Does obesity cause cancer?

  • Yes, obesity is the second biggest preventable cause of cancer in the UK- more than 1 in 20 cancer cases are caused by excess weight

  • The risk is higher the more weight you gain and the longer you are overweight for

  • The good news is small changes that you keep up over time can make a real difference

What’s my risk of developing cancer if I'm overweight or obese?

Being overweight doesn’t mean that you’ll definitely develop cancer. But if you are overweight you are more likely to get cancer than if you are a healthy weight.

You can help stack the odds against cancer by losing weight or avoiding gaining more weight.

People keeping a healthy weight could prevent around 22,800 cases of cancer every year in the UK.

How can obesity cause cancer?

Extra fat in the body doesn’t just sit there, its active, sending out signals to the rest of your body. These signals can tell cells in our body to divide more often, which can lead to cancer.

Scroll down to find out more about the science…

How do you know obesity is a cause of cancer?

Consistent results from decades of research involving millions of people show the link between obesity and cancer and means we can confidently rule out other explanations (such as chance or other lifestyle factors). There’s also what’s called a dose-response relationship, which means that the risk increases the more weight is gained – so we can be more sure the link is real. And there are good explanations for how extra fat cells in the body could cause cancer. 

International organisations like the International Agency for Research on Cancer and the World Cancer Research Fund agree.

A person’s risk of cancer depends on lots of different factors, including things you can’t change like your age and genes. Other things that can cause cancer, whether that’s tobacco, obesity or the sun, increase a person’s risk of cancer, but do not mean that person will definitely develop cancer. But when we look at a whole population, these lifestyle factors cause more people to develop cancer.

What types of cancer are caused by obesity?

Breast (in women after the menopause), bowel, womb, oesophageal (food pipe), pancreatic, kidney, liver, upper stomach (gastric cardia), gallbladder, ovarian, thyroid, myeloma (a type of blood cancer), and meningioma (a type of brain tumour).

This includes 2 of the most common types of cancer – breast and bowel cancers - and 3 of the hardest to treat – pancreatic, oesophageal and gallbladder cancers.

Is the link the same in children?

No. The link between obesity and cancer is only in adulthood. But a healthy body weight is important for children too.

Two in ten children are overweight or obese before they begin primary school, and one in three children are overweight or obese by the time they leave.

Children who are obese are around 5 times more likely to grow into adults who are obese.

What is my risk?

 
 
Try our new tool to find out how your habits stack up, and what you could do to maximise your cancer prevention potential.

 

How could obesity lead to cancer – a closer look at the science

Firstly, what does fat do in the body?
It has 2 main functions;

  • acts as a store of energy
  • constantly sending messages to the rest of your body which affect things like cell growth, chemical reactions in cells, and the body’s reproductive cycles.

So fat is active, telling other cells what to do. And if there is too much fat in the body, then the signals it sends around the body can cause damage.

These signals affect;

  • Growth hormones- too much body fat can cause levels of insulin and other growth factors to rise, which can tell cells to divide more often. This raises the chance that cancer cells will develop7,11.
  • Inflammation- when there are more fat cells in the body, specialised immune cells go to the area, possibly to remove dead and dying fat cells. This can lead to inflammation. Then cells divide faster, and when this happens over a long time it can raise the risk of cancer7.
  • Sex hormones- after the menopause, oestrogen made by fat cells can make cells divide faster in the breasts and womb (two of the cancer types most closely linked to obesity), increasing the risk of cell faults and cancer7.

These are the main ways scientists have identified so far, but research continues to find out more about the ways extra body fat can cause cancer.

Does it matter where the fat is stored in the body?

Yes, it can. When too much fat is carried around the belly, it can do even more damage16. So-called ‘apple’ shapes are linked to bowel, kidney, oesophageal, pancreatic, and breast cancers17–21.

It isn’t clear exactly why this is, but it could be to do with how quickly certain chemicals from fat can get into the blood7.

  • Bhaskaran, K. et al. Body-mass index and risk of 22 specific cancers: A population-based cohort study of 5·24 million UK adults. Lancet 384, 755–765 (2014).
  • Brown, K. F. et al. The fraction of cancer attributable to modifiable risk factors in England, Wales, Scotland, Northern Ireland, and the United Kingdom in 2015. Br. J. Cancer 118, 1130–1141 (2018).
  • Secretan, B. L. et al. Special Report Body Fatness and Cancer — Viewpoint of the IARC Working Group. (2016). https://www.nejm.org/doi/10.1056/NEJMsr1606602?url_ver=Z39.88-2003&rfr_i...
  • Renehan, A. G., Zwahlen, M. & Egger, M. Adiposity and cancer risk: New mechanistic insights from epidemiology. Nat. Rev. Cancer 15, 484–498 (2015).
  • Simmonds, M., Llewellyn, A., Owen, C. G. & Woolacott, N. Predicting adult obesity from childhood obesity: A systematic review and meta-analysis. Obes. Rev. 17, 95–107 (2016).
  • World Cancer Research Fund / American Institute for Cancer Research Diet, Diet, Nutrition, Physical Activity and Cancer: a Global Perspective. A summary of the Third Expert Report. (2018).
  • Calle, E. E. & Kaaks, R. Overweight, obesity and cancer: Epidemiological evidence and proposed mechanisms. Nat. Rev. Cancer 4, 579–591 (2004).
  • Renehan, A. G., Zwahlen, M. & Egger, M. Adiposity and cancer risk: New mechanistic insights from epidemiology. Nat. Rev. Cancer 15, 484–498 (2015). https://www.ncbi.nlm.nih.gov/pubmed/26205341
  • Schauer, D. P. et al. Bariatric Surgery and the Risk of Cancer in a Large Multisite Cohort. Ann. Surg. (2017). https://www.ncbi.nlm.nih.gov/pubmed/28938270
  • Kyrgiou, M. et al. Adiposity and cancer at major anatomical sites: Umbrella review of the literature. BMJ 356, 1–10 (2017). https://www.bmj.com/content/356/bmj.j477 
  • Birks, S., Peeters, A., Backholer, K., O’Brien, P. & Brown, W. A systematic review of the impact of weight loss on cancer incidence and mortality. Obes. Rev. 13, 868–891 (2012). https://www.ncbi.nlm.nih.gov/pubmed/22672203
  • Arnold, M. et al. Overweight duration in older adults and cancer risk: a study of cohorts in Europe and the United States. Eur. J. Epidemiol. 31, 893–904 (2016). https://www.ncbi.nlm.nih.gov/pubmed/27300353
  • Keum, N. et al. Adult weight gain and adiposity-related cancers: A dose-response meta-analysis of prospective observational studies. J. Natl. Cancer Inst. 107, 1–14 (2015). https://www.ncbi.nlm.nih.gov/pubmed/25757865