HOW COULD OBESITY LEAD TO CANCER?

Fat (also known as adipose tissue) has two main roles in the body. It exists to store calories in the form of chemicals called lipids, and a huge gland, sending out a constant stream of biological information and instructions that affect the rest of your body. This helps control processes like growth, metabolism and reproductive cycles. But because of their ability to turn biological processes on and off, the signals produced by fat have a darker side when it comes to cancer.

1. The oestrogen connection

One of the strongest links between obesity and cancer is an increased risk of breast and womb cancers in women who are overweight or obese after the menopause, and this relates to higher oestrogen levels. Large studies of women have shown a direct relationship between obesity, high oestrogen levels and breast and womb cancers and understanding this relationship has been critical in developing effective treatments – like tamoxifen and aromatase inhibitors – that work by cutting off oestrogen.

2. Metabolic chaos

The chemical processes going on constantly throughout the body – collectively known as metabolism – are complicated and tightly controlled, relying on a finely tuned web of information flowing between cells and organs. But the chemical signals produced by fat cells means that obesity can cause a major upset to this balance, and this is thought to be another way it makes cancer more likely.

One key hormone that acts as a master-controller of metabolism is insulin. It’s made by the pancreas and orchestrates how cells take up and process glucose from the blood.

Large studies of peoples’ blood chemistry have also shown links between high glucose (even at levels below those needed for a diagnosis of diabetes) and the risk of several types of cancer.

3. Inflammation

As people become obese, and more fat cells build up in their tissues, specialized immune cells (called macrophages) are called to the scene, possibly to clear up dead and dying fat cells. But as macrophages carry out their clean up job, they also release a potent cocktail of chemicals called cytokines that summon other cells to help them out. The number of macrophages in obese fatty tissue can be substantial – they can account for as many as four in 10 cells.

This ultimately creates a condition called chronic inflammation. The result of inflammation is a cocktail of signals that tell cells to divide, because after injury you need new cells for healing to occur. But the signals encouraging cell growth for healing can also support cancer cells dividing. In fact if we look at the genes that are turned on and off in inflamed tissue, it’s very similar to genetic changes we see in cancer cells.

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