Weighing yourself daily and adjusting diet and exercise levels based on what the scale says is the key to keeping pounds off, according to a study on maintaining weight loss.

Dieters in weight-loss programs may lose about 10 per cent of their weight and gain health benefits. But research suggests most regain about one-third of the dropped poundage within a year, and return to where they started in three to five years.

"Stepping on a scale isn't enough," said study author Rena Wing, a professor of psychiatry at Brown Medical School in Providence, R.I. "You have to use that information to change your behaviour, whether that means eating less or walking more.

"Paying attention to weight — and taking quick action if it creeps up — seems to be the secret to success."

The research by Wing and her colleagues is in Thursday's New England Journal of Medicine. 

The study involved 314 women who had lost about 20 per cent of their body weight, or about 42 pounds on average, in the previous two years.

The women were divided into three groups.

One group had participants in a weight maintenance program over the internet. Members of another group were in face-to-face meetings, and the rest were controls who received quarterly newsletters about eating and exercise.

The 18-month weight maintenance program offered advice such as what to eat for breakfast and how much exercise to get.

Participants reported their weight weekly, aiming to keep weight to within five pounds of their starting point.

The weight maintenance program used a colour-coded system:

• Green: Those who stayed within three pounds of their start weight received encouraging phone messages and green treats such as mint gum.
• Yellow: People gaining between three and four pounds were told to adjust their eating habits or exercise routine.
• Red: If someone gained five pounds or more, they were urged to use a toolbox containing items such as a meal replacement shake, a pedometer, a diet diary and their own weight-loss success story.

Daily weigh-ins

Among women in the control group, 72 per cent gained five or more pounds, compared with 46 per cent in the face-to-face group and 55 per cent for those receiving internet tips, the study reports.

Women in the intervention group who weighed themselves daily had an 82 per cent drop in the odds of regaining five or more pounds compared to those who did not weigh themselves daily. But daily weighing in the control group made little difference in putting the pounds back on, which suggests acting on what the scale shows is key, Wing said.

No differences were found in dietary intake or activity levels, although that could be because of the self-reporting nature of the study, the researchers said.

Concerns have been raised that people may become uptight about daily weight fluctuations, but the clinical guidelines of the U.S. National Heart, Lung, and Blood Institute say "regular self-monitoring of weight is critical for long-term maintenance."

The study also suggests interventions may help during weight maintenance, perhaps because it makes dieters more accountable, experts said. And the findings on people who lost about 20 per cent of their body weight may not apply to those who lose less.