While loosening your belt after Thanksgiving dinner, you may want to clip a pedometer to it. The reason: Wearing a step counter leads to weight loss and lower blood pressure, according to new research Tuesday. The researchers found that a pedometer is an unusually good motivator to get people to walk more.

People who used a pedometer for 18 weeks walked an average of seven additional miles weekly and shaved 0.4 points from their body mass index, a measure of weight that considers both pounds and height. That decrease is the equivalent of 2.5 pounds for a 5-foot, 6-inch person with an initial weight of 195 pounds, according to the report in the Journal of the American Medical Association.

The device “is a great little motivator,” said Stanford University internist and lead author Dr. Dena M. Bravata. “I never anticipated such a small intervention could have such a big effect.”

Two-thirds of U.S. adults are overweight or obese and more than half of all adults do not get the 30 minutes of daily exercise recommended by the Department of Health and Human Services, according to the report.

A pedometer, which can cost as little as $10 to $15, is an inexpensive tool to get people walking, researchers said. If 10 percent of U.S. adults began a regular walking plan, $5.6 billion in annual heart disease costs could be saved, according to the report, which was funded by a grant from the National Institute on Aging.

Bravata and colleagues from Stanford and the University of Minnesota analyzed results of 26 studies of pedometer use, with a total of 2,767 participants. Most were female, overweight and relatively inactive before they started their walking programs. The average duration of the studies was 18 weeks.

The walking programs varied considerably. Nearly all programs included a step goal and diary in which participants recorded their daily activity. Many of the programs included physical activity counseling, and five were centered in the workplace.

Researchers found that participants who wore a pedometer increased their activity by 27 percent, or by more than 2,000 steps daily, the equivalent of one mile.

Systolic blood pressure fell an average of 3.8 millimeters of mercury, a sizable improvement, because the blood pressure of participants in general was not that high, Bravata said. A reduction of 2 millimeters is associated with a 10 percent reduction in the risk of death from stroke and a 7 percent drop in the chance of cardiovascular death, according to the study.

Researchers found that participants who were given step goals or kept diaries increased their activity the most. Although most participants did not meet their goals, just having one to shoot for was a “potent motivator,” Bravata said.

Workplace programs were associated with smaller increases in activity, probably because people attracted to the programs already were fairly active, researchers said.

Dr. Allan Abbott, a professor at the Keck School of Medicine at the University of Southern California, who was not connected to the study, said the report changed his mind about pedometers and he now planned to add them to his patients' walking programs.

“This clearly shows the benefit of using pedometers as a motivator of physical activity,” said Abbott, who focuses on fitness and physical activity.

Kelly D. Brownell, director of the Rudd Center for Food Policy and Obesity at Yale University, said that although the amount of weight lost in the study was small, the cost of a pedometer also is small.

“The real issue is whether people out there on their own - not part of a program where there is an expectation that they will use a pedometer - will use the device long enough to achieve lasting benefit,” he said.