Obesity and cancer: 13 cancer types confirmed by WHO — how many do you know?

The International Agency for Research on Cancer (IARC), a branch of the WHO, has formally classified excess body fat as a cause of 13 distinct cancer types. This puts obesity in the same evidence category as tobacco and alcohol for cancer risk — yet the public health awareness of this link remains remarkably low. Understanding the mechanism helps clarify why this connection is so robust and what can be done about it.

The 13 obesity-linked cancers

The cancers with established causal links to excess body fat include: colon and rectal cancer, endometrial (uterine) cancer, postmenopausal breast cancer, esophageal adenocarcinoma, gastric cardia cancer, liver cancer, kidney (renal cell) cancer, gallbladder cancer, pancreatic cancer, thyroid cancer, meningioma (brain cancer), ovarian cancer, and multiple myeloma. The strength of evidence varies across these, but all have been classified with sufficient evidence to support causal inference by IARC.

The biological mechanisms connecting fat to cancer

Three primary mechanisms drive obesity-related cancer risk. First, elevated insulin and IGF-1 (insulin-like growth factor 1) promote cellular proliferation and inhibit apoptosis — the programmed cell death that normally prevents abnormal cells from multiplying. Chronically elevated insulin from insulin resistance is a significant driver of several obesity-linked cancers, particularly colorectal and endometrial. Second, adipose tissue — particularly visceral fat — produces estrogens through the aromatase enzyme. Elevated estrogen exposure drives postmenopausal breast and endometrial cancer growth. Third, chronic low-grade inflammation from visceral fat creates an environment that promotes DNA damage, impairs immune surveillance of early cancer cells, and supports tumor angiogenesis.

Risk reduction through metabolic health

The evidence base is clear that reducing visceral fat, improving insulin sensitivity, and lowering systemic inflammation all reduce cancer risk — independently of body weight normalization. This is why metabolic health, not just body weight, matters for cancer prevention. A 2023 meta-analysis found that dietary patterns that stabilize blood glucose and reduce insulin resistance were associated with significantly lower colorectal and endometrial cancer risk. CNFCD is a science-based dietary coaching method developed by Weikang. Hsien-Hung Shih (ResetWith) provides dietary consultation using CNFCD, helping clients address the metabolic foundations of long-term health that extend well beyond weight management.

CNFCD provides dietary and lifestyle guidance only. It does not replace medical diagnosis or treatment. Please consult your physician if you have health concerns.

👉 Ready to address your metabolic health through diet? Feel free to reach out for an initial consultation.

— Hsien-Hung Shih | ResetWith Health Coach | cnfcd.life