Tuesday, May 11, 2010

Rapid weight loss is the best way to keep it off?

You'd sure think so if you'd just been reading headlines.

You see a study came out last week in the International Journal of Behavioural Medicine that looked at the impact the initial rate of weight loss had on long term success in 262 women over the course of an 18 month weight management program.

The study is a mess. Before I get to the results, let's go over some methodological issues.

Firstly the study represents a secondary data analysis of a different randomized controlled trial. That pretty much always means trouble because it means that the trial wasn't in fact originally designed to properly answer the study question.

Secondly when analyzed, the racial makeup of the fast, medium and slow groups were markedly different with the slow group being primarily made up of visible minorities and the fast group Caucasians, and while the authors describe using ethnicity as a covariate in further data analysis, I wonder how that's possible given there were only 65 non Caucasians enrolled in the study with a grand total of 6 ending up in the fast group.

Results wise the authors conclude that it is the speed of loss that determines longterm success. Yet the authors also report that the fast and medium speed losers had better session attendance, better food diaries, consumed fewer calories and took more steps than those in the slow group. Wouldn't this then suggest that longterm success is dependent on adherence to one's treatment plan? Is that news?

Even the authors realize their study added nothing to the literature. In their words,

"This study used a correlational design and thus cannot directly assess causality. This post-hoc separation of groups according to initial rate of weight loss did not account for underlying physiology or behaviors that may have self selected participants into each group and determined longterm outcomes."
Translation? Even the authors realize that you can't make any conclusions about the results because there are a multitude of factors that may in fact provide better causal explanations.

But my biggest beef with the study is their use of the words FAST, MEDIUM and SLOW.


Because when people think about rapid weight loss, they think many pounds a week. They think about things like the very-low-calorie-diets (VLCDs) the authors themselves refer to in their discussion. They think of losses easily running into the 3-5lb/week range.


FAST was the term used to describe folks where an arbitrary post-hoc analysis not designed to look at cause revealed losses averaging more than 1.5lbs a week. MODERATE was for losses averaging between 0.5-1.5lbs per week and SLOW for those averaging less than 0.5lbs per week.

Not exactly dramatic between group differences and not exactly what most would think of when they heard the term, "FAST".

Why does that piss me off so much? Because when the media grabbed hold of it headlines, blogs and tweets all sounded off about how rapid weight loss is a great idea, the best way to lose weight, and yet there is a wealth of studies suggesting that rapid weight loss may in fact be a bad plan, that VLCDs are a really bad plan, and that there may be additional health risks to overly rapid weight loss.

Reporters and bloggers - while I recognize it's not your job to be experts, I would expect that at the very least your job is to read the article you're writing about and even a casual read would inform anyone that this study is not in fact talking about rapid or fast weight loss and moreover isn't a study that anyone can draw real conclusions from.

Peer reviewers - really? A post hoc analysis that certainly can't be relied upon for any real conclusions? Did you even read it?

Authors - Fast, medium, slow? Sure, a sexy title, but whether you meant to or not, all you've succeeded in doing here is use an admittedly useless study to promote unhealthy dieting practices.

Publish or perish, never mind the consequences.


Nackers, L., Ross, K., & Perri, M. (2010). The Association Between Rate of Initial Weight Loss and Long-Term Success in Obesity Treatment: Does Slow and Steady Win the Race? International Journal of Behavioral Medicine DOI: 10.1007/s12529-010-9092-y