Wednesday, February 16, 2011

Think the gym's gonna make you slim? Think again.

Not sure why we're still funding exercise for weight loss studies as two recent comprehensive reviews of the medical literature have concluded that weight loss by means of exclusively exercise interventions run in the order of a 1-3% loss in response to >180 mins/wk of exercise and no loss at all if less than 150 mins/wk, but yet here's another one to discuss.

What's a bit different about this study is that it was long - 18 months and hence perhaps will yield a different outcome.

So what'd the study involve?

Dr. John Jakicic and colleagues recruited and followed 248 initially sedentary, overweight adults between 2003 and 2006 to examine the impact of exercise on their weights. Recruits' ages ranged between 18-55 and their BMIs between 25-29.9. To help ensure completion of this long study, subjects were paid $50 at each of their biannual assessments, but remuneration wasn't dependent on exercise, just following up.

The study set out to examine the effect of 3 different prescribed doses of moderate to vigorous exercise on body weight - self-help with no prescribed duration, 150 mins a week, or 300 minutes a week. Secondary outcomes included body composition, fitness and minutes of activity.

Methodology wise, let me tell you, for folks in the 150 and 300 minutes/week groups, this was the Cadillac of exercise interventions.

Those prescribed 150 minutes per week participated in a behavioural intervention to promote progression to and maintenance of those 150min/week of structured physical activity. Subjects were encouraged to spread their activity out over at least 5 days per week, in bouts of at least 10 minutes duration, with intensity being moderate to vigorous. During months 1-6 subjects attended weekly behavioural intervention sessions to encourage exercise, and during months 7-18 they attended two monthly group intervention sessions and received two monthly telephone calls such that weekly contact was sustained for the full 18 months of the study. Subjects also received "healthy eating" guidance, but were not prescribed calorie reduced diets, along with monthly newsletters pertaining to the study. They were also encouraged and invited to exercise-on-site with their intervention staff following their meetings as well as on weekends during the first 3 months.

Those prescribed 300 minutes per week enjoyed all of the same interventions as the 150 minutes per week group, they were just aimed higher.

The control or so-called, "self help" group only attended assessment visits biannually with no additional intervention or personal contact. They did however receive a physical activity self-help manual along with the same monthly newsletter as the activity groups.

The results?

Don't worry about holding on to your hats.

There was a very significant group x time interaction effect whereby there was a dramatic increase in activity from baseline. 18 months later the previously sedentary self-help folks were averaging 74.6 mins weekly, the 150 minute folks 66.1 mins weekly and the 300 minutes group 154.8 minutes weekly. The fact that there was no statistically significant difference in activity between the 150 minute intervention and self-help, this despite tremendous resources thrown at the 150 minute group, suggests to me that if you're going to encourage physical activity through a behavioural intervention you should go big or go home.

Intake wise, there was no between group differences and an overall self-reported decrease in intake averaging 201 daily calories.

Weight wise, there was no between group differences with percent weight change at 18 months in the 300 minute group being -1.2%, the 150 minute -0.9% and the self-help -0.7%.

The authors then subdivided folks into people who lost more than 3% of their weight, stayed within 3% of their weight and gained more than 3% of their weight and did some further analysis.

What'd they find?

Overall, despite an 18 month significant increase in exercise 72.6% of subjects either stayed the same or gained weight while only 27.4% lost more than 3% of their initial weight.

Looking at the losers specifically the authors did find a dose-dependent association with exercise however as the authors themselves noted,
"despite these findings, concluding that physical activity alone can result in the magnitude of weight loss observed in the weight loss within the retrospective secondary analysis may be misleading."

Because the losers ate better as measured by their more significant changes in their completed Eating Behaviour Inventories.

Worth spending a moment on too was the finding that a full 20% of participants gained more than 3% of their presenting weight over the course of this very rigorous exercise intervention. Sadly too, their weight gain was also associated with an increase in their abdominal adiposity - the bad apple place to put weight.

The good news?

A very minimal intervention ($150, newsletters and a self-help manual) led the initially sedentary self-help group to markedly increase their daily amount of exercise and also markedly improve their fitness as measured by the increase in time it took for those same individuals to achieve 85% of their age-predicted maximal heart rate - an improvement that almost certainly has health benefits.

Bottom line?

We have to stop linking exercise with weight loss. Exercise should be promoted for its phenomenal health benefits, not for its role in weight management.

Weight's about food, not fitness, whereas health's about both.

Jakicic, J., Otto, A., Lang, W., Semler, L., Winters, C., Polzien, K., & Mohr, K. (2010). The Effect of Physical Activity on 18-Month Weight Change in Overweight Adults Obesity, 19 (1), 100-109 DOI: 10.1038/oby.2010.122