This is a topic I approach carefully, because it can easily tip into fear or blame — and neither of those things help anyone make sustainable, healthy changes. But it's an important conversation, and I'd rather have it honestly and compassionately than avoid it altogether.
What the evidence shows
Major health bodies, including the International Agency for Research on Cancer, now recognise excess body weight as an established risk factor for at least 13 types of cancer, including bowel, breast (after menopause), endometrial, kidney, liver, pancreatic and oesophageal cancers. This isn't a fringe finding — it's consistently supported across large population studies internationally.
It's worth being precise about what this means: obesity is a risk factor, not a cause in the way smoking directly causes lung damage. Plenty of people living in larger bodies never develop cancer, and plenty of people at "healthy" weights do. Risk factors shift probability — they don't determine individual outcomes.
Why the link exists — the biology
Researchers have identified several overlapping mechanisms:
- Chronic low-grade inflammation — excess fat tissue, particularly around the abdomen, produces inflammatory signalling molecules that, over years, can contribute to cellular changes linked to cancer development.
- Excess insulin and insulin-like growth factor — higher circulating insulin, common with insulin resistance, can promote cell growth in ways that may increase cancer risk.
- Altered sex hormones — fat tissue produces oestrogen, and higher levels are linked to increased risk of hormone-sensitive cancers such as postmenopausal breast and endometrial cancer.
- Gut microbiome changes — emerging research links microbiome imbalances associated with obesity to increased systemic inflammation, adding another layer to the picture.
What's actually within your control
This is the part I want to spend the most time on, because it's the genuinely useful takeaway. Research consistently shows that meaningful weight loss and improved metabolic health — even modest, sustainable changes rather than dramatic ones — are associated with measurably reduced cancer risk. You don't need a "perfect" body composition to meaningfully lower your risk.
- A predominantly plant-rich, fibre-rich diet supports both weight management and gut health, which independently connects to lower inflammation
- Regular physical activity, including resistance training, reduces cancer risk through pathways independent of weight change alone
- Limiting alcohol, which is itself an established, independent cancer risk factor
- Working on metabolic health markers (blood glucose, blood pressure, cholesterol) matters just as much as weight on the scale
A note on how I hold this with clients
Weight stigma in healthcare is real, and it's genuinely counterproductive — research shows stigmatising language and shame-based approaches make people less likely to engage with healthcare and less likely to succeed at sustainable change. My approach is to give people accurate information and then support them, without judgement, wherever they're starting from. Fear doesn't create lasting change; support and practical steps do.
The bottom line
The link between excess weight and cancer risk is real and worth understanding — not as a source of guilt, but as one more genuine reason that sustainable nutrition and movement habits matter. Small, consistent changes over years make a measurable difference, and it's never too late to start.