Diet Plus Exercise Is Better for Weight Loss than Either One Alone

Everyone knows that eating a low-fat, low-calorie diet and getting regular exercise helps shed pounds, but a new study led by researchers at Fred Hutchinson Cancer Research Center has found that when it comes to losing weight and body fat, diet and exercise are most effective when done together as compared to either strategy alone.

The results of this randomized trial, led by Anne McTiernan, M.D., Ph.D., director of the Prevention Center and a member of the Hutchinson Center’s Public Health Sciences Division, were published online April 14 in Obesity.

The majority of women in the study who both improved their diet and exercised regularly shed an average of nearly 11 percent of their starting weight, which exceeded the study’s goal of a 10 percent or more reduction in body weight.

“We were surprised at how successful the women were,” McTiernan said. “Even though this degree of weight loss may not bring an obese individual to a normal weight, losing even this modest amount of weight can bring health benefits such as a reduced risk of diabetes, heart disease and cancer.”

The year-long intervention involved 439 overweight-to-obese, sedentary, postmenopausal Seattle-area women, ages 50 to 75, who were randomly assigned to one of four groups:
• exercise only (goal: 45 minutes of moderate-to-vigorous aerobic exercise per day, five days a week, including three days at the Hutchison Center’s exercise facility);
• diet only (goal: 1,200 to 2,000 calories a day, depending on starting weight, and fewer than 30 percent of daily calories from fat);
• exercise and diet (with the same goals as above); and
• no intervention.

“Although numerous studies have examined the effect of lifestyle interventions on weight, few have focused on postmenopausal women, a group that experiences particularly high rates of overweight and obesity,” McTiernan said.

At the end of the intervention, the researchers found that the women in the exercise-only group lost, on average, 2.4 percent of their starting weight (with a mean weight loss of 4.4 pounds) as compared to an average weight loss of 8.5 percent among women in the diet-only group (with a mean weight loss of 15.8 pounds). The greatest weight loss was achieved by women who both changed their diet and exercised regularly; these women shed an average of 10.8 percent of their starting weight (with a mean weight loss of 19.8 pounds). Two-thirds of the women in this group achieved the study goal of losing at least 10 percent of their starting weight.

Body-mass index (height-to-weight ratio), waist circumference and percentage of body fat were also significantly reduced among the three intervention groups. The women who were assigned to the nonintervention control group, who did not change their diet or activity level, on average lost less than a pound – a statistically insignificant decrease.