Fat-mass continues to increase in middle-age women but menopause isn't to blame, according to new research from The Australian National University (ANU).

Mr Ananthan Ambikairajah, a PhD Scholar from ANU, says post-menopausal women do have higher belly fat compared to premenopausal women, which could increase their risk of cardiovascular disease and dementia.

"Older women can experience weight gain for many reasons. However, menopause is not one of them," said Mr Ananthan Ambikairajah, from the Research School of Population Health.

"The advice is to watch your shape, as well as your weight."

The research has debunked the widespread myth that menopause causes weight gain - and found that a weight redistribution occurs.

"This change in distribution of bodyweight happens post-menopause and there is an accumulation of visceral fat around the stomach," said Mr Ambikairajah.

"This study found that total leg fat percentage decreased for women after menopause but trunk-fat percentage increased."

Previous research has shown women are at a higher risk of dementia than men. People who are overweight at midlife are also at higher risk of dementia.

High amounts of fat around the stomach are also a risk factor for cardiovascular disease.

"Cardiovascular disease is often thought of as a male dominated disease but it is the leading cause of death in women worldwide," said Mr Ambikairajah.

"The results may help explain why premenopausal women have lower risk of developing cardiovascular disease compared with men of the same age, whereas, post-menopausal women have higher risk compared to men of the same age".

The study looked at weight changes in over one million women using Body Mass Index and Dual Energy X-ray Absorptiometry (DEXA) -- a technology to calculate body composition -- to measure body fat percentage and found menopause had "no significant influence" over total weight gain.

"The accumulation of that central fat is unhealthy and could be a risk factor for dementia," said Mr Ambikairajah.

"There are more women with dementia than men but the reasons for that are under debate."

The average age for menopause is 50-52 but women can also have it earlier or later in life.

"Menopause is a point in time when women stop having their period. After that women are post-menopausal," said Mr Ambikairajah.

"Post-menopausal women oestrogen levels decline and we know oestrogen can protect women's hearts and brains if used soon after menopause."

Mr Ambikairajah says further research about the impacts of oestrogen and fat changes is required.

"I want to make sure women have all the information needed to live healthy and happy lives."

The study is to be published in The American Journal of Obstetrics and Gynecology.