Cutting-back on as little as two pieces of chocolate per week could save Australia's health system $373 million a year in foregone knee-replacements, research has found.

According to a Monash University-led study, preventing weight-gain from young adulthood to late midlife to prevent obesity could reduce the need for knee surgery by almost 30 per cent.

Research author Flavia Cicuttini stressed the importance of prevention in improving health outcomes, and said weight-loss recommendations for overweight or obese people with osteoarthritis often came too late.

"Focusing on prevention, with small average long-term changes in energy balance, can make a big difference," Professor Cicuttini said.

The head of Monash's Musculoskeletal Epidemiology Unit said Australians tend to gain up to a kilogram per year over their adult lives.

"For example, eating the average equivalent of two fewer pieces of chocolate per week, or adding 10 minutes of exercise, can prevent the insidious half to 0.5-1 kg weight gain we see per person per year in Australia," Prof Cicuttini said.

"This can result in tangible health gains, improving lives and saving money."

The study tracked data from more than 24,000 people across different weight and age groups over more than 12 years.

In that time more than 5 per cent of participants required complete knee replacements.

The study found 28.4 per cent of surgeries could have been avoided if participants had moved one weight group lower, meaning an average weight-loss of 8-12kg from early adulthood to late midlife would translate to a $373 million saving for the annual health budget.

"We need to focus on preventing or slowing weight gain when people first present with any knee pain, even niggling knee pain," Prof Ciuttini said.

"This slow, steady accumulation of weight adds up, resulting in the obesity we see."