In an eight-year study of more than 40,000 runners, researcher Paul Williams, Ph.D., found that weight gain among men and women who decreased their running distances per week was significantly more than weight loss among men and women who increased their running distances per week by the same amount.
Additionally, substantial weight loss in participants did not occur unless running distances were more than 25 kilometers (15.5 miles) per week for men, and 48 kilometers (29.8 miles) per week for women. Participants who already ran a long distance per week and decreased their running, still maintaining a long distance per week, gained significantly less weight than those whose running distances started shorter and decreased to even less.

Williams believes that exercise has taken a back seat to controlling diet in addressing America’s obesity epidemic. The key, he says, is to start exercising before weight gain actually occurs.

ACSM and the American Heart Association recommend that healthy adults engage in physical activity for at least 30 minutes, five days per week, at a moderate intensity, or 20 minutes, three days per week, at a vigorous intensity. Individuals striving for weight loss may need to exercise as many as 60 to 90 minutes per day.