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This cross-sectional investigation of 6,931 U.S. adults examined the relationship between sitting time and insulin resistance. A primary objective was to evaluate how this relationship was mediated by the following variables: age, sex, race, year of assessment, cigarette smoking, physical activity, body mass index (BMI), and waist circumference. Self-reported sitting time, measured in minutes per day, was the exposure variable. Insulin resistance, indexed by the homeostatic model assessment of insulin resistance (HOMA-IR), was the outcome variable. Data were used from the 2011-2018 National Health and Nutrition Examination Survey (NHANES). Results showed a strong, positive association between sitting time and insulin resistance after adjusting for age, sex, race, and year of assessment (F = 13.3, p < 0.0001). Further controlling for cigarette smoking and physical activity did not alter the significance of the relationship. Adding BMI to the demographic covariates weakened the relationship but did not nullify it; however, the association was no longer significant after adjusting for differences in waist circumference (F = 1.39, p = 0.2563). Overall, waist circumference was a powerful mediating variable between sitting time and insulin resistance.

Negative body image can cause serious psychological problems. In some Western societies, body image concerns can develop at a young age, with early preadolescents preferring thinner bodies and reporting body dissatisfaction. The aims here were to clarify the significant gaps in published research, and to challenge existing assumptions around weight, muscularity, and body satisfaction in children. In addition, this novel research focused on young children’s body dissatisfaction, particularly young boys (aged 4-11 years). Traditional measures of body satisfaction are limited and do not incorporate muscularity, assess individual body parts, or indicate the direction of dissatisfaction. Here, new visual measures were developed along with a prototype application for a touch-screen tablet to measure body satisfaction in children. Through 4 innovative experimental studies the current research explored factors influencing body image: including gender, age, ethnicity, BMI, perceived body size, and sociocultural factors (e.g. cultural ideals and body size stereotypes). Results consistently supported the findings of study 1 which showed gender differences in body satisfaction: boys were more dissatisfied with their bodies than girls, and their dissatisfaction varied over the different body parts (torso, arms and legs). Stereotypical idealised body perception was evident: boys wanted to be muscular and girls desired to be lean. In study 2, ideal body choices saw boys choosing more muscular figures and girls more lean figures for the self, than the ones they choose for another boy or girl. Boys desired more muscular ideal figures than what they perceived the opposite sex would choose. Study 3 revealed the pattern of assigning positive attributes was gendered. Boys viewed the hypermuscular figure the most positively and girls the normal weight and lean figures the most positively. However, both sexes did not want to look like the overweight figure as a child or adult. Study 4 showed parent’s body satisfaction and their perception of their child’s current body size predicted child’s body satisfaction, and exposure to media predicted the child’s ideal and future ideal adult figure choices. Overall, a combination of factors involved in the development of children’s body image were revealed, including sociocultural influences, age, ethnicity, and perceived body size. The research carried out within this thesis has extended our knowledge of pre-adolescent’s body dissatisfaction, has developed innovative measures for use with younger children, and revealed fascinating findings around young boys’ body image.

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<p>Arterial stiffness is a natural and inevitable process for an ageing artery. In adults and school-aged children, increased stiffness of the central arteries is associated with cardiovascular disease (CVD) and CVD risk factors. Arterial stiffness, and its relationship with adiposity and physical activity (PA), has not been studied in preschool-aged children (3-5 years) despite the high prevalence of obesity and inactivity in this age group. Ninety-eight healthy preschoolers (4.4 ± 0.9 years; 50% boys) participated in this thesis, completing baseline and follow up assessments 12.5 ± 1.1 months apart. Whole-body PWV (carotid to dorsalis pedis; m/s) was used to assess arterial stiffness, body mass index percentile (BMI%ile) was a surrogate measure of adiposity, and PA levels (total, TPA; moderate-to-vigorous, MVPA) were quantified objectively with accelerometers and expressed as a percent of wear time. In our cohort, PWV increased significantly from baseline (4.3 m/s) to follow up (4.8 m/s; p< .001). PWV also tracked fair-to-moderately well (κ=0.25, r=0.37) with no sex differences (χ²=.485, p=.785). Girls had a higher BMI%ile than boys, and the prevalence of overweight/obese preschoolers increased from 18.8% to 21.3% over the 1-year period. Boys were more active than girls and engaged in more MVPA. 75% of preschoolers at baseline, and 70% at follow up, met the current PA guidelines (3-hrs of TPA/day). PWV was not related to BMI%ile or PA at baseline; however, it was weakly related to TPA (r=-0.28, p=.013) and MVPA (r=-0.25, p=.024) at follow up. Furthermore, longitudinal and cross-sectional regression models of sex, age, BMI%ile and TPA or MVPA could not predict PWV. Our findings indicate that adiposity and PA do not influence arterial stiffness in healthy 3 to 5 year old children. Nevertheless, maintaining a healthy body composition and engaging in regular PA has other health benefits and should be encouraged.</p> / Master of Science (MSc)

<p>Leptin, an adipose derived hormone, has emerged as a regulator of bone metabolism. Recent findings support a role of leptin in the process of fetal bone remodeling during pregnancy; however, the link between maternal leptin during pregnancy and offspring bone status is undocumented. Evidence exists that the intrauterine environment plays a role in programming peak bone mass that is achieved in late adolescence and thus osteoporosis risk later in life. We investigated the association between maternal leptin during the third trimester and offspring bone mass at 3 years of age.</p> <p><strong>Method:</strong> Based on a sub-sample of a prospective birth cohort study, we conducted analysis on 425 mothers from whom maternal blood samples in pregnancy were analyzed for leptin and 25- hydroxyvitamin D, and whole body bone mass by dual energy x-ray absorptiometry were available for both mother and child at 3 years. Data were collected for maternal prepregnancy body mass index (BMI), lifestyle, and nutrition during pregnancy, as well as the child’s nutrition and physical activity at 3 years.</p> <p><strong>Results:</strong> Women obese on entering pregnancy have a two-fold greater circulating leptin during pregnancy than women with normal weight BMIs. Maternal age and skinfold thickness were positively associated with maternal leptin status. However, maternal leptin status was not a significant predictor of offspring BMC z-score at 3 years of age, when adjusted for relevant maternal and child variables. Maternal vitamin D status was also not a predictor of offspring bone status. Rather the key predictors of child BMC z-score were maternal bone mineral density z-score and child’s weight and vitamin D intake at 3 years.</p> <p><strong>Conclusion:</strong> While maternal leptin status during pregnancy is highly variable among women of different BMI categories, in utero exposure to leptin is not a significant factor that influences child bone status at 3 years of age when adjusted for other relevant variables.</p> / Master of Science (MSc)

Background Middle-income countries are currently undergoing nutrition transition more rapidly than did high income countries. These populations are therefore at high risk of over-nutrition (obesity) and nutrition-related, non-communicable diseases before the elimination of under-nutrition and infectious diseases. Such nutritional double burden is most common in low SES groups of middle-income countries, such as the Maya of Mexico. Long-term poor environmental conditions during early life results in a population with high levels of chronic under-nutrition (stunting), and a consequent predisposition toward overweight/ obesity, and associated health risks later in life. It is important to be able to identify individuals at an increased risk of diseases related to double burden and to determine whether stunting impacts the ability to identify at risk individuals. Aims The overall purpose of this doctoral research was to examine double burden in the urban Maya, a low SES section of the Mexican population which is a current example of a population undergoing significant transition. The specific aims of this thesis were fourfold: 1) To describe the living conditions and population characteristics of the urban Maya of southern Merida in the spring and summer of 2010; 2) to determine whether body mass index (BMI) predicts adiposity indicators in a sample of women and children with a high prevalence of stunting, 3) to determine whether measures of linear growth in women can be predicted by their recalled childhood environment and 4) To determine whether the relationship between objectively estimated free-living energy expenditure and body composition is altered by stunting. Methods Data from interviews, anthropometric measurements and bioelectrical impedance analysis were collected on 58 Maya schoolchildren aged 7-9 years-old and their mothers living in the south of Merida, Mexico. Objective, free-living physical activity monitoring using combined accelerometry and heart rate monitoring of the children was also performed for one week. The interview data was used to describe the living conditions of the south of Merida. Whether stunting status or body proportions influenced the power of BMI to predict adiposity indicators was assessed for the mothers and the children. The mothers recalled early life SES was compared to their current measures of linear growth. The children s objectively estimated energy expenditure was compared to their body composition and measurements of body size. Results The Maya of southern Merida overall had access to clean drinking water and basic health care and have apparently eliminated acute under-nutrition. Yet they remained double burdened with simultaneous stunting and overweight/ obesity. Individual double burden levels were high, with 70% of the mothers were simultaneously stunted and overweight. Family level double burden was also high, with 28% of the families having an overweight mother and a stunted child. The rates of childhood malnutrition varied widely when using different cut-offs. Child stunting rates were between 15.5% and 37.9% when using -2 z-scores of Frisancho s Comprehensive (created using NHANES data) reference versus the 5th percentile of the WHO reference, respectively. Child overweight/ obesity rates were less than 10% when using weight-for-age on both the Comprehensive and WHO reference charts. Child overweight/ obesity as classified using BMI z-scores was between 27.5 to 34.5% using the Comprehensive and WHO reference, respectively, while child overfat was over 80% when using body fat percentage for age reference curves. BMI predicted adiposity indicators in these Maya children, explaining between 33 and 84% of the variance in arm fat index and waist circumference z-score, respectively. BMI was less strongly related to the mothers adiposity indicators, explaining between 19 and 70% of the variance in arm fat area and waist circumference. The relationship between BMI and adiposity indicators was unchanged by stunting or body proportions in either mothers or children. Mothers recalled early life SES was significantly related to but explained little of the variance in her measures of linear growth. Birth decade explained 5% of the variance in stature and the Modernisation index (urban/ rural birth, sugar sweetened beverage consumption, packaged food consumption) explained 5% of the variance in mothers leg length. Birth order, sibling number and consumer durable ownership were also significantly related to linear growth of the mothers. These Maya children had high levels of physical activity, as all exceeded the recommended 60 minutes of moderate-to-vigorous physical activity per day. After controlling for fat free mass, short stature did not predict lower resting energy expenditures in the children. However shorter stature did predict lower levels of activity energy expenditure, particularly in girls. Stunted girls had the lowest activity energy expenditures. Conclusions These urban Maya tend to have access to basic sanitation and services and are at a very high risk for NR-NCDs with the co-existence of chronic under-nutrition (stunting) and overweight/ obesity. The high rates of stunting do not impact the usefulness of BMI to estimate adiposity nor does stunting appear to impact children s energy expenditure. While BMI is useful to predict adiposity in these urban Maya children, it is not recommended for use in the mothers. Interventions to reduce childhood adiposity need to begin very early in life to most effectively reduce adiposity. Research into the low SES groups of middle-income countries, offers insight to what may occur in low-income countries as they advance in the nutrition transition.

Notre étude s’est intéressée chez l’enfant au modèle tempéramental de Rothbart : ce modèle suggère que la mise en balance des caractéristiques individuelles de réactivité et d’autorégulation explique le développement de l’enfant. Nous avons constaté l’intérêt de cette structure théorique pour enrichir la modélisation empirique des traits d’appétit de l’enfant, en lien avec le développement de son adiposité. Ainsi avons-nous défini les objectifs suivants: (a) valider un modèle de mesure des traits d’appétit de l’enfant inspiré des composantes tempéramentales du modèle de Rothbart; (b) valider une structure de relations entre autorégulation générale, traits d’appétit et adiposité; (c) valider la structure théorique du modèle de Rothbart appliquée au comportement alimentaire. Nous avons mesuré les traits d’appétit par questionnaire chez des enfants de 10 à 14 ans, puis via des tâches comportementales chez des enfants de 8 à 12 ans. Nous avons aussi pesé et mesuré les enfants. La méthode par questionnaire a permis de valider la modélisation tempéramentale des traits d’appétit via la réactivité de l’appétit et l’autorégulation de la prise alimentaire. Cette méthode a aussi montré que le lien entre autorégulation générale et adiposité de l’enfant pouvait s’expliquer par l’intermédiaire des traits d’appétit. Enfin, les deux méthodes ont confirmé certaines prédictions du modèle théorique de Rothbart : nous avons observé un impact positif d’une composante de réactivité de l’appétit sur l’adiposité et un effet négatif de l’autorégulation de la prise alimentaire sur la réactivité de l’appétit. Grâce à un modèle novateur de tempérament alimentaire mis en lien avec l’adiposité de l’enfant, notre étude peut impacter la prévention et le traitement du surpoids. / Our study focused on Rothbart’s temperament model in children: this model suggests that the balance between individual characteristics of reactivity and self-regulation underlies the child’s development. We noticed that empirical models of appetitive traits linked with adiposity development in children could potentially benefit from the theoretical structure of this model. We thus defined the following objectives: (a) validating a measurement model for children’s appetitive traits through temperamental components inspired by Rothbart’s model; (b) validating a structure of relationships between general self-regulation, appetitive traits and adiposity; (c) validating the theoretical structure of Rothbart’s model in the specific domain of food behaviour. We measured appetitive traits firstly through a questionnaire in 10 to 14 year-old children and secondly through behavioural tasks in 8 to 12 year-old children. Children’s height and weight were also measured. The questionnaire method allowed to validate a temperamental model of appetitive traits, measured through appetite reactivity and self-regulation in eating. We also showed with this method that the link between general self-regulation and adiposity in children could be explained through appetitive traits. Finally, both methods confirmed some of the predictions of Rothbart’s theoretical model: we observed a positive impact of one component of appetite reactivity over adiposity and a negative effect of self-regulation in eating on appetite reactivity. Thanks to an innovative eating temperament model linked with children’s adiposity, our study can impact overweight prevention and treatment.