Any weight loss campaigns are a waste of money and obese people will still retain any weight that is lost, according to obesity expert and University of Melbourne professor of medicine Joseph Proietto.

Proietto said in an opinion piece in "The Medical Journal of Australia" that weight loss in obese people only led to changes in energy expenditure and hunger-controlling hormones that encourage weight gain.

''It is likely that it is these physiological adaptations that make it so difficult to maintain weight loss,'' he said.

''Importantly ... in those who are already obese, public health messages encouraging people to eat healthy food and exercise are unlikely to have a long-term impact on their weight.''

Professor Proietto said that political leaders were so focused on lifestyle messages that they have completely ignored the biological reasons for obesity. The funding could be better used for bariatric surgery which does give long-term weight loss for the obese.

''All the money is put into giving messages on television, but actually that doesn't work - you can't convince someone not to eat who's hungry,'' he said.

''If a good tablet came along it would not make it on the PBS [Pharmaceutical Benefits Scheme] because everybody says obesity is a lifestyle disorder only and all you have to do is change your habits. We don't need tablets to lose weight but we do need them to keep it off."

He pointed out that it was important to focus government efforts on preventing obesity in children but that funds should also be available on those already obese. Gastric banding surgery could reverse obesity-related conditions such as type 2 diabetes and obstructive sleep apnea.

''We must help the long-suffering obese in their struggle to maintain a reduced weight,'' he wrote in the journal. ''In the absence of safe, effective pharmacological agents that can be used long-term, bariatric surgery is the most successful intervention for sustained weight loss. Why is it not more often conducted in public hospitals?''

The professor's views on bariatric surgery have been questioned by other experts who don't believe that surgery adequately addresses the causes of obesity.

Obesity Policy Coalition senior policy adviser Jane Martin said that surgery isn't a feasible solution to the nation-wide obesity problem.

''It's time for the government to implement policies that tackle the key drivers of obesity, including protecting children from pervasive junk-food marketing, implementing traffic-light labelling on processed foods, and taxing unhealthy foods together with subsidising healthy foods for those on low incomes,'' she said.