Intense exercise can help us eat less
STRENUOUS exercise seems to dull the urge to eat afterwards 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 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.
Researchers at the University of Western Australia in Perth recruited 17 overweight-but-otherwise-healthy young men in their 20s or 30s, who were made to participate in various workouts on four separate days.
One of these sessions was spent resting for 30 minutes, while on another day, the men cycled continuously for 30 minutes at a moderate pace. The third session comprised 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.
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.
As it turned out, gruel was quite appealing to the men after resting or pedalling moderately, but their appetites were noticeably blunted by each of the interval workouts, and in particular by the most strenuous 15-second intervals.
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.
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 after the very intense 15-second intervals than after any of the other workouts.
These results parallel those of another study published last year in the journal PLoS One, for which obese teenage boys were made to do similar workouts on three occasions.
After a highly intense session where they had burned about 330 calories, the boys ate significantly less overall, consuming about 10 per cent fewer calories.
The upshot of both of these studies is that intense exercise "leads to a short-term suppression of food intake", said Mr Aaron Sim, a postgraduate researcher at the University of Western Australia.
That conclusion would seem to be fine news for anyone hoping to embark on exercise to trim a waistline. But Mr Sim cautions that the studies available to date are very short-term.
Whether or not weeks or months of intense training would have an impact on long-term weight management remains to be determined, he said.
It's also important to note that both of these studies involved fairly young male volunteers, all of them overweight. Whether the findings would apply equally to women, older men and people of either gender who are of normal weight remains unknown.