Obesity and Cancer Risk: What the Evidence Shows

The link between obesity and cancer is one of the most important — and least widely known — findings in modern oncology. Cancer Research UK estimates that obesity causes around 22,800 cancer cases in the UK every year, making it the second most preventable cause of cancer after smoking. Yet surveys consistently show that public awareness of this link remains low: a 2016 Cancer Research UK survey found that fewer than half of UK adults knew that obesity increased cancer risk.

Which cancers are linked to obesity?

The International Agency for Research on Cancer (IARC) has identified 13 cancers with sufficient evidence of a causal link to excess body weight:

• Oesophageal adenocarcinoma
• Gastric cardia cancer
• Colorectal cancer
• Liver cancer
• Gallbladder cancer
• Pancreatic cancer
• Kidney cancer
• Endometrial cancer
• Ovarian cancer
• Postmenopausal breast cancer
• Thyroid cancer
• Multiple myeloma
• Meningioma

The strength of association varies. Endometrial cancer has one of the strongest links — women with a BMI above 40 have approximately seven times the risk of endometrial cancer compared to women of a healthy weight. Oesophageal adenocarcinoma risk increases fourfold with obesity.

What are the biological mechanisms?

Several pathways link obesity to cancer. Insulin and IGF-1: obesity-related insulin resistance raises circulating insulin and insulin-like growth factor 1 (IGF-1), both of which promote cell proliferation and inhibit apoptosis. Sex hormones: adipose tissue converts androgens to oestrogens via aromatase; elevated oestrogen drives endometrial and postmenopausal breast cancer. Chronic inflammation: pro-inflammatory cytokines from visceral fat create a tumour-promoting microenvironment. Adipokines: leptin promotes tumour cell proliferation; adiponectin, which is reduced in obesity, has anti-tumour properties.

Does weight loss reduce cancer risk?

Evidence from large cohort studies suggests yes. A 2018 analysis in the Journal of the National Cancer Institute found that intentional weight loss was associated with a 23% reduction in obesity-related cancer incidence. The effect was strongest for endometrial and postmenopausal breast cancer. Bariatric surgery studies — which produce large, sustained weight loss — show reductions in cancer incidence of 30 to 40 per cent compared to matched controls who did not have surgery.

Reducing cancer risk is one of the most compelling reasons to address excess weight with medical support. Book a consultation with Weight Loss Wales today.