Abstract: Despite evidence to the contrary, exercise interventions for obese youth target weight loss as a means for improving health. Using Exercise is Medicine(R) as a framework, we present a conceptual model for the beneficial effects of exercise independent of weight loss in obese youth and highlight novel biomarkers of cardiometabolic health that could prove useful as interventional targets for this population. Exercise, independent of weight loss, can improve traditional risk factors and novel biomarkers of cardiometabolic health in obese youth.
Alex’s Notes: The conventional method for weight loss promoted by the mainstream and many well-meaning practitioners is a simplistic behavioral model focused on reducing caloric intake and increasing caloric expenditure. There is no arguing that creating a negative energy balance is needed for weight loss, because it is, at least if we are talking about body tissue loss and not water weight. However, this calorie in, calorie out concept places an undo responsibility on exercise to increase energy expenditure. Exercise has many benefits that are too often overlooked in favor of weight loss.
Exercise is in fact horrible at aiding weight loss. The caloric expenditure is minimal compared to the time and intensity needed to produce meaningful outcomes. Rather, exercise is a great tool for body recomposition. It may not itself create the weight loss (that is the responsibility of the diet), but it can indeed influence the type of weight loss, with a focus on fat mass and preservation of lean body mass.
As outlined in the review at hand, exercise has also been shown to improve insulin sensitivity, beta-cell function, glucose tolerance, dyslipidemia, lipoprotein particle size, and vascular function. For instance, a recent study found that 20-40 minutes per day of “fun” activities that promoted “intermittent vigorous movement” such as running games, jump rope, and modified basketball and soccer improved insulin sensitivity and beta-cell function after 13 weeks. A single bout of aerobic exercise (45 minutes @ 75% peak heart rate) significantly reduced postprandial glucose concentrations at the 60, 90, and 120 minute marks by 8-14%.
Perhaps more amazing is that exercise without weight loss has been shown to increase LDL-c particle size, while reducing serum triglycerides, total cholesterol, and LDL-c concentrations. This was accomplished with a mere 60 minutes of structured and unstructured physical activity 3 days per week. This has been demonstrated in adults as well, with more intense exercise having more favorable outcomes. Additionally, it has been shown that following a progressive 8 week cycling program with workouts lasting 30-50 minutes 4 days/week improves endothelial function in obese children by 23%. Circuit training 3 days per week (cycling + resistance training) was shown to increase endothelial function in obese youth to a level similar to their lean peers. Neither of these studies resulted in weight loss, although the circuit training did improve the obese kids’ body composition.
What’s your point?
Simply, exercise is not a weight loss aid, it is a health aid. The constant promotion of exercise for weight loss has led (in my opinion) to a highly skewed notion about the amount of activity required to lose weight and prevent the consequences of a poor diet. In fact, I would likely go as far to say that the gross overestimate of calories burn through exercise is a main culprit in today’s obesity problem.
Basically, this myth has led to two things:
- We set up expectations for people (and especially children) who after failing to lose weight with exercise abandon it altogether because it didn’t work for them.
- We create a counterproductive scenario in which adhering to a crappy diet is rationalized by the thought that any extra calories can be burned off with more exercise.
The benefits of exercise extend far beyond changes in weight, and for any and all persons who advise on this topic that just happen to be reading this, we must make an effort to continue to tout exercise as a health aid and challenge the commonly held assumption about its role in weight loss.