Exercise as a weight loss strategy works in strange ways

Some types of exercise may be better than others at blunting appetite and potentially aiding in weight management, said a new study of workouts and hunger. It finds that pushing yourself during exercise affects appetite, sometimes in surprising ways.

As anyone who has begun an exercise program knows, the relationships between exercise, appetite, weight control and hunger are often counterintuitive. The arithmetic seems straightforward. You burn calories during exercise and, over time, should drop pounds.

But the reality is more vexing. Most people who start exercising lose fewer pounds than would be expected, given the number of calories they are burning during workouts. Many people even gain weight.

The problem with exercise as a weight-loss strategy seems to be in large part that it can make you hungry, and many of us wind up consuming more calories after a workout than we torched during it, a biological response that has led some experts and frustrated exercisers to conclude that exercise by itself — without strict calorie reduction — is useless for shedding pounds.

But much of the past research into exercise and appetite has concentrated on walking or other types of relatively short or light activities. Some scientists have begun to wonder whether exercise that was physically taxing, either because it was prolonged or intense, might affect appetite differently than more easeful exercise.

So for the new study, which was published in the Journal of Endocrinology, scientists from Loughborough University in Britain and other institutions who have been studying exercise and appetite for years recruited 16 healthy, fit young men.

They separated the men into two groups, each of which would concentrate on one element of exercise.

Throughout their workouts and for an additional few hours, the scientists drew blood to check for levels of a particular hormone, acylated ghrelin, that is thought to influence appetite. Generally, when acylated ghrelin levels rise, so does hunger.

Meanwhile, the second group of volunteers' workouts emphasized length. One day they ran for 45 minutes at a steady pace and on another, strode at the same pace, but for 90 minutes. During a final visit, they sat.

In general, exercise had lowered the men's levels of acylated ghrelin, compared to when they had sat continuously. Vigorous running had blunted acylated ghrelin production more than gentler jogging and longer runs more than briefer ones. The effects also had lingered longest when the exercise had been most protracted. More than an hour after their 90-minute run, most of the men's acylated ghrelin levels remained suppressed.

Interestingly, after the 90-minute run, the men reported feeling less hungry than when they had sat around the lab. But after the short, intense workout, the volunteers soon felt peckish, despite still having low levels of acylated ghrelin in their blood.