We have looked at a couple of festive season weight studies in previous years. In December 2018, we reviewed a study from Birmingham UK, which was designed to test the effectiveness of a brief behavioural intervention to prevent weight gain over the Christmas holiday period (Ref 1). The researchers recruited 272 adults before Christmas in 2016 and 2017. The intervention group was supposed to exercise restraint in eating and drinking by weighing and photographing all food and drink consumed over an average of 45 days. The control group approached Christmas as normal. The intervention group lost, on average, 0.13kg (130g – that’s the equivalent of a large apple in weight). The control group gained on average 0.37kg (370g – that’s a large steak). The difference in weight change between the two groups was 0.5kg over 45 days. This was statistically significant, but it wasn’t significant by any other meaning of the word. (For examples of conversions, 1lb is 0.45kg; 100lb is 45kg and 100lb is also 7 stone 2lb).
In December 2009, we looked at a study about weight gain between Thanksgiving & New Year (Ref 2). (Our north American friends have a longer period during which things can go awry.) This study was called “A Prospective Study of Holiday Weight Gain” and it was published in the New England Journal of Medicine in March 2000 (Ref 3). 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 took place with 165 of the adults the following September.
With the caveat of the survey size being small, the findings were as follows:
– The average weight gain during the holiday period was approximately 1lb, but the standard deviation was larger (that’s a measure of the spread of results) – plus or minus 3.3lbs. That means that some people gained over 4lb and some people lost weight.
– During the pre-holiday period, the average gain was about half a pound, but the standard deviation was very similar (c. 3lbs) – a larger 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 approximately 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. Hence some people might have been 4lbs down on the previous autumn and some people 6lbs heavier. There could be even bigger results outside this standard deviation range.
A more recent, and larger, study (2020) was called "Weekly, seasonal and holiday body weight fluctuation patterns among individuals engaged in a European multi-centre behavioural weight loss maintenance intervention" and it was published in PLoS One (Ref 4). This was a pan-European study which examined weekly, holiday and seasonal weight fluctuation patterns in 1,421, 1,062 and 1,242 participants respectively.
Within week fluctuations of 0.35% were observed – characterised by weekend weight gain and weekday reduction. That is interesting in itself – we tend to lose weight between Monday and Friday and then gain weight over the weekend. If we could just stop weekend gain, therefore, we could successfully lose weight over time.
Over the Christmas period, weight increased by an average (mean) 1.35%. As an example, if we take a 140lb (10 stone, 63.5kg) person, a gain of 1.35% would be almost 2lb (just under 1kg). Body weight decreased between January and March although it remained at least 0.35% greater than the pre-Christmas weight. Greater weight gain was observed in the UK (1.52%) than Portugal (1.13%), with Denmark somewhere in between (1.29%). Men and women were not significantly different (an average 1.3% gain in men; an average 1.37% gain in women). Participants with a BMI in the obese range (>30) at the start of the study gained more weight, on average, than those with a normal BMI. There was a noticeable age difference with those under 30 gaining on average 1.08% and those over 60 gaining on average 1.40%.
Weight gain is therefore known to be a possibility, if not a likelihood, over the festive period. Here are some top tips for avoiding this, if you don’t want to have to go on a diet in the New Year…