The effect of portion size on food intake is a well-documented phenomenon: when served larger portions, individuals significantly increase their food intake. Insofar authors have limited their research on presenting the potential outcomes, while identifying several conditions favorable to this phenomenon. Indeed, the mechanisms of this effect are poorly understood and no research has insofar provided conclusive evidence regarding the underlying mechanism that could help explain the portion size effect. The first part of this dissertation aimed to fill this gap. We argue that the anchoring and adjustment heuristic accounts for most of the favoring conditions evidenced in earlier research and present it as a possible mechanism underlying the portion size effect. In this view, the portion size served is used as an anchor whereas other influences (i.e. economical, metabolic, regulatory, physiological, sensory, social and environmental) may further contribute to adjust total amount of food consumed. Moreover, we argue that prevention strategies based on this decision making literature may be similarly effective to limit excess food intake from enlarged portions. <p><p>The second and third chapter of this dissertation focus on two other factors related to the portion size of foods, namely the container size and the structure of the portion (i.e. food item size). The discussion of this dissertation reviews the facilitating conditions put forward previously to understand the portion size effect, as well as those reinforcing this effect, and how they may be integrated in an anchoring and adjustment perspective of eating. Finally, it aims to provide a food intake model that may accommodate for most environmental influences, with a special focus on the three influences mentioned above. / Doctorat en Sciences Psychologiques et de l'éducation / info:eu-repo/semantics/nonPublished

1. Contextual outline of the PhD Research<p><p>Climate change is today often seen as one of the most challenging issue that our civilisation will have to face during the 21st century. This is especially so now that the most recent scientific data have led to the conclusion that the globally averaged net effect of human activities since 1750 has been one of warming (IPCC 2007, p. 5) and that continued greenhouse gas emissions at or above current rates would cause further warming (IPCC, 2007 p. 13). This unequivocal link between climate change and anthropogenic activities requires an urgent, world-wide shift towards a low carbon economy (STERN 2006 p. iv) and coordinated policies and measures to manage this transition.<p><p>The climate issue is undoubtedly a typical policy question and as such, is considered amenable to economic scrutiny. Indeed, in today’s world economics is inevitable when it comes to arbitrages in the field of policy making. From the very beginning of international talks on climate change, up until the most recent discussions on a post-Kyoto international framework, economic arguments have turned out to be crucial elements of the analysis that shapes policy responses to the climate threat. This can be illustrated by the prominent role that economics has played in the different analyses produced by the Intergovernmental Panel on Climate Change (IPCC) to assess the impact of climate change on society.<p><p>The starting point and the core idea of this PhD research is the long-held observation that the threat of climate change calls for a change of climate in economics. Borrowing from the jargon used in climate policy, adaptation measures could also usefully target the academic discipline of economics. Given that inherent characteristics of the climate problem (e.g. complexity, irreversibility, deep uncertainty, etc.) challenge core economic assumptions, mainstream economic theory does not appear as appropriately equipped to deal with this crucial issue. This makes that new assumptions and analyses are needed in economics in order to comprehend and respond to the problem of climate change.<p><p>In parallel (and without environmental considerations being specifically the driving force to it), the mainstream model in economics has also long been (and still is) strongly criticised and disputed by numerous scholars - both from within and outside the field of economics. For the sake of functionality, these criticisms - whether they relate to theoretical inconsistencies or are empirically-based - can be subsumed as all challenging part of the Cartesian/Newtonian legacy of economics. This legacy can be shown to have led to a model imprinted with what could be called “mechanistic reductionism”. The mechanistic side refers to the Homo oeconomicus construct while reductionism refers to the quest for micro-foundations materialised with the representative agent hypothesis. These two hypotheses constitute, together with the conjecture of perfect markets, the building blocks of the framework of general equilibrium economics. <p><p>Even though it is functional for the purpose of this work to present them separately, the flaws of economics in dealing with the specificities of the climate issue are not considered independent from the fundamental objections made to the theoretical framework of mainstream economics. The former only make the latter seem more pregnant while the current failure of traditional climate policies informed by mainstream economics render the need for complementary approaches more urgent. <p><p>2. Overview of the approach and its main insights for climate policy<p><p>Starting from this observation, the main objective of this PhD is thus to assess the implications for climate policy that arise from adopting an alternative analytical economic framework. The stance is that the coupling of insights from the framework of evolutionary economics with the perspective of ecological economics provides a promising way forward both theoretically as well as on a more applied basis with respect to a better comprehension of the socioeconomic aspects related to the climate problem. As claimed in van den Bergh (2007, p. 521), ecological economics and evolutionary economics “share many characteristics and can be combined in a fruitful way" - which renders the coupling approach both legitimate and promising. <p><p>The choice of an evolutionary line of thought initially stems from its core characteristic: given its focus on innovation and system change it provides a useful approach to start with for assessing and managing the needed transition towards a low carbon economy. Besides, its shift of focus towards a better understanding of economic dynamics together with its departure from the perfect rationality hypothesis renders evolutionary economics a suitable theoretical complement for designing environmental policies.<p><p>The notions of path-dependence and lock-in can be seen as the core elements from this PhD research. They arise from adopting a framework which is founded on a different view of individual rationality and that allows for richer and more complex causalities to be accounted for. In a quest for surmounting the above-mentioned problem of reductionism, our framework builds on the idea of ‘multi-level selection’. This means that our analytical framework should be able to accommodate not only for upward but also for downward causation, without giving analytical priority to any level over the other. One crucial implication of such a framework is that the notion of circularity becomes the core dynamic, highlighting the importance of historicity, feedbacks and emergent properties. <p><p>More precisely, the added value of the perspective adopted in this PhD research is that it highlights the role played by inertia and path-dependence. Obviously, it is essential to have a good understanding of the underlying causes of that inertia prior to devising on how to enforce a change. Providing a clear picture of the socio-economic processes at play in shaping socio-technical systems is thus a necessary first step in order to usefully complement policy-making in the field of energy and climate change. In providing an analytical basis for this important diagnosis to be performed, the use of the evolutionary framework sheds a new light on the transition towards low-carbon socio-technical systems. The objective is to suggest strategies that could prove efficient in triggering the needed transition such as it has been the case in past “lock-in” stories. <p><p>Most notably, the evolutionary framework allows us to depict the presence of two sources of inertia (i.e at the levels of individuals through “habits” and at the level of socio-technical systems) that mutually reinforce each other in a path-dependent manner. Within the broad perspective on path dependence and lock-in, this PhD research has first sketched the implications for climate policy of applying the concept of ‘technological lock-in’ in a systemic perspective. We then investigated in more details the notion of habits. This is important as the ‘behavioural’ part of the lock-in process, although explicitly acknowledged in the pioneer work of Paul David (David, 1985, p. 336), has been neglected in most of subsequent analyses. Throughout this study, the notion of habits has been studied at both the theoretical and applied level of analysis as well as from an empirical perspective. <p><p>As shown in the first chapters of the PhD, the advantage of our approach is that it can incorporate theories that so far have been presented opposite, partial and incomplete perspectives. For instance, it is shown that our evolutionary approach not only is able to provide explanation to some of the puzzling questions in economics (e.g. the problem of strong reciprocity displayed by individual in anonymous one-shot situations) but also is very helpful in bringing a complementary explanation with respect to the famous debate on the ‘no-regret’ emission reduction potential which agitates the experts of climate policy. <p><p>An emission reduction potential is said to be "no regret" when the costs of implementing a measure are more than offset by the benefits it generates such as, for instance, reduced energy bills. In explaining why individuals do not spontaneously implement those highly profitable energy-efficient investments ,it appears that most prior analyses have neglected the importance of non-economic obstacle. They are often referred to as “barriers” and partly relate to the ‘bounded rationality’ of economic agent. As developed in the different chapters of this PhD research, the framework of evolutionary economics is very useful in that it is able to provide a two-fold account (i.e. relying on both individual and socio-technical sources of inertia) of this limited rationality that prevent individuals to act as purely optimising agents.<p><p>Bearing this context in mind, the concept of habits, as defined and developed in this study, is essential in analysing the determinants of energy consumption. Indeed, this concept sheds an insightful light on the puzzling question of why energy consumption keeps rising even though there is an evident increase of awareness and concern about energy-related environmental issues such as climate change. Indeed, if we subscribe to the idea that energy-consuming behaviours are often guided by habits and that deeply ingrained habits can become “counter-intentional”, it then follows that people may often display “locked-in” practices in their daily energy consumption behaviour. This hypothesis has been assessed in our empirical analysis whose results show how the presence of strong energy-consuming habitual practices can reduce the effectiveness of economic incentives such as energy subsidies. One additional delicate factor that appears crucial for our purpose is that habits are not fully conscious forms of behaviours. This makes that individuals do not really see habits as a problem given that it is viewed as easily changed.<p><p>In sum, based on our evolutionary account of the situation, it follows that, to be more efficient, climate policies would have to both shift the incumbent carbon-based socio-technical systems (for it to shape decisions towards a reduction of greenhouse gas emissions) and also deconstruct habits that this same socio-technical has forged with time (as increased environmental awareness and intentions formulated accordingly are not sufficient in the presence of strong habits).<p><p>Accordingly, decision-makers should design measures (e.g. commitment strategies, niche management, etc.) that, as explained in this research, specifically target those change-resisting factors and their key features. This is essential as these factors tend to reduce the efficiency of traditional instruments. Micro-level interventions are thus needed as much as macro-level ones. For instance, it is often the case that external improvements of energy efficiency do not lead to lower energy consumption due to the rebound effect arising from unchanged energy-consuming habits. Bearing this in mind and building on the insights from the evolutionary approach, policy-makers should go beyond the mere subsidisation of technologies. They should instead create conditions enabling the use of the multi-layered, cumulative and self-reinforcing character of economic change highlighted by evolutionary analyses. This means supporting both social and physical technologies with the aim of influencing the selection environment so that only the low-carbon technologies and practices will survive. <p><p><p>Mentioned references:<p><p>David, P. A. (1985), Clio and the economics of QWERTY, American Economic Review 75/2: 332–337.<p><p>IPCC, 2007, ‘Climate Change 2007: The Physical Science Basis’, Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S. D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 996 pp. <p><p>Stern, N. 2006, ‘Stern Review: The economics of Climate Change’, Report to the UK Prime Minister and Chancellor, London, 575 p. (www.sternreview.org.uk)<p><p>van den Bergh, J.C.J.M. 2007, ‘Evolutionary thinking in environmental economics’, Journal of Evolutionary Economics 17(5): 521-549.<p> / Doctorat en Sciences économiques et de gestion / info:eu-repo/semantics/nonPublished

L'adolescence est une période cruciale dans le développement, la consolidation et parfois le déclin de certaines habitudes de vie. Durant cette période, l'activité physique tend à diminuer avec l'âge, en particulier chez les filles. Fillactive est un organisme qui offre des services qui aident les écoles canadiennes à mettre en oeuvre des interventions d'activité physique spécifiquement dédiées aux adolescentes. Les objectifs de cette étude étaient d’évaluer les changements dans la pratique d’activité physique et les habitudes de vie (temps sédentaire, durée du sommeil et habitudes alimentaires) des participantes du programme Fillactive et de déterminer si ces changements variaient en fonction du respect des Directives canadiennes en matière de mouvement sur 24 heures et des recommandations du Guide alimentaire canadien à l'inscription. Lors de l’inscription et à la fin de l’année scolaire, 73 participantes ont répondu à un questionnaire en ligne. Les participantes ont rapporté une augmentation du nombre de journées actives et une diminution de la consommation quotidienne de sucreries à la fin du programme. Des analyses de sous-groupes ont révélé des changements plus importants chez celles qui ne rencontraient pas les recommandations canadiennes à l’inscription. Celles-ci ont augmenté de façon significative leur nombre de journées actives et leur consommation de légumes et de fruits, et ont diminué leur temps d’écran. Les résultats indiquent que la participation à Fillactive a le potentiel d’améliorer plusieurs habitudes de vie liées à la santé chez les adolescentes. D’autres études s’avèrent nécessaires afin d’explorer les effets de programmes d’interventions en activité physique chez les adolescentes. / Adolescence is a crucial time in the development, maintenance and sometimes the decline of different lifestyle habits. During adolescence, physical activity typically decreases with age, particularly in girls. FitSpirit is an organizaton that offers services that help Canadian schools implement physical activity interventions for adolescent girls. The objectives of this study were to evaluate changes in participants’ physical activity levels and lifestyle habits (sedentary time, sleep duration and eating habits) and to assess whether these changes varied on adherence to the Canadian 24-Hour Movement Guidelines and Canada’s Food Guide recommendations at enrollment. At the time of FitSpirit registration and at the end of school year, 73 participants answered online questionnaire. The participants reported improvements, with an increase in the number of days with physical activity and a decrease in daily consumption of sweets. Subgroup analyzes revealed greatest changes in those who did not adhere to the Canadian recommendations at enrollment. These participants significantly increased their number of days with physical activity and their consumption of fruits and vegetables, and decreased their screen time. The results indicate that participation in FitSpirit has the potential to improve several health behaviors among adolescent girls. More research is needed to explore the effects of physical activity intervention programs among adolescent girls.

No description available.

Dans le cadre de ce mémoire de maîtrise, nous avons voulu savoir comment les pratiques alimentaires des Antoniennes de Marie du Saguenay-Lac-Saint-Jean exprimaient une part importante de l’identité de ces religieuses qui avaient comme vocation de faire la cuisine pour les prêtres et les élèves des séminaires. À partir d'un travail de terrain ethnologique et de recherches en archives, nous avons reconstitué les pratiques culinaires de ces religieuses depuis leur fondation en 1904 et soutenons qu’elles ont développé des pratiques alimentaires liées à leur identité religieuse et culturelle. Ainsi, certains usages sont liés à leurs appartenances religieuses, judéo-chrétienne, chrétienne, catholique, ascétique et communautaire, c’est-à-dire, antonienne. D’autres sont associés à leurs cultures nationale québécoise et régionale, saguenéenne et jeannoise. La dynamique et la hiérarchie de ces appartenances varient dans le temps et selon le type de pratique. Dans certaines circonstances, les Antoniennes de Marie ont mis de l’avant le rôle de l’alimentation dans l’affirmation de leur identité religieuse, à d’autres moments, son rôle dans le sentiment d’appartenance au groupe ethnique ou à la région. Ces pratiques se sont aussi modifiées au rythme des événements historiques, dont le Concile Vatican II, la Révolution Tranquille, l’Expo 67 et les différentes vagues migratoires en terre québécoise.

Tableau d’honneur de la Faculté des études supérieures et postdoctorales, 2008-2009 / La morue des bancs de Terre-Neuve (Canada) a dès le XVIe siècle attitré les Européens en Amérique, bien que ce ne soit qu’au début du siècle suivant qu’on assiste à l’installation de colonies permanentes, comme celle de Ferryland fondée par les Anglais (1621-1696). L’analyse des macro-restes végétaux (incluant les charbons de bois) prélevés lors des fouilles archéologiques effectuées sur ce site a permis de mieux comprendre les interrelations entre les habitants et leur environnement. Leur alimentation était composée d’une grande variété de fruits sauvages indigènes ainsi que de céréales, de pois, de fines herbes et de fruits séchés d’origine étrangère. On ne sait pas si l’agriculture était surtout pratiquée sur place ou si les denrées étaient principalement importées. Les habitants auraient également utilisé les ressources végétales (bois, branches de conifères, sphaigne) pour la construction et le chauffage. En outre, les activités menées par les habitants auraient pu faciliter l’introduction de nombreuses mauvaises herbes d’origine étrangère. / The rich cod stocks of Newfoundland’s Grand Banks (Canada) attracted Europeans to the Americas from the sixteenth century onwards. However, the establishment of permanent colonies like that of Ferryland, founded by the English (1621-1696), date to the seventeenth century. The analysis of macro botanical remains (including wood charcoal) from this archaeological site shed light on the relationships between settlers and their environment. Their diet included a great variety of native wild berries as well as cereals, peas, herbs and dried fruits of European origin. However, we can not tell if this food grew mostly on or around the site or was imported. Settlers also used other plant resources (wood, conifer twigs, peat moss) for building and heating. Also, the activities of the settlers appear to have facilitated the introduction of many non-native weeds.

L'obésité infantile et l'insécurité alimentaire sont deux problèmes majeurs de santé publique, qui ont pu être exacerbés par la pandémie de COVID-19. Par ailleurs, on sait peu de choses sur la façon dont l'insécurité alimentaire influence la prise en charge de l'obésité infantile. Ce mémoire présente donc les résultats de deux études qui ont 1) évalué l'insécurité alimentaire et ses corrélats au sein de ménages d'enfants avec embonpoint ou obésité recevant des soins dans une clinique pédiatrique spécialisée dans la prise en charge de l'obésité à Montréal avant et pendant la pandémie de COVID-19 et 2) évalué l'association entre l'insécurité alimentaire et les changements dans le score z de l'indice de masse corporelle (IMC-z) de ces enfants. Nos résultats ont montré que 40 % des enfants traités dans cette clinique vivaient dans un ménage en situation d'insécurité alimentaire et suggèrent que cette prévalence tendait à augmenter au cours de la première année de la pandémie de COVID-19. Nous avons également montré que les changements dans l'IMC-z au cours du suivi à la clinique étaient plus faibles chez les enfants vivant dans des ménages en situation d'insécurité alimentaire comparativement à ceux vivant dans des ménages en sécurité alimentaire. / Childhood obesity and food insecurity are two major public health issues, which may have been exacerbated by the COVID-19 pandemic. Furthermore, little is known about how food insecurity influences the management of childhood obesity. This thesis therefore presents the results of two studies that 1) evaluated food insecurity and its correlates among households of children with overweight or obesity receiving care at a pediatric clinic specializing in obesity management in Montreal before and during the COVID-19 pandemic and 2) assessed the association between food insecurity and changes in the body mass index z-score (BMIz) of these children. Our results showed that 40% of children treated at this clinic lived in a food insecure household and suggested that this prevalence tended to increase during the first year of the COVID-19 pandemic. We also showed that changes in BMIz during clinic follow-up were smaller in children who lived in food insecure households compared with those who lived in food secure households.

Depuis l’ère préhispanique, les paysans de la Communauté de Vicos, dans les Andes péruviennes, ont développé des pratiques et des habitudes alimentaires avec lesquelles ils se sont identifiés. Au cours de l’histoire, la cuisine locale a été le résultat de l’incorporation et l’abandon d’aliments, techniques, ustensiles, savoirs et comportements, néanmoins, au cours des dernières décennies, le développement d’un nouveau système planétaire, la mondialisation, a apporté de nouveaux changements dans ces pratiques alimentaires. Puisque Vicos est une communauté rurale et agricole, liée directement aux cycles de la nature et à des croyances locales, nous voulons dans ce travail de recherche, étudier comment la cuisine locale de cet endroit peut être influencée par les tendances de la mondialisation et par les « traditions » fruits de l’héritage de leurs ancêtres. / Desde tiempos prehispánicos, los campesinos de la Comunidad de Vicos en los Andes peruanos han ido desarrollando prácticas y hábitos alimenticios con los cuales se han sentido identificados. A lo largo de la historia, la cocina local ha sido el resultado de la incorporación y el abandono de insumos, técnicas, utensilios, saberes y comportamientos, pero sin embargo, en las últimas décadas el desarrollo de un nuevo sistema planetario, el llamado globalización, está causando nuevos impactos en las prácticas alimenticias. Siendo Vicos una población rural y agrícola, vinculada directamente a los ciclos de la naturaleza y a las creencias locales, nuestro interés reside en investigar cómo la cocina local de este lugar puede ser influencida en el presente, por las tendencias de la globalización y por las “tradiciones” heredadas de sus antepasados.

Contexte : Le diabète de type 1 et de type 2 apporte un fardeau considérable sur la santé et la qualité de vie de l’enfant, étant associé à des complications microvasculaires et cardiovasculaires et à une mortalité précoce à l’âge adulte. Il est essentiel de prévenir le diabète et les complications associées chez les enfants à risque. Néanmoins, on détient encore peu de connaissances sur comment le diabète de type 2 se développe ainsi que sur la présence de maladie cardiovasculaire chez les jeunes avec diabète de type 1. De plus, en comprenant mieux le rôle des habitudes de vie, comme l’activité physique et les comportements sédentaires sur le développement du diabète de type 2 et de la maladie cardiovasculaire dans le diabète de type 1, nous pourrons identifier des nouvelles stratégies préventives chez les enfants à risque. Objectifs : 1) Investiguer l’histoire naturelle du diabète de type 2 de l’enfance jusqu’à la fin de l’adolescence et identifier les déterminants sociodémographiques, biologiques et reliés aux habitudes de vie durant l’enfance qui sont associés au développement du diabète de type 2. 2) Estimer l’effet de l’activité physique et les comportements sédentaires sur la sensibilité à l’insuline, la sécrétion d’insuline et la glycémie de l’enfance à la fin de l’adolescence. 3) Comparer des marqueurs de maladie cardiovasculaire précoce en rapport à la structure et fonction vasculaire et du myocarde entre des adolescents avec diabète de type 1 et des adolescents sans diabète. 4) Évaluer l’association entre l’activité physique, les comportements sédentaires et les marqueurs de maladie cardiovasculaire précoce chez les adolescents avec diabète de type 1 et les adolescents sans diabète. Méthodes : Les données des visites aux âges de 8-10, 10-12 et 15-17 ans de 630 enfants québécois avec histoire parentale d’obésité de la cohorte QUALITY ont été utilisées pour répondre aux 2 premiers objectifs. À chaque cycle d’évaluation, les enfants faisaient un test d’hyperglycémie orale provoquée avec prélèvements à 0, 30, 60, 90 et 120 minutes, à partir duquel les niveaux de glucose et d’insuline ont été mesurés. Les données transversales de l’étude CARDEA incluant 100 adolescents avec diabète de type 1 et 97 adolescents sans diabète âgés entre 14 et 18 ans ont été utilisées pour répondre aux objectifs 3 et 4. La rigidité artérielle a été mesurée avec le test de la vitesse d’onde de pouls et la fonction endothéliale par le test de dilatation médié par le flux sanguin de l’artère brachiale. La structure et fonction du myocarde était évaluée par imagerie par résonance magnétique. Dans les études QUALITY et CARDEA, l’activité physique et le temps sédentaire ont été mesuré avec le port d’accéléromètre pendant sept jours. Aussi dans les deux études, la diète était mesurée par rappels alimentaires de 24 heures, le temps d’écran et les facteurs sociodémographiques par questionnaire et le pourcentage de masse adipeuse par dual energy x-ray absorptiometry. Pour l’objectif 1, nous avons utilisé des modèles généralisés additifs à effets mixtes pour modéliser les variations de sensibilité et sécrétion d’insuline durant l’enfance et l’adolescence et une analyse par moyennage de modèle pour identifier les déterminants à l’enfance. Des modèles structuraux marginaux longitudinaux ont été utilisés pour répondre à l’objectif 2. Pour les objectifs 3 et 4, nous avons estimé des modèles de régression linéaire multivariable et les analyses pour l’objectif 4 ont été stratifiées selon le statut de diabète. Résultats : Nous avons observé que 21% des enfants avec histoire parentale d’obésité développent une dysglycémie (basé sur les critères de prédiabète ou diabète de type 2 pour la glycémie) persistante durant l’enfance et l’adolescence. De plus, la glycémie à jeun et 2-h étaient les deux seuls déterminants à l’enfance associés au risque de dysglycémie à l’adolescence. Néanmoins, nous avons observé qu’un niveau d’activité physique plus élevé, moins de temps sédentaire total et moins de temps d’écran améliorait la sensibilité à l’insuline et diminuait les besoins en sécrétion d’insuline durant l’enfance et l’adolescence. De plus, nous avons constaté que les adolescents avec diabète de type 1 avaient une moins bonne fonction endothéliale et une masse du ventricule gauche plus petite que les adolescents sans diabète. Enfin, l’activité physique est associée positivement à la masse du ventricule gauche chez les adolescents sans diabète. Le temps sédentaire est associé à une moins bonne fonction endothéliale, ainsi qu’à une masse du ventricule gauche et une épaisseur du mur du ventricule gauche plus petites chez les jeunes sans diabète seulement. Conclusion : Plusieurs enfants avec histoire parentale d’obésité développent un prédiabète. L’activité physique et les comportements sédentaires durant l’enfance et l’adolescence constituent des cibles pertinentes pour la prévention du diabète de type 2 chez le jeune via leur action sur la sensibilité et la sécrétion d’insuline. Une dysfonction endothéliale et des différences dans la structure du myocarde sont perceptibles dès l’adolescence chez les jeunes avec diabète de type 1. Davantage d’activité physique et moins de comportements sédentaires pourraient ralentir l’apparition des premiers signes de maladie cardiovasculaire à l’adolescence, mais leur contribution reste à être confirmée. / Background: Type 1 and type 2 diabetes represent a considerable burden on children's health and quality of life, being associated with microvascular and cardiovascular complications and early mortality in adulthood. Focusing on the prevention of diabetes and associated complications in children at risk is essential. Nevertheless, little is known about how type 2 diabetes develops in children and on the presence of early cardiovascular disease in youth with type 1 diabetes. Furthermore, by better understanding the role of lifestyle factors, such as physical activity and sedentary behaviors, on the development of type 2 diabetes and cardiovascular disease in type 1 diabetes, we will be able to identify new preventive strategies in children at risk. Objectives: 1) Investigate the natural history of type 2 diabetes from childhood to late adolescence and identify the sociodemographic, biological and lifestyle determinants in childhood associated with the development of type 2 diabetes. 2) Estimate the effect of physical activity and sedentary behaviors on insulin sensitivity, insulin secretion, and blood glucose levels from childhood to late adolescence. 3) Compare markers of early cardiovascular disease pertaining to vascular and myocardial structure and function between adolescents with type 1 diabetes and adolescents without diabetes. 4) Examine the association between physical activity, sedentary behaviors and markers of early cardiovascular disease in adolescents with type 1 diabetes and adolescents without diabetes. Methods: To address the first 2 objectives, data from ages 8-10, 10-12, and 15-17 years follow-up visits from the QUALITY cohort of 630 Quebec children with a parental history of obesity were used. At each research visit, children underwent an oral glucose tolerance test with samples taken at 0, 30, 60, 90 and 120 minutes, from which glucose and insulin levels were measured. For objectives 3 and 4, data stem from the cross-sectional CARDEA study of 100 adolescents with type 1 diabetes and 97 adolescents without diabetes aged 14 to 18 years. Arterial stiffness was measured with the pulse wave velocity test and endothelial function by the brachial artery flow-mediated dilatation test. Myocardial structure was assessed by cardiac magnetic resonance imaging. In both QUALITY and CARDEA studies, physical activity and sedentary time were measured with accelerometry over 7 days. Also in both studies, diet was measured by 24-hour dietary recalls, screen time and sociodemographic factors by questionnaire, and by dual energy x-ray absorptiometry. For Objective 1, we used additive generalized mixed models to study variations in insulin sensitivity and insulin secretion from childhood to late adolescence, and model averaging analysis to identify determinants in childhood. Longitudinal marginal structural models were used to address objective 2. For objectives 3 and 4, we estimated multivariable linear regression models, stratified by diabetes status for objective 4. Results: We found that among children with a parental history of obesity, 21% developed persistent dysglycemia (based on glycemia cut-points for prediabetes or type 2 diabetes) during childhood and adolescence, and that fasting and 2-h glycemia were the only two childhood determinants associated with risk of dysglycemia in adolescence. Nevertheless, we observed that higher levels of physical activity, less sedentary time (accelerometer-measured), and less screen time improved insulin sensitivity and decreased insulin secretion requirements during childhood and adolescence. In addition, we found that adolescents with type 1 diabetes had worse endothelial function and smaller left ventricular mass than adolescents without diabetes. Finally, physical activity was positively associated with left ventricular mass in adolescents without diabetes. Sedentary time was associated with poorer endothelial function and smaller left ventricular mass and left ventricular wall thickness in youth without diabetes only. Conclusions: Many children with a parental history of obesity develop prediabetes. Physical activity and sedentary behaviors during childhood and adolescence are relevant targets for the prevention of type 2 diabetes in youth through their action on insulin sensitivity and secretion. Endothelial dysfunction and differences in myocardial structure are noticeable as early as adolescence in young people with type 1 diabetes. More physical activity and less sedentary behavior could slow the onset of cardiovascular disease in adolescence, but their contribution remains to be confirmed.