Exercise 'partly reverses' a fatty diet – but only if you work out in the evening

Young woman jogging at night in the city
Evening exercise may have more potent health benefits. (Stock, Getty Images)

Many people start their day with a morning exercise class, jog or trip to the gym, but new research suggests evening workouts may bring about more potent health benefits.

A sedentary lifestyle has long been linked to obesity and type 2 diabetes, however, less was known about the optimal timing of exercise.

To learn more, scientists from the Norwegian University of Science and Technology analysed 24 overweight or obese men – aged 30 to 45 – who ate a high-fat diet for 11 consecutive days.

Five days in, the men were told to exercise at 6.30am, 6.30pm or not at all for the next five days.

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The new diet "markedly" worsened the men's circulating fat levels, which was "partly reversed" only by exercising in the evening.

Working out at 6.30pm was also linked to reduced blood sugar and cholesterol levels.

Although it is unclear why this occurred, evening exercise may better correspond with our "body clock", leading to "additive effects".

Burger and fries on wooden board on dark stone background. Homemade burger or cheeseburger, french fries and ketchup. Tasty sandwich. Top view with copy space for text
A high-fat diet may be 'partly reversed' by evening workouts. (Stock, Getty Images)

Despite the results, lead author Dr Trine Moholdt told the New York Times: "I know people know this, but any exercise is better than not exercising."

Adults should be physically active every day, with experts stressing the more the better.

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Those of a working-age are advised to be moderately active for at least 150 minutes a week, which could include brisk walking, gentle cycling or even pushing a lawn mower.

If time-pressed, being vigorously active for 75 minutes is advised via jogging, cycling briskly or skipping rope.

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The study's participants, who did not regularly exercise beforehand, were fed a diet where 65% of their calorie intake came from fat. They then cycled at varying intensities across five days.

Being physically active brought about fewer changes to the men's circulating fat levels than the diet itself, however, "only exercise undertaken in the evening was able to partly reverse some of the HFD [high-fat diet] induced changes", as reported in the journal Diabetologia.

There were no "significant changes" between the morning and evening exercisers' blood sugar levels.

Compared to the men who did not exercise across the five days, "lower nocturnal glucose levels were observed in participants who trained in the evening".

"Oxygen uptake" improved in both the morning and evening exercisers, however, only the latter also saw positive changes to their cholesterol and insulin levels.

"Improvements in cardiorespiratory fitness were similar regardless of the time of day of exercise training," wrote the scientists.

That being said, "improvements in glycaemic [blood sugar] control and partial reversal of HFD-induced changes were only observed when participants exercise trained in the evening".

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