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

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  1. Yoni,

    The weight change observed in WT-LOSS group was a result of higher PA combined with adoption of eating behaviors to facilitate weight loss.

    The main results of the study is that the best strategy for weight loss is diet + Physical activity. That has been confirmed by many other studies including the Position Statement of Kino-Quebec.

    So please stop to say that PA is no use for weigth loss. You are pursuing your self into the attitude of bad faith.

  2. Main result: those who lose weight (-7%) are those who also exercise more (75 min over those who did not lose weight). Conclusion: higher PA to facilitate weight loss at the condition that is combined with the adoption of eating behaviors.

  3. Paul, bad faith is reading my blog for years, including this post, and concluding that my message, "exercise is not sufficient in and of itself for weight management", somehow strays from what you're stating.

  4. Paul, if I'm reading this right, this study showed that 3 of 4 people who exercised either 3 or 6 hours a week at a "moderate to vigorous" intensity either "stayed the same or gained weight."

    After a year and a half?

    I'm sorry, but I'm not sure how you don't read this as this kind of PA being nearly useless as far as weight *loss* goes.

    Me, I'm disappointed that the two non-control arms of the study were both chronic cardio-based. I would have loved to see a group whose exercise included very little cardio, and instead had participants doing short workouts that alternated high intensity interval training with resistance training. I suspect they might well have seen more encouraging results wrt weight loss.

  5. Alrighty, my bad, I skimmed over the part where it turns out the participants didn't actually average the 3 or 6 hours prescribed (as measured at the end of the study). The 3 hr group averaged an hour; the 6 hr group averaged 3. But the difference in weight loss between the three groups was nonetheless negligible.

    Me, I still think the answer is elsewhere. Having to do an hour of chronic cardio a day to see results is not a sustainable solution IMO.

  6. Beth, Weight management is clearly physical activity dose dependent. (fig 4, table 3)Weight gain group increases PA only 62 min/week, stable group increases PA 106 min/week and weight loss (-7kg ave) increases PA 191 min/week after 12 months. full access free today

  7. I suppose Paul, that you disagree with the study authors' own admonishment not to ascribe the loss in the secondary analysis to fitness.

    Confirmation bias much?

  8. Anonymous10:02 am

    It is funny, the majority of exercise weight loss studies rely on self reported nutrition logs. From my experience, patients typically under report their eating and over report their physical activity on self recorded journals. So this really limits the conclusions that can be drawn from this study.

    In order to get an accurate measurement of what exercise can do for weight loss you have to observe the exercise happening and you have to have a way of measuring the participants food intake. Otherwise most people increase their food intake when they increase their activity.
    If you do not control all the variables how can you possibly comment on the outcome?

  9. Yoni, I would be curious as to your take on this study:

    I blogged on it here:

    Basically, regardless of dietary intervention, and even increasing intake for the exercisers to account for calories burned during the activity, the exercisers lost more fat mass than the non-exercisers. (Attributed to increased non-exercise activity thermogenesis, NEAT)

    The participants kept daily food logs that were reviewed weekly for compliance. Exercise was supervised.

    Personally having lost the bulk of my perhaps 100 lbs w/o doing any exercise, I can't say it's necessary for weight loss. But being more active deliberately (I don't have an exercise routine ... yet ... just keep very active) has definitely contributed to my long term maintenance. It seems to have warded off the metabolism suppression of long term calorie restriction and going through menopause.

    I think the other study is useful in demonstrating human nature and the importance of a good diet. If one just increases activity but doesn't change their diet, they'll likely eat more to meet increased protein needs and/or consciously or subconsciously rewarding their good exercise behavior. However when combined with deliberate attention to diet, usually leads to intake reduction rather than increase. That's my n=1 anecdotal experience as well.

  10. Hi Carbsane,

    No doubt that exercise can affect body composition independently of weight and that those changes likely have tremendous health benefit.

    The problem is that folks still promote and push exercise as a weight loss tool and given that study after study after study, regardless of the reasons why, suggest that at best we're talking miniscule losses despite tremendous, non-sustainable for most increases in exercise, that promotion is dangerous. It's dangerous because just as the person who was sitting in my office no less than 1 hour ago stated, "I don't exercise because I'm mad at it. I used to exercise like crazy and my weight didn't change".

    We crush people's motivation if we encourage them to take on an activity that we know isn't going to help with their goals.

    Instead I think we need to reframe the role of activity. Beneficial changes in body composition? Absolutely. Increased likelihood of maintaining a weight loss? Absolutely. Umpteen different health benefits? Absolutely. But if we keep myopically clinging to exercise as a direct weight modifier, we're just going to do more harm than good.

    Perhaps exercise's most important role (and this one doesn't have a study that I can point to back it up, just my thinking) - it cultivates an attitude of healthy living and that in turn can help people sustain their dietary changes and lead healthier overall lives.

  11. I can agree with everything you just said. I would also add that I come from the "bias" of the prevailing attitude amongst low carbers that exercise is useless for weight loss and so many who outright shun it. Many of these people are now or were diabetic and insulin resistant and should probably exercise more eating high fat low carb even if it doesn't impact weight so as to keep lipid turnover in cells high.

  12. Forgot to add:

    I would point out that the results of this study were not just change in body composition, they were increased loss of fat mass. That's the type of weight loss we desire. This was with the exercisers even eating more to cover the caloric cost of the 3X 45 min exercise sessions each week. Pretty encouraging to me!

  13. My own non-academic take on exercise and food with respect to weight management is that neither are the main issue. How you feel is the main issue.

    Food acts like a drug to make us feel better. The more depressed you feel the more you eat (especially carbohydrates which can be quickly turned into sugar)and hence you gain weight.

    If you exercise you increase the feel good hormones in your body and therefore don't need to eat more to make you feel better. So to manage your weight manage how you feel and the rest will take care of itself. Telling people to exercise more or eat less are not effective if people don't understand the root cause.

    By the way I think this applies to smokers, alcoholics and other drug abusers, too. We need to stop telling people to quit smoking, control your alcohol and drug intake without helping them with the real issue which is depression.

    When I tell people this they get all upset and say "so you're telling me I'm depressed". And I say, "I'm not a doctor but at some level I think you are". I'm not saying everyone with these challenges is clinically depressed but at some level depression is an issue.

    Have you ever seen a public service campaign about cigarette smoking, obesity or drug use that ever mentions the "D" word? Instead of "just say no" how about "just say depression" Why do we always bypass this issue?

  14. Anonymous7:52 am

    Yoni what's your investment in dissing every kind of weight control but bariatric surgery? That's sure what I get from this blog.

    Exercise causes "weight" loss in that muscle weighs more than fat.

  15. I laughed out loud when I read that last comment.

  16. Anonymous9:06 am

    So will you tell us how much you receive from industry for your research?

  17. I laughed even harder at that!

  18. Anonymous10:14 am

    Right now, readers are wondering why you don't answer.