Body weight and cancer

On this page:

Overweight and obesity is a major cause of cancer

After choosing not to smoke, keeping a healthy weight is the most important way you can reduce your risk of cancer.

Being overweight or obese clearly increases your risk of the following cancers:

  • Breast cancer
  • Pancreatic cancer
  • Bowel cancer
  • Oesophageal cancer
  • Gallbladder cancer
  • Kidney cancer
  • Womb cancer

Click here to read the evidence about how being overweight increases your risk of these cancers.

There is also growing evidence that being overweight could increase the risk of many other cancers, including:

  • Thyroid cancer
  • Brain cancer
  • Leukaemia 
  • Liver cancer
  • Multiple myeloma 
  • Non-Hodgkin lymphoma 
  • Ovarian cancer (before the menopause)

As a nation, we are getting fatter

Overweight and obesity levels have risen dramatically over the last 50 years. Most adults in Ireland now weigh more than they should.

  • Nearly two thirds (61 per cent) of all adults are overweight or obese
  • Nearly one quarter (23 per cent) of all adults are obese
  • Men are more likely to be overweight than women, but obesity rates are about the same

Most worrying is that a quarter of 5-12 year olds are overweight or obese. Obesity in Irish children is higher than most other northern European countries, but similar to Britain.

As a nation, we are getting fatter. And being overweight does not just increase your risk of cancer. It also increases your risk of diabetes, high blood pressure, heart diseases and stroke.

How does being overweight increase my cancer risk?

Research has shown that the most likely cause is that fat cells release hormones that are linked with a higher risk of cancer. For example:

  • Fat cells in your body make the hormone oestrogen and higher levels of oestrogen increase the risk of breast cancer (in women who have had the menopause) and womb cancer.
  • Being overweight also increases the level of the hormone insulin in your body, which can encourage the growth of cancer cells. Higher levels of insulin are a common feature of many cancers, including bowel, kidney and pancreatic cancers.

In summary, excess body fat is not harmless extra ‘padding’. It is active tissue which produces hormones that increase your risk of cancer.

Being overweight is also associated with:

  • gastric acid reflux, where stomach acid leaks out of the stomach and into the oesophagus. This damages the lining of the oesophagus and increases your risk of oesophageal cancer
  • gallstones, which increase your risk of gallbladder cancer.

Overweight people are also more likely to have a poor diet and be inactive, two other risk factors for cancer.

Waist size matters

If you have an apple-shaped body, with fat stored around your waist, you have a higher chance of getting cancer than if you are pear shaped, where fat is stored at your hips and thighs. Simply put, extra fat stored around your waist puts you at greater risk. This is because fat cells in the upper part of the body appear to have different qualities from those found in the lower parts.  

Are you a healthy weight?

There are two ways of finding out if you are a healthy weight: 

  • Body mass index (BMI)
  • Waistline measurement

Body mass index (BMI)

Click here to use our BMI calculator, designed by Safefood.eu

Remember, though, BMI is not always an accurate measure if you are an athlete, pregnant or very short in height.

Waistline measurement

To measure your waistline:

  • Place a tape measure around your waist at the narrowest point between the bottom of your ribs and the top of your hip bone.
  • At this point, measure around your waist. Make sure the tape measure is snug but not marking your skin.
  • Take the measurement at the end of your normal breath.

You are at an increased risk of cancer if:

  • your waistline is greater than 94 cm or 37 inches for men
  • your waistline is greater than 81cm or 32 inches for women. 

Take control of your weight

Weight gain happens when you take in more energy than you use up. Losing weight is a gradual process which takes time. There are no quick fixes.

Being a healthy weight is about getting the balance right between what you eat and how active you are. To lose weight permanently, you will need to change the way you think about food and physical activity for good. Be realistic. For most people who are overweight, losing one or two pounds a week is excellent progress. Some weeks will be more difficult than others, the key is to keep going.

Eating for health and being active go hand-in-hand if you want to take control of your weight and reduce your risk of cancer. The Irish Cancer Society also has developed this page detailing 10 healthy weight habits to help you lose weight and keep your weight in check.

Revised 2016, next revision 2018