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Evening is the best time of day to exercise for glycaemic control, ACU study

Men who were overweight and at risk of diabetes had better overnight blood sugar control when they exercised in the early evening rather than in the morning, a new ACU study has found.

The study, which looked at men who were inactive, at risk of type 2 diabetes and fed a high-fat diet, found that those who completed later workouts upped their metabolic health more than those who performed the same exercise earlier in the day.

The results, published in the journal Diabetologia, add to growing evidence that when we exercise may alter how we benefit from that exercise.

Researchers at ACU’s Mary MacKillop Institute for Health Research have known for some time that the circadian clock and metabolism are tightly intertwined. 

Lead author Trine Moholdt, who is also with the Norwegian University of Science and Technology, said these new findings were especially important for people with diabetes as they often have glucose regulation problems.

“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,” Dr Moholdt said.

“The group who exercised in the early evening had lower nocturnal glucose concentrations.  That is important 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. 

“Our 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.

The study pooled data from the 24 men who consumed a high fat diet for 11 consecutive days. They either worked out in the morning, afternoon or not at all.

Participants were between the ages of 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.

After five days, researchers found that the benefits of evening workouts decisively trumped those of morning exercise.

Fasting blood glucose, insulin, cholesterol, triacylglycerol and LDL-cholesterol concentrations decreased only in participants allocated to evening exercise training.

“This study does suggest that evening exercise may be more beneficial for people with disrupted metabolism than the same exercise done earlier in the day, but I think it is vital to point out that it is much more important that you keep exercising than what time of day you are doing it,” she said.