In a recent study published in International Journal Of Obesity, researchers investigated how baseline weight status influences the relationship between physical activity, sedentary behavior, and diet quality with Fat Mass Index (FMI) changes over time in children transitioning from childhood to adolescence.
Study: Association of physical activity, sedentary behavior, diet quality with adiposity: a longitudinal analysis in children categorized by baseline weight status. Image Credit: Dimmo/Shutterstock.com
Background
Since the 1980s, the prevalence of childhood obesity has surged. Despite many public health campaigns advocating for healthier eating habits and increased physical activity, the effectiveness of these initiatives has been modest.
In the United States (U.S.), around 19.3% of children are obese, with an additional 16.1% overweight. While controlled trials show that both diet and physical activity affect children’s adiposity, and longitudinal studies suggest physical activity reduces weight gain, interventions have largely been generic.
Further research is necessary to refine our understanding of how weight status influences the impact of physical activity, diet, and sedentary behavior on adiposity, enabling the creation of tailored interventions that address the gradation of childhood obesity as it evolves from childhood into adolescence.
About the study
The Transitions and Activity Changes in Kids (TRACK) study, initiated in South Carolina, observed the physical activity patterns of children as they progressed from fifth grade in elementary school to middle school.
Sourced from 21 elementary schools, the cohort comprised fifth graders closely followed through their sixth and seventh-grade years to identify and analyze the patterns of change in their physical activity. Consent and assent were appropriately secured upon recruitment following the University of South Carolina’s Institutional Review Board approval.
A skilled team took measurements precisely, and children were given accelerometers for movement tracking and completing surveys. Consistent data collection methods were used to measure height and weight, allowing for accurate BMI calculations for each child at the same time annually.
Of the 1,083 fifth-grade students who initially entered the TRACK study, representing a diverse range of racial backgrounds, the sample size ultimately narrowed to 658 children after accounting for exclusions due to missing data.
Adiposity was measured using the FMI, with bioelectrical impedance analysis as the estimation method. Accelerometer data informed on activity levels, discounting periods when the devices were not worn. A validated food screener appraised diet, contributing to a diet quality score based on the Healthy Eating Index (HEI).
Statistical analysis segmented the children into normal, overweight, and obese groups using BMI percentiles, comparing these groups across various demographics.
The study’s comprehensive methodology encompassed repeated measures ANOVAs and growth curve analyses to explore the dynamic between physical activity, sedentary behavior, dietary habits, and fat accumulation through different weight categories over time.
Study results
In the present comprehensive study involving 658 children, the participants were categorized into three groups based on their BMI percentiles at the fifth grade: 53% were considered normal weight, 18% were overweight, and 29% were obese.
The demographic composition was diverse, with 33% black, 9% Hispanic, 18% of other or mixed races, and 40% white children. The sample included a nearly balanced gender distribution, with 45% boys and a considerable % of the children’s parents—37%—achieving a college or advanced degree.
The study found no substantial differences among the weight groups regarding racial or ethnic makeup, age, gender proportion, or parental education level.
Children in the normal weight group were distinctively shorter and lighter with a lower BMI and less advanced in their growth development compared to their peers in the fifth grade.
When revisited over the following two years, of the children whose data was consistently tracked, 403 had complete records. 79% remained within their original weight category throughout the study period.
The study measured and compared diet quality, physical activity, sedentary time, weight, height, and Fat Mass Index (FMI) across different weight statuses and school grades. It found clear disparities, such as children with normal weight engaged in more moderate-to-vigorous physical activity (MVPA) and had lower FMI and height than their peers.
Those in the obese category showed higher sedentary behavior and FMI. Additionally, there was a general decline in MVPA and diet quality from fifth to seventh grade. The data also showed a pronounced weight gain in obese children over the years compared to their normal-weight counterparts.
The growth curve analyses provided a deeper insight into the relationships between physical activity, sedentary behavior, diet quality, and adiposity as measured by FMI within each weight category from the fifth to seventh grade.
A consistent negative correlation was evident between MVPA and FMI among all weight groups. Interestingly, higher levels of MVPA were associated with lower FMI over time, especially for those in the normal weight and obesity categories at the outset.
Moreover, for those initially obese, a positive relationship was found between sedentary behavior and FMI, but this association diminished over time. Diet quality, however, showed that higher scores in the seventh grade were linked to healthier FMI levels.
Analyzing the data, the multivariate models accounting for the variance in FMI between children from the fifth through the seventh grade were quite telling. They explained 29.0%, 54.7%, and 35.8% of the variance for children with normal weight, overweight, and obesity, respectively.
These findings underscore the complex interaction of physical activity, sedentary lifestyle, and diet quality on children’s adiposity and highlight the importance of considering these factors in interventions to maintain a healthy weight status in childhood.
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