How does obesity cause cancer?

Cancer Insight newsletters

Written by experts, stay up-to-date with best practice advice on prevention, screening and diagnosis, and the latest evidence, training materials and patient resources.

Sign up

In a nutshell

  • Obesity is the second biggest preventable cause of cancer in the UK- more than 1 in 20 cancer cases are caused by excess weight 1  
  • The risk is higher the more weight someone gains and the longer they are overweight for 2,3 
  • The good news is small changes that your patients keep up over time can make a real difference 4 

What’s the risk of developing cancer if your patient is overweight or obese?

Being overweight doesn’t mean that someone will definitely develop cancer. But if your patient is overweight they are more likely to get cancer than if they are a healthy weight1.  

Someone can help stack the odds against cancer by losing weight or avoiding gaining more weight5,6.  

People keeping a healthy weight could prevent around 22,800 cases of cancer every year in the UK1.  

How can obesity cause cancer?

Dr Dawn Harper, a GP in Stroud, Gloucestershire, explains how obesity can cause cancer.

Extra fat in the body doesn’t just sit there, its active, sending out signals to the rest of your body. It can affect growth, metabolism and reproductive cycles. These signals can tell cells in our body to divide more often, which can lead to cancer7,8

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 real3,9. And there are good explanations for how extra fat cells in the body could cause cancer7,8.   

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 cancer1. But when we look at a whole population, these lifestyle factors cause more people to develop cancer1,10,11.  

What types of cancer are caused by obesity?

Being overweight or obese increases the risk of 13 types of cancer:  

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)12,13

This includes two of the most common types of cancer – breast and bowel cancers - and three 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 leave14

Children who are obese are around 5 times more likely to grow into adults who are obese15.  

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

 Fat has two main functions; 

  • acts as a store of energy 
  • it’s an endocrine gland, constantly sending a constant stream of biological information and instructions to the rest of the body which affect things like cell growth, metabolism, and the body’s reproductive cycles. 

So, because of body fat’s ability to affect our physiology, it can signal our cells to divide more often, increasing the chances of cancer cells developing.  

Researchers have identified three main ways obesity is linked to cancer: 

  • 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

It is likely different mechanisms are working in different cancer types- for example gastric acid reflux is likely one of the main ways obesity increases the risk of oesophageal and gastric cardia cancer, whereas higher levels of oestrogen are almost certainly how obesity causes womb and breast cancer.     

But because extra body fat can affect so many different biological processes, and affects different people in different ways, untangling all the ways obesity is linked to cancer is a complicated and ongoing area of research.  

 

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

 

Does losing weight reduce cancer risk? 

Never gaining excess weight is the best thing people can do. But since many patients will already be overweight or obese, you might have questions about the benefits of weight loss on cancer risk for these groups. It’s difficult to study, but research so far suggests that losing weight does help reduce cancer risk5,6. Plus, the steps most people take to lose weight, like eating and drinking healthily, can also reduce cancer risk on their own. But we know losing weight and keeping it off isn’t easy, which is why many of your patients would benefit from your support and help to access weight management services. 

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_id=ori:rid:crossref.org&rfr_dat=cr_pub%3dwww.ncbi.nlm.nih.gov  

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  

 

Full Bibliography 

1.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). 

2.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). 

3.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). 

4.Lally, P. & Gardner, B. Promoting habit formation. Health Psychol. Rev. 7, (2013). 

5.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). 

6.Schauer, D. P. et al. Bariatric Surgery and the Risk of Cancer in a Large Multisite Cohort. Ann. Surg. (2017). doi:10.1097/SLA.0000000000002525 

7.Renehan, A. G., Zwahlen, M. & Egger, M. Adiposity and cancer risk: New mechanistic insights from epidemiology. Nat. Rev. Cancer 15, 484–498 (2015). 

8.Calle, E. E. & Kaaks, R. Overweight, obesity and cancer: Epidemiological evidence and proposed mechanisms. Nat. Rev. Cancer 4, 579–591 (2004). 

9.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). 

10.Bianchini, F., Kaaks, R. & Vainio, H. Overweight, obesity, and cancer risk. Lancet. Oncol. 3, 565–74 (2002). 

11.De Pergola, G. & Silvestris, F. Obesity as a major risk factor for cancer. J. Obes. 2013, (2013). 

12.Secretan, B. L. et al. Special Report Body Fatness and Cancer — Viewpoint of the IARC Working Group. (2016). 

13.Kyrgiou, M. et al. Adiposity and cancer at major anatomical sites: Umbrella review of the literature. BMJ 356, 1–10 (2017). 

14.Noo & Ncmp. National Child Measurement Programme. Changes in children ’ s body mass index. 1–36 (2013). 

15.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). 

16.WCRF & AICR. Diet, Nutrition, Physical Activity and Cancer: a Global Perspective. A summary of the Third Expert Report. (2018). 

17.Luo, J. et al. Body Size, Weight Cycling, and Risk of Renal Cell Carcinoma among Postmenopausal Women: The Women’s Health Initiative (United States). Am. J. Epidemiol. 166, 752–759 (2007). 

18.Dong, Y. et al. Abdominal obesity and colorectal cancer risk: systematic review and meta-analysis of prospective studies. Biosci. Rep. 37, BSR20170945 (2017). 

19.Genkinger, J. M. et al. Central adiposity, obesity during early adulthood, and pancreatic cancer mortality in a pooled analysis of cohort studies. Ann. Oncol. 26, 2257–2266 (2015). 

20.Du, X., Hidayat, K. & Shi, B.-M. Abdominal obesity and gastroesophageal cancer risk: systematic review and meta-analysis of prospective studies. Biosci. Rep. 37, BSR20160474 (2017). 

21.Chen, G. C. et al. Central obesity and risks of pre- and postmenopausal breast cancer: a dose–response meta-analysis of prospective studies. Obes. Rev. 17, 1167–1177 (2016). 

Last reviewed

Rate this page:

Currently rated: 2 out of 5 based on 3 votes
Thank you!
We've recently made some changes to the site, tell us what you think