Diet plus exercise is more effective for weight loss than either method 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.

"This study shows that you get the biggest bang for your buck by combining a healthy weight-loss diet -- which in this case meant reducing calories by cutting fat intake and boosting the consumption of low-calorie foods -- with regular, moderate-intensity aerobic exercise," McTiernan said. "You don't need to be an athlete; walking, biking or gym cardio machines all work well. Start slowly and gradually increase to 45 minutes of activity a day, more if you are able."

In addition to promoting weight loss and preventing weight gain over time, regular exercise helps with balance, strength and fitness. "This helps older people keep active overall, which has been shown to prolong a healthy life," McTiernan said.

The study also found that the women who lost the most weight and body fat kept a food journal, writing down everything they ate and drank with the exception of water and no-calorie drinks. Other strategies associated with the most successful weight loss included preparing meals at home and eating out less often at restaurants. "Doing your own cooking gives you the most control over calories," McTiernan said.

The combined diet-plus-exercise arm of the study followed the current nutrition and physical activity recommendations by the National Institutes of Health Obesity Education Initiative Expert Panel. "Our clinical trial supports these recommendations," McTiernan said.

Despite the overwhelming evidence for the benefits of lifestyle-induced weight loss, there are still major barriers to implementing these programs, the authors wrote. To this end, McTiernan and colleagues are conducting ongoing follow up of these study participants to try to determine factors -- both psychological and behavioral -- that are associated with long-term weight-loss maintenance. "Identifying factors that help women not only lose weight but keep it off long term will help steer the development and implementation of obesity-treatment programs that have the greatest promise to impact public health," she said.

The National Cancer Institute funded the research, which also involved investigators from the University of Washington School of Medicine, the NCI Office of Cancer Survivorship, the University of British Columbia and Harvard Medical School.