Women who are clinically obese don't need to diet to improve their health, say UK researchers.
Obese people can get healthier without losing weight
A programme which encouraged women not to diet but to take part in exercise classes found significant improvements in health and mental well-being.
The women in the study were also taught about good eating habits, such as how to cook, and received social support.
After a year, the women had only lost a little weight but were significantly fitter and happier with themselves.
The team from Leeds Metropolitan University and the University of Hull who are presenting the results at the UK Society of Behavioural Medicine Scientific Meeting in Cambridge said a healthy lifestyle could improve health risks regardless of weight.
People of all sizes and shapes can reduce risk of poor health by adopting a healthier lifestyle
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The 62 women aged 24 to 55 years who took part in the study all had a Body Mass Index (BMI) over 30, which is classed as clinically obese.
They were required to do four hours a week of exercise, such as tai chi, aqua aerobics or circuit classes.
The programme also included educational sessions to teach how to read food labels and cook food, and behavioural therapy to help the women respond to body cues such as hunger and feeling full.
One exercise used by the dietician encouraged participants to eat a chocolate bar in small portions over the course of a week.
But the women were encouraged not to diet and eat whatever they wanted in moderation.
Women who took part in the scheme lost a small amount of weight from an average 17st (108.4kg) to an average 16st 7lbs (104.6kg) after the first three months whereas women in the control group put on an average of 7lbs (3kg).
But, despite only a small amount of weight loss, the women in the programme ended up significantly fitter.
Blood pressure, heart rate and cholesterol fell and respiratory fitness increased.
Women also felt better in terms of general well-being, body image, self-perception and stress.
Dr Erika Borkoles, exercise psychologist at Leeds Metropolitan University said health professionals needed to shift their focus from weight loss to helping people become healthier.
"What is important is we don't set people up for failure. Psychological and physical health and metabolic risk factors greatly improved so that should lead us to think differently about intervention programmes.
"Don't go on a diet," she advised. "Change the way you eat, you can eat what you want in moderation."
Dr Borkoles said the programme, which has been set up with Leeds City Council was sustainable as women were taught skills which meant they could take part in exercise classes and they were given discounts to encourage them to continue with physical activity after the 12-month project finished.
"People of all sizes and shapes can reduce risk of poor health by adopting a healthier lifestyle," she added.
Next year the researchers will be measuring the progress of the women four years after the initial intervention.
Dr David Haslam, clinical director of the National Obesity Forum said there was a lot of truth in the message.
"It is quite well known that you can improve your lifestyle and reduce your risk of cancer, stroke and heart disease.
"You can improve fitness without losing weight as you can gain muscle and lose fat and weigh the same or even gain weight.
"But I don't think we should move the focus, it's important to think across the board," he added.