Cancer Research UK : Body weight and cancer: the evidence

Body weight and cancer: the evidence

Evidence linking bodyweight to cancer.

This page contains information about the links between bodyweight and cancer. Click on the links below to read about specific topics.

Obesity and cancer
Breast cancer
Bowel cancer
Other cancers

Why does obesity increase cancer risk?

Reducing your risk
Helping your children

You can find out more about the evidence behind other health topics in our other How do we know? pages.

Obesity is a major preventable cause of cancer

Major studies confirm that being overweight or obese increases your risk of various cancers 1-3. The World Health Organisation (WHO) says that overweight and obesity are the most important known avoidable causes of cancer after tobacco 4.

A recent study estimated that in Europe, 5% of cancers in women and 3% in men are caused by being overweight or obese. In the UK alone, 12,000 people every year might avoid getting cancer if they maintained a healthy body weight 5. This number is only going to increase in the future since more cancers are being linked to obesity, and the number of people who are overweight is increasing.

Obesity increases the risk of breast cancer in women after menopause

Scientists have estimated that anywhere between 9% and 15% of breast cancer cases in developed countries are caused by obesity.3,6,7 Over a hundred studies show that post-menopausal women who are overweight or obese have higher breast cancer risks 2,8,9.

Recently, the large EPIC study found that postmenopausal obese women have a 31% higher risk of breast cancer than women with a healthy weight 10. This means that if the average lifetime risk of breast cancer is one in nine, an obese woman’s lifetime risk is one in seven.

Obesity does not increase breast cancer risk in women before their menopause 8,11. However, women who are overweight or obese at this point in their lives often find it hard to lose weight after their menopause.

Obesity increases the risk of bowel cancer

International organisations such as the WHO and the International Agency for Cancer Research (IARC) agree that obesity is the major diet-related cause of bowel cancer 2,4. Some groups have estimated that obesity causes about 11-14% of bowel cancer cases.3,6

When measured using BMI, the links between obesity and bowel cancer are twice as strong in men as in women 1. Several studies and reviews, including the large EPIC study, have found that obese men have about 60% higher risks of bowel cancer than men with a healthy weight.1,5,12->15

When obesity is measured using waist circumference or waist-to-hip ratio, both obese men and women have higher risks of bowel cancer. This suggests that fat around your stomach is more of a problem than fat elsewhere on the body 14.

Obesity also increases the risk of cancers of the oesophagus (food pipe), womb and kidney, and other diseases

Many scientists have consistently found that obese people are twice as likely to develop kidney,16-19 and three to four times more likely to develop oesophageal 1,20 and womb cancers.21-23 The link between obesity and womb cancer is especially strong and convincing 2.

Studies have also estimated that obesity causes:

a quarter of kidney cancer cases 5
a third of oesophageal cancer cases 3
four in ten cases of womb cancer 5,6

The rising levels of obesity in the UK could explain why some of these cancers, such as oesophageal cancer, are becoming more common.20,24,25

There is also growing evidence that being overweight or obese could increase the risk of:

pancreatic cancer26,27
gallbladder cancer5,28
aggressive prostate cancer29-31
ovarian cancer32,33
thyroid cancer34
multiple myeloma35
some types of leukaemia36
non-Hodgkin lymphoma37
liver cancer38

Obesity may increase cancer risk by changing hormone levels

Obesity most likely increases the risk of cancer by raising levels of hormones such as oestrogen and insulin.

In early life, oestrogen is mainly produced by a woman’s ovaries, but this stops after menopause. Instead, fat in the body becomes the main source of oestrogen and obese women have up to twice as much oestrogen as women with a healthy weight.39 They also have lower levels of SHBG, or ‘sex hormone binding globulin’, which mops up oestrogen in the body 40. This is almost certainly why obesity increases the risk of breast and womb cancers.40-42

Obesity also increases levels of insulin in the body. It’s not clear how this could lead to cancer, although high insulin levels are a common feature of many cancers. High insulin levels could explain why being obese increases the risk of bowel, kidney and pancreatic cancer.43-45

Obesity may also cause ‘gastric acid reflux’, where the stomach’s acids are briefly pushed back into the throat.46 This can damage the oesophagus and lead to oesophageal cancer.

People who are obese usually do not do enough physical exercise or may eat unhealthy diets. These can also independently increase cancer risk.

Keeping a healthy weight reduces cancer risk and losing weight may reduce cancer risk

Maintaining a healthy body weight can definitely help to reduce your cancer risk 2,4.

We are still trying to establish if losing weight can reduce cancer risk, but the evidence is growing 2. A study of over 87,000 women found that women who lost 10kg since menopause and kept the weight off more than halved their risk of breast cancer 7. Other studies have found similar results for breast and other types of cancer 47-49.

We also know that losing weight significantly reduces your risk of heart disease, diabetes and hypertension 2.

When people try lose weight through short-term fixes, in most cases, the end up putting the weight back on. It’s unclear how this ‘weight cycling’ affects the risk of cancer. But at least one study found that women whose weight had gone up and down by over 10 pounds, more than ten times, had higher risks of kidney cancer than those whose weight was stable.18 While this was just a single study, it does suggest that the best way to reduce the risk of cancer is to maintain a healthy bodyweight over time.

Parents can reduce their children’s cancer risk in adult life by encouraging them to eat healthily and keep active

Eating habits established in childhood often endure after many years. In 1993, a group of scientists showed that at least half of obese children were still obese as adults 50. And this proportion is likely to be even higher now. Another study of Scottish and English children found that people who are obese as children have higher risks of some cancers later on in life 51.

Many studies have shown that children with obese parents are much more likely to be obese themselves 52. But this may not be due to parenting styles. Some research from Cancer Research UK indicates children’s attitudes towards food may be due to genes. By inheriting certain genes from their parents, some children may have a higher chance of being overweight or obese 53.

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