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.
As readers of this column know, 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. 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 percent 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 percent of their endurance capacity, then spinning gently for 4 minutes.
The final session was the toughest, as the men strained through 15 seconds of pedaling at 170 percent of their normal endurance capacity, then pedaled at barely 30 percent 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 standardized 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 pedaling 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 after the very intense 15-second intervals than after any of the other workouts.
These results parallel those of another recent study of exercise intensity and appetite, published last year in the journal PLoS One, for which obese teenage boys were asked to spend 24 hours within an enclosed metabolic chamber that constantly measured their energy intake and output. The boys made three visits, once resting throughout their stay, and on the other two occasions exercising on a stationary bicycle at either a moderate or highly intense pace until they had burned about 330 calories.
Afterward, they were allowed to eat whatever they chose from a varied buffet, and being teenaged boys, they chose plenty, more than replacing their energy output each time. But after the intense session, they ate significantly less over all, consuming about 10 percent fewer calories than after resting or pedaling moderately.
The upshot of both of these studies is that intense exercise “leads to a short-term suppression of food intake,” said Aaron Sim, a postgraduate researcher at the University of Western Australia, who led the study of adults and interval exercise.
That conclusion would seem to be fine news for anyone hoping to deploy exercise to trim a waistline. But Sim cautions that the studies available to date, including his, are very short-term, covering only one session of the various exercise options. “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 normal weight remains unknown.
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 grueling exercise every bit as much.
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