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The purpose of this study was to describe sources of variability in obesity-related variables in 6022 children aged 9-11 years from 12 countries. The study design involved recruitment of students, nested within schools, which were nested within study sites. Height, weight and waist circumference (WC) were measured and body mass index (BMI) was calculated; sleep duration and total and in-school moderate-to-vigorous physical activity (MVPA) and sedentary time were measured by accelerometry; and diet scores were obtained by questionnaire. Variance in most variables was largely explained at the student level: BMI (91.9%), WC (93.5%), sleep (75.3%), MVPA (72.5%), sedentary time (76.9%), healthy diet score (88.3%), unhealthy diet score (66.2%), with the exception of in-school MVPA (53.8%) and in-school sedentary time (25.1%). Variance explained at the school level ranged from 3.3% for BMI to 29.8% for in-school MVPA, and variance explained at the site level ranged from 3.2% for WC to 54.2% for in-school sedentary time. In general, more variance was explained at the school and site levels for behaviors than for anthropometric traits. Given the variance in obesity-related behaviors in primary school children explained at school and site levels, interventions that target policy and environmental changes may enhance obesity intervention efforts.

Objective: To examine independent and combined cross-sectional associations between movement behaviors (physical activity (PA), sedentary time, sleep duration, screen time and sleep disturbance) and fat mass index (FMI), as well as to examine longitudinal associations between movement behaviors and FMI., Methods: Cross-sectional and longitudinal analyses were done using data from the OPUS school meal study on 785 children (52% boys, 13.4% overweight, ages 8-11 years). Total PA, moderate-to-vigorous PA (MVPA), sedentary time and sleep duration (7 days and 8 nights) were assessed by an accelerometer and FMI was determined by dual-energy X-ray absorptiometry (DXA) on three occasions over 200 days. Demographic characteristics, screen time and sleep disturbance (Children's Sleep Habits Questionnaire) were also obtained., Results: Total PA, MVPA and sleep duration were negatively associated with FMI, while sedentary time and sleep disturbances were positively associated with FMI (P⩽0.01). However, only total PA, MVPA and sleep duration were independently associated with FMI after adjustment for multiple covariates (P<0.001). Nevertheless, combined associations revealed synergistic effects among the different movement behaviors. Changes over time in MVPA were negatively associated with changes in FMI (P<0.001). However, none of the movement behaviors at baseline predicted changes in FMI (P>0.05), but higher FMI at baseline predicted a decrease in total PA and MVPA, and an increase in sedentary time (P⩽0.001), even in normal-weight children (P⩽0.03)., Conclusion: Total PA, MVPA and sleep duration were independently associated with FMI, and combined associations of movement behaviors showed a synergistic effect with FMI. In the longitudinal study design, a high FMI at baseline was associated with lower PA and higher sedentary time after 200 days but not vice versa, even in normal-weight children. Our results suggest that adiposity is a better predictor of PA and sedentary behavior changes than the other way around.

Background: Lack of sleep and increased consumption of energy-dense foods and sugar-sweetened beverages (SSBs) have all been suggested as factors contributing to the increased prevalence of overweight and obesity., Objective: To evaluate whether objectively measured sleep duration (average and day-to-day variability) as well as parent-reported sleep problems are independently associated with proposed dietary risk factors for overweight and obesity in 8-11-year-old children., Design: In this cross-sectional study, data on sleep duration and day-to-day variability in sleep duration were measured in 676 Danish, apparently healthy children by an objective measure (actigraphy) for 8 nights, and the Children's Sleep Habits Questionnaire (CSHQ) was filled out by the parents. Diet was recorded using a web-based food record for 7 consecutive days. Fasting blood samples were obtained for measurements of plasma leptin and ghrelin levels., Results: Sleep duration (h per night) was negatively associated with energy density (ED) of the diet (β = -0.32 kJ g(-1)), added sugar (β = -1.50 E%) and SSBs (β = -1.07 E%) (all P ≤ 0.003). Furthermore, variability in sleep duration (10-min per night) was positively associated with SSBs (β = 0.20 E%, P = 0.03), independent of sleep duration, and CSHQ score was positively associated with ED (β = 0.16 kJ g(-1), P = 0.04). All of these associations were independent of potential confounders (age, sex, pubertal status, height, weight, screen time, moderate-to-vigorous physical activity and parental education and ethnicity)., Conclusion: Our study suggests that short sleep duration, high sleep duration variability and experiencing sleep problems are all associated with a poor, obesity-promoting diet in children.

The decrease in energy expenditure that occurs during weight loss is a process that attenuates over time the impact of a restrictive diet on energy balance up to a point beyond which no further weight loss seems to be possible. For some health professionals, such a diminished energy expenditure is the normal consequence of a progressive decrease in the motivation to exercise over the course of a weight-reducing program. Another explanation of decreased energy needs during weight loss is the decrease in body energy stores (that is, fat mass and muscle mass) and its related obligatory costs of living. Many studies have also documented the existence of adaptive thermogenesis in the context of weight loss, which represents a greater-than-predicted decrease in energy expenditure. In this paper, we pursue the analysis of this phenomenon by demonstrating that an adaptive decrease in thermogenesis can have a major role in the occurrence of resistance to further lose fat in weight-reduced obese individuals. Evidence is also presented to support the idea of greater hunger sensations in individuals displaying more pronounced thermogenic changes. Finally, as the decrease in thermogenesis persists over time, it is also likely associated with a greater predisposition to body-weight regain after weight loss. Globally, these observations suggest that the adaptive reduction in thermogenesis that accompanies a prolonged negative energy balance is a major determinant of the ability to spontaneously lose body fat.

The objective of this longitudinal, observational study was to verify whether a favorable change in sleep duration over 6 years could impact objective indicators of adiposity in adults aged 18-64 years. Short-duration sleepers (≤6 h per day; n=43) at baseline were divided into two groups: (i) those who increased their sleep duration to a 'healthy' length of 7-8 h per day at year 6 (mean increase: 1.52±0.66 h per day; n=23); and (ii) those who maintained their short sleep duration habits (mean change: -0.11±0.38 h per day; n=20). Adult individuals who reported sleeping 7-8 h per day at both baseline and year 6 (n=173) were used as a control group. Change in adiposity indicators for each sleep-duration group was compared by analysis of covariance. We observed that the two short-sleep-duration groups had similar baseline characteristics. However, short-duration sleepers who maintained their short sleep duration experienced a greater increase in body mass index (BMI) (difference: 1.1±0.36 kg m(-2), P<0.05) and fat mass (difference: 2.4±0.64 kg, P<0.05) over the 6-year follow-up period than short-duration sleepers who increased their sleep duration, even after adjustment for relevant covariates. We did not observe any significant difference in adiposity changes between the control group and short-duration sleepers who increased their sleep duration. This study suggests for the first time that shifting sleep duration from a short to a healthier length is associated with an attenuation of fat mass gain.

More than 50 years ago, Jean Mayer proposed that changes in blood glucose concentrations or arteriovenous glucose differences are detected by glucoreceptors that affect energy intake. According to this theory, an increase in blood glucose concentrations results in increased feelings of satiety whereas a drop in blood glucose concentrations has the opposite effect. The pioneering work of Mayer has recently received support from our group as low glycemia has been shown to be linked with body weight gain prospectively and has been considered as a strong predictor of the amount of weight regained after weight loss. This state of mild hypoglycemia also predicts the increase in depressive symptoms with weight loss and a greater propensity to glucose intolerance and type 2 diabetes, particularly for individuals having short sleep durations. Furthermore, knowledge-based work has been shown to induce a significant increase in spontaneous energy intake being related to changes in glycemic control. In accordance with the glucostatic theory, this oriented review suggests that factors favoring a trend toward hypoglycemia and/or glucose instability might induce excess energy intake, overweight and impaired glucose tolerance. Data also raise the possibility that fat gain might be protective against mild hypoglycemia by providing compensation to the stimuli promoted by a modern environment.

Objective: To evaluate physical fitness and body composition of children involved in the 'Québec en Forme' (QEF) Project and to compare data obtained to the reference values of the 1981 Canada Fitness Survey (CFS)., Design: Cross-sectional study., Subjects: A total of 1140 children (591 boys and 549 girls) of first (7 years), second (8 years) and fourth (10 years) grade from primary schools in the City of Trois-Rivières (Québec) were selected to participate in this study., Measurements: Body mass index (BMI) and waist circumference (WC) were measured. The physical fitness tests included standing long jump, 1-min speed sit-ups and speed shuttle run., Results: The prevalence of overweight in children ranged between 20 and 30%, which represents a substantial increase compared to the 1981 CFS. The relationship between BMI and WC was highly significant in boys and girls (r=0.90 and 0.86, respectively, P<0.0001). The negative correlations between BMI or WC and the performance in all physical fitness tests were mostly significant in children of both genders (-0.16 < or = r < or = -0.45, at least P<0.05), and these relationships were significantly greater in older children (P<0.05). Based on the 1981 CFS, only 4.7-14.1% of QEF boys still performed in the upper quartile of the distribution (fit boys), whereas 32.1-69% performed not much higher than the lower quartile (unfit boys) for each fitness test. In girls, the relative fitness decrease observed in 2003 was more pronounced since only 1-9.9% of subjects performed in the upper quartile of the distribution compared to 42.8-81.4% who did not perform higher than the lower quartile of the 1981 reference scores of the CFS., Conclusion: This study shows that BMI and WC are negatively correlated with physical fitness and that these associations are more pronounced in older children. Furthermore, physical fitness of our cohort, especially in girls, was much lower than what was documented in the 1981 CFS in subjects of the same age. This study thus emphasizes the necessity to develop early interventions to improve physical fitness in children and to prevent the increase of childhood obesity.

Objective: To assess the relationship between short sleep duration and obesity-related variables in children involved in the 'Québec en Forme' Project., Design: Cross-sectional study., Subjects: A total of 422 children (211 boys and 211 girls) aged between 5 and 10 years from primary schools in the City of Trois-Rivières (Québec) were selected to participate in this study., Measurements: Body weight, height and waist circumference were measured. The children were classified as normal, underweight, overweight or obese, according to body mass index (BMI) per age. An exhaustive questionnaire was administered by telephone to the parents of children., Results: The percentage of overweight/obesity was 20.0% in boys and 24.0% in girls. When compared to children reporting 12-13 h of sleep per day, the adjusted odds ratio for childhood overweight/obesity was 1.42 (95% confidence interval 1.09-1.98) for those with 10.5-11.5 h of sleep and 3.45 (2.61-4.67) for those with 8-10 h of sleep after adjustment for age, sex, and other risk factors. Parental obesity, low parental educational level, low total family income, long hours of TV watching, playing videogames or computer utilization, absence of breastfeeding and physical inactivity were also significantly associated with childhood overweight/obesity. In addition, we observed a significant negative association adjusted for age between sleep duration and body weight (-0.33, P<0.01), BMI (-0.12, P<0.01) and waist circumference (-0.24, P<0.01) in boys., Conclusion: An inverse association was observed between sleep duration and the risk to develop childhood overweight/obesity. Longitudinal research will be required to confirm a potential link of causality between these variables.