Being above a healthy weight has been linked to 13 cancers, including bowel, breast and pancreatic cancer. 

What is overweight and obesity?

Overweight and obesity are terms to describe high body weight and body fat. They can be measured by: 

  • Body Mass Index (BMI) - a calculation based on weight in relation to height.
  • Waist circumference tells us how much fat is around our waist and internal organs. The fat around our internal organs, known as ‘visceral fat’, can be harmful to our health if our bodies have a lot of it.

What causes overweight and obesity?

Weight gain happens gradually as a result of either:

  • Consuming more energy (kilojoules from food and drinks) than your body needs
  • Decreasing the amount of energy that your body is using (through physical activity).

Other factors can also lead to weight gain, like:

  • The genes you inherited from your parents
  • Your surroundings: food supply, increased food serving sizes, workplace, sleep, built environment
  • Stress, low energy, low mood, lack of motivation or emotional eating may cause us to over-consume food and drinks
  • How efficiently your body turns food into energy (metabolism).

How to calculate your BMI and measure your waist

For some groups of people, the healthy BMI range might be higher (as for older people and people of Pacific Islander background) or lower (as for people of Asian or Aboriginal background). Click here to learn more about BMI.   

What is cancer?

Cancer is a disease of the body’s cells. Cells in our body are constantly reproducing and regenerating to keep our bodies functioning. Sometimes, these cell processes become abnormal and can turn into the early stages of cancer. This can sometimes spread through the body.

What causes cancer?

Cancer can be caused by many uncontrollable factors such as age, genetics and hormonal factors. But we know that one third of cancers are caused by factors that are preventable. These include:

  • Being above a healthy weight
  • Smoking
  • Drinking alcohol
  • Sun exposure
  • Physical inactivity
  • Unhealthy diet
  • Not participating in early cancer screening.

What is toxic fat?

Scientists used to think that fat tissue was just our body’s way of storing extra energy that we didn’t need. It was assumed that fat was just stored under the skin and didn’t really do much. Now we know that body fat is also stored deep inside our bodies, including on our organs. This is called visceral fat. Fat tissue produces chemicals and hormones which travel around our bodies. Visceral fat produces more of these chemicals than the fat under our skin. These chemicals can be damaging to our bodies. That’s why we call it toxic fat. 

What is the link between toxic fat and cancer?

More toxic fat leads to more chemicals and hormones being released into the body. It also causes inflammation. This environment makes it more likely that cells will start to divide abnormally, and that a cancer will grow. Being above a healthy weight increases the risk of 13 different cancers.

Diagram of fat cells and cancer

What can I do about it?

  1. Avoid sugary drinks
  2. Limit junk food
  3. Eat more vegetables and fruit
  4. Be active every day
  5. Avoid alcohol

These actions are great for health regardless of our weight.

What if I am overweight and can’t lose weight?

Even if you don’t lose weight, eating healthy foods, moving more and preventing weight gain will reduce your risk of certain types of cancer, type 2 diabetes and heart disease.

Where can I get more information?

Adapted from Cancer Council ‘Obesity and cancer: what is the link?’ factsheet 2019

Are you at increased risk?

Calculate your BMI and waist measurement

Want to make some changes?

Check out our top tips

Debunking common cancer myths

Despite evidence showing lifestyle-related risk factors are the main known causes of cancer, it can be hard to distinguish fact from fiction. We debunk some of the common cancer myths and controversies myths