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Obesity & Cancer

Posted on: 10 Feb 2016

Obesity & Cancer


Dr. Aoife Ryan, Dietitian and Lecturer in Nutritional Sciences in University College Cork and Principal Investigator with Cork Cancer Research Centre explains how better nutrition and physical activity can lower your cancer risk. 



We can help prevent cancer by knowing what causes it. Through scientific research, we know that our risk of developing cancer depends on a combination of our genes, our environment and aspects of our lifestyle. We have control over many of these factors and can directly alter our chances of developing cancer.



What causes cancer?


Cancer is caused by damage to our DNA, the chemical instructions that tell our cells what to do. Things in our environment, such as our lifestyle, can damage our DNA. This damage builds up over time and can lead to the cells in our body dividing uncontrollably. Cancer occurs when cells rapidly divide and multiply without control.


Do we inherit our cancer risk?


Some people inherit damaged DNA from their parents, which can give them a higher risk of certain cancers. But the proportion of cancers caused by inherited faulty genes is very small. Cancer is often thought to be a mainly inherited disease, but only 5-10% of cancers are due to genetics. Some people have inborn high vulnerability to specific cancers. In the greater majority of cases, such susceptibility only leads to actual disease when driven by external factors, such as excess body fat. Diet and lifestyle account for 90-95% of cancers. Living a healthy lifestyle does not guarantee that you will not develop cancer, but it can greatly reduce your risk of it.


Can lifestyle changes really make a difference?


In 2008, a large UK study worked out how a combination of the following four healthy behaviours would affect your health,

  • not smoking;
  • keeping active;
  • moderating how much alcohol you drink; and
  • eating five daily  portions of fruit and vegetables.


People who ticked all four healthy boxes gained an average of 14 years of life compared to people who did not do any of them. By the end of the study, these people were less likely to have died from any cause.


In high income countries smoking, alcohol use, and being overweight or obese are the most important causes of cancer. Being overweight and inactive accounts for up to 41% of worldwide cases of colon, kidney, oesophageal, breast and endometrial cancer. Furthermore between 9-19% of cancer cases in Europe could be linked to insufficient physical activity.


A large proportion of cancers are entirely preventable by appropriate food, nutrition, physical activity and body fat.  In fact the following are preventable by good nutrition and regular physical activity:


  • 67% of cancers of the mouth and throat cancers;
  • 75% of oesophageal (gullet) cancers;
  • 40-45% of cancers of the stomach, pancreas, colon, large bowel, and breast;
  • 20% of cancers of prostate, liver and kidney cancers; and
  • 56% of cancers of womb


The most reliable source on diet and cancer is an expert report prepared by the World Cancer Research Fund (WCRF) that is endorsed by the World Health Organisation (WHO) and several other renowned international bodies called ‘Food, Nutrition, Physical Activity and the prevention of cancer: a global perspective’. This report represents the cumulative efforts of 200 scientists who reviewed the evidence linking diet to 17 different forms of cancer.  500,000 studies were reviewed and whittled down to the 7,000 most relevant scientific studies which were then consolidated and rated in the report.


The WCRF panel, based on the above systematic review, concluded that,

avoidance of tobacco in any form, together with appropriate food and nutrition, physical activity, and body composition, have the potential over time to reduce much and perhaps most of the global burden of cancer’.


What are the recommendations for cancer prevention?

The WCRF report highlights the following eight key recommendations for cancer prevention. Click on each recommendation learn more.


A Note on Smoking


Experts agree that tobacco is the single biggest avoidable cause of cancer in the world. Worldwide, tobacco caused an estimated 5.1 million deaths in 2004 due to cancers or other smoking related conditions – that’s one every six seconds. Up to two thirds of all long-term smokers will be killed by their habit. And half of those killed by smoking-related diseases will die in middle age. On average smokers lose around a decade of life compared with non-smokers.


The biggest anti-cancer step you can take is to stop smoking, or never start. But even if you’re having trouble quitting entirely, you can reduce your cancer risk significantly by just cutting back. A study that appeared in the Journal of the American Medical Association in 2010 found that smokers who cut back from about 20 cigarettes per day to less than 10 per day reduced their lung cancer risk by 27%. It’s a good first step, but don't stop there; quit completely for your health's sake.


Even if you’re a non-smoker, don’t assume smoke isn’t permeating your life. About 3,000 cases of lung cancer each year occur as a result of exposure to second-hand smoke, and there are strong indicators that other cancers may be linked to second-hand smoke as well.