietary restraint (using the Three Factor Eating Questionnaire) was significantly higher in weight maintainers and low regainers compared to high regainers using clinical subscales (p < 0.05). Weight regain was associated with higher “liking” of high-fat sweet foods (measured with the Leeds Food Preference Questionnaire) among high weight regainers. Conclusion: Weight regain after RYGB may be associated with higher preferences for high-fat sweet foods, whereas, higher dietary restraint may be associated with lower wanting of high-fat sweet foods among weight maintainers. Findings provide insight into why some patients after RYGB regain weight, while others maintain their weight. Future research is needed to further explore the relationships between appetite-related factors and weight regain after RYGB employing a longitudinal study design.

The main objective of this thesis was to examine the independent effects of sleep duration and timing on appetite, food reward and energy balance. Study 1 investigated the associations between satiety quotient (SQ) with habitual, self-reported sleep duration, quality and timing. No significant associations were noted between SQ and sleep parameters. Short-duration sleepers had a lower mean SQ vs. those with ≥7h sleep/night (P=0.04). Study 2 evaluated associations between changes in sleep duration, efficiency and timing with changes in next day food reward. Greater sleep duration and earlier wake-times were associated with greater food reward (P=0.001). However, these associations were no longer significant after controlling for elapsed time between awakening and completion of the food reward task. Study 3 examined the effects of 50% sleep restriction (SR) anchored during the first (delayed bedtime) or second (advanced wake-time) half of the night on appetite, SQ, food reward, energy intake (EI) and energy expenditure (EE). Greater appetite ratings and explicit high-fat food reward were noted following SR with an advanced wake-time vs. control and SR with a delayed bedtime (P=0.03-0.01). No difference in SQ was noted between sessions. Energy and carbohydrate intakes were greater on day 2 and over 36h in the delayed bedtime vs. control session (P=0.03). Activity EE and moderate-intensity physical activity (PA) time were greater following delayed bedtime vs. control and advanced wake-time on day 1, whereas vigorous-intensity PA time was greater following advanced wake-time vs. delayed bedtime on day 1 (P=0.01-0.04). Greater sleep quality and slow-wave sleep duration between SR sessions were associated with lower EI and increased vigorous-intensity PA time, respectively (P=0.01-0.04). Collectively, these findings suggest that appetite, SQ and food reward are influenced by sleep parameters, but these changes may not alter EI. These findings also suggest that individuals with greater sleep quality in response to SR had greater vigorous-intensity activity time and lower EI.

Background: Dopamine levels has been implicated in obesity, feeding behaviour, and hedonic control of appetite like olfactory cues and food palatability. Methylphenidate (MPH) is a dopamine reuptake inhibitor that increases brain dopamine levels and has been shown to reduce appetite and promote weight loss in patients with attention deficit hyperactivity disorder (ADHD). As such, the objectives of this study were to test the possible effect of MPH on appetite, olfaction, and food palatability as well as its effects on energy intake and body weight of healthy individuals with obesity. Methods: In a randomized, double-blind study, 12 participants (age 28.9±6.7 yrs) (BMI 36.1±4.5 kg/m2) were assigned to receive MPH (0.5mg/kg) (n=5) or placebo (n=7) twice daily for two months. Appetite and palatability (Visual Analog Scale (VAS)), odour threshold (Sniffin’ Sticks®), in-lab energy intake (ad libitum buffet), free-living energy intake (3-day food boxes) and body weight (DEXA scan) were measured at baseline (day 1) and final visit (day 60). Results: MPH intake caused significantly greater suppression of appetite sensations (desire to eat (p=0.001), hunger (p=0.008), and prospective food consumption (p=0.003)) and increase in fullness (p=0.028) over time compared to placebo. There was a significant increase in odour threshold scores in the MPH group (6.3±1.4 vs. 9.4±2.1) compared to placebo (7.9±2.3 vs. 7.8±1.9) (p=0.029). Both placebo and MPH groups showed decreases in their energy intake (p=0.021) and body weight (p=0.005) over time but with large effect sizes favouring greater reduction in the MPH group compared to placebo. Conclusions: Compared to placebo, MPH intake over 60 days suppressed appetite and improved olfactory sensitivity in individuals with obesity. These data provide novel findings into the possible efficacy of MPH to favourably impact appetite and therefore promoting weight loss in individuals living with obesity.

The present study aimed to evaluate associations between sleep duration and food-related inhibitory control and food reward in adolescents aged 12-18. Potential moderating effects of physical activity and weight status on the association between sleep, inhibitory control, and food reward were also examined. To evaluate these associations, the study employed a two-phase crossover design in which participants spent either 5 hours per night (restricted sleep) or 9 hours per night (habitual sleep) in bed for 5 nights. Participants completed a food-related inhibitory control task and a questionnaire assessing for food reward on the 6th day of each study phase. Repeated measures analyses of variance examined the effect of sleep restriction on food-related inhibitory control and food reward, and explored the moderating impact of weight status and physical activity. Adolescents performed more poorly on a food-related inhibitory control task and have heightened food reward following sleep restriction. Though no differences were noted across weight status in performance of a food inhibitory control task, adolescents with overweight/obesity demonstrated heightened food reward. An interaction between sleep duration and weight status predicted food reward, indicated that normal-weight adolescents are more susceptible to heightened food reward following sleep restriction compared to overweight/obese adolescents. Conversely, overweight/obese adolescents showed consistently high food reward with no effect of sleep duration, suggesting that they consistently view food as rewarding. These study findings may suggest that shortened sleep duration increased food reward for normal weight individuals, potentially putting them at risk for development of overweight/obesity.

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Il a été largement démontré que la saveur sucrée était la saveur la plus appréciée chez les nouveau-nés et que cette attirance demeurait élevée tout au long de l’enfance et de l’adolescence. Il semble primordial de mieux caractériser le comportement alimentaire des enfants pour cette saveur en s’intéressant au rôle joué par les expériences alimentaires et aux apprentissages qui en découlent dans la mise en place de l’attirance pour les aliments et boissons sucrés. Pour répondre à cette problématique nous avons allié une approche comportementale et une approche en imagerie cérébrale (IRMf) chez les enfants de 7-12 ans afin de caractériser leur comportement alimentaire envers la saveur sucrée. Les résultats montrent peu de liens entre expositions à la saveur sucrée et attirance pour la saveur sucrée. Cependant, l’attirance pour la saveur sucrée est fortement associée à la quantité de glucides simples consommés en situation de libre choix. De plus, les sucres caloriques jouent un rôle renforçateur dans l’apprentissage de l’appréciation d’une flaveur nouvelle et l’exposition répétée à des boissons sucrées et édulcorées permet aux enfants d’apprendre à compenser l’énergie consommée aux repas suivants l’ingestion des boissons. La compensation n’est cependant que partielle. Enfin, les analyses en IRMf suggèrent que plus les enfants sont exposés aux boissons sucrées moins il y a d’activation en réponse aux sucres au niveau de régions du circuit de la récompense. Par une approche originale, ces travaux ont permis de mieux caractériser l’attirance des enfants pour la saveur sucrée et soulignent le rôle des apprentissages dans la mise en place des préférences alimentaires. / It has been widely demonstrated that infants have a higher preference for sweetness than for any other tastes and that sweetness attraction remain high throughout childhood and adolescence. Therefore, better characterizing children’s eating behavior toward sweetness by evaluating the role of food experiences and learning in the development of children’s attraction toward sweet foods and drinks seems essential. To better address this issue behavioral and brain imaging (fMRI) protocols were combined in 7 to 12 year-old children in order to characterize in different ways their eating behavior toward sweetness. Results showed few links between early and current sweetness exposure and attraction toward sweet taste. However, attraction toward sweet taste is strongly associated with simple carbohydrate intake in a free choice buffet. Moreover, nutritive carbohydrates play a reinforcing role in food learning in terms of children’s food liking. Children’s capacities to compensate the calories consumed in a preload drink are learned after repeated exposures to caloric and non-caloric drinks. However, caloric compensation remains uncomplete. Furthermore, fMRI data suggest that sweet drink exposure could lead to decreased activations in regions involved in food reward. Using an original methodological approach, the present work resulted in a better characterization of children’s attraction toward sweetness. Moreover, these results give an interesting insight regarding the role of experiences with sweet foods and drinks during childhood in the development of children’s food preferences.

Background. Previous studies have highlighted the role of the brain reward and cognitive control systems in the etiology of anorexia nervosa (AN). In an attempt to disentangle the relative contribution of these systems to the disorder, we used functional magnetic resonance imaging (fMRI) to investigate hemodynamic responses to reward-related stimuli presented both subliminally and supraliminally in acutely underweight AN patients and age-matched healthy controls (HC). Methods. fMRI data were collected from a total of 35 AN patients and 35 HC, while they passively viewed subliminally and supraliminally presented streams of food, positive social, and neutral stimuli. Activation patterns of the group × stimulation condition × stimulus type interaction were interrogated to investigate potential group differences in processing different stimulus types under the two stimulation conditions. Moreover, changes in functional connectivity were investigated using generalized psychophysiological interaction analysis. Results. AN patients showed a generally increased response to supraliminally presented stimuli in the inferior frontal junction (IFJ), but no alterations within the reward system. Increased activation during supraliminal stimulation with food stimuli was observed in the AN group in visual regions including superior occipital gyrus and the fusiform gyrus/parahippocampal gyrus. No group difference was found with respect to the subliminal stimulation condition and functional connectivity. Conclusion. Increased IFJ activation in AN during supraliminal stimulation may indicate hyperactive cognitive control, which resonates with clinical presentation of excessive self-control in AN patients. Increased activation to food stimuli in visual regions may be interpreted in light of an attentional food bias in AN.