Weight loss: How to optimise your body clock to lose weight

The time of day at which you exercise is a big factor in effective weight loss, a new study has found.

If you’re really serious about losing weight, you’ll be working out while the rest of the world is pouring their first cup of Earl Grey. According to a new study of more than 5000 people from Franklin Pierce University in New Hampshire in the US, the best time to exercise is between the hours of 7am and 9am.

Researchers found that people who did 150 minutes of pre-work exercise a week were 2.7kg lighter and had a lower BMI than those who exercised later in the day. They were also less likely to have unhealthy diets and consumed fewer calories than those who exercised mid-morning or later.

“Our findings propose that the diurnal [daily] pattern of moderate to vigorous physical activity could be another important dimension to describe the complexity of human movement,” says study author Dr Tongyu Ma.

Is it possible to continue this calorie-burning fest throughout the day? Here’s our round-the-clock guide

While it’s true that some people are naturally night owls, the 21st-century rat race is geared to the morning larks. Photo / Getty Images

7am: Time to wake up

While it’s true that some people are naturally night owls, the 21st-century rat race is geared to the morning larks.

“The idea now is that every organ, and possibly every cell has its own clock, and these are synchronised by a clock in the brain, which itself is set by photo-receptors in the eye that respond to light,” says Professor David Whitmore, who specialises in chronobiology (the way that our biology is affected by time) at University College London.

Ideally, you’ll be consistent with your wake-up times. “If you keep a regular sleep-wake cycle, regular meal times and regular light-exposure times, that keeps the whole body clock on time, which in turn keeps everything else on time,” says Dr Guy Meadows, sleep expert and founder of Sleep School.

A key recommendation is to undertake 40 minutes of aerobic exercise, such as running or biking, before breakfast. Photo / Unsplash

7.20am: Get your running shoes on

According to Dr Ma, cardiovascular exercise is likely to be key for those who work out in the mornings. “Exercise can burn fat and glucose,” he says.

“After an overnight fast, the glucose stored in our body is low. Therefore, when we exercise our muscles are likely to burn more fat. I would recommend 40 minutes of aerobic exercise before breakfast, such as running or biking.”

Focus on starting your day with protein. Photo / Getty Images

10am: Eat breakfast

Various studies have shown the benefits of intermittent fasting for weight loss and scientists from King’s College London recommend eating within a 10-hour window. Having breakfast at 10am offers the chance to fast slightly later into the morning, so you can finish eating before 8pm in the evening and give your body time to digest before bed. A study from the University of Surrey found that pushing your eating time 1.5 hours later results in you eating fewer calories.

“There’s evidence to show that eating in line with your body clock will improve your metabolic health, inflammation and weight,” says Dr Sarah Berry, a leading nutritional scientist.

Focus on starting your day with protein: eggs or salmon. Studies from Japan have found that people are better at metabolising and building muscle from protein when it is consumed in the morning compared to when in the evening.

It takes up to six hours for your system to clear the caffeine from a single shot of espresso. Photo / 123rf

Midday: Finish your last cup of coffee

While one unit of alcohol takes an hour for the body to break down, it takes up to six hours for it to clear the caffeine from a single shot of espresso from your system.

“At minimum, you need to leave at least a six-hour break between drinking coffee and going to sleep,” advises Dr Meadows. “Drink two or three cups a day if you like, but ideally stop at noon.”

This is important because a lack of good-quality sleep can lead to increased consumption.

“When we’re sleep-deprived, our bodies raise levels of [the hormones] ghrelin, and lowers leptin, meaning we’re hungrier and find it harder to feel satiated,” says hormone expert Emma Bardwell.

These hormones are vital in regulating appetite. Ghrelin tells the brain you’re hungry, while leptin tells you that you’re full and can stop eating. That means if you’re sleep-deprived you’re likely to eat more.

A midday to early-afternoon meal is where you should get most of your carbs. Photo / 123rf

2pm: Eat some carbs now

This is the meal where you should get most of your carbs, says Ulrike Kuehl, head of nutrition at the metabolism-tracking app, Lumen. “Consuming carbs midday will be important to give you some fuel to get you through the rest of the day.

“It makes sense for most people if you look at the average metabolic flexibility to have more carbs in the middle of the day, that’s when people tend to be more sensitive to insulin and so better at processing them.” All this is even more important to give you energy to exercise after work.

Factoring in simple breaks to just do nothing is essential to sleep better later. Photo / Getty Images

3.42pm (or whenever you feel like it): Give yourself a short break to daydream or do nothing

“One of the big problems these days is that the only time we take to pause is when we go to bed,” says Dr Meadows. “That’s when your mind races because your Default Mode Network, the part of your brain responsible for mental chatter, hasn’t had the chance to catch up on the day. Factoring in simple breaks to just do nothing is essential to sleep better later.”

In 2015, a group of scientists from around the world published guidelines in the British Medical Journal, advising that we should get up from our desks every hour and walk for two minutes. Doing so cuts the risk of premature death by 33 per cent by burning calories and keeping the body active.

Between 4pm and 6pm your core body temperature is at its highest and your muscles and joints are most warmed up. Photo / 123rf

5pm: Grab some weights (or your yoga pants)

A 2019 study from the Scripps Research Institute in California found that between 4pm and 6pm your core body temperature is at its highest and your muscles and joints are most warmed up. Now is the time when you’ll get the most out of strength and movement exercises. Exercises like this are good for building muscle which, in turn, is vital for burning fat. This is because muscle tissue requires more calories to maintain than fat tissue.

“The more muscle you have, the more calories you will burn,” says three-time Olympic speed skater and top personal trainer, Sarah Lindsay. “Of course, cardio and general activity are great for you in all sorts of ways, but it needs to be combined with getting stronger.”

A 2018 review of 23 different studies about exercise timings found that people who exercised in the evening fell asleep faster and spent more time in deep sleep. Be wary of exercising too close to your bedtime or exercising too intensely late into the night though: the review found that intense exercise in the hours before bed delayed sleep onset by an hour.

The most effective thing people can do for their weight loss is to eat a couple of hours earlier in the evening than they might otherwise think to.

6pm: Finish dinner

“The most effective thing people can do for their weight loss is to eat a couple of hours earlier in the evening than they might think - I’d say three or four hours before bed,” says Kuehl.

“If you eat late at night, it increases blood glucose and insulin, which negatively impacts sleep. The cells of your metabolism need time to rest and regenerate so if those cells are active your body has trained itself not to shut down until they do. If you don’t sleep well, you’re more likely to gain weight.”

It might be tempting to crash on the sofa with a glass of wine, but it’s generally unwise.

8pm: Skip the glass of wine while you’re watching TV

It might be tempting to crash on the sofa with a glass of wine, but it’s generally unwise.

“The body detects alcohol and sees it as a toxin, so it focuses all its resources on detoxifying that alcohol,” explains Inside Performance sports scientist Nigel Stockill. All the processes by which the body would normally start to get you ready to sleep, such as slowing down the heart rhythm, get neglected until the body has detoxified the alcohol.

“As little as one unit of alcohol in your system at bedtime can delay the onset of restorative sleep by about an hour. Have two large glasses of wine (about six units) late in the evening and sleep for six hours and you may not get any restorative sleep, and therefore won’t recover overnight. And you’ll also crave carbs the next day.”

Going to bed 75 minutes earlier than you would otherwise helps you consume 270 fewer calories (the equivalent of three biscuits). Photo / 123rf

10pm: Get to bed

Ideally you’ll have been slowing down, closing your curtains and switching off your smartphone before this point, but aim to get about eight hours of sleep to help lose weight. A 2022 study from the University of Chicago Medical Centre found that going to bed 75 minutes earlier than you would otherwise helps you consume 270 fewer calories (the equivalent of three biscuits).

In 2016, one study found that levels of a chemical called 2-arachidonoylglycerol (2-AG), which increases the amount of pleasure we derive from eating, rose by a third when volunteers were sleep-deprived. In short: you’ll want to eat more. So do yourself a favour and off you go to bed.