Tuesday, July 19, 2011

Are large amounts of exercise essential for weight loss maintenance?


Let me start things off by telling you that I do believe exercise to be extremely helpful in long term weight management. I'll also tell you that I'm a huge fan of the National Weight Control Registry. For those of you who aren't familiar with the Registry, Registrants are folks who are supremely good at maintaining their weight-losses. In fact, the average Registrant has lost 67lbs and kept it off for 5.5 years!

There's a great deal of variety in the Registry. Different types of dietary approaches and different strategies as a whole, but there are some commonalities, and exercise is one.

Studies on Registrants have their self-reported exercise as being quite high - an average of 58.6 minutes a day!

What we didn't have was an objective measurement of same, and sadly, despite a new study with Registrants and accelerometry, I'd argue we still don't, though it seems it wasn't the researchers fault.

26 Registrants were recruited to wear accelerometers for a full week and were matched with a never obese group, and an overweight, not Registrant control group.

The results were pretty interesting. Measured exercise actually turned out to be significantly less than self reported at 41.5 minutes a day (rather than nearly an hour), but was still of greater duration in Registrants than overweight non-Registrant controls and marginally more than never obese weight-matched controls.

But are the results useful? Do they really answer the question as to the importance of exercise in successful weight maintenance?

I'm not so sure. The problem I've got with the study's methodology is that Registrants were recruited with a description of the study's aim. Meaning that prior to enrolling they knew they were enrolling themselves in a study that involved objectively measuring their activity levels.

To me that's a big deal. It's a big deal because I would imagine that human nature would dictate that the folks who respond to just such a study are the ones who are the most proud of their activity levels (or the least embarrassed depending on how you want to look at it).

I suspect too that this was a limitation the authors were aware of as beside the disclosure in the methodology section is the parenthetic explanation, "(as required by our institutional review board)".

Another frustration from the study was the fact that individual data points weren't provided. Given the small number of subjects, I would have loved to see the distribution of minutes of exercise - especially given that in their discussion they mention that 2/3 of subjects engaged in >150 minutes weekly, and 1/3 of subjects >300. Did exercise reflect a normal distribution? Was it bimodal? Were there dramatic outliers?

Bottom line for me, I'd have loved to see this study performed with a random sample of Registrants, not a sample who may have self-selected for being more active. That's not to say the findings wouldn't necessarily be the same, but given this study's methodology, I wouldn't be hanging my hat on these results.

[Also fascinating (though not surprising) was the result that objectively measured exercise was significantly less than self-reported. Furthermore, if my assertion that folks who were better exercisers were more likely to have agreed to enroll, that result casts major doubt on the National Weight Control's finding of massive amounts of exercise being integral to maintenance.]

Catenacci VA, Grunwald GK, Ingebrigtsen JP, Jakicic JM, McDermott MD, Phelan S, Wing RR, Hill JO, & Wyatt HR (2011). Physical activity patterns using accelerometry in the national weight control registry. Obesity (Silver Spring, Md.), 19 (6), 1163-70 PMID: 21030947

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9 comments:

  1. Alexie7:48 am

    I'm maintaining a weight loss of 30% of my body weight and am just past my one year anniversary. I do a lot of the things recommended - I track all my food in Sparkpeople and try not to underreport! I eat food prepared from scratch, with no processed ingredients, I stick to regular meal times, and I also weigh myself at the same time each morning. And I eat roughly the amount of calories that's right for my age and height. The thing I don't do is any formal exercise, though I normally manage to get in at least 10,000 steps a day, as measured by my pedometer. Lately, though, because of health problems, I have dropped much of the walking and only manage about 5,000 steps a day. My weight hasn't changed as a result of the lower rate of exercise. I should add that I eat the number of daily calories recommended for someone of my age and height who is relatively sedentary. If I do several days in a row of lots of walking (recently I did four days of 25,000 steps a day), then I notice I do lose some weight.

    So for me, anyway, it really does come down to calories in and out.

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  2. I haven't read the study itself yet, but I just wanted to point out that it's almost guaranteed that objective measures of physical activity are going to be lower than self-report measures.

    Consider a 60 minute game of hockey - most people would list that as 60 minutes of MVPA on a self-report form, even though they may only actually be moving for 30-40 minutes during that hour. It's just something that you have to expect when moving from self-report to direct measures of activity, rather than being a specific fly in the ointment of the registry itself.

    One other note on the study - it would be really nice to have a study of randomly selected registry participants... but I don't think it will ever happen. You could randomly select them, but many would be uninterested and self-select themselves out of the study anyway, and you'd be in the same boat as now. Similarly, I don't see how it would be possible to recruit a large number of participants for a study like this (which has no real benefit for the participants, and is therefore a tough sell to begin with) without telling them at least some of the details of the study in the recruitment letter. And even if you managed to get people into a recruitment meeting without telling them about the study, you'd still need to give them the details during the consent process, at which point people would still self-select out... I guess what I'm getting at is that in practice there really isn't a way around this problem of selection bias so long as we believe in informed consent.

    It's just a nature of this kind of study that you will always have a ton of limitations, and the only way around them is to have a ton of studies coming at it from different angles, with systematic reviews trying to tease out the "truth".

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  3. Anonymous10:23 am

    That's interesting. I suspect the questions that trigger the self-reported activity levels lead to a fair amount of inaccuracy, although I don't know how better to capture accurate figures other than constantly re-surveying. For example, I'm a Registrant, and when I filled out the big packet of initial surveys, I was training to walk a marathon. So at that time, I was going on five hour walks on the weekend, and as I recall (after some deliberation) included that in the "how many minutes of exercise do you get per week" question. Now that I've completed the marathon, that number is significantly lower for me.

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  4. As Travis said - you could randomly select people, and even when people select out, you could do analyses to see if those who remain are different on baseline characteristics than those who leave.

    I'd be interested to know the distribution also - since it's an average, I can imagine it being sensitive to outliers.

    It's definitely an interesting study, but with so many confounders and covariates unmeasured, the external generalizability is limited.

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  5. I don't have time to read it now, but hope to in the future.

    I'm a fair weather friend of the NWCR . . . and a registrant, in my eight year of maintaining at negative 27%; in my sixth year with the NWCR. I haven't been chosen for a special study, but I do the annual report (some years short form other years long). Their surveys leave a lot to be desired. AND, they are SURVEYS, which aren't the best research methodology. I would adore them asking me to submit a vial of blood for an endocrine analysis. Not gonna happen.

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  6. We need to stop pretending. All NWCR people must get a DEXA scan done to measure their TRUE level of adiposity. The BMI and the scale are worthless.

    All bariatric sugery people, all NWCR who claim being lean and maintaining . The DEXA scan does not lie. It will tell you extactly how much body FAT you are carrying.

    THAT is the measure of success.

    Plenty of people I see have terrible physiques or noraml weight obesity- neither of these are success.


    Face it, doctors CANNOT treat obesity effectively because they do not understand it well.It's a waste of the patient's time.

    We need to move past a failed dogma.

    Obesity is fat cell disregulation via their receptors. MANY things can disregulate fat cells. We hardly understand fat cell regulation , and we know virtually nothing about the chemical regulation of fat cell receptors.


    It's time to let obese people recover from their DISEASE, and stop the worthless treatments and dogma.

    The medical estbalishment has FAILED them. They are suffering and want answers. And EFFECTIVE answers and advice.

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  7. I am a fan of the NWCR because I think some of their findings can be quite inspiring to people who are attempting to manage their weight. For example (and it's probably linked to the amount of exercise question) that 62% of NWCR registrants watch less than 10 hours of TV per week. Emulating the habits of people who are already successfully controlling their weight is intrinsically motivating.

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  8. I'm a member of the NWCR and I agree that the yearly surveys have a lot to be desired. When I fill them out, I'm fully aware that the survey structure in no way captures the true, ongoing struggle of maintaining a large weight loss.

    As for exercise, I walked briskly for an hour this morning then did a hard free weight workout for 30 minutes (both timed). I have a 45-minute yoga workout planned at lunch. That is my typical weekday pattern. I sit at a computer all day for work, so I also try to get up every hour and move. Sitting kills!

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  9. Francine Bigney10:13 pm

    I too am a member of the NWCR. I have lost about 50 lbs (all totaled) thru high school, college and thereafter and have kept it off for over 38 years. I am one of 6 daughters and the only "fat" one in the bunch. I got the "thrifty scottish gene" according to my mother, who was wise beyond her years. Consequently, I am driven to help others. I am a veteran certified personal trainer, group exercise instructor and certified lifestyle and weight management coach. I teach 3 classes a week in addition to my one-on-one training, my personal weight lifting, as well as train for 1/2 marathons and shorter races. I know of what I speak and this I can say: although we are all very different, making the connection between the choices in what we eat and what we do and *how* we are are at the crux of the matter. I learned long ago that I have to be more active than most of my peers and acquaintances and, for the most part, very disciplined in what I eat. Many people are completely disconnected to the cause and effect relationship of their nutrition and activity and the effect on their bodies. Folks like Carrie Dennett and I are not. We have had to become painfully (at times) aware of the consequences and are members of the NWCR so that we can help others help others.

    Yoni, Travis, there is the nature of the Hawthorne effect at work in all the subjective information gathering, in that if we, (meaning all people) know that we are being monitored, we will change our behavior.

    Roswell, although I feel your plea viscerally, and yes we do have much to learn about fat as an endocrine system, as well as metabolism. I can't agree with you. I am living proof that you can alter your destiny via epigenetics. I think that if you are genetically inclined to be a fat hoarder (without getting into the physiology that we understand thus far), you have to accept your fate (in my case) and be willing to consistently do the work in all realms of your life. On the other hand if you are overweight because of your lifestyle, then you must accept the causal relationship and put the time and effort into learning what works for you with regard to nutrition and physical activity.

    Besides living my own life, taking charge and maintaining my weight and body fat, I have helped many others lose lots of weight and body fat, building muscle and self esteem in the process.

    I you are still reading this, get up now. Move. Carrie's right, "Sitting kills!" Get NEAT (look up Dr. James Levine).

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