Every year, millions of us commit to a new exercise regimen, seeking a quick way to trim our waistlines.
But what if the secret to burning fat effectively is not merely exercising, but when we choose to work out?
Scientists are increasingly finding that the circadian rhythm — i.e. our internal body clock — within each of our tissues plays an important role in how efficiently they perform at different times of the day.
For example, research suggests athletes tend to perform best in the late afternoon and early evening.
When Dutch sports scientists examined the performances of swimmers at the Athens, Beijing, London and Rio Olympics, they found they achieved their fastest times at around 5pm. It’s thought these principles hold true for all of us.
Scientists are increasingly finding that the circadian rhythm — i.e. our internal body clock — within each of our tissues plays an important role in how efficiently they perform at different times of the day (file image)
Dutch sports scientists examined the performances of swimmers at the Athens, Beijing, London and Rio Olympics (file image)
‘Exercise timing might play a role in fine-tuning some of the outcomes of exercise,’ says Juleen Zierath, a professor of integrative physiology at Karolinska Institute in Sweden, and a leading expert on the connection between body clock and biology.
‘A lot of our physiology — from body temperature to heart rate and genes that control the metabolism of fat — operates on a 24-hour cycle.’
Scientists are beginning to learn how all tissues and organs have their own unique schedules in accordance with fluctuations of different hormones.
For while our muscles are at their most powerful and flexible later in the day, new research demonstrates that we can burn fat more efficiently when we exercise in the morning.
Professor Zierath says there are thousands of genes which produce enzymes that help convert fat stored in cells into the energy we use when we exercise. And it seems these genes are at their most active in the morning.
So while you may not be at your strongest and quickest then, it is the best period for losing weight.
In a recent study, published in the journal Proceedings of the National Academy of Sciences, Professor Zierath and colleagues investigated this for the first time, using mice.
They found that when the mice exercised on a treadmill in the first three hours after waking, their body fat showed much higher levels of the enzymes used to metabolise fat.
When they did the same amount of exercise much later in the day, there were far lower levels of these enzymes.
‘The implication is that if you’re a regular morning exerciser, your body is likely to be more sensitive to breaking down fat and using it as energy,’ says Professor Zierath.
‘And what that could mean is that one might potentially be able to lose a bit more weight. Exercise also helps with weight maintenance, so morning exercise may prevent weight gain.’
Scientists suspect the body’s preference for burning fat after morning exercise is linked to the natural pattern of hormones called glucocorticoids, which control how the body maintains and accumulates fat.
Glucocorticoids are found throughout the body, most notably in fat tissue. Their natural pattern is to peak around 8am, which gets us moving and switches on our appetites, before reaching their lowest level around 3am when we are fast asleep.
Exercising in the morning fits nicely with this daily cycle, as glucocorticoid levels are already raised, and so the body does not generate any additional fat cells.
However, if we exercise in the evening, this causes a surge of glucocorticoids, triggering the body to produce new fat cells to replace some of the ones you have just burnt, minimising the benefit to your waistline.
This may help explain why shift workers are more prone to weight gain: their nocturnal patterns of being stressed and active cause big surges in glucocorticoids at times when the body would normally be asleep, leading to more fat cells being created.
And as a result, shift workers are more likely to gain weight compared with people who have normal circadian patterns, even if they eat a similar number of calories a day.
This is the consequence of evolution, explains Dr Mary Teruel, an associate professor of biochemistry at Weill Cornell Medicine in New York, and a world-leading expert on glucocorticoids. She points to how our bodies have developed around a pattern of being awake during the day and asleep at night.
‘Fat is strongly influenced by hormones,’ says Dr Teruel. ‘If the levels of glucocorticoids are disrupted, that has a huge effect on fat.
‘If you exercise later, these hormones start being secreted to a much greater extent in the evening, which isn’t good,’ she explains.
Scientists suspect the body’s preference for burning fat after morning exercise is linked to the natural pattern of hormones called glucocorticoids (file image)
‘Your body wants to rest at this time, and if you pump it up it’s equivalent to staying up really late and not sleeping.’
Instead, Dr Teruel suggests that a morning workout, no matter the length or type of exercise, will yield greater benefits for losing weight.
However, working out post-lunch can have different benefits. Professor Zierath says your blood sugar will be more stable if you exercise in the afternoon — meaning it’s the best time for people who either have type 2 diabetes or are at risk of developing it.
This is important because if your blood sugar fluctuates too much, the excess sugar starts to be stored as fat.
Professor Zierath says: ‘We’ve studied people with type 2 diabetes and found that when they did high-intensity interval training in the afternoon, this led to the most optimal improvement in their blood sugar control compared with morning or evening exercise.’
She also points to a study of more than 92,000 people, published in the journal Nature Communications in February, which found those who exercised between 11am and 5pm were less likely to die of heart disease, compared with those who exercised earlier in the day or later at night, possibly due to the link between blood sugar stability and heart health.
But she emphasises that while morning or daytime exercise might have the most optimal outcomes, exercise at any time is better than none at all.
The Nature Communications study demonstrated that people who frequently engaged in moderate-to-vigorous physical activity lived longer than those who did barely anything.
‘You have to listen to your body because there are many people who say they prefer being evening runners, while others prefer being morning runners,’ says Professor Zierath.
She feels that while the evidence might suggest that a morning workout can offer more short-term benefits for losing weight, it is better to have a routine which enables you to be a consistent exerciser.
‘That’s really important,’ she says. ‘But you might be able to boost the beneficial effects of exercise by doing it at certain times.’
Under the microscope…
Singer Engelbert Humperdinck, 87, answers our health quiz.
Can you run up the stairs?
I actually enjoy going up and down the stairs. It’s part of my fitness routine. I also have a treadmill and a rowing machine at home.
Get your five a day?
I’m a really healthy eater. When I was a child in Leicester my dad always said: ‘Eat slowly and eat well.’ That stayed with me.
Many times. At the moment I’m 15st [he’s 6ft 1½in] but one time, years ago, I weighed over 17st and went on one of the new fad diets going around the Hollywood crowd, which was severely restrictive and made me ill.
I started being very conscious of what I ate and working out for a TV special in Hawaii a few years ago, and I’ve stuck with it.
HOW DID THE PANDEMIC AFFECT YOU?
My darling wife, Patricia, wasn’t well [she had dementia] — but while the pandemic stopped my life on the road temporarily, it afforded me precious time with her.
I was with her every day for a year and a half until God called her [in February 2021].
I love my wine in moderation, and I like an occasional Cuban cigar when I’m out celebrating or have friends over.
When I did my National Service aged 18 everyone smoked, but I gave up when I was about 23 after I developed tuberculosis.
I spent six months in hospital and at one point it was so bad I was given the last rites.
Any family ailments?
My Dad was pretty strong and lived to 91. My mother had a heart condition, I think because she had so many children: there were ten of us.
Even so, she died at 88. There is longevity in the family. One of my sisters reached 99 and another was over 100.
I had a ski accident in Austria in my late 30s. I didn’t break my leg, but it was horribly twisted. It took me ages to get it back in shape.
Pop any pills?
Multi-vitamins because I sometimes don’t get the same nourishing foods when I’m on the road as I do at home.
EVER HAVE PLASTIC SURGERY?
In the event of an accident, I would, but not otherwise. I use really good creams and drink lots of water to keep the wrinkles away.
Tried alternative remedies?
About 40 years ago, during a stressful period, I was introduced to acupuncture.
Dr Ha, who performed the helpful treatment, remains one of my closest friends.
What keeps you awake?
Streaming TV series that I can’t stop watching in bed.
Like to live for ever?
I am grateful for the life I have. When God calls me, I hope that I will have a backstage pass to the gates of Heaven.
Eneglbert’s new album, All About Love, is out now.