Eating your last meal for the day at 2pm may sound like torture – but it may help you lose weight.
Scientists found fasting with a six hour eating window starting at 8am can suppress the appetite and lower levels of hunger hormones.
Fasting diets have previously been thought to help people shed the pounds by way helping them burn more calories.
However, the study suggests restricting meal times helps people to simply eat less, and it may be due to eating in line with the natural body clock.
Eating all meals between 8am and 2pm may help to lose weight as scientists at University of Alabama show fasting diets can suppress the appetite
Although experts have long argued it’s not what you eat, but when, researchers said this is the first time a study has shown how meal times affect metabolism.
The study at the University of Alabama tested Early Time-Restricted Feeding (eTRF), which is a type of fasting where dinner is eaten in the afternoon.
Researchers enrolled 11 men and women who needed to lose weight, aged between 20 to 45 with a BMI between 25 and 35.
Participants tried two different meal timing strategies, one where they ate three meals over 12 hours, between 8am and 8pm.
The other strategy saw them have only six hours to eat three meals, between 8am and 2pm.
The same amounts and types of foods were consumed on both schedules which the participants carried out for four days in a row.
On the fourth day, researchers measured the metabolism of participants by placing them in a respiratory chamber.
This allowed them to see how many calories, carbohydrates, fat and protein were burned by each of the volunteers.
Researchers also measured the appetite levels of participants every three hours while they were awake, as well as hunger hormones in the morning and evening.
They discovered the six-hour eating window improved the ability to switch between burning carbs to fat for energy.
It also increased fat-burning, the researchers led by Dr Courtney Peterson reported in the journal Obesity.
EXPLAINED: HOW THE CIRCADIAN RHYTHM WORKS
In a healthy person, cortisol levels peak at around 8am, which wakes us up (in theory), and drop to their lowest at 3am the next day, before rising back to its peak five hours later.
Ideally, this 8am peak will be triggered by exposure to sunlight, if not an alarm. When it does, the adrenal glands and brain will start pumping adrenalin.
By mid-morning, the cortisol levels start dropping, while the adrenalin (for energy) and serotonin (a mood stabilizer) keep pumping.
At midday, metabolism and core body temperature ramp up, getting us hungry and ready to eat.
After noon, cortisol levels start their steady decline. Metabolism slows down and tiredness sets in. Gradually the serotonin turns into melatonin, which induces sleepiness. Our blood sugar levels decrease, and at 3am, when we are in the middle of our sleep, cortisol levels hit a 24-hour low.
The six-hour eating window also helped lower levels of the hunger hormone ghrelin, which stimulates appetite.
The researchers said eating earlier in the day syncs with circadian rhythms – the body’s internal body clock.
Circadian rhythms determine the body’s hormones and metabolism, relating to hunger, tiredness and mood, based on exposure to sunlight.
Co-author Dr Eric Ravussin said coordinating meals with circadian rhythms ‘may be a powerful strategy for reducing appetite’.
Dr Peterson added: ‘We suspect a majority of people may find meal timing strategies helpful for losing weight or to maintain their weight.’
She said this is because these strategies naturally appear to curb appetite, which may help people eat less.
Dr Peterson added: ‘Whether these strategies help people lose body fat need to be tested and confirmed in a much longer study.’
The use of fasting diets for health are heavily disputed. Yesterday, scientists said teenagers who skipped breakfast were more likely to have a high BMI.
Advocates swear by fasting diets for reducing stress, improving energy, protecting against type 2 diabetes and reducing weight.
Previously, research on the topic was conflicted on whether meal timing strategies helped with weight loss by burning more calories or by lowering appetite.
This study did not test other fasting methods, including the popular 5:2, which is fasting for two days on 500 calories and eating healthily but normally for five.
Nor did it test the 16:8, which restricts eating to midday to 8pm, with a 16 hour fasting window overnight.
But researchers have previously found that eating between 8am and 2pm, followed by an 18-hour daily fast kept appetite levels more even throughout the day, in comparison to eating between 8am and 8pm.
WHAT IS THE INTERMITTENT FASTING 16:8 DIET?
The 16:8 diet is a form of intermittent fasting.
Followers of the eating plan fast for 16 hours a day, and eat whatever they want in the remaining eight hours – typically between 10am and 6pm.
This may be more tolerable than the well-known 5:2 diet – where followers restrict their calories to 500–to-600 a day for two days a week and then eat as normal for the remaining five days.
In addition to weight loss, 16:8 intermittent fasting is believed to improve blood sugar control, boost brain function and help us live longer.
Many prefer to eat between noon and 8pm as this means they only need to fast overnight and skip breakfast, but can still eat lunch and dinner, along with a few snacks.
When you do eat, it is best to opt for healthy options like fruits, vegetables and whole grains.
And drink water and unsweetened beverages.
Drawbacks of the fasting plan may be that people overindulge in the hours they can eat, leading to weight gain.
It can also result in digestive problems over the long-term, as well as hunger, fatigue and weakness.