It is an often quoted ‘fact’ that Americans gain up to half a stone on average between Thanksgiving and New Year. Thanksgiving in America falls on the last Thursday in November, so it was on November 26th in 2009. Whilst not such a big even in Canada, Canadians celebrate Thanksgiving on the second Monday in October (October 12th 2009), so overeating can potentially start even earlier in Canada. The Europeans don’t really start the eating marathon until the work Christmas party lunch and dinner and Christmas Eve and Christmas Day festivities, but the Brits particularly, seem able to get through an extraordinary amount of festive processed food (sweets, chocolates, mince pies, Christmas cake, Christmas Pudding) in just a few days over the Christmas holidays.
Whilst looking into the facts behind this weight gain ‘urban myth’, I came across a great obesity journal article “A Prospective Study of Holiday Weight Gain” in “The New England Journal of Medicine” (March 2000). Well done to the authors: Jack A. Yanovski, M.D., Ph.D., Susan Z. Yanovski, M.D., Kara N. Sovik, B.S., Tuc T. Nguyen, M.S., Patrick M. O’Neil, Ph.D., and Nancy G. Sebring, M.Ed., R.D. for the idea and the analysis on this interesting topic…
195 adults were weighed four times, 6-8 weeks apart, so that the distinct periods could be reviewed: 1) pre holiday (from late September/early October to mid-November); 2) holiday period (from mid-November to early/mid-January), and 3) post holiday (from early or mid-January to late February/early March). A follow up measure of body weight was managed with 165 of the adults the following September.
With the caveat of the survey size being small (195 adults), the findings were as follows:
– The average weight gain during the holiday period was approximately 1lb, but the standard deviation was much higher – plus or minus 3.3lbs. (The standard deviation is a measure of ‘spread’ in the results – did everyone gain 1lb or did some people lose and some people gain lots more?) The standard deviation doesn’t measure the full range (the very highest weight gain to the smallest gain, or even the biggest loss). In a normal distribution, the standard deviation will pick up about 70% of the results. This is still quite a big variation around an average of just 1lb. (Without getting too excited about statistics, this is likely to be a skewed distribution with few people, if any, losing; lots of people gaining around 0-1lb and a smaller number gaining more than 1lb).
– During the pre holiday period, the average gain was about half a pound, but the standard deviation was very similar (c. 3lbs) – a big range again, therefore.
– During the post holiday period, there was a tiny average loss – barely one tenth of a pound. This had a standard deviation of plus or minus 2.5lbs, so (if the curve followed a normal distribution) we can say that 70% of people fell into the range of losing just over 2.5lbs or gaining almost this amount.
– Comparing late Feb/March with late Sept/early Oct, the average net weight gain was 1lb, but the variation again was significant – with the standard deviation of approximately 5lbs. So some people might be 4lbs down on the previous autumn and some people 6lbs heavier. There could be even bigger results outside this standard range.
– For those adults that attended the follow up, the average further gain was again small – half a pound. But the variation again was again large – plus or minus 5lbs either side of this average and even more extreme results not captured.
From this excellent study, albeit on a small sample, we can conclude that average weight gain is likely to be small and lower than the 5-7lbs that is often quoted. However, there are definitely some people experiencing a 5-7lb weight gain and others likely more. Some people may be bucking the trend and losing a little over the winter period – perhaps being alert to how easy it is to gain weight and being extra careful to avoid the festive carbs. The real danger is if the same person is gaining each Thanksgiving and not losing in between and that’s when a fit student can turn 30 and wonder how they became obese!