When is the best time to eat if you don’t want to put on weight?

If you eat late, you will gain weight” has long been an unwritten rule for dieters who believe that calories consumed after 6pm will settle more easily as body fat.

However, preliminary findings from a new study into the effects of mealtimes on our waistlines suggest that eating in the evening might not be as bad as previously thought.

Tim Spector, professor of genetic epidemiology at King’s College London, has been tracking the eating habits of 80,000 users of the Zoe Health Study app with his colleagues to find out if the timing of meals affected their health and weight.

For three weeks, participants in the Big IF Study on intermittent fasting (IF) were asked to try time-restricted eating (TRE): fasting for 14 hours and consuming all their daily calories within a self-selected ten-hour window that best suited their lifestyles. “Previous studies that have looked at this type of fasting have often asked small, tightly controlled groups to restrict their calories while adhering to an eating window,” says Sarah Berry, associate professor in nutrition at King’s College London and chief scientist at Zoe Health, a health science company. “What was lacking in scientific literature is evidence on how the approach plays out in busy, real lives so here we had a large number of people testing it for us.”

Data is still being analysed by Spector and Berry and the final verdict will not be published for several months. However, surprising preliminary results suggest that even eating a meal as late as 9.30pm might not thwart your metabolic health and weight-loss progress.

Previous findings from the Zoe Health study indicate that everyone responds differently to food and meal timings, but the good news is that the 14:10 approach can be manipulated to meet your needs.

“We know that when people stick to a TRE window they unintentionally reduce their daily calorie intake by an average of 300, which obviously helps with weight loss, but even when there are no changes in calorie intake TRE seems to produce improvements in metabolic health, which makes it very worthwhile,” Berry says.

Here are the new rules of when to eat.

Does the new study mean I can eat late and not gain weight?

It’s not quite that simple. You will need to stick to a 14-hour fasting window, so if you are usually a late eater or have an occasional meal at 9.30pm, you will need to postpone breakfast until 11.30am at the earliest the next morning to keep your metabolism on track.

“And while any 14:10 window seems to produce benefits, they are much greater if you stick to an earlier eating window,” Berry says. So, you might lose weight and boost metabolic health if you eat dinner and breakfast later than most, but better results will come if you move both meals forward.

Does a late-night snack count as a meal?

The last morsel of food or calorie-containing drink (hot chocolate, tea or coffee with milk, wine) that passes your lips will close your TRE eating window for the day. It’s no good kidding yourself that a corner of cheese from the fridge doesn’t count.

“It’s a fasting window, which means no snacking after your final meal and before your breakfast the next day,” Berry says. “Even if you do eat later in the evening you should ideally try not to go to bed within two hours of eating dinner.” This means you have time to digest food and also gives your gut microbes, which follow a circadian rhythm, a break from digesting food.

What is the best time to have a first meal of the day?

According to the new research, if you eat dinner at 9.30pm you should stick to the 14-hour fast, which means not eating breakfast before 11.30am the next day. But if you can front-load your calories by eating earlier in the morning and evening it will likely pay off.

A recent review of 12 studies involving 730 overweight adults in The Journal of Clinical Endocrinology and Metabolism concluded that people should “choose early TRE for more effective weight management”.

And last year researchers from the Rowett Institute at the University of Aberdeen found those who eat their biggest meal in the morning felt less hungry later on, meaning you might not reach for a mid-afternoon biscuit.

Eating breakfast before 8.30am could be the best bet — it has been shown to stabilise blood sugar levels, which might prevent cravings and would lower your risk of type 2 diabetes over time. As for late lunches, those who eat after 3pm lose weight less effectively than people who eat lunch early.

Is it still best to stop eating at 6pm?

Until now this has been a widely touted rule of dieting, but Berry says it stems from lab-based studies that do not translate to most lifestyles. It is best to have your last meal earlier in the evening for weight loss, although there are no strict guidelines about the precise time to stop eating.

“In everyday life a 6pm cut-off is just not practical,” she says. “There is evidence to suggest finishing your meals by 8pm is favourable — and more manageable — for metabolic and weight-loss effects, although that is not set in stone.”

Can you chop and change eating times?

You can be forgiven for occasionally straying off track on a night out, but you should try to stick to a regular eating routine for the sake of your waistline.

Several studies have shown that food intake helps to synchronise our internal body clocks, and researchers at the University of Surrey recently reported that these are primed to predict regular mealtimes.

Any food consumed at irregular times can send blood sugar soaring, they suggested, making you more inclined to snack when you don’t need to.