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by Anne Finch, Accredited Practising Dietitian for LiveLighter, Melissa Ledger, Cancer Prevention & Research Director, Cancer Council WA

Two in every three Australian adults are overweight or obese. There is strong evidence that carrying extra body fat increases the risk of 13 cancers. Around 5% of cancers in Australia are due to overweight and obesity.

LiveLighter research shows that more than 40% of West Australians don’t know that carrying extra weight can lead to cancer. That’s why we’re running our 13 cancers campaign; to let West Aussies know about the link between weight and cancer, and how to reduce their risk.

How does body fat increase cancer risk?

Scientists used to think that fat tissue was just the body’s way of storing extra energy. It was assumed that all fat was stored under the skin and didn’t really do much. Now we know that fat is active; producing hormones, growth factors and other chemicals that travel through the body.

Some fat is stored deep inside our body on our organs – this is called visceral fat. Visceral fat produces more chemicals that travel around our bodies causing damage. That’s why we call it ‘toxic fat’.

More toxic fat leads to more growth factors and hormones being released into the body. It also causes inflammation. This creates an environment that makes it more likely that cells will start to divide abnormally, and that a cancer will grow.

Cells in our body are constantly regenerating to keep our bodies functioning. Sometimes, these cell processes become abnormal and can turn into the early stages of cancer. Cancer is not a single disease – there are many different types of cancer and they don’t all develop in the same way or have the same causes. For some cancers the exact pathways aren’t fully understood, but for others we have a good idea of how extra body fat increases cancer risk. Let’s take a closer look at a few examples.

Breast and endometrial cancer

In post-menopausal women, most of the body’s oestrogen is made by fat tissue. More body fat means more oestrogen. This oestrogen increases the risk of endometrial, ovarian and breast cancer (particularly ER-positive cancers) in these women.

Stomach and oesophageal cancer

Carrying extra weight is the most significant risk factor for acid reflux (heartburn), which is where the acidic contents of the stomach moves back up into the oesophagus. Over time, the acid damages the upper part of the stomach and the bottom part of the oesophagus. This increases the risk of developing cancers in these areas.

Bowel cancer

Higher body fatness can change the levels of different hormones in the blood, including insulin. And higher levels of insulin have been found to encourage the abnormal growth of cells in our large bowel, putting us at risk of bowel cancer.

How does toxic fat increase cancer risk

How much does being overweight increase our cancer risk?

This really depends on the cancer. For some cancers the more body fat you have the higher your risk of developing cancer. For some cancers, the location of where the body fat is stored makes a difference. Fat stored around the waist seems to be much more harmful than fat stored on the hips.

Is all body fat bad?

No - we all need some body fat to survive! Not having enough body fat also carries health risks. Just like carrying extra weight, the risk increases as a person moves further from a healthy weight. How much fat we store, and where we store it (under the skin or around our organs) is very individual, and has an impact on our health. There’s more information about BMI, waist measurement and health over here.

How can we reduce our risk?

We’re not completely sure yet about the link between weight loss and cancer risk, but there’s some research to suggest that losing weight can reduce the levels of cancer-causing factors in our body and our cancer risk.

The problem is that long term weight loss can be difficult. However, not putting on more weight will reduce our future cancer risk and is a great goal to aim for. We typically put on small amounts of weight over time – about ½ kg a year. We can bring this to a halt by changing our food and exercise habits. Habits, no matter your size, are what really matter! Adopting healthy habits will also reduce our risk of cancer, as well as heart disease and type 2 diabetes, independently of weight or body shape. For simple and practical ideas about how to do this, check out this page.

Avoid sugary drinks

Reducing the number of sugary drinks we have is one of the best ways to reduce our risk of developing toxic fat and therefore reduce our cancer risk. Soft drinks, sports drinks, slushies, flavoured milks, energy drinks, fruit drinks, iced tea and flavoured water all count as sugary drinks. A soft drink can contain the same number of kilojoules as a small meal, but doesn’t fill you up or provide the cancer fighting nutrients that your body needs.