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Diet quality does not affect relationship between television time, BMI in adolescents
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Among U.S. adolescents, dietary intake did not mediate the relationship between television watching and BMI z score, whereas both sugar-sweetened beverage consumption and fruit and vegetable intake partly mediated the relationship between screen time and metabolic syndrome, recent findings suggest.
“This suggests that it is important to target TV viewing in interventions; however, the mechanisms explaining the health associations are still unclear,” Elly A. Fletcher, a PhD student at the Institute for Physical Activity and Nutrition at Deakin University in Australia, and colleagues wrote. “Further research examining other sedentary behaviors (eg, computer use, video gaming) and total sedentary time is needed to determine if these behaviors have similar findings.”
In a cross-sectional study, Fletcher and colleagues analyzed data from 3,161 adolescents participating in the 2003-2004 and 2005-2006 National Health and Nutrition Examination Survey (53.1% boys; mean age, 15 years). Participants provided two separate 24-hour food recalls, self-reported TV viewing habits via questionnaire, physical activity intensity and height and weight measurements to calculate BMI z score; a subset of patients provided a fasting blood sample to measure fasting blood glucose, insulin and serum lipids (n = 1,379; 9.1% classified as having metabolic syndrome). Using the MacKinnon method, researchers conducted mediation analyses to examine five dietary mediators (total energy intake, fruit and vegetable intake, discretionary snacks, sugar-sweetened beverages and diet quality) and their relationships with TV viewing, BMI z score and metabolic syndrome.
Researchers observed a “small, positive relationship” between TV viewing habits and BMI z scores (beta = 0.99; 95% CI, 0.52-1.46), implying that BMI z score increased by a mean of 0.99 units (0.8 kg/m²) for every hour spent watching TV. TV viewing habits were also associated with metabolic syndrome (OR = 1.18; 95% CI, 1-1.38).
After accounting for each dietary mediator, the association between TV viewing and BMI z score persisted, and in some cases was stronger, according to researchers (P < .05); however, sugar-sweetened beverage consumption and fruit and vegetable intake partially mediated the relationship between TV viewing and metabolic syndrome, explaining 8.7% and 4.1% of the relationship, respectively.
“For example, even after accounting for discretionary snacks, [BMI z score] increased by 1.02 units for every hour spent watching TV,” the researchers wrote. “However, in the [metabolic syndrome] sample, the direct effect between TV and [metabolic syndrome] was no longer significant after separately accounting for fruit and vegetable intake, [sugar-sweetened beverage] consumption and diet quality.” – by Regina Schaffer
Disclosure: The researchers report no relevant financial disclosures.
Perspective
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Diana Thomas
Understanding the mechanistic relationship between children with obesity, dietary intake and sedentary behaviors is critical to guide policy and develop effective and feasible interventions. In order to evaluate this complex relationship, Fletcher and colleagues analyzed data from more than 3,000 adolescents in the most recently available National Health and Nutrition Examination Survey (NHANES). The authors’ analysis revealed that TV viewing, poor diet quality and sugar-sweetened beverage consumption were associated with high BMI. While most of the habitual lifestyle data were self-reported, the NHANES dataset did contain a subsample consisting of accelerometer-measured physical activity. It is plausible that energy intake is higher than reported. Mathematical models suggest the average energy intake exceeds 2,500 kcal/day. More high-quality studies that determine energy intake using the doubly labeled water method and other biomarkers are needed to accurately determine the true relationship between energy intake, sedentary behavior and BMI. Nevertheless, the study findings support interventions that reduce screen time and improve dietary quality in children as a potential method to combat obesity during adolescence.
Disclosure: Thomas reports no relevant financial disclosures.
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