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Obese women can improve their health without dieting by changing their eating habits and exercising more, say researchers.

They showed that lifestyle changes including exercise programmes such as tai chi, aqua aerobics and circuit training, coupled with behaviour modification, can improve health risks in obese women even if they do not lose significant amounts of weight.

"People of all sizes and shapes can reduce their risk of poor health by adopting a healthier lifestyle," said Dr Erika Borkoles, of Leeds Metropolitan University in England.

Obesity is a growing public health problem worldwide and a leading preventable cause of death. An estimated 300 million people worldwide are obese.

Public health experts expect the figure to increase unless urgent action is taken. Being overweight or obese increases the risk of diabetes, heart disease and some cancers.

Borkoles and her colleagues, who are presenting their research at the UK Society of Behavioural Medicine meeting, tested the programme that focuses on health benefits rather than weight loss in 62 obese women.

Although the average weight loss was small, from 108.4kg to 106kg, after a year on the programme, the women showed improvements in their self-image, were fitter and less stressed.

"Psychological and physical health improved independent of substantial weight loss," said Borkoles, adding that weight is a poor predictor of health.

There were also improvements in blood pressure, cholesterol levels and heart rates.

The women, aged 24 to 55, were encouraged not to diet but were taught about healthy eating, how to read food labels and prepare nutritious meals. They also had to do four hours of exercise a week.