Research finds reducing body mass lowers cancer risk

A study by QIMR Berghofer Medical Research Institute scientists has exposed further links between obesity and cancer. Find out how much weight you need to lose to cut your risk of dying before retirement by up to 30 per cent.

OVERWEIGHT and obese people can slash their risk of dying of cancer before retirement age by up to 30 per cent if they shed their excess kilograms, Queensland research has found.

The study by QIMR Berghofer Medical Research Institute scientists also found that by reducing body mass index by about five points – or 15 kilograms in a person of average height – an obese person can cut their chances of developing cancer in later life by 10 per cent.

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Statistical geneticist Stuart MacGregor said the research, involving hundreds of thousands of people, looked at genetic markers related to a person’s weight to explore the relationship between obesity and cancer.

Associate Professor MacGregor said the study added to growing evidence that obesity caused cancer and may explain why rates had increased as populations had become heavier.

He said people who were genetically predisposed to being overweight were at increased risk of developing particularly aggressive tumours that could result in death, such as cancers of the oesophagus and endometrium.

But he stressed that all overweight and obese people could change their cancer risk by shedding kilograms because only a third of weight gain was attributable to their genes and two-thirds to lifestyle and other factors.

“I want to make it clear that everyone who’s overweight should be able to reduce their cancer risk by losing weight,” he said.

Dr Stuart MacGregor from the QIMR Berghofer Medical Research Institute. Picture: Sarah Marshall

Using complex genetic mathematics, the study found the likelihood of developing any type of cancer by age 65 escalated with each five-unit increase in body mass index (BMI) – calculated by dividing weight in kilograms by height in metres squared.

The World Health Organisation guideline for ideal weight is a BMI of between 18.5 and 24.9.

People with BMIs between 25 and 29.9 are considered overweight and those with BMIs 30 and above are obese.

Prof MacGregor said the study highlighted the need for more research into whether the BMI-cancer relationship varied with different types of weight gain, such as fat versus muscle mass, and between body types.

“You have pear-shaped and apple-shaped bodies where the fat distribution is in different areas around the hips or the waist,” he explained. “The relationship between the subtleties of that and cancer rates is less clear. It’s something we’re looking into.”

About two-thirds of adult Australians are classified as overweight or obese.

“In terms of overall public health, we already know that being overweight is a risk factor for cardiovascular disease and other diseases,” Prof MacGregor said.

“There’s many reasons to lose weight. This is just an extra one which will hopefully motivate people. No-one wants to die before retirement due to cancer.”

The QIMR Berghofer study is published in the British Journal of Cancer.