This pilot randomized controlled trial found preliminary evidence that targeting greater physical activity along with dietary change could better help decrease abdominal fat relative to targeting only dietary change among overweight children engaged in family-based behavioral weight control treatment. With all children and parents targeted for dietary change, the differential effects of less versus more emphasis on changing physical activity on children’s abdominal fat were most evident in MRI-derived measures. Findings highlight the potential stronger influence of physical activity on visceral fat versus subcutaneous abdominal fat reduction among overweight children within the context of simultaneous dietary change. However, given the small sample size and resulting low statistical power, and the greater absolute magnitude of post-treatment differences in subcutaneous versus visceral abdominal fat between the ADDED and STANDARD conditions by treatment end, the approach targeting increases in physical activity appears to be impacting overweight children’s overall abdominal fat. In contrast to condition differences in abdominal fat measures, smaller or minimal differences between children or parents in the ADDED versus STANDARD condition were observed the overall weight status (e.g., BMI, z-BMI) and whole-body fat measures.
Evidence continues to emerge regarding the benefits of greater physical activity and physical fitness on various aspects of children’s health, including better insulin sensitivity (42
), blood pressure (43
), lung function (44
), and vascular function (particularly for vigorous physical activity) (45
). More recent research that employed accelerometers to measure children’s physical activity finds that not just overall quantity, but higher physical activity intensity and bouts may be important for obesity prevention and lower central adiposity (46
). Physical activity also appears to reduce cardiovascular health risk independent of its impact on overall weight status or whole body fat (48
). Finding in the present study are also consistent with other findings regarding the incremental health benefit of more physical activity above and beyond the benefits achieved by dietary modification alone among children (50
). In adults increasing exercise intensity may add to or interact with exercise volume to more dramatically reduce visceral fat (51
). More research is needed in overweight children regarding the impact on visceral fat of modifying physical activity intensity, volume, and other aspects of physical activity.
The present study demonstrated the ability of focused behavioral strategies to increase physical activity and the impact of establishing a higher physical activity recommendation (90 minutes versus 60 minutes as recommended for general children health; (52
)) among overweight youth in weight management treatment. After adjusting for pre-treatment physical activity, children in the ADDED condition nonetheless had on average more than 15 more minutes per day of physical activity at post-treatment. The average child in the present trial was similarly active to the average child in a sample of U.S. 9–15 year olds (not selected based on weight status) measured with similar accelerometers and the same thresholds for determining moderate and vigorous physical activity (3.0+ METs) (37
). It is noteworthy that the estimates of MVPA were markedly lower when the higher 4.0+ METs threshold was used, with children having approximately 50% less physical activity on average. The average child in the ADDED condition was self-reporting meeting physical activity goals only slightly more than ½ the treatment weeks in which the goal was established, with considerable variability (range 0–11 weeks met goal; 3 weeks was the 25th
percentile and 7 weeks was the 7th
percentile) in goal attainment. Individual children’s change in physical activity, defined in this study as the change from the 1 week period of accelerometry measured before treatment and at post-treatment, was only very weakly associated with their pre- to post-treatment change in visceral fat. Objective assessment of physical activity throughout intervention would likely better determine whether physical activity was the primary mechanism of visceral fat change.
The pattern by condition for the parents’ physical activity was similar to that of their children. The overall discrepancy in physical activity at post-treatment between parents in the ADDED versus STANDARD conditions was similar to the condition differences for the children. There were no MRI data among parents to test whether condition differences existed in parents’ visceral versus subcutaneous abdominal fat.
Children and parents had the expected decreases in caloric and specifically dietary fat intake, based on the prescribed intervention eating plan. Given the eating plan did not differ by condition, the lack of differences in all child and most parent dietary intake outcomes between conditions was expected. The difference between the parents in the ADDED versus STANDARD conditions in protein intake at post-treatment was unexpected and may be related to possible insufficient number of days that parents recorded dietary intake.
As found in the present study, waist circumference may not be a sufficient proxy for visceral fat or change in visceral fat, at least among already overweight children (53
). The use of MRI herein allowed for distinct estimates of change in subcutaneous abdominal and visceral fat and demonstrated where changes in the abdominal fat depot occurred. The present study is among the first to directly measure change in different abdominal fat depots in children provided comprehensive weight management treatment (56
). Simple waist circumference measures appeared somewhat sensitive to differential change in total abdominal fat in the ADDED versus STANDARD conditions, but this may be due to the sensitivity of this measure to the larger subcutaneous fat depot (18
). Waist circumference measurement does not allow for estimating the potential differential effect on visceral versus subcutaneous abdominal fat. There may also be gender-based differences in the utility of waist circumference to estimate visceral fat (57
). More evidence is needed to determine how weight management in general and different approaches to weight management among overweight children impacts abdominal fat and the methods needed to evaluate such changes.
There were many strengths of this pilot study, including the high quality measurement of whole body and abdominal fat among children, the more objective measure of physical activity through accelerometry, and the high treatment session attendance. The clinical significance of the observed child abdominal fat changes is not totally clear. In adults, there is evidence that distribution of visceral versus subcutaneous abdominal fat depots may confer specific health risks (i.e., cardiovascular disease risk versus insulin sensitivity) (58
). Such evidence in children is more limited and equivocal (13
). Limitations to this trial included the small sample size (observed power of only .52 for p<.10), the relatively short length of treatment with no assessments of physical activity throughout treatment or any outcomes beyond post-treatment, and the predominantly White middle-class sample (although representative of the geographic areas in which the trial took place). In addition, using accelerometers and common child-based thresholds for activity intensity, the average child before treatment was already meeting the 90 min/day physical activity goal of the trial. The threshold used may be capturing some light intensity, rather than moderate-to-vigorous intensity physical activity. Applying significantly more stringent thresholds for activity intensity (62
) yielded much smaller absolute minutes of physical activity (e.g., 19.6 minutes/day at pre-treatment across conditions (SD=13.0)), although the direction and magnitude of condition differences at post-treatment were similar. The small sample size precludes an adequate evaluation of factors that might interact with treatment to impact abdominal fat outcomes. However, given the interest in individual factors (e.g., child age, sex, ethnicity) that impact fat distribution (57
), post-treatment differences for visceral fat by condition are presented separately for boys and girls in . These data should be viewed cautiously given the small sample sizes and large confidence intervals. The dietary assessment used in this study may have been sufficient for group comparisons, but likely included under-reporting (e.g., younger children not being able to recall well and parents not being able to assist if not having observed the child, like at school lunch) and bias (e.g., children and parents knowing it is socially desirable to report less intake at post-treatment) (63
). Future impacts of child or other factors (e.g., parental predispositions for abdominal fat distribution) on visceral fat outcomes should be explored.
Post-treatment visceral fat volume (cm3) estimates separately for girls and boys by condition
Future trials in pediatric overweight treatment should also continue to explore the specific impacts on body fat distribution resulting from different dietary and physical activity change approaches and evaluate these changes more completely throughout treatment (e.g., in the present study, physical activity was not assessed throughout treatment) and their impact on other health indicators (e.g., insulin resistance). Further testing in child overweight treatment could also explore the benefit of matching children with specific health risks with different intervention approaches. This pilot demonstrates it is feasible to increase physical activity more in pediatric weight management treatment and that this increase may have significant health benefits beyond those conferred by whole body weight or fat changes alone resulting from dietary intervention. Data from the present study will also help to estimate the sample size needed to conduct a larger randomized clinical trial to further elucidate the specific effects of physical activity within the context of pediatric weight management.
In summary, this study provides some preliminary evidence of an incremental benefit of interventions that target increased physical activity and dietary change on reducing abdominal fat, particularly visceral fat, among overweight children in a family-based weight management treatment. It is noteworthy that condition-based visceral fat differences were observed in the absence of whole body composition (e.g., BMI) or fat measure differences between conditions. Increasing physical activity is commonly a target in obesity-related interventions, but it is important to document its potential specific effects, perhaps particularly when dietary intervention is challenging.