How Not to Gain Weight Over Christmas: An Australian Guide

Every December the same advice comes out: skip the second helping, walk after lunch, have a glass of water between drinks. None of it is wrong, and almost none of it has been tested. A couple of things have, and one of them takes about ten seconds a day.

#How much weight do Australians gain at Christmas?

The best Australian data comes from a University of South Australia study published in JAMA Network Open in 2023. Researchers led by Carol Maher gave adults smart scales and fitness trackers and followed their weight for a year; 368 had enough data to analyse.

Two details stand out. First, summer is our heaviest season, the reverse of the northern hemisphere, where Christmas falls in winter. Australians in the study were lightest in autumn. Second, there's a weekly rhythm: lightest on Friday, heaviest on Monday and Tuesday. The Christmas break is, in effect, a fortnight of weekends.

The researchers also found that about a quarter of participants finished the year at least 2% heavier than they started, an average of 1.7 kg.

#Why half a kilo matters

Half a kilo sounds like nothing, and over one season it is. The problem is that a good part of it tends not to come back off.

In the study most often cited on this, published in the New England Journal of Medicine in 2000, 195 American adults gained an average of 0.37 kg over the holidays and didn't lose it in the months that followed. For the group tracked over a full year, the holiday period accounted for about half of their total gain.

Repeat that every year for a decade and you have the slow creep most people can't explain. It's also why the habits that protect against it look a lot like the ones the people who keep weight off long-term rely on all year.

#Where the kilojoules actually come from

Christmas Day itself is rarely the problem. One big lunch is one big lunch. It's the season around it: work parties, catch-ups, leftovers, a fridge full of ham and a bowl of chocolates on the bench, from early December to the first week of January.

The Australian Dietary Guidelines have a handy unit for this. A discretionary serve is however much of a treat food or drink contains 600 kJ. Some Christmas-relevant examples:

Source: Eat for Health (NHMRC). Now count a normal work Christmas party. Four schooners of full-strength beer is about 2,600 kJ, more than four discretionary serves, before anyone has touched the canapés. A large 250 mL glass of wine is about 770 kJ. (Full drink-by-drink figures here.)

Drinks are the biggest single variable in the season, and the one people almost never log. For health rather than kilojoules, the NHMRC guideline is no more than 10 standard drinks a week and no more than 4 on any one day for healthy adults, and a schooner of full-strength beer is about 1.6.

#What actually works

1. Weigh yourself, often. This is the one with a trial behind it. In the Winter Weight Watch Study, published in the BMJ in 2018, researchers in Birmingham randomly split 272 adults before Christmas. One group was asked to weigh themselves at least twice a week, ideally daily, and record it; they also got ten weight-management tips and a list of how much activity it takes to burn off festive food (one mince pie is about 21 minutes of running). The comparison group got a healthy-living leaflet.

By January and February the comparison group had gained 0.37 kg on average. The weighing group was down 0.13 kg. The difference, about half a kilo, is similar in size to the Christmas gain in the Australian study.

The authors couldn't separate which part did the work, so treat it as a package: weigh in, write it down, keep the season in view. Use a weekly average rather than reacting to any single morning; the weekend swing alone is a quarter of a kilo.

2. Think in weeks, not days. Christmas lunch is going to be big. That's fine. Plan the heavy days and keep the ordinary days around them ordinary, rather than writing off the whole fortnight.

3. Log the drinks, afterwards. Nobody logs drink three at the party. One line the next morning, four schooners and two glasses of bubbles, is far closer to the truth than the zero most logs show.

4. Keep logging, roughly. If you stop tracking in December and restart in January, the gap lines up exactly with when the gain happens. A rough log of the big items beats a perfect log you've paused. (You don't have to log everything.)

5. Use the Australian advantage. A summer Christmas is unusually kind: prawns, cold ham, salads and fruit. Fill up on those first and there's less room for the third mince pie. The goal isn't avoiding Christmas food. It's avoiding six weeks of unlogged Christmas food.

#What not to do

Don't skip meals to bank kilojoules for a party. Arriving starving makes the canapés harder to pass up, and drinking on an empty stomach is its own problem. Eat normally and count the drinks honestly.

Don't plan a January crash diet to undo it. For most people, getting back to normal meals and normal logging in the first week of January is enough. In the UniSA data, participants were on average lightest in autumn; the summer peak doesn't have to become the new baseline.

#Getting back on track in January

Expect the first weigh-in after New Year to look worse than it is. Salty, carb-heavy food holds extra water, so part of a post-Christmas jump may settle over the following days. Judge by your seven-day average, not the first morning.

Then go back to what was working. If you'd like a target, the calorie deficit calculator gives one in a couple of minutes, and a modest deficit you can hold beats a heroic one you abandon by Australia Day.

If you're worried about how much you're drinking rather than what it adds in kilojoules, that's a different and more important conversation: your GP, or the Alcohol and Drug Foundation's resources, are better places to start than a nutrition app.