Para #17 Objective measurements obtained at least twice during a four year period in 500 healthy children between the ages of 8 and 12 yr showed that boys and girls of higher percent body fat were less physically active, but did not consume more energy, fat, carbohydrates, or sugar than their leaner counterparts. These cross-sectional findings were supported by the one longitudinal relationship of significance which indicated that if a child became more active during the four years he or she became leaner; alternatively, a child who became less active increased his or her percent body fat.
As a practical illustration of the cross-section relationships we can compare two 12 year-old boys of average weight, percent body fat, and physical activity. Should one boy be more active than the other, with a physical activity index (the square root of steps/day) of 110 compared with 100, or 2100 more steps per day, then (from the β value in ) his percent body fat will be, on average, 0.5 lower (95% confidence interval 0.2–0.7). Using equivalent calculations with the accelerometer data also in , a boy whose (square root of) moderate and vigorous physical activity is 1 unit or 15 minutes per day higher than another boy will have a 0.86 lower percent body fat (95% confidence interval 0.4–1.3). We can illustrate the longitudinal relationship between percent body fat and physical activity similarly. If a child’s physical activity increased 10% during the study then on average their percent body fat decreased by 0.23 units (95% CI −0.45 to 0.007). As mentioned above, this was not a strong relationship but provided valuable support for the strong cross-section findings.
Our negative relationships between percent body fat and physical activity are consistent with several previous reports where body fatness has been measured or estimated, rather than body weight or body mass index 
. A recent review of the literature 
, which included a cross-sectional study of a large cohort of 12 year-old children with DXA measures of percent body fat 
, also concluded that vigorous physical activity, and to a lesser extent moderate physical activity, were negatively related to adiposity. The lower daily energy intake in fatter children may at first seem counterintuitive, but the logical inference is that in terms of energy equivalents, the generally reduced energy intake of fatter children is insufficient to fully offset their decreased energy output. This scenario is not only consistent with an above-mentioned study 
but there is also some evidence from an international observation that increasing childhood obesity over recent decades has coincided with a reduction in energy and percentage of dietary fat intake 
. It is also consistent with data from an Australian national nutrition survey in 2007 
where the average energy intake of 4 to16 year-old boys and girls classified as ‘normal weight’ was greater than those classified as obese, although it has been pointed out that we cannot be sure that misreporting was not influential in this survey 
. So, while it is clear that a positive energy balance predisposes increased adiposity, and that individual cases of overweight and obesity may eventuate from excess in energy intake and/or insufficient physical activity, our data and those cited above suggest that across the community, it is the child who expends less energy, rather than consuming more energy, who is most likely to become overweight or obese before the age of 12 yr. A detailed account of potential mechanisms is outside the scope of this paper, but several metabolic and psychological pathways by which physical activity has the potential to control energy balance and body composition (e.g. through unfavourable sleep patterns and stress) have been well-reviewed 
Dietary intake of fat and sugar, especially high sugar beverages, have been implicated in the increase in obesity in recent decades 
, a premise supported by two reviews 
. However, our data concerning pre-adolescents in the contemporary setting do not lend support to this premise; nor does a recent study from the USA National Health and Nutrition Examination Surveys involving children between 6 to 18 years of age 
. Furthermore, although it has been reported that the proportion of dietary fat intake relative to total energy intake is associated with adiposity in pre-adolescent children 
, we found no evidence of this in our cohort, consistent with another study of 9 year-olds who were followed for a period of 6 years 
The experimental control to offset misreporting of dietary information and the subsequent analyses of subsets of our cohort were important aspects of our study, as one interpretation of our findings may have been that under-reporting by children with higher adiposity confounded the results. As set out above, our strategies included removing obvious measures and discussion of obesity and strongly reinforcing the importance of dietary records for assessing the children’s health. We also demonstrated that similar relationships to the group as a whole were obtained in subgroups where adiposity-related underreporting would be absent or minimal. All evidence suggested an absence of any influence of any adiposity-related under-reporting, if indeed it existed. There are three further points of support for this conclusion. Firstly, Australian children with lower physical activity levels have been shown to be less likely to underreport their dietary intake 
and in the current study these were the children with higher percent body fat. Secondly, a higher incidence of misreporting occurs in Australian children of lower socioeconomic circumstances 
, but our cohort was of uniformly midrange socioeconomic status. Finally it might be argued that there was insufficient statistical power to detect relationships between percent body fat and dietary intake, but this did not appear to be the case. Not only did our statistical analyses indicate a very clear absence any positive relationships, but relationships did emerge in the boys, and they showed that fatter children consumed less, not more kilojoules.
Strengths of this study included the statistical model and adjustments for potential confounding covariates, the measurement of percent body fat by DXA in a large cohort so avoiding the use of body mass index, an unsatisfactory surrogate of adiposity, especially in growing children 
; the careful dietary assessments carried out by nutritionists experienced in survey methodology and the investigation of potential underreporting; and the objective measurements of physical activity. On the other hand, the pedometer and accelerometer measurements were limited in that they were unable to detect common physical activities such as cycling, swimming or climbing, so may have dampened relationships. Moreover, DXA measurement of body composition are not without problems in terms of validity in children 
, but they are likely to be sufficiently reliable. Finally, our predominantly White cohort with ready access to food and active recreation may not permit generalization of our findings to non-White and less affluent communities.
In summary, community-based preadolescent Australian children with higher percent body fat were less physically active than their leaner counterparts, but there was no evidence that they consumed more total energy, fat or sugar. Our strong cross-sectional data supported by longitudinal effects in the same direction support the premise that reduced physical activity may have a greater impact than excessive dietary intake on the development of childhood adiposity in the general community. Strategies involving dietary intake and physical activity designed to target childhood obesity in similar communities might achieve best outcomes by ensuring that physical activity assumes the foremost focus of attention.