CHILDHOOD OBESITY CONTINUES TO RISE
Globally, the prevalence of obesity continues to rise, including among children.1 It is well understood that obese children are at increased risk of premature onset of non-communicable diseases (NCDs), particularly cardiometabolic diseases.2
The global rise in childhood obesity prevalence has been linked to modifiable lifestyle factors.3 However, there are polarized opinions. According to one opinion piece,4 the evidence suggests that obesity prevention should target nutrition and not exercise. A recent meta-analysis5 aimed to address some of these polarizing opinions, by determining whether exercise intervention is effective for weight loss in overweight-obese children, and additionally determined whether exercise intervention improves cardiometabolic risk factors. This article: i) reports the outcomes of the meta-analysis; ii) discusses the appropriate amount and form of exercise prescription for overweight-obese children; and iii) addresses appropriate outcomes for monitoring success of exercise interventions.
META-ANALYSIS FINDINGS
The meta-analysis identified 15 trials which lasted between 6 and 36 weeks and included a total of 556 participants (176 male; 193 female; 187 unknown). The analysis revealed that exercise intervention decreases body mass index (BMI) by a mean of 2.0 kg/m2, body weight (mean: 3.7 kg), body fat percentage (absolute 3.1 percent), waist circumference (3.0 cm) and increases lean body mass (mean: 1.6 kg).
The meta-analysis also reported that exercise intervention improves a number of cardiometabolic risk factors, including a mean 7.1 mmHg decrease in systolic blood pressure (SBP), and moderate-to-large improvements in the capacity to regulate glucose and insulin during an oral glucose tolerance test (39 percent and 44 percent improvement, respectively). The effects of exercise on total cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, fasting insulin and fasting blood glucose were inconclusive.
It should be noted that the 7.1 mmHg decrease in SBP is greater than the expected 6.7 mmHg decrease expected when an adult with a blood pressure of 130 mmHg is prescribed one blood-pressure lowering drug.6
APPROPRIATE AMOUNT AND FORM OF EXERCISE PRESCRIPTION
The World Health Organization recommends 6- to 17-year-old children engage in at least 60 minutes of moderate-to-vigorous intensity physical activity (MVPA) every day. However, due to physical and cardiovascular constraints, obese children may experience discomfort and pain when engaging in conventional MVPA. Alternatively, resistance training has been shown to be well-tolerated by this population and recent research suggests that high-repetition resistance training, combined with low-intensity aerobic exercise and behavioural modification, is the most effective exercise paradigm for improving body composition.7 Further, a recent study in adults reported that obese individuals with high strength fitness exhibit cardiometabolic risk profiles similar to normal-weight, fit individuals.8 Additional investigations are required to further confirm these exploratory findings in obese children and to determine how exercise prescription can best cater to these children.
APPROPRIATE OUTCOMES FOR MONITORING SUCCESS
Typically, one of the main outcomes of weight loss studies is BMI. The calculation of BMI assumes that the ratio between height and weight provides an index of body fatness.9 However, it should be recognized that BMI is imperfectly associated with body composition. Findings from the meta-analysis indicate that overweight-obese children lose body fat while gaining fat free tissue, which would not be reflected by changes in body weight, and may lead to false conclusions about the effectiveness of an intervention.
Besides recognizing the limitations of BMI, we should not lose site of the purpose of weight loss - decreasing the risk of NCDs, particularly cardiometabolic diseases.10 The meta-analysis indicates that cardiometabolic risk factors can be directly monitored, including SBP. Blood pressures are easily obtainable and are valid and reliable under standardized conditions. Simple options are also available for monitoring glucose regulation.
CONCLUSION
The current evidence suggests that exercise intervention in overweight-obese children improves body composition, particularly by lowering body fat. The limited available evidence further indicates that exercise intervention improves some cardiometabolic risk factors. Those conducting exercise interventions in overweight-obese children should consider the addition of resistance exercise, particularly early on, and should also consider including direct cardiometabolic outcome measures, such as systolic blood pressure and indices of glucose regulation.
Lee Stoner, PhD, MPH, FACSM, ACSM-CEP, ACSM-EIM, is a professor in exercise physiology at the University of North Carolina, Chapel Hill. He is interested in "tuning your ticker," particularly when it comes to children and young adults. More specifically, he is interested in the following inter-related lines of enquiry: i) Interactions between lifestyle risk factors and cardiometabolic disease etiology; ii) development and interpretation of noninvasive methodologies for assessing cardiometabolic health; iii) the translation of basic and applied science into public health outcomes.
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