Association of physical activity and body composition with insulin sensitivity in a community sample of adolescents

Comparison of the HEI and HEI-2010 Diet Quality Measures in Association with Chronic Disease Risk among Low-Income, African American Urban Youth in Baltimore, Maryland

OBJECTIVE

Overall diet patterns may be a better predictor of disease risk than specific nutrients or individual foods. The purpose of this study is to examine how overall diet patterns relate to nutritional intake, body composition, and physiological measures of chronic disease risk among low-income, urban African American adolescents.

METHODS

Cross-sectional data were collected from two samples of African American adolescents (n = 317) from a low-income urban community, including dietary intake using the food frequency Youth/Adolescent Questionnaire and anthropometric measures. Serum cholesterol, serum lipoproteins, and glucose tolerance were measured in a subsample. Means testing compared differences in Healthy Eating Index (HEI) and Healthy Eating Index-2010 (HEI-2010) component and total scores. Pearson correlations examined how HEI and HEI-2010 scores related to nutrient, food intakes, and markers of disease risk, including body mass index, percent body fat, abdominal fat, serum cholesterol, serum lipoproteins, and impaired glucose tolerance. Fisher R-Z transformations compared magnitude differences between HEI and HEI-2010 correlations to nutritional intake and chronic disease risk.

RESULTS

Both HEI and HEI-2010 scores were positively associated with micronutrient intakes. Higher HEI scores were inversely related to serum cholesterol, low-density lipoprotein, impaired glucose tolerance, percent body fat, and percent abdominal fat. HEI-2010 scores were not related to biomarkers of chronic disease risk.

CONCLUSIONS

Compared to the HEI-2010, the HEI is a better indicator of chronic disease risk among low-income, urban African American adolescents.

Targeting skeletal muscle mitochondria to prevent type 2 diabetes in youth

The prevalence of type 2 diabetes (T2D) has increased dramatically over the past two decades, not only among adults but also among adolescents. T2D is a systemic disorder affecting every organ system and is especially damaging to the cardiovascular system, predisposing individuals to severe cardiac and vascular complications. The precise mechanisms that cause T2D are an area of active research. Most current theories suggest that the process begins with peripheral insulin resistance that precedes failure of the pancreatic β-cells to secrete sufficient insulin to maintain normoglycemia. A growing body of literature has highlighted multiple aspects of mitochondrial function, including oxidative phosphorylation, lipid homeostasis, and mitochondrial quality control in the regulation of peripheral insulin sensitivity. Whether the cellular mechanisms of insulin resistance in adults are comparable to that in adolescents remains unclear. This review will summarize both clinical and basic studies that shed light on how alterations in skeletal muscle mitochondrial function contribute to whole body insulin resistance and will discuss the evidence supporting high-intensity exercise training as a therapy to circumvent skeletal muscle mitochondrial dysfunction to restore insulin sensitivity in both adults and adolescents.

Angiotensin II type 2 receptor stimulation improves fatty acid ovarian uptake and hyperandrogenemia in an obese rat model of polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is mainly defined by hyperandrogenism but is also characterized by insulin resistance (IR). Studies showed that overexposure of nonadipose tissues to nonesterified fatty acids (NEFA) may explain both IR and hyperandrogenism. Recent studies indicate that treatment with an angiotensin II type 2 receptor (AT2R)-selective agonist improves diet-induced IR. We thus hypothesized that PCOS hyperandrogenism is triggered by ovarian NEFA overexposure and is improved after treatment with an AT2R agonist. Experiments were conducted in 12-week-old female JCR:LA-cp/cp rats, which are characterized by visceral obesity, IR, hyperandrogenism, and polycystic ovaries. Control JCR:LA +/? rats have a normal phenotype. Rats were treated for 8 days with saline or the selective AT2R agonist C21/M24 and then assessed for: 1) fasting testosterone, NEFA, and insulin levels; and 2) an iv 14(R,S)-[(18)F]fluoro-6-thia-heptadecanoic acid test to determine NEFA ovarian tissue uptake (Km). Compared with controls, saline-treated PCOS/cp rats displayed higher insulin (100 vs 5.6 μU/mL), testosterone (0.12 vs 0.04 nmol/L), NEFA (0.98 vs 0.48 mmol/L), and Km (20.7 vs 12.9 nmol/g·min) (all P < .0001). In PCOS/cp rats, C21/M24 did not significantly improve insulin or NEFA but normalized testosterone (P = .004) and Km (P = .009), which were strongly correlated together in all PCOS/cp rats (ρ = 0.74, P = .009). In conclusion, in an obese PCOS rat model, ovarian NEFA uptake and testosterone levels are strongly associated and are both significantly reduced after short-term C21/M24 therapy. These findings provide new information on the role of NEFA in PCOS hyperandrogenemia and suggest a potential role for AT2R agonists in the treatment of PCOS.

The perceived and built environment surrounding urban schools and physical activity among adolescent girls

BACKGROUND

Neighborhood perceived/built environment and physical activity (PA) associations have been examined for adolescents around homes, but not surrounding schools.

PURPOSE

The purpose of this paper is to examine if positive perceptions/built environment in neighborhoods surrounding schools predict PA among low-income, urban adolescent girls.

METHODS

Measures include: minutes in moderate-vigorous PA (MVPA, ankle accelerometry), perceptions of the school environment (questionnaire), built environment (neighborhood audit). Analyses include multi-level models.

RESULTS

Two hundred twenty-four sixth and seventh grade girls [mean(sd) age = 12.1(0.7) years] from 12 schools serving low-income, primarily African American communities; mean MVPA 35.4 min (mean days assessed = 5.8). Girls in schools with more positive perceptions of the neighborhood environment surrounding the school were less active (β = 7.2, p = 0.043). Having "places to go within walking distance" (perceptions) and number of food stores near school (built environment) positively relate to MVPA (β = 5.5, p = 0.042 and β = 0.59, p = 0.047).

CONCLUSIONS

Among neighborhoods surrounding urban schools, positive perceptions do not predict PA; accessibility, via both perceived and built environment, support PA.

Evaluation of a mathematical model of diabetes progression against observations in the Diabetes Prevention Program

The seminal publication of the Diabetes Prevention Program (DPP) results in 2002 has provided insight into the impact of major therapies on the development of diabetes over a time span of a few years. In the present work, the publicly available DPP data set is used to calibrate and evaluate a recently developed mechanistic mathematical model for the long-term development of diabetes to assess the model's ability to predict the natural history of disease progression and the effectiveness of preventive interventions. A general population is generated from which virtual subject samples corresponding to the DPP enrollment criteria are selected. The model is able to reproduce with good fidelity the observed time courses of both diabetes incidence and average glycemia, under realistic hypotheses on evolution of disease and efficacy of the studied therapies, for all treatment arms. Model-based simulations of the long-term evolution of the disease are consistent with the transient benefits observed with conventional therapies and with promising effects of radical improvement of insulin sensitivity (as by metabolic surgery) or of β-cell protection. The mechanistic diabetes progression model provides a credible tool by which long-term implications of antidiabetic interventions can be evaluated.

Physical activity is related to insulin sensitivity in children and adolescents, independent of adiposity: a review of the literature

In adults, there is evidence that physical activity effectively improves insulin sensitivity regardless of adiposity. Whether this is also the case in children and adolescents is less clear. Clarifying this matter may help to identify the best outcomes to target in exercise programs for these age groups, where changes in adiposity may not always be desirable or realistic. A review of the literature was conducted on studies that examined the relationships of physical activity, cardiorespiratory fitness and strength with insulin sensitivity independent of adiposity in children and adolescents. Experimental (intervention) and correlational (longitudinal and cross-sectional) studies on participants ages 18 years and younger were identified. A total of 42 studies were included in this review. Sample sizes in the studies ranged from 14 to 4955 participants, with individual ages ranging from 5 to 19 years. A significant relationship with insulin sensitivity existed in 78% of studies on physical activity, 69% of studies on cardiorespiratory fitness and 66% of studies on strength. In studies that examined both physical activity and cardiorespiratory fitness concurrently, evidence suggests that they are both correlated with insulin sensitivity independent of adiposity, especially when physical activity is at higher intensities. However, the strength of this relationship might be influenced by study design, measurement techniques and participant characteristics. This is the first review of its type to take research design into account and to examine study outcomes according to participant ethnicity, gender, age, pubertal status and weight status.

[Determining factors of physical activity level in school children and adolescents: the OPACA study]

INTRODUCTION

Physical activity is a key factor for human health. This study attempts to measure the level of physical activity in children and to find out what are the factors that determine it.

METHOD

In a sample of the 11 and 14 year-old population of the centre-south area of Palencia, physical activity was measured using a three day diary, and anthropometric and socioeconomic variables were collected. Three variables were analysed: fat-free mass adjusted activity energy expenditure (AEE/FFM), physical activity level (PAL), and categorical physical activity (active/inactive).

RESULTS

A total of 179 children were included, of whom 71.5% were active or very active. Males were more active than females, and activity was also higher in summer. Physical activity declined between 11 and 14 years, and was lower during the weekends than in working days. There were no differences related to obesity, overweight or percent body fat. More active children had lower blood pressure. Physical activity was directly related to weekly hours spent in sport activities, and inversely related to time spent on sedentary activities. Multivariate analysis showed that children from families with low educational levels had a higher activity level not related to sport activities.

CONCLUSIONS

The level of physical activity in this population is acceptable, although there are sex differences and there is a declining trend through the adolescence.

Challenge! Health promotion/obesity prevention mentorship model among urban, black adolescents

OBJECTIVES

The objective of this study was to evaluate a 12-session home/community-based health promotion/obesity prevention program (Challenge!) on changes in BMI status, body composition, physical activity, and diet.

METHODS

A total of 235 black adolescents (aged 11-16 years; 38% overweight/obese) were recruited from low-income urban communities. Baseline measures included weight, height, body composition, physical activity (PA), and diet. PA was measured by 7-day play-equivalent physical activity (> or =1800 activity counts per minute). Participants were randomly assigned to health promotion/obesity prevention that is anchored in social cognitive theory and motivational interviewing and was delivered by college-aged black mentors or to control. Postintervention (11 months) and delayed follow-up (24 months) evaluations were conducted. Longitudinal analyses used multilevel models with random intercepts and generalized estimating equations, controlling for baseline age/gender. Stratified analyses examined baseline BMI category.

RESULTS

Retention was 76% over 2 years; overweight/obese status declined 5% among intervention adolescents and increased 11% among control adolescents. Among overweight/obese youth, the intervention reduced total percentage of body fat and fat mass and increased fat-free mass at delayed follow-up and increased play-equivalent physical activity at postintervention but not at delayed follow-up. Intervention adolescents declined significantly more in snack/dessert consumption than control adolescents at both follow-up evaluations.

CONCLUSIONS

At postintervention, there were intervention effects on diet and PA but not BMI category or body composition. At delayed follow-up, dietary changes were sustained and the intervention prevented an increase in BMI category. Body composition was improved for overweight/obese youth. Changes in body composition follow changes in diet and PA and may not be detected immediately after intervention.

Increased physical activity and reduced adiposity in overweight Hispanic adolescents

PURPOSE

The objectives of this study were to examine 1) whether changes in total physical activity (PA; counts per minute, cpm) and time spent in moderate to vigorous PA (MVPA) are associated with changes in adiposity and 2) whether energy intake influences the relationship between changes in PA and changes in adiposity in overweight Hispanic adolescents.

METHODS

Analysis included 38 overweight (body mass index, >85th percentile) Hispanic adolescents with complete pretest and posttest data on relevant variables after participating in a 16-wk intervention. The intervention treatment did not influence PA, so the sample was combined and the randomization group was adjusted for in the analysis. Body composition by dual-energy x-ray absorptiometry, 7-d PA by accelerometry, and dietary intake by 3-d diet records were assessed before and after intervention.

RESULTS

Within individuals, the mean increase of PA (n = 19) and mean decrease of PA (n = 19) was approximately 105 cpm. A 100-cpm increase in total PA was associated with a decrease of 1.3 kg of fat mass and 0.8% body fat after adjusting for pretest adiposity, PA, age, sex, and treatment (P < 0.05). Controlling for energy intake modestly strengthened the relationships between total PA and fat mass and percent body fat. Changes in MVPA were not related to changes in adiposity after controlling for total PA (P > 0.05).

CONCLUSIONS

Increasing total PA by 28% (100 cpm) was associated with a decrease of 1.4 kg of fat mass and 1% body fat for 16 wk in overweight Hispanic adolescents independent of intervention group assignment. Increases in total PA, compared with MVPA, may be sufficient to improve body composition in overweight Hispanic adolescents.

Long-term effects of dietary glycemic index on adiposity, energy metabolism, and physical activity in mice

A high-glycemic index (GI) diet has been shown to increase adiposity in rodents; however, the long-term metabolic effects of a low- and high-GI diet have not been examined. In this study, a total of 48 male 129SvPas mice were fed diets high in either rapidly absorbed carbohydrate (RAC; high GI) or slowly absorbed carbohydrate (SAC; low GI) for up to 40 wk. Diets were controlled for macronutrient and micronutrient content, differing only in starch type. Body composition and insulin sensitivity were measured longitudinally by DEXA scan and oral glucose tolerance test, respectively. Food intake, respiratory quotient, physical activity, and energy expenditure were assessed using metabolic cages. Despite having similar mean body weights, mice fed the RAC diet had 40% greater body fat by the end of the study and a mean 2.2-fold greater insulin resistance compared with mice fed the SAC diet. Respiratory quotient was higher in the RAC group, indicating comparatively less fat oxidation. Although no differences in energy expenditure were observed throughout the study, total physical activity was 45% higher for the SAC-fed mice after 38 wk of feeding. We conclude that, in this animal model, 1) the effect of GI on body composition is mediated by changes in substrate oxidation, not energy intake; 2) a high-GI diet causes insulin resistance; and 3) dietary composition can affect physical activity level.

Physical Activity: The Epidemic of Obesity and Overweight Among Youth: Trends, Consequences, and Interventions

Childhood and adolescent overweight and obesity are an epidemic problem in the United States. Studies show that approximately one third of youth are overweight or obese, representing a tripling since the 1960s and 1970s. The average male and female adult in the United States has gained 25 lbs and 24 lbs, respectively, since 1962. The body mass index of the average adult has increased from 25 to 28. Among youth, the average body mass index has increased from 21.3 to 24.1 since 1963. This increase in bodyweight among adults and youth is partially due to the decreased levels of physical activity. The economic and health consequences of this epidemic are enormous. Type 2 diabetes mellitus, a disease that was rare among youth 20 to 30 years ago, now represents as many as 45% of all cases of diabetes among youth. Cardiovascular risk factors are worsened in overweight and obese youth, and early evidence of atherosclerosis manifested by endothelial dysfunction and increased coronary artery calcium is present in a high percentage of overweight youth. Numerous psychosocial problems also are increased among overweight and obese youth. However, there are numerous examples in the scientific literature of successful approaches to the prevention and management of overweight and obesity in youth. This article summarizes statistics concerning the prevalence of overweight, obesity, and physical inactivity among youth; discusses the numerous physical and psychosocial consequences of overweight and obesity among youth; and presents information regarding interventions that have been demonstrated to be effective in preventing childhood and adolescent overweight and obesity.