Monday, December 21, 2009
Today I'd like to revisit an issue which we first reported on last January, and which unfortunately appears to be happening again this holiday season. Several of our colleagues attend a major Canadian fitness chain (I have decided not to post the name yet, but it shouldn't be too hard to guess) which has a poster of a chubby gingerbread man on the wall throughout the holidays (both in 2008 and again this year). Under the gingerbread man is a caption that reads "The average person gains 7-10 lbs over the holidays!". This poster immediately raises a few questions:
1. Where does this information come from? Who is the "average" person they are speaking of? Aged 18-80? Does it include kids? Seniors? Different ethnicities?
2. If the average person gains 7-10 pounds, that means that some people are gaining much more. Is that even physically possible over a 1 or 2 week period (the definition of 'holiday season' varies pretty widely from person to person)? Canada has a population of roughly 33 million - if we gained an average of 9 lbs over the holidays, as a nation we are about to put on 297 million lbs this year alone! In the USA, it would mean a collective holiday weight gain of roughly 3 billion lbs!!
This 7-10 lb weight gain statistic seems a bit strange, so I decided to look it up on Google Scholar. Fortunately, I came across an excellent article from the New England Journal of Medicine which examines this very issue. Back in 2000, Yanovsky and colleagues examined the amount of weight gain during the American holiday season (from American Thanksgiving until New Year's). Then, as now, this claim of 7-10 lbs holiday weight gain was quite common - Yanovsky reports that organizations ranging from CNN to the Texas Medical Association used the information in press releases during the holiday season of that year. In addition, self-report studies tell us that people believe that they gain 5 lbs or more over the holidays, but that does not necessarily mean that they do.
Fortunately, Yanovsky and colleagues objectively measured the body weight of 195 men and women over the course of the year. They report that the average weight gain from mid-November to mid-January was less than 1 lb! Less than 10% of the participants gained 5lbs or more. The weight gain during the holiday season was, however, significantly greater than that during the pre- or post-holiday period, and the holiday weight-gain was not lost over the course of the year.
So, what does this study tell us? First of all, it tells us that the statement on the gingerbread poster is complete bunk. While it might be appealing to rip on the gym chain for spreading this information, the same information has been peddled by medical associations, so it's hard to say they are completely to blame. Still, the article by Yanovsky and colleages was published 9 years ago (and was the first study to pop up on Google Scholar), so it wouldn't have been too tough to realize that the statistic might be questionable. Keep in mind that I also emailed the Yanovsky paper to the gym chain last February to alert them to the issue, and I received a pleasant reply stating that my feedback had been passed along for future consideration. So I was more than a little bit disappointed when I heard that the posters are back up on the walls this holiday season (it appears that Obesity Panacea may have less clout than I had hoped!).
On a somewhat more serious note, the Yanovsky study also tells us that on average, people do gain a small but significant amount of weight over the holidays which is maintained throughout the course of the year. Not enough to warrant fear mongering, but enough to cause some concern - a pound or two a year can add up over time. And some people do experience significant weight gain, a phenomonen which was sigificantly more common in overweight and obese individuals. It is an issue which is worth following, but one that I hope people aren't losing sleep over.
So remember, as we move deeper into the holiday season, don't let the gingerbread men (whether on your plate or a poster) get you down.
Big thanks to our friends Wendy and Geoff Stephen for letting us know about the poster and for their helpful comments.
UPDATE: We now have a picture of the poster itself, which you can see at the top of this post.
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Yanovski JA, Yanovski SZ, Sovik KN, Nguyen TT, O'Neil PM, & Sebring NG (2000). A prospective study of holiday weight gain. The New England journal of medicine, 342 (12), 861-7 PMID: 10727591
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