If you've spent the past few weeks starting the day with a Quality Street at 7am and finishing off with a mince pie at midnight, you are probably desperate to give your body a rest and shift that festive flab.
When it comes to cutting calories, the path of least resistance is often to skip a meal. For many, it's breakfast which gets the heave-ho, especially on a time-restricted diet plan which limits the time you can eat to eight or 10 hours a day.
But the latest scientific research reveals eating later in the day could lead to weight gain. By ignoring our circadian rhythm - our internal clock which tells us when to eat and when to sleep - we're storing up a host of health problems.
Chrono-fasting is a new wellness trend which aims to bring our eating habits back in line with our body clock. But how does it work?
Chrono-fasting is a time-restricted diet based on the principles of chrono-nutrition - which is "the study of how our circadian rhythm and nutrition interrelate," says Rhian Stephenson, a nutritionist and the founder of supplement brand Artah.
Stephenson explains: "Our internal clock, like a master clock, maintains a daily rhythm. This influences essential processes such as hormone release, energy levels, sleep, hunger, repair and regeneration. Our body has distinct functions throughout the day whether it be digestion, problem-solving, physical activity or an ability to respond to stress."
The aim is to eat in the "biological day" and let the body rest in the "biological night". Instead of eating between, for example, 8am and 8pm, eat between an early time-restricted window, having breakfast between 7am and 8am and dinner by 4pm or 5pm. Front-load calories early in the day: eat breakfast like a king, lunch like a prince and dinner like a pauper, and make sure each meal has a good balance of fibre, protein, fat and phytonutrients.
A 2022 meta-analysis of studies found dieters who consumed a greater proportion of their calories in the morning lost more weight than those who had more calories at dinner, possibly because of better alignment with their circadian rhythm.
The same meta-analysis found early eaters had lower levels of "bad" cholesterol, blood sugar and insulin resistance. Meanwhile, a 2020 meta-analysis of studies found insulin and blood sugar levels were higher after the same meal was eaten between 8pm and 4am, than between 7am and 4pm - while eating carbs in the evening is known to spike blood sugar levels compared to the morning. All of that means eating early in the day helps with weight loss as we're less likely to reach for a sugary snack to give ourselves a boost.
We all know that sluggish feeling we get in the morning when we've gone to bed on a full stomach. Stephenson says: "When we sleep, changes in heart rate, blood pressure, cortisol and various other hormones allow time for extensive physical and emotional recovery; our muscles, organs and cells repair, our immune system is strengthened, and our cognitive function is restored."
The most common time to empty our bowels is after breakfast. Dr Emma Derbyshire, a public health nutritionist from the Health and Food Supplements Information Service, says: "You are most likely to go to loo in the morning - waking up triggers gut motility. But if your body clock gets disrupted, it can lead to constipation."
One 2011 study found that dieters who ate more in the morning continued to lose weight even after coming off their calorie-controlled diet, while those who ate more in the evening put weight back on.
Time-restricted diets are a type of intermittent fasting. But there are other methods of intermittent fasting such as the 5/2 approach where you eat around 500 calories each day for two days a week. The problem is consuming such a small amount of calories on two days of the week runs counter to the principles of chrono-nutrition - especially if you save that up for dinner.
Stephenson explains: "Chrono-fasting may be helpful for people suffering from chronic stress - especially perimenopausal females - because if you wake up and don't eat until 12, you can exacerbate that stress."
Plus, we may actually alter our sleep times if we eat too late. A 2024 German study which compared early and late time-restricted eating found that eating later in the day altered the circadian body clock, causing a delay in sleep timing. Those on the earlier plan also felt hungrier in the morning.
Eating within a shorter window is known to lower the amount of calories consumed - plus, there's no snacking in front of the television in the evening. The balance of food you eat is important: a breakfast of cornflakes isn't going to cut it. "Every meal should be high-protein and high in fibre: you're aiming to get 25g of protein and 20g of fibre into each meal, so you're still well nourished," says Stephenson.
Dr Derbyshire reiterates the importance of fibre in our daily diets: "None of us are eating enough fibre," she says. "We all need to get at least 10g more a day." She suggests oat-based breakfasts with yogurt to boost protein levels and seeds, and making sure you include white meat, fish, eggs or cheese at lunch, alongside fresh veg and salad and wholegrains.
For example, 250g of Greek yogurt for breakfast will give you around 25g of protein. Chicken offers 27g of protein per 100g and salmon 25g. Foods with 6g of fibre per 100g are called high-fibre foods and include lentils and wholegrain cereals.
If you're a night owl, bring the eating window forward in the day, but consider starting at 10am and finishing at 6pm or at the latest by 7pm. But bear in mind 70 per cent of us are actually "bears" - neither a lark nor an owl. Plus, says Stephenson, while our chronotype is influenced by our genes, "our circadian rhythm is not, and you can train it - as we do when we fly to a different time zone".
Do it in January. The hours of daylight we currently have match the suggested window of eating perfectly: when it gets dark at 4pm your body will naturally start getting ready for bed. Stephenson says: "At this time of year people are willing to stop drinking alcohol, one of the biggest disruptors of sleep, circadian rhythm and the gut microbiome."
Preparation is key. Eating a good breakfast takes planning and Dr Derbyshire suggests, "Preparing some overnight oats before you go to sleep. Feeling time-poor in the morning is a reason people skip breakfast."
If you are working from home, then making a bigger lunch than usual shouldn't be a problem. But if you're in the office and usually eat lunch on the go, Dr Derbyshire suggests, "Either pack a lunch (a light sandwich made with wholemeal bread and packed with protein and salad would work well) or choose a shop-bought salad which has a balance of protein, fibre and a wholegrain like quinoa."
Plan your dinner. Having soup at 4pm or 5pm if you're working in the office can be tricky but make it the night before and take it in a thermos rather than resort to a shop-bought soup. Dr Derbyshire adds: "Plus, it's good if you are restricting calories in any way to take a multivitamin each day."
Stephenson's supplement brand Artah is launching its own post-Christmas diet reset diet that lasts for three weeks. Stephenson says: "It's possible to lose half a stone following the chrono-fast. The absence of sugar, alcohol, and ultra processed food combined with a focus on fibre, protein, and phytonutrients should lead to weight loss. As long as you're following the core foods and the meal-timing principles, you'll get great results. "
The average daily calorie intake in weeks one and three is around 1,500-1,600kcal per day, with the option to increase portion size depending on your goals and activity level.
"Calorie intake during the chrono-fast is between 1,000-1,200kcals. Calorie intake is front-loaded in the day with around 450-550kcal for breakfast and lunch, and then for it's soup (180kcal) or a broth (50kcal) [depending which plan you're on]. There's a 'circuit breaker' mid-way through the week, where people can eat one of our suggested meals in the evening should they need it."
How long does the chrono-fast last?
"Follow the strict chronofast for seven days only - and make sure you rest and recover while you do so," says Stephenson
Can I drink alcohol on the chrono-fast?
No: alcohol disrupts sleep and wreaks havoc on our body clock, so ditch it for this diet.
What if I can't eat until later?
If you can't do it perfectly, then just do what you can. If you can't have the soup until 7pm, this is fine as the calories are negligible.
Can I exercise while I'm doing the seven-day chrono-fast?
Give a hard training schedule a swerve and focus on a week of yoga and breathwork, plus don't train hard in the evening. Artah are running on demand and weekly live sessions of yoga as part of the plan.
Is the chrono-fast a calorie-controlled diet?
Calorie intake might be lower than your usual diet but Stephenson says, "It's not about trying to eat five almonds and a few grapes. It's about eating good quality meals and understanding how much the timing of what you eat can impact your health."
How can I adapt it to everyday life once I've done the fast?
"You can follow the principles of chrono-nutrition in your daily life. Aim for eating earlier and to finish eating by 7pm three or four days a week, or at weekends if that's easier," Stephenson says. "You don't have to stick to it every day - we all have social lives!"
If the seasoning list intimidates you, you can buy a pre-made jerk spice blend. But, if you have the herbs and spices you need then it's well worth the effort.