Obese or overweight adults can improve their health by losing even a small amount of weight if they keep it off, a British health watchdog said.
The National Institute for Health and Care Excellence (NICE) has issued new guidelines to help people shed weight and avoid putting it back on.
"We all know that eating less and being more active will help us lose weight, but it can be quite hard to put it into action especially in the long-term, which is why some people need additional support," said Professor Kate Jolly, professor of public health at the University of Birmingham and NICE guidance developer.
Providers of weight management programmes would need to demonstrate that participants maintain their weight loss and their programmes are effective at 12 months or beyond.
Professor Mike Kelly, director of the Centre for Public Health at NICE, said: "The number of people who are overweight or obese in England is rising. More than a quarter of adults are now classified as obese and a further 42 percent of men and a third of women are overweight."
"It not only damages their health but dealing with the long-term consequences of obesity costs the NHS around Ģ5.1 billion each year. It is a huge cost to the health service."
The watchdog said that obesity increases the risk of serious conditions including diabetes, heart disease and some cancers and even a modest weight loss of 3 percent kept off for life may improve or prevent health problems.
Carol Weir, guidance developer for Nice and head of service for nutrition and dietetics at Leeds Community Healthcare NHS Trust said: "Programmes focusing on diet, activity and making changes to behaviour really are effective in helping people lose weight, and this guidance will help ensure that these programmes are commissioned and run in the best possible way."