Obesity and cancer risk: Obesity is commonly linked to diabetes, heart disease and high blood pressure, but it also raises the risk of several cancers, a connection many people overlook. Researchers say excess body fat can drive chronic inflammation, alter hormones, and affect cell growth, all of which may contribute to tumour development.
This guide explains how and why that link exists.
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What is obesity?
Clinically, obesity refers to an unhealthy amount of body fat, not just body size or appearance. Doctors often screen using body mass index (BMI), with a BMI of 30 or higher typically classified as obese. BMI is a starting point, not the whole picture. Body shape, muscle mass and other health factors also influence risk.
Does research prove a link between obesity and cancer?
Large studies worldwide point to a strong link between excess body fat and cancer risk. The World Health Organization ranks overweight and obesity as the second-largest preventable cause of cancer after smoking.
The American Cancer Society reports that obesity is associated with at least 13 cancers, including postmenopausal breast, colorectal, uterine (endometrial), oesophageal, kidney, pancreatic, liver, ovarian, thyroid and stomach cancers, among others.
Why does obesity raise cancer risk?
Excess fat tissue alters the body’s internal environment in several ways that can promote tumour growth:
- Hormones: Fat cells produce extra estrogen, which can fuel hormone-sensitive cancers such as breast and endometrial cancer.
- Chronic inflammation: Persistent low-grade inflammation can damage DNA over time, increasing the chance of malignant changes.
- Insulin and growth signals: Insulin resistance increases insulin and insulin-like growth factor levels, which promote cell growth and division.
- Immune effects: Too much adiposity can impair immune surveillance, making it harder for the body to detect and eliminate abnormal cells.
Taken together, these changes help explain why carrying excess body fat is linked to higher cancer risk, and why weight management, alongside regular screening and healthy lifestyle habits, is an important part of cancer prevention.
How does obesity’s cancer risk differ for men and women?
Obesity does not raise cancer risk uniformly. In women, excess body fat is strongly linked to postmenopausal breast cancer and uterine (endometrial) cancer, because after menopause, fat tissue becomes the body’s main source of estrogen, a hormone that can drive certain tumours. In men, obesity has been associated with a higher likelihood of aggressive prostate cancer. Several cancers, including kidney cancer, are elevated in both sexes.
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When to seek help?
Doctors advise speaking with a clinician if you’re concerned about weight or cancer risk. A check-up can include counselling on safe weight loss and screening for risk markers such as blood sugar, cholesterol and, when appropriate, hormone levels.
While obesity increases the chance of several cancers, the risk can be reduced. Gradual changes like improving diet quality, moving more, and managing stress offer meaningful protection against cancer and other chronic conditions.