Friday November 29 2013
The volunteers in the study gained just under 0.8kg over the holidays
"Most of us gain 2lb over Christmas and never lose it," is the uncheerful news on the Mail Online website. It reports on a study that found that volunteers gained around 0.8kg between November and January that they then struggled to lose.
In this small study, researchers assessed 148 people around the time of Thanksgiving in the US (the last Thursday in November) and again in early January. They found there were significant increases in body weight and fat, body mass index, blood pressure and resting heart rate.
Significantly, they found no differences between people who exercised at the recommended levels and those who didn't. They also found that someone's initial weight could be used to predict whether or not their weight or body fat percentage increased.
However, the researchers didn't do further long-term assessments, so we can't say if these increases were sustained. It is possible that the small increase in weight was lost in the New Year.
As people reported their own physical activity levels, this may not have accurately reflected how much exercise they did – many of us tend to overestimate the amount of exercise we do.
If you are concerned about not being able to lose the weight you gain over Christmas, not gaining the weight in the first place could be your best bet. Read more about how to Avoid winter weight gain.
Where did the story come from?
The study was carried out by researchers from Texas Tech University in the US. Sources of funding were not reported. It was published online in May 2013 in the peer-reviewed European Journal of Clinical Nutrition.
The headline on Mail Online is not supported by the findings of this study. Because the study did not perform ongoing assessments, it is not possible to say if the small increases in weight gain ended up "spending a lifetime on the hips", as it reports.
Headlines aside, the reporting of the study was accurate and contained some useful advice from one of the lead researchers.
What kind of research was this?
This was a small observational study looking at whether or not body changes occurred in a group of Americans over the "holiday period".
An observational study is when researchers simply observe groups of people without changing their exposures or circumstances.
What did the research involve?
The study included and analysed 48 men and 100 women aged 18 to 65 who were recruited using flyers, by word of mouth and electronic announcements at a university in the US.
Researchers carried out initial assessments on participants in mid-November (around 10 to 14 days before Thanksgiving in the US) and repeated the assessments in early January. The average time between assessments was 57 days.
Assessments were carried out for:
- body weight
- body fat (as a percentage of total weight)
- blood pressure (systolic blood pressure [SBP] and diastolic blood pressure [DBP])
- resting heart rate
- self-reported physical activity, including the type and intensity of physical activity, how long it lasted and how often it occurred
Height and weight measurements allowed the researchers to calculate body mass index (BMI), which is used to measure if a person's weight is healthy (a BMI between 18.5 and 24.9 is considered in the healthy range).
The researchers used the second physical activity assessments carried out in mid-January to group participants as either:
- "exercisers" – people who met the US physical activity guidelines and reported at least 150 minutes of moderate-intensity exercise per week
- "non-exercisers" – people who reported exercising for less than 150 minutes per week
The researchers then used statistical techniques to compare the results of the November and January assessments to see if there were any changes during this "holiday period".
The study authors report the participants were "blinded" to the purposes of the study and were told that the study was about short-term changes in health. This was done to prevent the participants from altering their eating or physical activity patterns because of their involvement in the study.
What were the basic results?
Of the 148 participants, 78 reported that they met the US guidelines for physical activity (at least 150 minutes of moderate-intensity exercise per week), and 71 reported exercising for less than this and were considered "non-exercisers".
The main findings of the study were:
- the average body weight of participants significantly increased from November to January by 0.78kg (95% confidence interval [CI] 0.57 to 0.99kg) – changes in body weight ranged from -2.6kg to +6.3kg
- the average body mass index of participants significantly increased from 25.1 in November to 25.4 in January (change of 0.3)
- the average body fat percentage of participants significantly increased from November to January by 0.5% (95% CI 0.12 to 0.77)
- the average heart rate and blood pressure of participants significantly increased from November to January
There were no statistically significant differences for men and women for any of the assessed outcomes, and there were no significant differences between "exercisers" and "non-exercisers" for changes in body weight, body fat percentage or body mass index.
Participants who were considered obese at the first assessment had significantly greater increases in body fat percentage than participants with a healthy weight. Initial body weight (but not initial body fat percentage, age, gender or exercise) was a predictor of changes in body weight and body fat percentage.
How did the researchers interpret the results?
The researchers conclude that significant increases in body weight, body fat percentage, blood pressure and heart rate were seen in healthy adults during the "holiday season". They report participants gained 0.78kg on average, which indicates the majority of average annual weight gain – reported by other researchers to be about 1kg per year – may occur during the "holiday season".
They say the likelihood of gaining more body fat increases as the extent of how overweight a person is increases, and that initial body weight was a factor that predicted gain in body weight and body fat percentage.
The researchers said it was possible that the total energy intake exceeded any potential benefits of daily physical activity.
Overall, this study provides limited evidence of so-called "weight creep" during the "holiday period".
There were only a relatively small number of people (148) included in the study who were all from one area in the US, so the findings may not be generalisable to other groups.
The study has some other limitations, some of which were noted by the researchers:
- Nobody had follow-up assessments in the long term, so it is not possible to say whether the average weight gain seen was maintained or whether it was lost in the coming months.
- Physical activity assessments were self-reported, which relies on people's memory. It is possible that participants did not accurately report their levels of activity. The study authors note that about half of the participants said they met the US guidelines for physical activity and this was significantly higher than the national average of about 25%. This indicates that participants may have over-reported their physical activity levels or that they were not a representative population. More accurate methods of measuring physical activity would be to use accelerometers or heart rate monitors.
- The method used to assess body fat percentage was not the accepted "gold standard" and this may have affected the accuracy of the readings.
This study does not provide evidence that "most people gain 2lb over Christmas and never lose it", as the Mail Online reports.
It also does not change the recommended physical activity guidelines in the UK, which are at least 150 minutes of moderate-intensity physical activity per week.
If you are concerned about gaining weight over Christmas, there are steps you can take without ruining your fun.
Read more about Avoiding winter weight gain and Exercising in winter.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter.