People who weigh in daily are more likely to catch small changes in body weight. 'It's much easier to get back on track if you've just gained a pound or two.'

That's important because experience shows that most dieters regain a third of what they lost within the first year, and two-thirds of it in the second year.

"That's the biggest problem we have. We have lots of ways to help people lose weight. What's the real challenge is getting people to keep their lost weight off over the long term," said Dr. Susan Yanovski, director of the obesity and eating disorders program at the National Institute of Diabetes and Digestive and Kidney Diseases. She had no role in the study, which was funded by her institute.

The Red Zone

The study was led by Rena Wing, a psychologist and director of the weight control center at Brown University Medical School in Providence, Rhode Island.

It involved 291 people, mostly women, who in the previous two years had lost at least 10 percent of their body weight, an average of 44 pounds (20 kilograms). They weighed 171 pounds (77 kilograms) on average when the weight maintenance study began.

They were randomly put into three groups. The Internet and face-to-face groups met through online chat rooms or in person, respectively, with a weight-loss counselor weekly for four weeks and then monthly for 17 months. All submitted weekly weight reports and were counseled if they were in the "red zone," meaning they had regained 5 pounds (2.25 kilograms) or more.

The third group received counseling via monthly newsletters. Participants in all three were advised at the outset on diet and exercise, and were given scales and encouraged to use them daily.

Intensive Support and Contact

A year and a half later, researchers checked on participants, assuming that those who dropped out of the program had regained 5 pounds (2.25 kilograms) or more.

They found that 46 percent of the face-to-face and 55 percent of the Internet groups were in the "red zone," compared with 72 percent in the newsletter group. The median weight gain was 2.5 pounds (1.125 kilograms) in the face-to-face group, 6 pounds (2.7 kilograms) in the Internet group and 10.4 pounds (4.68 kilograms) in the newsletter group.

This, like other research, shows that intensive support and contact, whether in person or online, help dieters maintain weight loss. What surprised researchers was how well the results tracked with how often people stepped on the scales.

Achilles Heel of Obesity Treatment

At the start of the study, about 40 percent of participants in each group were weighing themselves daily. Eighteen months later, that had fallen to 30 percent in the newsletter group, but had increased to 65 percent of the Internet group and 72 percent of the face-to-face group.

Among daily weighers, only 39 percent regained 5 pounds or more, but 68 percent of those who weighed themselves less frequently did.

"You're more likely to catch small changes in body weight" if checking weight daily, Wing said. "It's much easier to get back on track if you've just gained a pound or two."

Gary Foster, clinical director of the weight and eating disorders program at the University of Pennsylvania, said the study "focuses on the Achilles heel of obesity treatment" -- finding ways to make weight-loss last for many years.

People need concrete, simple things to do like weighing themselves to help them stay in line, he said.

Other things known to help keep lost pounds from coming back are getting regular exercise and eating a low-fat, low-calorie diet.