What is the link between obesity and cancer?

29th October 2020

Research has shown that there are several health risks linked to carrying too much extra weight, including high blood pressure, diabetes and cardiovascular problems. And you might also have heard that obesity raises the risk of several cancers, including bowel, breast and pancreatic cancer. In fact, it is thought that about 1 in 20 cancers are linked to obesity, and the longer you are overweight for and the more weight you carry, the higher the risk is – though it is important to remember that not everyone who is obese will develop cancer in their lifetime, and being a healthy weight does not preclude you from developing it either.

So what exactly is the link between obesity and cancer?

To understand why people that fall into the obese weight group are at higher risk of developing cancer, we first need to understand what fat is doing in the body.

Excess fat doesn’t just hang around the body, it’s an active tissue that constantly sends out signals to cells, thereby influencing many processes in the body.

While it is speculated that a larger organ size might be partially to blame for the increased cancer risk in people with obesity, most researchers agree that fat plays the most important role.

There are three main ways in which too much fat can increase the risk of cancer:

Growth hormones

Fat is stored in fat cells, which can produce growth hormones such as insulin, which can tell cells to multiply more often. The more cells divide, the higher the chances of an error in the DNA, and therefore mutations that can lead to cancer. Insulin can also increase the production of other hormones, such as oestrogen (see below), further increasing cancer risk.

Sex hormones

Fat cells also release oestrogen, which can trigger cells to divide more quickly in the breasts and the womb. This can be especially problematic for people who are past their menopause, as they naturally produce less oestrogen.


The accumulation of fat around internal organs - also called visceral fat – is thought to be especially problematic. Visceral fat cells of people with obesity tend to be large in size and number and exist in an environment with relatively little oxygen. As well as this, certain immune cells migrate to the fatty areas to clear up dying or dead fat cells. This can lead to inflammation, and if this inflammation goes on for too long, it can damage the body’s ability to respond to insulin, meaning that more insulin is produced, leading again to increased cell division. The inflammation itself can also stimulate cells to divide faster, further increasing the risk of cancer.

What can you do to reduce your risk?

Losing weight isn’t easy and studies have shown that crash diets are unlikely to bring long-term success. Small changes to lifestyle habits are likely the most successful way of reducing weight and health risks. It is also important not to forget about healthy habits such as increasing your physical activity and eating a well-balanced diet, as well as improving stress and sleep habits.

And most importantly, please remember that you should always check in with your GP if you notice any concerning symptoms - regardless of your weight. 

Please remember to seek advice from your doctor before embarking on any new diet or exercise programme. To find out more about how to reduce the risk of cancer by tackling lifestyle habits, take a look at the new Better Health campaign by the NHS.

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