HEALTH Here’s how exercise can help you eat less

Strenuous exercise seems to dull the urge to eat afterward better than gentler workouts, several new studies show, adding to a growing body of science suggesting that intense exercise may have unique benefits.

Short, intense workouts, usually in the form of intervals that intersperse bursts of hard effort with a short recovery time, have become wildly popular lately, whether the sessions last for four minutes, seven minutes or slightly longer.

Studies have found that such intense training, no matter how abbreviated, usually improves aerobic fitness and some markers of health, including blood pressure and insulin sensitivity, as effectively as much longer sessions of moderate exercise.

What has not been clear, though, is whether interval training could likewise also aid in weight control.

So for a study published online in The International Journal of Obesity , researchers at the University of Western Australia in Perth and other institutions set out to compare the effects of easy versus exhausting exercise on people’s subsequent desire to eat.

To do so, they recruited 17 overweight but otherwise healthy young men in their 20s or 30s and asked them to show up at the university’s exercise physiology lab on four separate days. One of these sessions was spent idly reading or otherwise resting for 30 minutes, while on another day, the men rode an exercise bike continuously for 30 minutes at a moderate pace (equivalent to 65 per cent of their predetermined maximum aerobic capacity).

A third session was more demanding, with the men completing 30 minutes of intervals, riding first for one minute at 100 per cent of their endurance capacity, then spinning gently for four minutes. The final session was the toughest, as the men strained through 15 seconds of pedalling at 170 per cent of their normal endurance capacity, then pedalled at barely 30 per cent of their maximum capacity for a minute, with the entire sequence repeated over the course of 30 minutes.

Before and after exercise and rest, the scientists drew blood from the men to check for levels of various substances known to influence appetite. They also provided their volunteers with a standardised liquid breakfast at the end of each 30-minute session.

Then, about 70 minutes later, they let the men loose at a table loaded with a sweetened but bland porridge. The researchers wanted to avoid rich aromas or other aspects of food that might influence the men’s desire to eat; they hoped to isolate the effects of pure appetite — which needs to be robust to make porridge enticing. As it turned out, gruel was quite appealing to the men after resting or pedalling moderately; they loaded their bowls. But their appetites were noticeably blunted by each of the interval workouts, and in particular by the most strenuous 15-second intervals. After that session, the men picked at their porridge, consuming significantly less than after resting or training moderately.

They also displayed significantly lower levels of the hormone ghrelin, which is known to stimulate appetite, and elevated levels of both blood lactate and blood sugar, which have been shown to lessen the drive to eat, after the most vigorous interval session than after the other workouts.

And the appetite-suppressing effect of the highly intense intervals lingered into the next day, according to food diaries that the men completed. They consumed fewer calories during the subsequent 24 hours.

Still, the results are heartening, not least because in Sim’s study, although the exertion involved in the interval sessions was much greater than in the moderate workout, the men reported that they enjoyed the gruelling exercise every bit as much.

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