Q: Is weight loss truly greater when exercising at a moderate level (say, 60 percent of capacity) instead of a more intense level (85 percent)?
A: Actually, the reverse is true. Minute for minute, you expend more energy, and burn more calories, if you exercise intensely rather than moderately. In other words, running for 30 minutes uses more calories than walking for half an hour.
I suspect, though, that many refer to the widespread belief that they burn more fat when they exercise moderately rather than strenuously, which is true. During intense exercise, the body needs rapidly combustible calories from carbohydrates, but when you're moving at a relatively unhurried pace, the energy demands are lower, and the body can turn to slower-burning fat for fuel.
According to a 2009 study in The Journal of Strength and Conditioning Research, exercising at 65 to 80 percent of your maximum heart rate, or 105 to 130 beats per minute, maximizes the amount of fat that you burn during a workout, but uses fewer calories per minute than tougher exercise.
Intense exercise may also quell later appetite. In a study this year, men who rode stationary bicycles hard for 30 minutes consumed far fewer calories afterward than when they rode moderately for 30 minutes and had lower blood levels of the hormone ghrelin, which is known to stimulate appetite.
Still, the keys to losing weight with exercise are common sense and restraint.
"It all comes down to energy balance," or calories in and calories out, said Edward Melanson, a professor at the University of Colorado-Denver School of Medicine, who has conducted many studies of exercise and weight loss.
Most of us burn only 200 or 300 calories in a moderate 30-minute exercise session, he said, adding, "you replace that with one bottle of Gatorade."