Tuesday, February 15, 2011

Exercise won't prevent obesity in 8 year olds.

From the, “weight ain’t about exercise” file comes a small study that was reported on during the Obesity Society's 2010 Annual Scientific Assembly.

The presenters reported on the impacts of 6 years worth of energy expenditure data on children’s weights, BMIs, waist circumferences, fat percentiles and total fat masses at the age of 8. Forty-five children were investigated using doubly labeled water to determine total energy expenditures and both bio-impedance analysis and dual energy X-ray absorptiometry were used to explore fat free mass.

The working hypothesis of course was that kids with higher total energy expenditures (more active kids) should have lower BMIs and less fat mass than kids with the lowest energy expenditures.

There are two ways to look at the results. The more negative way to do so would be to harp on the fact that high levels of exercise didn’t associate with lower BMIs as gloomy, and in a move that may seem surprising to some of my readers, I'm not going to do that. Instead I find the results somewhat heartening in that at least as far as absolute weight goes, inactive kids are at no greater risk than active ones. For me that's somewhat heartening given how we can’t seem to figure out ways to make kids more active.

While far from a large study, the fact that there was no association found between energy expenditure and weight or body fat percentage is yet another redundant nail in the coffin of exercise being the answer to the prevention of childhood obesity.

That said, one thing the authors didn’t mention was whether or not there was any differences in the distribution of body fat among the more active kids in that there have been studies that demonstrate that while not having a marked impact on weight, exercise does seem to impact on how fat is distributed which in turn may well have an impact on health and weight related comorbidities.

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  1. I'd be curious to see if there were other biomarkers differences between the groups. E.g. lower C-reactive protein in the group that gets more exercise. Might be too young to be substantial, but for me, exercise is first about health and fitness and second about weight management.

  2. Anonymous6:29 am

    These studies don't surprise me, because my husband always gains weight when he exercises! In the summer, when he's more active, his weight goes up, and in the winter, it goes back down again.

  3. I agree with Bill. Exercise is also about a healthy lifestyle not only weight loss. Weight loss is complex and sometimes based on the individual as to what it needed to succeed. But exercise must be a part of a healthy lifestyle, along with healthy eating habits.

  4. Two things jump out at me:

    1. If the more active kids added more lean muscle from age 2 to age 8, BMI as a measure will obscure this.

    2. They looked at total energy expenditure. It would not surprise me for a larger sedentary kid to have a higher TDEE than a smaller active kid.

    Taken together it comes as no surprise that TDEE & BMI don't correlate well.

  5. Hi Carbsane,

    BMI/lean tissue point is fair, except for the fact that the study didn't show any association with body composition and TEE. Were the study clouded by lean tissue/BMI, I'd expect too to have seen a difference in body composition in the kids who were more active and theoretically expected to have more lean tissue.

  6. Do you have a link to that study?

    I do also wonder what impact activity has during a period of rather rapid growth for a child.

    Americans seem to be getting taller!!

  7. Sadly no link yet. I had hoped by now it would have got published (was waiting on these blog posts forever - more presentation posts coming the next few days), but all that was published was an abstract in the Obesity Society's Scientific Assembly program.

    I personally think activity's absolutely crucial to health, possibly even more so than diet, I just don't think it impacts weight all that much.

  8. This points out the irony of Michelle Obama's "Let's Move" campaign here the states. Watching such NON-evidence-based health campaigns is like watching Murphy's law in slow motion.

  9. bananancat10:23 am

    I do think that Michelle Obama is misguided but well-intentioned. However, it's still a good idea for kids to move more, even though it won't result in weight loss. I don't really like the conflation of movement with weight loss because then we lose sight of the benefits of doing it for its own sake. Weight control is not the only goal of exercise and we should definitely encourage kids and adults to do more of it.

  10. I do agree with Bill too! Exercise is great for the mind and one's health as a whole. Weight loss needs not to be a focus. The more that children get into exercise (fun), the less they will want to be sedentary.
    Young athletes are only further set up for good body maintenance in the future.

  11. Exercise makes one hungry.
    Eating low processed carb diet decreases hunger.
    What or who gave Michelle Obama the doctorate in obesity's causes?

  12. I'm afraid BMI is a poor way to measure the relative health of a young pediatric population. Increasing muscle mass, a good outcome of daily exercise, is hidden when looking at BMI alone