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How does being overweight lead to cancer?

It’s very clear that there is a link between cancer and obesity. But it’s still not completely understood how exactly obesity causes cancer. Research so far has identified three leading explanations. It’s helpful to start by knowing what fat is, and what it does in the body.

Fat in the body has two main functions. It acts as a store of energy. And it’s constantly spreading information and instructions to the rest of your body. These messages affect things like cell growth, chemical reactions in cells, and the body’s reproductive cycles.

So fat doesn’t just sit there doing nothing. It’s active, telling your cells what to do. And if there is too much fat in the body, then the signals it sends around the body can cause damage. It’s likely that this is how obesity raises the risk of cancer.

  • Growth hormones– too much body fat can cause levels of insulin and other growth factors to rise, which can tell cells to divide more often. This raises the chance that cells will change and lead to cancer.
  • Inflammation– when there are more fat cells in the body, specialised immune cells go to the area, possibly to remove dead and dying fat cells. They release a cocktail of chemicals called cytokines, which can lead to inflammation. This makes cells divide faster, and when this happens over a long time it can raise the risk of cancer.
  • Sex hormones– after the menopause, oestrogen made by fat cells can make cells divide faster in the breasts and womb (two of the cancer types most closely linked to obesity), increasing the risk of cell faults and cancer.

Belly fat has harmful effects

When too much fat is carried around the belly, it can do even more damage. So-called ‘apple’ shapes are linked to bowel, kidney, oesophageal, pancreatic, and breast cancers.

It isn’t clear exactly why this is, but it could be to do with how quickly certain chemicals from fat can get into the blood.

A healthy body weight is important for children as well as adults

One in five children are overweight or obese before they begin primary school, and one in three children are overweight or obese by the time they leave.

Obese children are more likely to grow into obese adults, and obese adults are more at risk of cancer. It is possible overweight children may be at increased risk of cancer as adults, regardless of what they grow up to weigh, but the evidence isn’t clear.

By encouraging your children to lead a healthy lifestyle, you can help them keep a healthy body weight as a child as well as later on in life.