A team of psychologists helped clinically obese women to take exercise and eat sensibly, but told them not to try losing weight.
After a year the women were only slightly lighter but significantly more healthy.
Tests showed they were also happier with themselves and less stressed.
Dr Erika Borkoles, from Leeds Metropolitan University, who led the study, said: “People have a natural diversity of body size. Dieting is not effective long term and can be very dangerous.
“My take home message is, don’t go on a diet, change the way you eat.”
A total of 62 women aged 24 to 55 took part in the study. They were split into two groups, one of which underwent the three-month training programme set up with the help of Leeds City Council.
All the women were clinically obese with a body mass index (BMI) of more than 30. BMI is a measurement based on a person’s height and weight.
Those in the programme took part in activity classes such as tai chi, aqua aerobics and circuits for four hours a week.
They were also given advice on reading food labels, cooking food and knowing how to respond to feelings of hunger or feeling full.
One exercise involved making a chocolate bar last a whole week.
However the women were not told to follow any kind of slimming diet.
After three months the average weight of women taking part in the programme dropped from 108.4 kilograms to 104.6 kilograms.