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Cancer risk from obesity differs for men and women

Press release issued: 17 December 2020

A new study, led by researchers at the University of Bristol and the International Agency for Research on Cancer (IARC), has revealed that where fat is on our body may lead to different health outcomes for men and women. The research, co-funded by World Cancer Research Fund (WCRF), Cancer Research UK and Diabetes UK, found that having more body fat around your waist is more dangerous for women than it is for men when it comes to risk of developing colorectal cancer (also known as bowel cancer).

This large study, published in BMC Medicine today [17 December], included over 100,000* people. They found that a higher BMI (body mass index; a measure of total fat) is more dangerous for men, whereas a higher waist-to-hip ratio (your waist circumference divided by your hip circumference; a measure of abdominal fat) is more dangerous for women. To discover this, they used an approach, called Mendelian randomisation, that uses genetic information as a proxy measure for weight to investigate the effect of different body fat measures on colorectal cancer risk in men and women.

An increase in BMI of about five kg/m2 raised the risk of colorectal cancer by 23 per cent for men, but only nine per cent for women. Whereas an equivalent increase in waist-to-hip ratio raised the risk for women by 25 per cent, this was only five per cent for men. Colorectal cancer is the fourth most common cancer in the UK but the second deadliest1, yet it is one of the most preventable cancers by eating a balanced diet, being active and maintaining a healthy weight.

Dr Emma Vincent, Research Fellow in the Bristol Medical School: Populational Health Sciences (PHS) and one of the researchers who led the study, said: "Our study, which is the largest to look at the difference between body fat and colorectal cancer risk in men and women, reveals the need for a more nuanced approach when trying to prevent cancer. We are now working to understand exactly how increased body fat causes colorectal cancer, which may give us new targets for reducing risk. This is important because maintaining weight loss is still very difficult."

Dr Anna Diaz Font, Head of Research funding at WCRF, said: "We know that being overweight or obese increases the risk of at least 12 different types of cancer, including colorectal cancer. But this new research reinforces how important it is to include a wide and diverse range of people in research studies, as we don’t yet fully know the differences gender or race may play when it comes to risk of cancer."

Natasha Paton, Cancer Research UK’s health information manager, said: "It's well established that keeping a healthy weight affects many types of cancer. Most research linking excess weight to cancer uses BMI, but this study adds to the evidence that carrying excess fat around the waist is also important.

"People can reduce their risk of bowel cancer by keeping a healthy weight, eating a diet with lots of fibre and less red and processed meat, drinking less alcohol, and not smoking. Diagnosing bowel cancer early saves lives, so if you notice any changes that aren’t normal for you tell your doctor. And we'd encourage people to consider taking up bowel cancer screening when invited."

More research is needed to help understand why this difference between men and women may exist.

* 58,221 people with colorectal cancer and 67,694 controls who did not have colorectal cancer.


'Adiposity, metabolites, and colorectal cancer risk: Mendelian randomization study' by Caroline J. Bull, Joshua A. Bell, Emma E. Vincent, Marc J. Gunte et al in BMC Medicine (open access)

Further information


About World Cancer Research Fund

World Cancer Research Fund is part of a network of cancer charities with a global reach, dedicated to the prevention and survival of cancer through a healthy diet, maintaining a healthy weight, and being more physically active. By funding and supporting research, developing policy guidance and providing health information, we ensure that people can make informed lifestyle choices to reduce their risk of developing a preventable cancer.

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About Cancer Research UK

  • Cancer Research UK is the world’s leading cancer charity dedicated to saving lives through research.
  • Cancer Research UK’s pioneering work into the prevention, diagnosis and treatment of cancer has helped save millions of lives.
  • Cancer Research UK receives no funding from the UK government for its life-saving research. Every step it makes towards beating cancer relies on vital donations from the public.
  • Cancer Research UK has been at the heart of the progress that has already seen survival in the UK double in the last 40 years.
  • Today, 2 in 4 people survive their cancer for at least 10 years. Cancer Research UK’s ambition is to accelerate progress so that by 2034, 3 in 4 people will survive their cancer for at least 10 years.
  • Cancer Research UK supports research into all aspects of cancer through the work of over 4,000 scientists, doctors and nurses.
  • Together with its partners and supporters, Cancer Research UK's vision is to bring forward the day when all cancers are cured.

About Diabetes UK

1.     Diabetes UK’s aim is creating a world where diabetes can do no harm. Diabetes is the most devastating and fastest growing health crisis of our time, affecting more people than any other serious health condition in the UK - more than dementia and cancer combined. There is currently no known cure for any type of diabetes. With the right treatment, knowledge and support people living with diabetes can lead a long, full and healthy life. For more information about diabetes and the charity’s work, visit  

2.     Diabetes is a condition where there is too much glucose in the blood because the body cannot use it properly. If not managed well, both type 1 and type 2 diabetes can lead to devastating complications. Diabetes is one of the leading causes of preventable sight loss in people of working age in the UK and is a major cause of lower limb amputation, kidney failure and stroke. 

3.     People with type 1 diabetes cannot produce insulin. About 10 per cent of people with diabetes have type 1. No one knows exactly what causes it, but it’s not to do with being overweight and it isn’t currently preventable. It’s the most common type of diabetes in children and young adults, starting suddenly and getting worse quickly. Type 1 diabetes is treated by daily insulin doses – taken either by injections or via an insulin pump. It is also recommended to follow a healthy diet and take regular physical activity.

4.     People with type 2 diabetes don’t produce enough insulin or the insulin they produce doesn’t work properly (known as insulin resistance). Around 90 per cent of people with diabetes have type 2. They might get type 2 diabetes because of their family history, age and ethnic background puts them at increased risk. They are also more likely to get type 2 diabetes if they are overweight. It starts gradually, usually later in life, and it can be years before they realise they have it. Type 2 diabetes is treated with a healthy diet and increased physical activity. In addition, tablets and/or insulin can be required. 

For more information on reporting on diabetes, download our journalists’ guide: Diabetes in the News: A Guide for Journalists on Reporting on Diabetes (PDF, 3MB).

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