The link between cancer and fat explained
The timing of weight gain also matters. For example, women who gradually gain weight from puberty through adulthood, and especially in the third decade of life, should be considered at higher risk of developing breast cancer.
The link between weight and disease is not necessarily definitive, however. Although being overweight increases your chances of developing cancer, it is not always a direct cause. Obese people may have other lifestyle factors that contribute to their development of the disease.
“There could be confounding factors,” says Dr Dipender Gill, a researcher at Imperial College London. “For example, smoking can affect body weight, and smoking can also affect cancer risk. They can also exercise less or have higher cholesterol.
Given the growing evidence linking obesity to particular cancers, scientists have been trying to determine the precise role that excess body fat plays in increasing the risk of the disease.
Inflammation is one of the major underlying factors behind a third of all cancers. Overweight people tend to carry more visceral fat — body fat surrounding internal organs — which can slowly trigger chronic inflammation. This happens because the visceral fat cells are very large, which means there is not enough room for oxygen, and this oxygen-poor environment triggers inflammatory processes.
“As we get heavier, the fat cells in our body get compressed,” notes Dr. Michelle Harvie, cancer researcher at the NIHR Manchester Biomedical Research Centre. “This low-grade inflammation that runs through the body damages healthy tissue, and the damaged cells are the ones that become cancerous.”
Harvie explains that while cell damage occurs naturally throughout our lives, the inflammatory environment created by obesity causes the body’s normal repair mechanism to not work as effectively, increasing the risk that damaged cells will turn into tumors.
Being overweight can also disrupt your hormonal processes, which is believed to be one of the reasons why it plays a major role in uterine cancer, ovarian cancer, post-menopausal breast cancer and possibly even prostate and kidney cancer.
The extra fat doesn’t just sit there, it’s active and sends signals to the rest of your body. These signals can tell cells to divide more often, which can lead to cancer.
“It is responsible for activating and metabolizing a range of hormones, as well as producing hormones,” says Gill. “It is this effect in particular that may have implications for the development and progression of cancer.”
Once women go through menopause, the body stops diverting the hormone estrogen from the ovaries and instead takes it from body fat. As a result, overweight post-menopausal women have much higher estrogen levels. This becomes a risk for some cancers as it leads to increased cell production.
Chronic inflammation caused by obesity can lead to the development of insulin resistance, whereby the body does not respond properly to the hormone insulin. This induces a destructive cycle where the body produces excess insulin, which leads to the production of more cells and in turn increases the risk of developing cancer.