La grossesse est une période de la vie d’une femme qui s’accompagne d’une augmentation des besoins nutritionnels dont la satisfaction est nécessaire à la bonne santé de la mère et de l’enfant à naître. Durant cette période, les femmes seraient plus enclines à l’adoption de pratiques alimentaires plus saines. L’objectif de ce travail de thèse était d’étudier ces différents aspects de la nutrition pendant la grossesse puis d’élaborer et d’évaluer une méthode de conseils alimentaires personnalisés et pas-à-pas afin d’améliorer l’adéquation nutritionnelle des femmes enceintes en France. Un indice de qualité nutritionnelle de l’alimentation existant : le PANDiet, a été adapté à la période de la grossesse en tenant compte des références nutritionnelles spécifiquement définies pour cette période. Il a été montré qu’en l’absence de modifications qualitatives du régime en début de grossesse, l’adéquation nutritionnelle ne pouvait pas être maintenue. Trois types de conseils alimentaires personnalisés ont alors été élaborés et se sont révélés efficaces pour améliorer la qualité nutritionnelle de l’alimentation. Cependant, plus les conseils étaient efficaces moins ils étaient acceptables par les femmes enceintes. Un compromis a donc été trouvé pour sélectionner les deux types de conseils les plus acceptables par les femmes enceintes tout en étant efficaces pour améliorer la qualité nutritionnelle de leur alimentation. Ces deux types de conseils alimentaires personnalisés, fondés respectivement sur des modifications des quantités consommées d’aliments et sur des substitutions au sein du même sous-groupe d’aliments, ont été proposés à des femmes enceintes françaises lors d’un essai randomisé contrôlé. Par ailleurs, des données qualitatives, ont permis d’identifier que ces dernières étaient à la recherche d’informations positives et crédibles concernant l’alimentation pour contribuer au bien-être de leur bébé mais aussi au leur. Durant l’essai randomisé contrôlé, l’approche proposant des recommandations alimentaires génériques associées aux conseils alimentaires personnalisés, générés pas-à-pas par notre algorithme, s’est révélée plus efficace pour améliorer la qualité nutritionnelle de l’alimentation de femmes enceintes qu’une approche proposant uniquement les recommandations génériques. Par ailleurs, selon l’étude qualitative menée auprès de participantes à l’essai randomisé contrôlé il apparaît que proposer des conseils alimentaires pendant la grossesse permet de résoudre la cacophonie informationnelle. / Pregnancy is a specific period in life characterized by an increase in nutrient needs that should be met for the health of both the mother and her baby. During this period, women would be keener on adopting healthier dietary practices. The objective of this thesis was to study these different aspects of nutrition during pregnancy and to design and evaluate a tailored, stepwise dietary advice method which aims to improve the nutrient adequacy of the diet of French pregnant women. The PANDiet score, a diet quality index, has been adapted to pregnancy by using the nutrient requirements established for this period. It has been shown that the absence of qualitative changes in a woman’s diet in the beginning of pregnancy prevented the maintenance of the nutrient adequacy. Three types of tailored dietary changes were then designed. They proved to be efficient in improving the nutrient adequacy of the diet. The more efficient the type of dietary changes was, the less acceptable it was by pregnant women. Thus, a trade-off has been considered to select the two types of dietary changes that were the most acceptable by pregnant women while showing efficiency in the improvement of the nutrient adequacy of their diet. These two types of tailored dietary changes, which respectively involved modifications of the amount consumed of foods and substitutions of foods within the same food subgroup, have been proposed to French pregnant women during a randomized controlled trial. Furthermore, qualitative data revealed that pregnant women sought for positive and trustworthy information about nutrition-related in order to contribute towards the well-being of both their baby and themselves. In the randomized controlled trial, the approach proposing tailored dietary advice, generated in a stepwise process, in addition to generic dietary guidelines proved to be more efficient in improving the nutrient adequacy of the diet of pregnant women than the approach using only generic dietary guidelines. Furthermore, according to semi-directive interviews led with some women included in the randomized controlled trial, it appeared that dietary counseling during pregnancy resulted in solving the confusion related to nutrition issues.

This thesis is about food practices and change among Mexican migrants living in West Queens, New York City. Public health research suggests that Mexican migration to the US has a negative impact on food practices, with diets being less nutritious over a migrant’s stay in the United States and obesity being more common among longer-term than more recently-arrived individuals. Through ethnography, I explore how migration shapes food practices and examine the nuanced process of nutritional change that is often obscured in large-scale epidemiological studies. Food practices are important not just because they shape vulnerabilities to chronic diseases but also because they serve as prisms by which to examine migrants’ lives, pressures and aspirations. The three aims of this ethnography are to explore the food practices that Mexicans engage in after migration; to examine the social, temporal and political-economic contexts shaping food practices and change; and to describe how migrants themselves makes sense of nutritional change. I explore these themes using the approach of structural vulnerability, which views health practices and outcomes as influenced by social structures, relationships and inequalities. In so doing, I provide a critique of the public health literature’s use of the concept of acculturation to explain food practices, which largely obscures the role played by structural contexts and constraints. Through participant observation, conversations and interviews with Mexican migrants in West Queens, NYC, I have identified three contexts shaping food practices and change after migration: household dynamics and labour division; time constraints and work schedules; and the ‘food environment’, referring to the availability of food items and weight loss products. Gender dynamics, documentation status and class modified the way in which these contexts were perceived and negotiated by informants, which had further consequences on food practices. In these settings, informants were often encouraged to consume high-energy foods and large portions, to replace meals with snacks, to eat prepared or convenience foods, and to experiment with weight loss products. To rationalize nutritional change and body size disparities, informants employed multiple discourses. Some discourses emphasized the role of structural contexts and constraints related to time, money and documentation status, while others emphasized the role played by cultural beliefs, habits and acculturation. An ethnographic approach informed by structural vulnerability serves to articulate how the everyday lives and social contexts in which Mexican migrants are embedded, shape experiences of nutritional change. This thesis exposes a disconnect between the way in which the public health literature conceptualizes nutritional change and how it is lived ‘on the ground’.