Current obesity levels will explain 10,000 cases of thyroid cancer in the next 10 years and most of those will be men, a new Australian study shows.

Being overweight is more likely to cause thyroid cancer in men, than in women, the study published in the International Journal of Cancer says.

On the whole, women are two to three times more likely to develop thyroid cancers but when caused by excess body fat, there is more risk for men.

Two in five cases are then attributable to being overweight or obese, as opposed to one in 10 for women.

Thyroid cancer has already been linked to fatness but in this world-first study, Dr Maarit Laaksonen from the University of NSW has evaluated the thyroid cancer burden attributable to current obesity statistics and compared this by sex.

"It is still not well understood what causes the sex difference in overweight/obesity-related thyroid cancer risk," she said.

"But our findings add evidence to the urgent need to halt and reverse the current global trend in weight gain, especially obesity and especially in men."

Right now, 75 per cent of Australian men and 60 per cent of Australian women are deemed to be overweight or obese.

In all, Dr Laaksonen found one in five future thyroid cancers in Australia would be attributable to the current levels of obesity.

This is worrying, she says, as the prevalence of obesity in Australia has doubled in the past two decades.

"This finding translates to close to 10,000 thyroid cancers in the next 10 years," Dr Laaksonen said.

"Obesity explains 75 per cent of this burden in Australia."

The study's findings were based on seven Australian cohort cancer studies involving about 370,000 participants, taking in obesity/overweight data from the 2017-2018 National Health Survey.

It is not well understood what causes the remaining four in five cases of thyroid cancer, Dr Laaksonen says. Other lifestyle factors do not seem to play a significant role.

"Thyroid cancer is a bit like prostate cancer that its risk factors are not yet very well understood," she said.