Friday, February 1, 2013

The myth-takes of myth-busters

Maggie Fox of NBC News writes about a group of researchers who published an article in the New England Journal of Medicine exposing seven myths about diet and exercise.  The researchers, Fox says, “don’t want people to stop trying [to lose weight], but they do fear there are some misguided policies out there.”


The first myth the group attacks, one promoted by government agencies, diet books and the web, is that doing a little something every day will add up to pounds lost over the years.  It doesn’t take into account laws of physics and biology, the researchers argue.
It’s the idea that if someone burns even 100 extra calories a day, he or she will lose a pound every 35 days.  This is what the researchers call the 3,500 calorie myth — that burning 3,500 calories burns off a pound for everyone, every time.  Over five years that person should lose 50 pounds, but studies have shown the true weight loss over five years is 10 pounds.
What it doesn’t take into account is that as I lose weight, I get smaller and it takes less energy to push my mass through space,” Allison says.  In other words, the body will compensate.


 Here we have a serious disconnect between the “myth” that (according to Fox) the researchers supposedly busted and the explanation for its presumed falseness.  It’s not the only counterargument that sounds iffy; a couple of other “myth-busting” explanations give you the impression that the researchers were either attacking straw men or just missing the point.

As the “myth” is stated above, a person at weight w performs activity a, which burns 100 calories, once a day every day should lose 1 pound every 35 days, because it takes 3,500 calories of energy to burn 1 pound of adipose tissue.  Allison’s counter-argument is that, when the person drops to 0.8w, activity a only burns (say) 95 calories rather than 100, because “it takes less energy to push … mass through space”.

The counter-argument as stated is correct.  However, this doesn’t change the number of calories needed to burn one pound of adipose; it simply means that you have to do at least 5.26% more a to burn 100 calories at 0.8w than you did at w. This is why, if you’re on a weight-loss regimen where you eat the same number of calories and do the same amount of exercise for several months, your rate of weight decrease will diminish over time — as your body begins to do everything with a smaller energy cost, it will start making less demands on the energy stored in fat.

Put differently, the researchers busted the wrong “myth”.  The real myth here is in the semi-standardized number of calories associated with exercises and activities that diet and exercise resources pass around uncritically.  Losing weight does not increase the number of calories required to burn a pound of fat.  Rather, it lowers the amount of energy needed to perform any given physical task, whether that task be walking up a flight of stairs, running a mile, or having a romp in the bedroom with your spouse.

What are the other iffy arguments in the article?


  • [“Myth”:] Setting realistic goals for weight loss is important, because otherwise patients will become frustrated and lose less weight.  So-called realistic goals may actually be too modest, the researchers say.

Which brings up the obvious question: what do we mean by “realistic goals”?  And how may a “realistic” goal be “too modest”?  I think the researchers are misinterpreting here; by “realistic goals” fitness experts mean setting intermediate goals on the path to the final target weight so that one gets to have a series of significant “wins” to keep him/her going.

  • [“Myth”:] It is important to assess the stage of change or diet readiness in order to help patients who request weight-loss treatment.  The researchers note that studies show people who sign up for weight-loss programs may say they are ready, but often actually lose little weight.

Mighty perceptive of them to notice this; nobody in the healthcare or fitness worlds could have figured this one out.  Perhaps this is just Fox oversimplifying the researchers’ response, but I really can’t see that the researchers have contradicted the “myth” so much as pointed out how difficult such an assessment is.

  • [“Myth”:] Large, rapid weight loss is associated with poorer long-term weight-loss outcomes, as compared with slow, gradual weight loss.  In fact, some people can successfully lose a lot of weight very quickly, the researchers said. 

Yes, some people can successfully lose a lot of weight very quickly.  But no one has said that rapid weight-loss plans always fail, just that the success rate is poor when compared to slower plans focused on “re-behaving”.
 
In sum, then, the study succeeds only in muddying the already unclear waters of weight loss.  At least one person Fox quotes, Marion Nestle of New York University, implies that the researchers have past histories with companies in the weight-loss industry, and thus have an institutional bias if not a financial interest in pushing surgical and pharmaceutical interventions.  For my part, I believe their intentions are honest but their approach based on false premisses.  You can’t debunk a myth if you don’t get the myth right — a failure not uncommon among skeptics.

One last note:  NBC News uses as its teaser the claim that, rather than 100-300 calories per participant, “A man in his early-to-mid-30s might expend approximately 21 calories during sexual intercourse.  Of course, he would have spent roughly one third that amount of energy just watching television, so the incremental benefit of one bout of sexual activity with respect to energy expended is plausibly on the order of 14 calories.”  This is based on an average duration of six minutes.  But then again, “The only study the team could find that came even close to a scientific measurement of calories burned during sex was done in 1984 on 10 men — hardly a representative sample.”

It’s just as well; since I’m all about respecting the procreative function of sex, I could hardly recommend using other people as substitutes for Bowflex machines.  However, when it comes to samples for medical studies — I gotta say it: Size does matter.