For most of us, Christmas and its festivities revolve around consuming tasty food and drinks with colleagues, friends and family. Between work Christmas parties, Christmas lunch or dinner, edible presents and New Year's Eve, it can be an effort not to gain weight.
The human body can be quite remarkable in its ability to maintain a stable weight over the long term. One small American study reported average fluctuations of just 0.5 kg throughout a year. Weight peaked in winter, which may be due to poorer weather and lower physical activity, but returned to normal. Others, however, gradually gain weight over the years. A study of 120,000 Americans found weight gain averaged 1.52 kg (3.35 lb) over four-year periods.
The good news is that reducing your energy intake by around 100 calories (418 kilojoules) per day can prevent such weight gain. This could equate to not having that extra biscuit, or walking more each day.
We often don't follow our normal routines during the holidays. Therefore our lifestyle behaviours and body weight can change. There aren't many high-quality studies that look at body weight and fat changes over the Christmas period, but the studies that have been done report conflicting results.
A 2009 American study of 195 adults over the six- to eight-week winter holiday reported an average weight increase of 0.37 kg. Another study of 26 English adults over a two-week Christmas holiday found they gained an average of 1 kg, even though five were sick (and three lost weight). The maximum weight gain was 4.4 kg.
Yet another study reported a weight change of around 0.4 kg in non-obese Swedish adults over a two- to three-week Christmas break. Obese participants, however, reported highly variable changes in weight, from a gain of 6.1 kg to a loss of 8.8 kg.
This difference between people of contrasting starting weights was also found in another American study of 94 college students. Over a two-week Thanksgiving period, the overweight/obese students gained an average of 1.0 kg, while those with a normal body mass index (BMI) gained just 0.2 kg.
Some studies reported no weight gain, but found an increase in body fat over the holidays. However, other studies found no change in either body weight or body fat over festive periods, even if there were changes to eating and physical activity patterns.
What's to blame?
In the large study of 120,000 American adults, the foods associated with weight increase over four-year periods include potato chips, potatoes, sugar-sweetened beverages and unprocessed and processed red meats. Foods that were associated with lower weight included vegetables, whole grains, fruits, nuts, and yoghurt.
Other lifestyle behaviours were also associated with weight gain: physical inactivity (including television watching), alcohol intake and sleeping less than 6 or more than 8 hours each day.
It's not hard to imagine these factors at play in someone's Christmas holidays. Potato chips, soft drinks and alcohol might fill the table at the work Christmas party. Hangovers and too little or too much sleep might mean that you indulge excessively in fast food burgers while binge-watching Netflix.
Five tips to avoid a belly like Santa's
1) Choose foods that have been associated with healthier body weights in the longer term and increased satiety in the shorter term, such as fruits and vegetables, and leaner foods that are higher in fibre and protein.
- salads (including fruit, green, potato and quinoa ones) over white bread
- oat slices or biscuits over shortbread biscuits
- roasted nuts over potato chips
- turkey breast over salami
- shrimps and other seafood over sausages.
2) Eat intuitively: try to listen to your hunger and fullness. This will help with the feeling of sickness that can come at the end of Christmas day due to overconsumption.
Choose smaller plates, as these are associated with reduced food intake compared to larger plates - even if you have a level of intuitive eating.
Put a smaller variety of foods on your (smaller) plate - and don't go back for seconds. If you have a large variety of foods, you are more likely to eat more - something called sensory-specific satiety.
3) Self-monitor! One study reported that systematically recording what you eat, drink and how much you move during holiday periods was associated with improved weight. Use goal-setting and self-monitoring sheets or apps to help regulate the amount of alcohol or potato chips you consume each day.
4) Go for walks or swims if the weather allows, and avoid spending the whole break binge-watching television.
5) Avoid soft drinks and excessive alcohol every day. When you do drink alcohol, choose a soda mixer with a piece of fresh lime to have with your spirits and drink water in between each alcoholic drink.
At the end of the silly season, you may still have gained some weight. But keep it in perspective: it might have been due to quite pleasurable activities and it's unlikely to be a problem in the long term, if you get back to your usual balanced exercise and eating routine. It's fine to indulge every now and then, even if it means going back for seconds of Christmas pudding on Christmas day. Just don't indulge every other day of the holidays, too.