Yes. After reviewing more than a thousand studies, the International Agency for Research on Cancer (part of the World Health Organization) concluded that excess body fat raises the risk of at least 13 types of cancer, including cancers of the womb (endometrium), oesophagus, bowel, liver, kidney and pancreas and breast cancer after the menopause [1]. In the United States, excess weight is the second most important preventable cause of cancer after smoking [3]. The good news is that, in studies, people who lost weight and kept it off developed these cancers less often [5, 7].
Key points
- 13 types of cancer are linked to excess body fat; the largest increases in risk are seen for cancer of the womb and one type of oesophageal cancer [1].
- Obesity is not one person's fault: it is a chronic disease in which the living environment, social conditions, genes and behaviour all play a part [4].
- Weight loss helps: in women aged 50 and over, even a loss of a few kilograms that was kept off was linked to a lower risk of breast cancer [7]; after weight-loss surgery, obesity-related cancers also became less common [5].
- Being active helps regardless of weight: the risk of 13 types of cancer was lower in more active people, whether they had a normal weight or excess weight [9].
Which cancers are linked to obesity?
In 2016 the International Agency for Research on Cancer linked these 13 cancers to excess body fat [1]. For some of them the risk is several times higher, and for others only slightly higher:
| Cancer | Increase in risk in the highest weight group, compared with a normal weight |
|---|---|
| Cancer of the womb (endometrium) | About 7 times [1] |
| One type of oesophageal cancer (adenocarcinoma) | About 5 times [1] |
| Liver cancer | Nearly 2 times [1] |
| Kidney cancer | Nearly 2 times [1] |
| Cancer of the upper part of the stomach (cardia) | Nearly 2 times [1] |
| Pancreatic cancer | About one and a half times [1] |
| Multiple myeloma (a type of blood cancer) | About one and a half times [1] |
| Meningioma (tumour of the membranes around the brain) | About one and a half times [1] |
| Bowel (colorectal) cancer | About a third higher [1] |
| Gallbladder cancer | About a third higher [1] |
| Breast cancer after the menopause | Slightly higher [1] |
| Ovarian cancer | Slightly higher [1] |
| Thyroid cancer | Slightly higher [1] |
A normal weight means a body mass index of 18.5 to 24.9 [1].
How does excess fat raise the risk of cancer?
Fat tissue is not just an energy store; it also makes hormones and other substances [2]:
- More oestrogen: fat tissue produces extra oestrogen, and high levels of this hormone can lead to cancer [2].
- More insulin: people with obesity often have higher blood levels of insulin and of an insulin-like growth factor (IGF-1) [2].
- Chronic inflammation: long-lasting inflammation helps tumours grow [2].
- Fat tissue hormones: some of them, such as leptin, stimulate cells to divide [2].
If I lose weight, will my risk go down?
The evidence is encouraging, but most of it comes from studies that observed people rather than testing a treatment [1, 2]:
- Weight-loss surgery: in a study of more than 30,000 people in the United States, those who had surgery (and lost about 25 kg more over 10 years) were about a third less likely to develop obesity-related cancers, and their risk of dying from cancer was nearly halved [5]. In a study in Sweden, this reduction was seen in women but not in men [6].
- Weight loss without surgery: in women aged 50 and over, weight loss that was kept off, even a few kilograms, was linked to a lower risk of breast cancer; the greater the loss, the lower the risk [7]. In a study of adults with type 2 diabetes, an intensive diet and exercise programme slightly reduced obesity-related cancers, but the difference could have been due to chance [8].
In 2016 the International Agency for Research on Cancer judged that the evidence on intentional weight loss was not enough for a firm conclusion [1]; later studies have made the picture clearer [5, 7].
What should I do? Start with one small, lasting step
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Plant-based, high-fibre food; fewer fast foods and sugary drinks
Make whole grains, vegetables, fruit and pulses the basis of your diet; limit fast foods and processed foods high in fat, starch or sugar, and drink mostly water and unsweetened drinks [11]. See sugar and cancer and red meat and processed meat.
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Get help from your doctor
Body mass index (BMI) is your weight in kilograms divided by the square of your height in metres; 25 or more is overweight and 30 or more is obesity [4]. This number does not measure body fat directly, and waist size also gives useful information [2]. If your BMI is high, talk to your doctor about a weight-loss plan that suits your situation.
Frequently asked questions
Does fat around the waist matter more?
Body mass index does not measure body fat directly and cannot on its own show an individual's risk; waist size and where fat is stored give more information [2].
Do weight-loss injections (such as semaglutide) lower the risk of cancer?
It is not yet known. In a review of medical records of people with diabetes in the United States, medicines in this group (GLP-1) were linked to fewer of some obesity-related cancers compared with insulin; but compared with the diabetes medicine metformin, no such benefit was seen and kidney cancer was even more common [10]. More rigorous studies are needed before drawing conclusions [10].
I am slim; does that mean I am not at risk of cancer?
No. Weight is only one factor; smoking, alcohol and infections matter too. Physical activity is linked to a lower risk of several cancers for everyone, at any weight [9]. See Can cancer be prevented?
If I have cancer, should I lose weight now?
Do not start a strict diet on your own during treatment. The American Society of Clinical Oncology says the evidence for weight-loss diets during treatment is very limited, but recommends regular exercise [12]. Talk to your care team and see Nutrition during cancer treatment and exercise during treatment.
Does obesity affect the results of cancer treatment?
Research suggests that obesity may worsen quality of life, the chance of the cancer coming back, its progression and survival [2].
Notes for doctors (for physicians)
For physicians
IARC Handbook 16 (Lauby-Secretan, NEJM 2016). More than 1,000 epidemiological studies; sufficient evidence for 13 sites. RR for the highest BMI category evaluated vs normal BMI (18.5 to 24.9): corpus uteri 7.1 (6.3 to 8.1), oesophageal adenocarcinoma 4.8 (3.0 to 7.7), gastric cardia 1.8 (1.3 to 2.5), liver 1.8 (1.6 to 2.1), renal cell carcinoma 1.8 (1.7 to 1.9), pancreas 1.5 (1.2 to 1.8), multiple myeloma 1.5 (1.2 to 2.0), meningioma 1.5 (1.3 to 1.8), colorectum 1.3 (1.3 to 1.4), gallbladder 1.3 (1.2 to 1.4), postmenopausal breast 1.1 (1.1 to 1.2), ovary 1.1 (1.1 to 1.2) and thyroid 1.1 (1.0 to 1.1). Limited evidence: male breast cancer, fatal prostate cancer and DLBCL. Mechanisms: strong evidence for sex hormones and chronic inflammation, moderate for insulin and IGF signalling. Evidence on intentional weight loss was insufficient for a formal evaluation [1].
Burden. In the United States (2019), excess body weight accounted for 7.6% of cancers and 7.3% of cancer deaths in adults aged 30 and over, second only to smoking (19.3% and 28.5%) [3].
Weight loss. SPLENDID (1:5 matched cohort; 30,318 people with BMI ≥35, 5,053 operated; median follow-up 6.1 years): 10-year incidence of obesity-associated cancer 2.9% vs 4.9%, HR 0.68 (0.53 to 0.87); cancer mortality 0.8% vs 1.4%, HR 0.52 (0.31 to 0.88); weight difference at 10 years 24.8 kg [5]. SOS (2,010 surgical patients vs 2,037 controls, median 10.9 years): HR for first cancer 0.67 (0.53 to 0.85); women 0.58 (0.44 to 0.77) and men 0.97 (0.62 to 1.52) [6]. Pooling Project (180,885 women aged 50 and over, 6,930 breast cancers): sustained weight loss in women not using postmenopausal hormones, >2 to 4.5 kg HR 0.82 (0.70 to 0.96), >4.5 to <9 kg 0.75 (0.63 to 0.90) and ≥9 kg 0.68 (0.50 to 0.93) [7]. Look AHEAD (RCT; 4,859 people with type 2 diabetes, median 11 years): obesity-related cancers HR 0.84 (0.68 to 1.04) and all cancers 0.93 (0.80 to 1.08) [8].
Physical activity. 12 cohorts, 1.44 million people, 186,932 cancers: high vs low activity (90th vs 10th percentile) was associated with a lower risk of 13 cancers, including oesophageal adenocarcinoma HR 0.58, liver 0.73, lung 0.74, kidney 0.77, endometrium 0.79, colon 0.84 and breast 0.90; 10 of the 13 associations remained significant after adjustment for BMI [9].
GLP-1 receptor agonists. Retrospective electronic health record cohort (1.65 million patients with type 2 diabetes): compared with insulin, lower risk of 10 of 13 obesity-associated cancers (for example HCC 0.47 and colorectal 0.54); compared with metformin, no reduction and a higher risk of kidney cancer (HR 1.54; 1.27 to 1.87). Hypothesis-generating [10].
In practice. Ask about weight and waist circumference without judgement and in non-blaming language; obesity is a chronic multifactorial disease [4]. During cancer treatment, regular aerobic and resistance exercise is recommended, and evidence for weight-loss interventions is limited [12].
Related cancer types
Related questions
References
12 referencesShow all references, 1 with a study cardClose the reference list
Numbers in the text, such as [1], refer to these sources. Sources with a “Study card” button are summarised in the site’s evidence library.
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- 12Exercise, Diet, and Weight Management During Cancer Treatment: ASCO Guideline
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