Why you should exercise in the morning to lose weight… and in the afternoon if you have diabetes 

Every year, millions of us commit to a new exercise regimen, looking for a quick way to trim our waistlines.

But what if the secret to effectively burning fat isn’t just through exercise, but when we choose to exercise?

Scientists are increasingly learning that the circadian rhythm – ie our internal body clock – in each of our tissues plays an important role in how efficiently they perform at different times of the day.

For example, research shows that athletes perform best in the late afternoon and early evening.

When Dutch sports scientists investigated the performance of swimmers at the Olympic Games in Athens, Beijing, London and Rio, they found that they achieved their fastest time around 5 p.m. These principles are believed to apply to all of us.

“Exercise timing may play a role in fine-tuning some exercise outcomes,” says Juleen Zierath, a professor of integrative physiology at the Karolinska Institute in Sweden, and a leading expert on the link between body clock and biology.

“Much of our physiology — from body temperature to heart rate and genes that control fat metabolism — works 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 various hormones.

Because while our muscles are most powerful and flexible later in the day, new research shows that we can burn fat more efficiently if we exercise in the morning.

Professor Zierath says there are thousands of genes that produce enzymes that help convert fat stored in cells into the energy we use when we exercise. And it seems that these genes are most active in the morning.

So while you may not be at your strongest and fastest, it’s the best time to lose 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 up, their body fat showed much higher levels of the enzymes used to metabolize fat.

When they did the same amount of exercise much later in the day, there were much lower levels of these enzymes.

‘The implication is that if you are a regular morning exerciser, your body is probably more sensitive to breaking down fat and using it as energy,’ says Professor Zierath.

“And what that could mean is that you could potentially lose a little more weight.” Exercise also helps with weight maintenance, so morning exercise can prevent weight gain.’

Scientists suspect that the body’s preference to burn fat after morning exercise is related to the natural pattern of hormones called glucocorticoids that control how the body retains and accumulates fat.

Glucocorticoids are found throughout the body, particularly in adipose tissue. Their natural pattern is to peak around 8am, which gets us moving and whets our appetite, before reaching their lowest level around 3am when we’re deep asleep.

Exercising in the morning fits well into this daily cycle, because glucocorticoid levels are already elevated, so the body doesn’t produce extra fat cells.

However, when we exercise in the evening, it triggers a surge of glucocorticoids, causing the body to produce new fat cells to replace some of the fat cells you just burned, minimizing the benefit to your waistline.

This may help explain why shift workers are more prone to weight gain: Their nighttime patterns of stress and activity cause large spikes in glucocorticoids at times when the body would normally be asleep, causing more fat cells to be produced.

And as a result, shift workers are more likely to gain weight compared to people with normal circadian patterns, even if they eat a similar number of calories per day.

This is due to 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 evolved around a pattern of being awake during the day and sleeping at night.

“Fat is strongly influenced by hormones,” says Dr. Teruel. “If glucocorticoid levels are disrupted, it has a huge effect on fat.

“If you exercise later, these hormones are secreted much more strongly in the evening, which is not good,” she explains.

“Your body wants to rest right now, and pumping it up equates to staying up really late and not sleeping.”

Instead, Dr. Teruel that a morning workout, regardless of length or type of exercise, will have more weight loss benefits.

However, exercising after lunch can have several 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 will be stored as fat.

Professor Zierath says: ‘We studied people with type 2 diabetes and found that doing high intensity interval training in the afternoon led to the most optimal improvement in their blood sugar levels compared to morning or evening training.’

She also points to a study of more than 92,000 people, published in the journal Nature Communications in February, which found that those who exercised between 11 a.m. and 5 p.m. were less likely to die from heart disease, compared with those who exercised earlier. exercised the day or later. at night, possibly because of the link between blood sugar stability and heart health.

But she stresses that while exercise in the morning or during the day may have the most optimal results, exercise at any time is better than no exercise at all.

The Nature Communications study showed that people who regularly engaged in moderate to vigorous physical activity lived longer than those who did little.

‘You have to listen to your body, because there are a lot of people who say they prefer to be evening runners, while others prefer to be morning runners,’ says Professor Zierath.

She believes that while the evidence might suggest that a morning workout may have more short-term benefits for weight loss, it’s better to have a routine that allows you to be a consistent exerciser. .

“That’s very important,” she says. ‘But maybe you can increase the beneficial effects of exercise by doing it at certain times.’