Obesity doctor shares the simple reason you gain weight over Christmas – and it’s NOT because of overeating

You can’t attribute festive weight gain to eating too many mince pies, handfuls of celebrations and two servings of roast potatoes, a leading doctor has claimed.

Previous research has estimated Britons consume up to 6,000 calories on Christmas Day alone; this was three times the NHS recommended 2,000 calories for men and four times the 1,500 calories recommended for women.

But Consultant in Endocrinology, Diabetes and Obesity and Dr. Professor Franklin Joseph, founder of the Frank Weight Loss Clinic, says festive meals alone rarely lead to fat gain, but sitting around doing nothing does.

He said: ‘People greatly exaggerate how much harm a few days’ worth of richer food can do.

‘Fat gain occurs gradually. ‘You won’t gain kilos of fat from a handful of mince pies.’

In reality, the biggest reason for the Christmas podium rally comes from a habit that millions of people don’t think twice about: sitting idle for hours, if not days.

Inactivity has a huge detrimental effect on our metabolism, increasing fat storage and causing overeating; all of which lead to weight gain, even if we keep what we eat at Christmas in check.

Professor Joseph explained: ‘Hours spent sitting (watching television, socializing, traveling or lying on the sofa) have a much greater impact on weight than the food itself.

‘When you sit for long periods of time, your body becomes less efficient at managing blood sugar and fats.

‘This means most of what you eat is stored rather than burned.’

During the Christmas holidays, it’s normal to lie down on the sofa to watch a box set or movie and reach for the accompanying plate of snacks.

Inactivity also affects the body’s natural appetite signals, making people more likely to mindlessly eat, making the last few weeks of December a perfect storm.

‘You don’t eat because you’re hungry, you eat because you’re bored,’ he warned.

So what’s the solution to not ending 2025 with a few belt notches (in the wrong direction) and a silhouette that makes Santa look like Kate Moss?

Professor Joseph says it’s not about cutting calories or avoiding treats, it’s something much simpler.

‘You don’t need to diet for Christmas,’ he said.

Staying sedentary for days can tip the scales towards real fat gain

‘You just need to move your body.’

And before you start pulling out your old Davina McCall fitness DVDs, you don’t even have to break a sweat to reap the benefits.

Professor Joseph says taking a short walk after meals, standing up regularly, helping with cooking or tidying up, and making time for regular, gentle stretching can help keep unwanted pounds off.

He added: ‘Even light movement improves the way your body processes food.

‘It’s much more powerful than skipping dessert.’

It can be hard not to panic when you weigh yourself for the first time after Christmas, but Professor Joseph says the body is often swollen with fluids, not yellow globules of fat.

However, he is quick to remind people that being sedentary for days on end can tip the scales towards actual fat gain if the feeling of inactivity continues into January.

He said: ‘Most of what people see after Christmas is water weight and inflammation, not fat.

‘Saltier foods, alcohol and less exercise cause the body to retain fluid.’

He also urges people to think twice about setting aside Boxing Day or New Year’s Day as the first day of a new, strict, healthy eating plan.

‘A crash diet implemented on Boxing Day or January 1 often backfires,’ he said.

‘It increases stress hormones, increases appetite and leads to another urge to overeat.’

‘Mince pies don’t cause weight gain at Christmas; This is because all movement is stopped and you punish yourself afterwards.

‘Enjoy the food, move lightly and return to your normal habits in January. This way the weight stays stable in the long run.’