Associations between sedentary behaviours and dietary intakes among adolescents.

OBJECTIVE: The purpose of the current study was to examine associations of individual and aggregated screen-based behaviours, and total sitting time, with healthy and unhealthy dietary intakes among adolescents. DESIGN: Cross-sectional study of adolescents. Participants self-reported durations of television viewing, computer use, playing electronic games (e-games), total sitting time, daily servings of fruits and vegetables, and frequency of consumption of sugar-sweetened beverages (SSB), diet beverages, fast foods and discretionary snacks. Logistic regression models were conducted to identify associations of screen-based behaviours, total screen time and total sitting time with dietary intakes. SETTING: Victoria, Australia. SUBJECTS: Adolescents (n 939) in School Year 11 (mean age 16·8 years). RESULTS: The results showed that watching television (≥2 h/d) was positively associated with consuming SSB and diet beverages each week and consuming discretionary snacks at least once daily, whereas computer use (≥2 h/d) was inversely associated with daily fruit and vegetable intake and positively associated with weekly fast-food consumption. Playing e-games (any) was inversely associated with daily vegetable intake and positively associated with weekly SSB consumption. Total screen (≥2 h/d) and sitting (h/d) times were inversely associated with daily fruit and vegetable consumption, with total screen time also positively associated with daily discretionary snack consumption and weekly consumption of SSB and fast foods. CONCLUSIONS: Individual and aggregated screen-based behaviours, as well as total sitting time, are associated with a number of indicators of healthy and unhealthy dietary intake. Future research should explore whether reducing recreational screen time improves adolescents' diets.

Cross-sectional and prospective mediating effects of dietary intake on the relationship between sedentary behaviour and body mass index in adolescents.

BACKGROUND: Cross-sectional evidence suggests TV viewing, but not objectively-measured sedentary time or bouts of sedentary time, is consistently associated with body mass index (BMI) in adolescents. However, it is unclear whether dietary intake is a potential mediator of these relationships. The aim of this study was to explore the cross-sectional and prospective mediating effects of dietary intake on the association of sedentary behaviour with BMI z-score (zBMI) in a cohort of Australian adolescents. METHODS: Cross-sectional and prospective analyses were conducted in adolescents aged 12-15 years participating in the 2002/03 (baseline) and 2004/05 (follow-up) Nepean Growing Up Study. The independent variables were television (TV) viewing, an objective measure of total sedentary time and average sedentary bout duration, and the outcome variable zBMI. Using the Sobel-Goodman method with bootstrapping, mediation analyses were conducted examining three dietary components (discretionary foods, sugar-sweetened beverages [SSB] and takeaway foods) as mediators of associations between TV viewing and zBMI (n = 259) and between total sedentary time and average sedentary bout duration with zBMI (n = 140). RESULTS: No significant cross-sectional or prospective total or direct associations were observed for TV viewing, total sedentary time and average sedentary bout duration with zBMI. However, TV viewing was positively associated with consumption of takeaway foods cross-sectionally (ß = 0.06; 95% CI 0.01 to 0.12), prospectively at baseline (ß = 0.07; 95% CI 0.01 to 0.12) and prospectively at follow-up (ß = 0.10; 95% CI 0.04, 0.16), and average sedentary bout duration was inversely associated with SSB consumption both cross-sectionally (ß = -0.36; 95% CI -0.69 to -0.02) and prospectively at baseline (ß = -0.36; 95% CI -0.70 to -0.02). No mediation effects were identified. CONCLUSIONS: TV viewing, total sedentary time and bouts of sedentary time were not associated cross-sectionally or prospectively with adolescents' zBMI, and three elements of dietary intake (e.g. intake of discretionary foods, SSB and takeaway foods) did not mediate this relationship. The role of dietary intake and sedentary behaviour in relation to adolescent health requires further clarification.

Patient freedom to choose a weight loss diet in the treatment of overweight and obesity: a randomized dietary intervention in type 2 diabetes and pre-diabetes.

BACKGROUND: Offering the overweight or obese patient the option of choosing from a selection of weight loss diets has not been investigated in type 2 diabetes. The aim of the study was to investigate if the option to choose from, and interchange between a selection of diets ("Choice"), as opposed to being prescribed one set diet ("No Choice"), improves drop out rates and leads to improved weight loss and cardio-metabolic outcomes. METHODS: The study was a 12 month, randomized parallel intervention. A total of 144 volunteers with type 2 diabetes or pre-diabetes and a BMI >27 were randomized to "No Choice" or "Choice". Those in the No Choice group were placed on a set weight loss diet (CSIRO) with no change permitted. Those in the Choice group could choose from, and interchange between, the CSIRO, South Beach or Mediterranean diets. RESULTS: There were no differences in attrition rates or weight loss between the "Choice" and "No Choice". In a secondary analysis of the intention-to-treat weight loss data with last measured weight carried forward gave a highly significant diet group by time by gender interaction (p = 0.002) with men doing better in the No Choice group overall (maximum difference "No Choice "-2.9 ± 4.6 kg vs. "Choice"-6.2 kg ± 5.3 kg at 6 months) and women doing better in the Choice group overall (maximum difference Choice -3.1 ± 3.7 kg vs. "No Choice" -2.0 kg ± 2.6 kg at 6 months). CONCLUSIONS: Men prefer direction in their weight loss advice and do less well with choice. A gender-specific approach is recommended when prescribing weight loss diets. TRIAL REGISTRATION: anzctr.org.au ACTRN12612000310864.

Preschool children's physical activity and cardiovascular disease risk: A systematic review.

OBJECTIVES: Higher physical activity (PA) levels in adults are associated with lower cardiovascular disease risk, however it is unclear whether this association is evident in children younger than five years. Given that cardiovascular disease has early life origins, this study systematically reviews evidence of associations between PA and cardiovascular disease risk factors among children aged 3-5.5years. DESIGN: Systematic review. METHOD: A systematic search of multiple data bases was conducted to identify published papers reporting associations between any measure of PA and cardiovascular disease risk factors. INCLUSION CRITERIA: English language; peer-reviewed; original quantitative research; mean age or majority of sample to be between 3.0-5.5years. Studies where the sample was characterised by a health condition (e.g. obese, hypertensive) were not eligible for inclusion. RESULTS: Twelve papers met the inclusion criteria. At least one study for each cardiovascular disease risk factor except inflammation was included. PA was not associated with insulin resistance, and inconsistently associated with the remaining cardiovascular disease risk factors. Studies were mostly cross-sectional and methodologically heterogeneous. Longitudinal and experimental study designs and objective measurement of PA may help provide a clearer indication of the interplay between PA and cardiovascular disease risk in the preschool population.

Effects of breaking up sitting on adolescents' postprandial glucose after consuming meals varying in energy: a cross-over randomised trial.

OBJECTIVES: To explore the impact of uninterrupted sitting versus sitting with resistance-type activity breaks on adolescents' postprandial glucose responses while consuming a diet varying in energy. DESIGN: Cross-over randomised trial. METHODS: Thirteen healthy participants (16.4±1.3years) completed a four-treatment cross-over trial: (1) uninterrupted sitting+high-energy diet; (2) sitting with breaks+high-energy diet; (3) uninterrupted sitting+standard-energy diet; and (4) sitting with breaks+standard-energy diet. For all four conditions, two identical meals were consumed; at 0h and 3h. A continuous glucose monitoring system (CGM) recorded interstitial glucose concentrations every five minutes. Linear mixed models examined differences in glucose positive incremental area under the curve (iAUC) and total AUC between the sitting and diet conditions for the first meal, second meal and entire trial period. RESULTS: Compared to the uninterrupted sitting conditions, the breaks condition elicited a 36.0mmol/L/h (95%CI 6.6-65.5) and 35.9mmol/L/h (95%CI 6.6-65.5) lower iAUC response after the first and second meal, respectively, but not for the entire trial period or for total AUC. Compared to the standard-energy diet, the high-energy diet elicited a 55.0mmol/L/h (95%CI 25.8-84.2) and 75.7mmol/L/h (95%CI 8.6-142.7) higher iAUC response after the first meal and entire trial, respectively. Similar response to the high-energy diet were observed for total AUC. CONCLUSIONS: According to iAUC, interrupting sitting had a significant effect on lowering postprandial glucose for both dietary conditions, however, it was not significant when examining total AUC. Larger studies are needed to confirm these findings. CLINICAL TRIAL REGISTRATION NUMBER: ACTRN12615001145594.

Does diet mediate associations of volume and bouts of sedentary time with cardiometabolic health indicators in adolescents?

OBJECTIVE: Examine the mediating role of diet in the relationship between volume and duration of sedentary time with cardiometabolic health in adolescents. METHODS: Adolescents (12-19 years) participating in the 2003/04 and 2005/06 U.S. National Health and Nutrition Examination Survey (NHANES) were examined. Cardiometabolic health indicators were body mass index z-scores (zBMI) (n = 1,797) and metabolic syndrome (MetS) (n = 812). An ActiGraph hip-worn accelerometer was used to derive total sedentary time and usual sedentary bout duration. Dietary intake was assessed using two 24-hour dietary recalls. Mediation analyses were conducted to examine five dietary mediators [total energy intake, discretionary foods, sugar-sweetened beverages (SSB), fruits and vegetables, and dietary quality] of the relationship between total sedentary time and usual sedentary bout duration with zBMI and MetS. RESULTS: Total sedentary time was inversely associated with zBMI (ß = -1.33; 95% CI -2.53 to -0.13) but attenuated after adjusting for moderate-to-vigorous physical activity. No significant associations were observed between usual sedentary bout duration with zBMI or either sedentary measure with MetS. None of the five dietary variables mediated any of the relationships examined. CONCLUSIONS: Further studies are needed to explore associations of specific time periods (e.g., after school) and bout durations with both cardiometabolic health indicators and dietary behaviors.