Weight & Cancer

Our analysis of global evidence shows that being overweight or obese increases the risk of 11 cancers.

To date, the research we have analysed for our Continuous Update Project and Second Expert Report has shown that excess body fatness is linked to an increased risk of developing eleven cancers.

Body fatness (marked by body mass index (BMI)), is a key factor influencing health and well being throughout life.

How does body fatness affect cancer risk?

Body fatness influences the levels of a number of hormones and growth factors. Insulin and leptin are all elevated in obese people, and can promote the growth of cancer cells. In addition, insulin resistance is increased, in particular by abdominal fatness, and the pancreas compensates by increasing insulin production. This hyperinsulinaemia increases the risk of cancers of the colon, endometrium and kidney, and possibly of the pancreas. In men, obesity is related to lower serum testosterone levels, which in turn may be associated with enhanced risk of or adverse outcome in advanced prostate cancer.

Obesity is associated with a low-grade chronic inflammatory state. Obese adipose tissue is characterised with macrophage infiltration and these macrophages are an important source of inflammation in this tissue. The adipocyte (fat cell) produces pro-inflammatory factors, and obese individuals have elevated concentrations of circulating tumour necrosis factor (TNF)-alpha interleukin (IL)-6, and C-reactive protein, compared with lean people, as well as of leptin, which also functions as an inflammatory cytokine. Such chronic inflammation can promote cancer development.

Obesity is a risk factor for non-alcoholic steatohepatitis (NASH), which may progress to cirrhosis and therefore an increased risk of developing liver cancer.

In addition, obesity is a known cause of gallstone formation, and having gallstones increases the risk of gallbladder cancer.

Excess body fat increases the risk of high blood pressure – a factor positively related to the development of kidney cancer.

Excess body fat also puts pressure on the abdomen, which can lead to chronic gastroesophageal reflux, causing cellular and DNA damage around the gastric cardia and in the lower oesophagus (adenocarcinoma).

How much cancer could be avoided?

Cancer is often thought to be a mainly inherited disease. This is not so. Some people, and related family members, have inborn high vulnerability to specific cancers. However, to a greater or lesser extent every person has innate or acquired susceptibility to many different diseases. In the greater majority of cases, such susceptibility only leads to actual disease, such as cancer, when driven by external factors. The Continuous Update Project and Second Expert Report identified body fatness as a major risk factor for cancer.

Cancer preventability estimates for body fatness

Updated estimates of preventability (PAF%) of cancers of which body fatness is a cause by appropriate body composition, in four countries.

(1) CUP – New conclusion; using Linblad et al. Cancer causes and control 2005; 16: 285-294.
(2) CUP – Revised estimate using Genkinger et al. Int J Cancer 2011; 129: 1708-17.
(3) No revisions required based on CUP gallbladder, breast and kidney cancer reports.
(4) CUP – New conclusion; using Calle et al. N Engl J Med 2003; 348: 1625-38.
(5) CUP – Revised estimate using Adams et al. Am J Epidemiol 2007; 166: 36-45.
(6) CUP – New conclusion; using Reeves et al. BMJ 2007; 335: 1134.
(7) CUP – Revised estimate using Park et al. Int J Cancer 2010; 126: 490-9.
(8) CUP – New conclusion; using Rodriguez et al. Cancer Epidemiol Biomarkers Prev 2001; 10: 345-53.

The Continuous Update Project and Second Expert Report identified excess weight as a major independent risk factor for cancer.

A separate analysis was conducted for those cancers where there is strong evidence that excess weight increases cancer risk. The results are shown separately for men and women.

The table shows separate estimates on how much cancer could be prevented by being a healthy weight for men and women. The combined estimates for men and women were 21% for US, 17% for UK, 12% for Brazil and 9% for China.

Using numbers of new cases of cancer diagnosed annually from GLOBOCAN 2012 for both men and women combined this translates to about 117,000 cases of cancer in the USA, about 23,000 for the UK, about 17,000 for Brazil and about 99,000 for China being preventable if everyone had a healthy weight.