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Aerobic Exercise Burns Fat All on Its Own (even if you don’t lose weight)

August 29, 2013

Weight LossFat HealthFat ScienceExerciseDiet TalkFat News

Trigger warning: This post is about the belief that exercise is for weight loss.

This article is another of those “No shit, Sherlock” moments:40141

In obese teenage girls, bwoth aerobic exercise and resistance training were effective at reducing total fat — even if the girls didn’t cut calories or lose weight, researchers found.

WTF is so surprising about that? Exercise of most kinds burns fat and builds muscle, so of course total fat is going to be reduced even if weight isn’t (remember, a cubic inch of muscle weighs more than a cubic inch of fat).

Aerobic exercise was also associated with reductions in visceral obesity and liver fat and improvements in insulin sensitivity, SoJung Lee, PhD, of Pittsburgh Children’s Hospital, reported here at the American Diabetes Association meeting.

Didn’t they already see these improvements with exercise in adults? Why would they be so surprised to see those same improvements in kids?

Previous research by Lee and colleagues has shown that increasing physical activity — without caloric restriction — is effective in reducing total fat, visceral obesity, and liver fat in obese adolescent boys. So the team wanted to find out if the same strategy is helpful for teenage girls as well.

The study involved 40 obese adolescent girls with BMIs in the 95th percentile or greater for their age. They were randomized to 3 months of aerobic exercise, with three 60-minute sessions on a treadmill a week; resistance exercise consisting of working out on a weight machine three times a week, for 60 minutes a session; or a sedentary control group.
The teens were allowed to continue to eat as before.

If it works for boys, why wouldn’t it also work for girls? Yes, girls need more body fat than boys, but it’s still possible for girls to exercise and improve their fat to muscle ratio. That’s just common sense, I would think.

Compared with controls, body weight dropped 1.3 kg in the aerobic exercise group and 0.3 kg in the resistance training group (P>0.1).

Despite the absence of weight loss, total fat decreased 1.5% in the aerobic exercise group and 1.4% in the resistance training group compared with controls (P<0.05 for both).

Visceral fat dropped 19% and lipid fat decreased 43% in the aerobic arm compared with the control arm (P<0.05). Also, insulin sensitivity improved 23% in the girls who did aerobics compared with the sedentary teens (P<0.05).

There was no significant change in any of these parameters in the resistance training group.

So the girls who exercised on the treadmill lost a whopping three pounds in three months, and the girls who exercised on the weight machines lost a whole two-thirds of a pound in three months. Resistance training didn’t work, but aerobic exercise did, to lessen the amount of visceral fat and lipid fat, and to improve insulin sensitivity. So it seems this is saying that if you want to improve those health parameters for your kids, make sure they do at least an hour of walking (or similar aerobic exercise) three times a week. And it made modest improvements in insulin sensitivity as well, which is ultimately the goal of improving metabolic health.

Patricia Gatcomb, MSN, a nurse practitioner at Yale University, said she was surprised at the lack of weight loss given the increase in the exercise arms.
To achieve clinically meaningful improvements in fat or insulin sensitivity levels, the intervention needed to be longer, she added.

Why was she surprised at the lack of weight loss with an increase in exercise? Haven’t there been enough studies done with adults to show that exercise doesn’t really work for weight loss? Why would it be any different in kids? And of course, three months’ worth of exercise will create some improvements, but to achieve the kind of improvement that researchers consider “clinically significant,” this kind of regimen would need to go on for at least a year – and it would be great if kids could find aerobic exercise they enjoy and will continue for the rest of their lives. That would create and sustain those metabolic improvements that researchers and physicians like to see.


2 Comments leave one →
  1. Duckie permalink
    August 29, 2013 11:25 pm

    “Move the goal post and declare victory.” Maybe this strategy is what they’re doing now that they can see that Mrs. Obama’s “Let’s Move” campaign isn’t causing children to shrink as predicted.

  2. Nof permalink
    August 30, 2013 10:40 am

    In promoting exercise, the emphasis cannot be on weight loss (and I would argue it should not be on health either). The emphasis should be that these things are fun, and if they’re not fun for you then there are other activities you can try which are also fun.

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