Why obese people regain weight after dieting

Obese people may regain weight after dieting due to hormonal changes, a University of Melbourne and Austin Health study has shown.

The study was published in the New England Journal of Medicine.

Worldwide, there are more than 1.5 billion overweight adults, including 400 million who are obese. In Australia, it is estimated more than 50 per cent of women and 60 per cent of men are either overweight or obese.

Although restriction of diet often results in initial weight loss, more than 80 per cent of obese dieters fail to maintain their reduced weight.

The study involved 50 overweight or obese adults, with a BMI of between 27 and 40, and an average weight of 95kg, who enrolled in a 10-week weight loss program using a very low energy diet. Levels of appetite-regulating hormones were measured at baseline, at the end of the program and one year after initial weight loss.

Results showed that following initial weight loss of about 13 kgs, the levels of hormones that influence hunger changed in a way which would be expected to increase appetite. These changes were sustained for at least one year. Participants regained around 5kgs during the one-year period of study.

Professor Joseph Proietto from the University of Melbourne and Austin Health said the study revealed the important roles that hormones play in regulating body weight, making dietary and behavioural change less likely to work in the long-term.

"Our study has provided clues as to why obese people who have lost weight often relapse. The relapse has a strong physiological basis and is not simply the result of the voluntary resumption of old habits," he said.

Dr Proietto said although health promotion campaigns recommended obese people adopt lifestyle changes such as to be more active, they were unlikely to lead to reversal of the obesity epidemic.

"Ultimately it would be more effective to focus public health efforts in preventing children from becoming obese."

"The study also suggests that hunger following weight loss needs to be addressed. This may be possible with long-term pharmacotherapy or hormone manipulation but these options need to be investigated," he said.

The study was done in collaboration with La Trobe University.

(Source: The University of Melbourne: New England Journal of Medicine)