Does being overweight or obese increase the risk of cancer?

Individuals who are overweight or obese have a 50% increase in the risk of dying compared to individuals who are a healthy weight¹¹. Approximately 10% of these additional, obesity-related deaths are due to cancer ⁵⁵.

Obesity is associated both with cancer incidence and cancer-related mortality⁵⁶.

There is a long list of cancers which are associated with having overweight or obesity. These include:

• Breast cancer
• Uterine cancer
• Prostate cancer
• Pancreatic cancer
• Gallbladder cancer
• Thyroid cancer
• Colorectal cancer
• Cancer of the head and neck
• Oesophageal cancer

How do fat cells influence cancer?

Increasingly, evidence demonstrates a role of adipocytes (fat cells) in the progression of cancer, influencing the growth of tumours. The adipocytes secrete various factors which can influence both local and systemic effects — known as ‘adipocyte-cancer cell crosstalk’ — and are believed to contribute to a favourable microenvironment for the growth and development of tumour cells ⁵⁶.

Adipose also increases levels of the hormone estrogen, which can help some cancers (such as breast cancer) to develop⁵⁷.

Poor prognosis in cancer patients is also thought to be related to adipocyte-promoted resistance to chemotherapy treatment, and to the occurrence of phenotypes which are resistant to radiotherapy, meaning treatment may be less effective in individuals with excess fat mass ⁵⁶.

What are the benefits of weight loss?

Preclinical studies suggest that weight loss in individuals who are overweight or obese may reduce the risk of cancer.

Bariatric surgery studies also show that a sustained 20kg weight loss was associated with a reduction in cancer risk ^{58, 59}. Specific studies have shown cancer risk reduced with intentional lifestyle-mediated weight loss.

For example, intentional weight loss of more than 5% significantly reduced the risk of endometrial cancer in postmenopausal women⁶⁰.