Julien Aucouturier

Effect of android to gynoid fat ratio on insulin resistance in obese youth.

BACKGROUND Upper body fat distribution is associated with the early development of insulin resistance in obese children and adolescents. OBJECTIVE To determine if an android to gynoid fat ratio is associated with the severity of insulin resistance in obese children and adolescents, whereas peripheral subcutaneous fat may have a protective effect against insulin resistance. SETTING The pediatric department of University Hospital, Clermont-Ferrand, France. DESIGN A retrospective analysis using data from medical consultations between January 2005 and January 2007. PARTICIPANTS Data from 66 obese children and adolescents coming to the hospital for medical consultation were used in this study. MAIN OUTCOME MEASURES Subjects were stratified into tertiles of android to gynoid fat ratio determined by dual-energy x-ray absorptiometry. Insulin resistance was assessed by the homeostasis model of insulin resistance (HOMA-IR) index. RESULTS There were no differences in weight, body mass index, and body fat percentage between tertiles. Values of HOMA-IR were significantly increased in the 2 higher tertiles (mean [SD], tertile 2, 2.73 [1.41]; tertile 3, 2.89 [1.28]) compared with the lower tertile (tertile 1, 1.67 [1.24]) of android to gynoid fat ratio (P < .001). The HOMA-IR value was significantly associated with android to gynoid fat ratio (r = 0.35; P < .01). CONCLUSIONS Android fat distribution is associated with an increased insulin resistance in obese children and adolescents. An android to gynoid fat ratio based on dual-energy x-ray absorptiometry measurements is a useful and simple technique to assess distribution of body fat associated with an increased risk of insulin resistance.

Effect of physical activity intervention on body composition in young children: influence of body mass index status and gender.

Aim: To fight overweight and obesity in childhood, this study proposes an additional physical activity (PA) in young children aged 6–10 years. The objective was to evaluate the effect of school‐based PA on the body composition according to body mass index (BMI) categories (nonobese vs. obese) and gender.

Fat and Carbohydrate Metabolism during Submaximal Exercise in Children

During exercise, the contribution of fat and carbohydrate to energy expenditure is largely modulated by the intensity of exercise. Age, a short- or long-term diet enriched in carbohydrate or fat substrate stores, training and gender are other factors that have also been found to affect this balance. These factors have been extensively studied in adults from the perspective of improving performance in athletes, or from a health perspective in people with diseases. During the last decade, lifestyle changes associated with high-energy diets rich in lipid and reduced physical activity have contributed to the increase in childhood obesity. This lifestyle change has emerged as a serious health problem favouring the early development of cardiovascular diseases, insulin resistance or type 2 diabetes mellitus. Increasing physical activity levels in young people is important to increase energy expenditure and promote muscle oxidative capacity. Therefore, it is surprising that the regulation of balance between carbohydrate and lipid use during exercise has received much less attention in children than in adults. In this review, we have focused on the factors that affect carbohydrate and lipid metabolism during exercise and have identified areas that may be relevant in explaining the higher contribution of lipid to energy expenditure in children when compared with adults. Low muscle glycogen content is possibly associated with a low activity of glycolytic enzymes and high oxidative capacity, while lower levels of sympathoadrenal hormones are likely to favour lipid metabolism in children. Changes in energetic metabolism occurring during adolescence are also dependent on pubertal events with an increase in testosterone in boys and estrogen and progesterone in girls. The profound effects of ovarian hormones on carbohydrate and fat metabolism along with their effects on oxidative enzymes could explain that differences in substrate metabolism have not always been observed between girls and women. Finally, although the regulatory mechanisms of fat and carbohydrate balance during exercise are quite well identified, there are a lack of data specific to children and most of the evidences reported in this review were drawn from studies in adults. Isotope tracer techniques and nuclear magnetic resonance will allow non-invasive investigation of the metabolism of the different substrate sources in skeletal muscle.

Daily energy balance in children and adolescents. Does energy expenditure predict subsequent energy intake

Both physical and sedentary activities primarily impact energy balance through energy expenditure, but they also have important implications in term of ingestive behavior. The literature provides scarce evidence on the relationship between daily activities and subsequent nutritional adaptations in children and adolescents. Sedentary activities and physical exercise are generally considered distinctly despite the fact that they represent the whole continuum of daily activity-induced energy expenditure. This brief review paper examines the impact of daily activities (from vigorous physical activity to imposed sedentary behaviors) on acute energy intake control of lean and obese children and adolescents, and whether energy expenditure is the main predictor of subsequent energy intake in this population. After an overview of the available literature, we conclude that both acute physical activity and sedentary behaviors induce food consumption modifications in children and adolescents but also that the important discrepancy between the methodologies used does not allow any clear conclusion so far. When considering energy intake responses according to the level of energy expenditure generated by those activities, it is clear that energy expenditure is not the main predictor of food consumption in both lean and obese children and adolescents. This suggests that other characteristics of those activities may have a greater impact on calorie intake (such as intensity, duration or induced mental stress) and that energy intake may be mainly determined by non-homeostatic pathways that could override the energetic and hormonal signals.

The role of the endocannabinoid system in skeletal muscle and metabolic adaptations to exercise: potential implications for the treatment of obesity

The results of recent studies add the endocannabinoid system, and more specifically CB1 receptor signalling, to the complex mechanisms that negatively modulate insulin sensitivity and substrate oxidation in skeletal muscle. CB1 receptors might become overactive in the skeletal muscle during obesity due to increased levels of endocannabinoids. However, quite surprisingly, one of the most studied endocannabinoids, anandamide, when administered in a sufficient dose, was shown to improve muscle glucose uptake and activate some key molecules of insulin signalling and mitochondrial biogenesis. This is probably because anandamide is only a partial agonist at CB1 receptors and interacts with other receptors (PPARγ, TRPV1), which may trigger positive metabolic effects. This putative beneficial role of anandamide is worth considering because increased plasma anandamide levels were recently reported after intense exercise. Whether the endocannabinoid system is involved in the positive exercise effects on mitochondrial biogenesis and glucose fatty acid oxidation remains to be confirmed. Noteworthy, when exercise becomes chronic, a decrease in CB1 receptor expression in obese metabolically deregulated tissues occurs. It is then tempting to hypothesize that physical activity would represent a complementary alternative approach for the clinical management of endocannabinoid system deregulation in obesity, without the side effects occurring with CB1 receptor antagonists.

Metabolic flexibility and obesity in children and youth

The concept of metabolic flexibility describes the ability of skeletal muscle to switch between the oxidation of lipid as a fuel during fasting periods to the oxidation of carbohydrate during insulin stimulated period. Alterations in energy metabolism in adults with obesity, insulin resistance and/or type 2 diabetes induce a state of impaired metabolic flexibility, or metabolic inflexibility. Despite the increase in the prevalence of type 2 diabetes in obese children and youth, less is known about the factors involved in the development of metabolic inflexibility in the paediatric population. Metabolic flexibility is conditioned by nutrient partitioning in response to feeding, substrate mobilization and delivery to skeletal muscle during fasting or exercising condition, and skeletal muscle oxidative capacity. Our aim in this review was to identify among these factors those making obese children at risk of metabolic inflexibility. The development of ectopic rather than peripheral fat storage appears to be a factor strongly linked with a reduced metabolic flexibility. Tissue growth and maturation are determinants of impaired energy metabolism later in life but also as a promising way to reverse metabolic inflexibility given the plasticity of many tissues in youth. Finally, we have attempted to identify perspectives for future investigations of metabolic flexibility in obese children that will improve our understanding of the genesis of metabolic diseases associated with obesity.

Metabolic Syndrome in Obese Children and Adolescents: Dichotomous or Continuous?

BACKGROUND Defining and detecting the metabolic syndrome in children and adolescents is difficult because of ongoing discussion of components and thresholds. The aim of this work was to highlight the limitations of a dichotomous definition of the metabolic syndrome, leading to considerable overlap between those with and without the metabolic syndrome, by computing different continuous scores. METHODS A total of 50 children and adolescents ages 6-16 years were studied. Height and weight were measured; body mass index (BMI) was calculated, and obesity was defined by age- and sex-specific 97(th) percentiles of French reference values. Metabolic syndrome prevalence was based on the criteria reported by Chen et al. in 2006 and compared with five scores reflecting specific metabolic syndrome components (MetScores): Fat mass, waist circumference, BMI, homeostasis model assessment (HOMA), and systolic blood pressure. RESULTS Using a standard clinical definition, 48% of obese children and adolescents were diagnosed with metabolic syndrome. The prevalence of metabolic syndrome in the sample was much higher using specific MetScores: Fat mass, 92%; waist circumference, 94%; BMI, 94%; HOMA, 98%; and systolic blood pressure, 84%. Insulin resistance (IR), assessed as a high HOMA index, was present in 68% of the sample, and was the metabolic syndrome component with the highest prevalence. CONCLUSIONS The use of a continuous indicator of the metabolic syndrome, such as MetScores, may help to overcome limitations imposed by dichotomous definitions, particularly among obese children and adolescents. A high prevalence of IR indicates the relevance of HOMA in detection of the metabolic syndrome.

Muscle Mitochondrial Oxidative Phosphorylation Activity, But Not Content, Is Altered with Abdominal Obesity in Sedentary Men: Synergism with Changes in Insulin Sensitivity

CONTEXT Abdominal obesity is a major risk factor for muscle insulin resistance. Mitochondria may play a key role in this etiology. OBJECTIVE Changes in muscle mitochondrial content and function were examined according to abdominal obesity and insulin sensitivity in men. STUDY DESIGN AND SETTING The descriptive MitHyCal study was conducted on the general population of Clermont-Ferrand, France. PARTICIPANTS Forty-two healthy sedentary men (41.7 +/- 4.3 yr) were divided into four groups according to waist circumference: 87 cm or less (group 1, n = 10); 88-93 cm (group 2, n = 12); 94-101 cm (group 3, n = 10); and 102 cm or greater (group 4, n = 10). INTERVENTION Plasma metabolic check-up was performed, and insulin sensitivity index was calculated from glucose and insulin responses to a 3-h oral glucose tolerance test. Muscle biopsies were obtained to assess mitochondrial content, oxidative phosphorylation activity, and superoxide anion (reactive oxygen species) production. MAIN OUTCOME MEASURES Assessment of muscle mitochondrial content and function was planned before data collection began. RESULTS Abdominal obesity was negatively correlated to insulin sensitivity index (r = -0.39; P < 0.01), and only group 4 was insulin-resistant (P < 0.05). There were no between-group differences in muscle mitochondrial content and maximal activity of key oxidative enzymes. In contrast, muscle mitochondrial ADP-stimulated respiration rate was 24% higher in groups 2 and 3 compared to groups 1 and 4 (P < 0.05). Mitochondrial ATP and reactive oxygen species production rates were 27 and 48% lower in group 4 than in group 1 (P < 0.05). CONCLUSION Abdominal obesity is associated with alterations in intrinsic muscle mitochondrial function but not content. These adaptations mainly result in reduced mitochondrial ATP production rate in response to insulin resistance.

Comparison of total body and abdominal adiposity indexes to dual x-ray absorptiometry scan in obese adolescents.

While indexes have been proposed to estimate total and abdominal adiposity in adults, the assessment of adiposity among obese adolescents remains difficult in clinical setting. The aim of this study was to evaluate the clinical applicability of total and visceral and fat mass indexes in obese adolescents.

The effects of imposed sedentary behavior and exercise on energy intake in adolescents with obesity.

Objective: Exercise has been shown to decrease subsequent energy intake, without modification of appetite, in adolescents who are obese. This study compared the impact of acute exercise with imposed sedentary behaviors on the daily nutritional adaptations and energy balance of youths with obesity. Methods: Body composition and maximal oxygen uptake were assessed in 10 12- to 15-year-old adolescents with obesity. Energy consumption, appetite, and energy expenditure were assessed during 3 experimental sessions: (1) exercise session (EX), (2) bed rest session (BR), and (3) control session (CON). Results: Total and morning energy expenditures were significantly higher during EX compared to CON and BR sessions (p < .001), and no differences were found during the afternoon energy expenditure between conditions (BR: 1056.5 ± 121.5; CON: 1185.7 ± 173; EX: 996.1 ± 153.4 Kcal). Total energy intake was significantly reduced on EX (p < .001). Dinner energy intake was significantly reduced during EX (491.65 ± 75.74 Kcal) and CON (666.55 ± 152.09 Kcal) compared with BR (818.87 ± 122.97 Kcal) (p < .001). Appetite was not affected. Conclusion: Whereas intense exercise reduces daily energy balance in adolescents with obesity by mainly affecting ad libitum dinner energy consumption, imposed sedentary behaviors lead to increased energy intake and then positive energy balance. The impact of exercise or imposed sedentary behaviors on the energy balance of adolescents with obesity is not only related to the exercise-induced energy expenditure, but also to their energy intake.