The importance of physical activity & fitness in maintaining a healthy weight from childhood into adulthood

Little is known about whether the physical activity and cardiorespiratory fitness levels of healthy weight children who successfully maintain a healthy weight into adulthood are different to those healthy weight children who become overweight as adults. A better understanding of these factors may provide useful insights for obesity prevention strategies, which have had limited success to date. This is of concern because overweight and obesity is increasing in prevalence in Australia and internationally in both children and adults. This prospective cohort study therefore aimed to examine the role of physical activity and fitness in healthy weight maintenance from childhood into adulthood. Subjects were 2,053 Australian adults examined at age 26-36 years in 2004-5, who were first examined as 7-15 year olds in 1985 as part of a national survey of the health and fitness of Australian children. Body mass index (BMI) was calculated at both time-points from measured weight and height (kg/m²); healthy weight was defined as a BMI less than internationally accepted cutpoints for overweight in children, and as a BMI<25kg/m² in adults. Healthy weight maintainers were healthy weight children who remained healthy weight as adults. Physical activity was estimated from a questionnaire at both time-points and also from pedometers at follow-up. Fitness was estimated from a cycle ergometer test at both time-points (9, 12 and 15 year olds at baseline). Baseline (language spoken at home, parental smoking and parental exercise at baseline) and follow-up (smoking, occupation, education level and marital status) sociodemographic factors, were self-reported. •At follow-up: o 37% of men and 59% of women were healthy weight defined using BMI cutpoints; 71% of men and 69% of women were healthy weight defined using waist circumference cutpoints o Physical activity and cardiorespiratory fitness were positively associated with being a healthy weight o Objective measures (pedometer) of physical activity showed stronger associations with healthy weight than did cardiorespiratory fitness o Healthy weight defined using waist circumference demonstrated stronger associations than BMI with physical activity and fitness in men •Longitudinally: o 35% of healthy weight boys and 65% of healthy weight girls remained healthy weight as adults o Child and adult BMI were well correlated in females (r=0.51) and males (r=0.47); tracking was weaker in the youngest and oldest males o Physical activity showed poor tracking from childhood to adulthood (males: r=0.06, females: r=-0.01 for self-reported activity); fitness tracked more strongly (males: r=0.24; females: f=0.27) o The most active children were no more likely to be healthy weight maintainers than the least active (RR 0.77,95% Cl: 0.57-1.02 in males; RR 0.98, 95% Cl: 0.84-1.13 in females) o The fittest children were no more likely to be healthy weight maintainers than the least fit children (RR 0.93, 95% Cl: 0.67-1.29 in males; RR 0.97, 95% Cl: 0.81-1.15 in females) o There was some evidence that younger participants whose cardiorespiratory fitness increased over time were more likely to maintain a healthy weight than those whose fitness decreased (RR 2.30, 95% Cl: 1.21-4.38 in males; RR 2.66, 95% Cl: 1.46-4.84 in females) o There was also evidence that younger participants whose fitness remained stable over time were more likely to be healthy weight maintainers than those whose fitness decreased (RR 1.77, 95% CI: 0.98-3.20 in males; RR 2.25, 95% Cl: 1.34-3.79 in females) While some limitations were evident in this investigation, in particular measurements at only two points in time, it had many key advantages over previous studies, including its size, duration of follow-up and extensive measures of adiposity, physical activity and cardiorespiratory fitness. Little previous research has investigated factors associated with maintaining a healthy weight, and no published reports have examined this relationship from childhood into adulthood. In doing so, this study has provided insights into the physical activity behaviours and cardiorespiratory fitness levels of healthy weight maintainers. In conclusion, physical activity and cardiorespiratory fitness appeared to play a minor role in the maintenance of a healthy weight from childhood to adulthood. The strongest associations were observed in younger participants. Associations with fitness were stronger than associations with physical activity, suggesting that imprecision in the physical activity measures may have resulted in an underestimation of the effects. The limited contribution of physical activity and fitness to healthy weight maintenance from childhood into adulthood must be considered in the planning of future obesity prevention strategies. There is still much to learn about the behavioural, biological and genetic characteristics of those who manage to maintain a healthy weight in the current obesity-promoting environment.