'Nudging' people to lose weight by thinking about their lifestyle shows little evidence of success, an analysis of published data suggests.
It showed the step-by-step behavioural approach used in hospitals and clinics led to an average weight loss of 2kg (4.4lb) or less.
The report, by The Cochrane Library, looked at studies involving nearly 4,000 people around the world.
A nutritionist said changing one's mindset was not enough.
The method, known as the transtheoretical model stages of change, is used to encourage people to move towards more healthy forms of behaviour.
The five-step process encourages people to see the need to change and then give it a go.
It has been shown to be successful in helping people quit smoking, and has also been used in alcohol and drug addiction.
The analysis looked at five trials - in the UK, US, Netherlands, Canada, and Australia - involving 1,834 overweight or obese patients, and 2,076 people of normal weight.
The authors, led by Prof Azeem Majeed and Dr Nik Tuah of Imperial College London, found no convincing evidence of any sustained or significant weight loss.
Prof Majeed told the BBC: "Changing people's dietary patterns is very difficult - that's why we've got such a problem with obesity."
Dr Tuah added: "This review does not necessarily challenge the notion that diet and exercise are effective weight loss strategies, but instead raises questions about how to approach lifestyle changes for individuals who want to adopt them."
A spokesperson for the charity, the British Nutritional Foundation, said the report emphasised the need to take concerted action when trying to lose weight.
She said: "Changing one's mindset is not enough. People need to eat less and exercise more to lose weight."