Stick with the program: Some time at the gym is no excuse for blowing your diet.

RODALE NEWS, EMMAUS PA—The results of an Australian study published last month in the online edition of the American Journal of Clinical Nutrition reveal that the relationship between exercise and appetite is more complicated than it seems.

THE DETAILS: Researchers from the Institute of Health and Biomedical Innovation at Queensland University in Brisbane, Australia, recruited 58 overweight people (19 men and 39 women) to complete a 12-week exercise program designed to burn 500 calories per session, five days a week. The exercise—performed on the treadmill, stationary bike, or step or rowing machine—was supervised in the lab and adjusted to make sure each participant continued to burn 500 calories per session as the study progressed. Before working out, the participants ate a fixed breakfast specifically designed for each of them, and answered questions about their appetite and, after breakfast, about their satiety. They ate whatever they wanted for lunch and dinner, and tracked their total calories for each day.

At the end of the 12 weeks, the weight lost by the participants varied widely, but they did, as a group, lose body weight, fat mass, and weight circumference. During that time, the participants’ hunger increased with exercise, but their postbreakfast satiety increased as well. So while exercise seemed raise appetite levels, it also decreased hunger following a meal. It’s these two processes, the study authors conclude, that determine the effects of exercise on the motivation to eat and, consequently, on body weight.

Further complicating the weight-loss equation: Your mileage may vary. “These processes do not operate with the same strength in all individuals who undertake exercise,” they write. So some people may find that exercising makes it easier to eat more, while others will tend to eat less if they work out. “Together, the strength of these two processes may determine whether individuals lose weight with exercise or maintain weight through energy compensation," the researchers say.