In the morning? In the evening? Researchers have been chasing the idea that the time of day we exercise is key to getting best results – for losing weight, clearing fats and sugars from the blood stream, or improving heart health.

The results appear to have been contradictory at times, except when the studies have focused on people with or at-risk of type 2 diabetes – which is actually most of us.

One vexing problem we all face as we put on weight and try to shift it with exercise: our metabolism has become lazy and putting it back into high gear seems impossible.

Can working out at a particular time of day be the key?

New study focuses on the typical Australian man

A small new study, from the Australian Catholic University, looked at a group of men who were on the brink of tipping into diabetes. In other words, the men were fat and loath to get moving – which accounts for three out of four of us.

These participants were aged between 30 and 45 with a BMI ranging from 27 to 35 kg/m2, did not have known cardiovascular disease or type 2 diabetes, and were not taking prescription medications or undertaking shift-work.

The researchers, from ACU’s Mary MacKillop Institute for Health Research, pushed the point – and brought some consistency – by putting all 24 participants on a high-fat diet for 11 days.

The men were split into three groups in which they exercised in the morning, the afternoon or not at all.

Did they survive?

After five days, the men who exercised in the morning enjoyed a lift in cardiorespiratory fitness – but otherwise were equal with the no-movement control group with unhealthy cholesterol levels, blood-sugar chaos, and molecular signals of impending heart disease and a metabolic slump.

In other words, they were in worse shape than when they started the study.

For those who exercised in the evening, it was happier story: fasting blood glucose, insulin, cholesterol, triacylglycerol and LDL-cholesterol concentrations all decreased.

Useful advice for diabetics

Lead author Dr Trine Moholdt, who is also with the Norwegian University of Science and Technology, said in a prepared statement:

“We found that exercising in the morning or evening induced similar improvements in cardiorespiratory fitness, but nocturnal glycaemic control only improved in the evening exercise group.”

This was an important finding, Dr Moholdt said, because “one of the things that individuals with type 2 diabetes experience are nocturnal spikes in glucose, so when they go to sleep their glucose peaks and spikes in the night.”

The study was able to show “that we could flatten those nocturnal spikes and that’s a really important finding because not only were the night-time glucose concentrations lower, the cholesterol was lower as well.”

Dr Moholdt said optimising both the timing of exercise and meals may have additional effects on the circadian clock to further improve metabolic health.

Other studies

A 2015 study concluded that individuals with type 2 diabetes can lower their risks of cardiovascular diseases more effectively by exercising after a meal.

A 2018 study found that “afternoon exercise is more efficacious than morning exercise at improving blood glucose levels in individuals with type 2 diabetes”.

This study also found that intensely exercising in the morning upsets blood sugar regulation – which tends to be more unstable in the morning, anyway.

A different 2019 study found that consistency in the time of day one exercised was associated with successful weight loss.