Evidence suggests that maintaining a healthy weight throughout life is one of the most important ways to protect against many types of cancer. It is estimated that around one quarter of all cancers could be prevented through appropriate food, nutrition and physical activity. Collectively, overweight and obesity, physical inactivity, and unhealthy eating are second only to tobacco as preventable risk factors for cancer. Addressing these risk factors is an important objective for reducing Australia’s cancer burden.
Overweight and obesity, and the underlying factors of physical inactivity and unhealthy eating are each independent risk factors for cancer. Healthy eating and physically active lifestyle are thought to protect against certain cancers both directly, and indirectly, through their impact on maintaining a healthy body weight.
According to the World Cancer Research Fund and American Institute for Cancer Research, there is evidence of a convincing and probable link between a number of related factors and cancer risk. 'Convincing' and 'probable' are the highest levels of evidence as determined by the World Cancer Research Fund and American Institute for Cancer Research, and denote that the relationship is causal or probably causal in nature.
There is convincing evidence that overweight and obesity increase the risk of cancers of the oesophagus, pancreas, bowel, breast (post-menopausal), endometrium and kidney.
Physical activity has been shown convincingly to protect against bowel cancer and to probably protect against post-menopausal breast cancer and endometrial cancer.
Unhealthy eating increases cancer risk; healthy eating can help protect against cancer. For example, convincing evidence shows that consumption of red meat and processed meat increases the risk of bowel cancer, and dietary fibre decreases the risk of bowel cancer. There is probable evidence that fruit and vegetable consumption decreases the risk of a number of cancers including cancers of the mouth, pharynx, larynx, oesophagus and stomach.
In addition to their impact on cancer risk, obesity/overweight, physical inactivity and unhealthy eating are among the largest risk factors for a number of other chronic diseases including cardiovascular disease and type 2 diabetes. As an individual's weight increases from a healthy weight to overweight or obesity, the risk of chronic disease increases.
As well as being a direct cause of several cancers, alcohol consumption may indirectly increase cancer risk by contributing to obesity and overweight. For further information on the link between alcohol consumption and cancer risk (not covered in detail in this chapter), see the Alcohol chapter of the National Cancer Prevention Policy.
This chapter of Cancer Council Australia’s National Cancer Prevention Policy discusses: the impact in Australia of cancers related to obesity/overweight, physical inactivity, and unhealthy eating; evidence on the links between these factors and cancer; the public policy context; and effective policy interventions that can reduce the prevalence of these cancer risk factors. It also summarises Cancer Council Australia’s recommended, evidence-based policy priorities for reducing the cancer burden in Australia attributable to obesity and overweight, physical inactivity and unhealthy eating.
Definition of overweight and obesity
Body mass index (BMI) is a common measure used as a proxy for human body fat based on an individual's weight and height. BMI is calculated by taking weight in kilograms and dividing by height in metres squared (kg/m2).
Table 1. Body mass index definitions according to the World Health Organization
|Healthy weight||18.5 - 24.99|
|Overweight||25 - 29.99|
|Obese||30 and above|
For children and adolescents, BMI-for-age percentile charts are used to determine healthy weight ranges. A BMI above the 85th percentile is indicative of overweight, and a BMI above the 95th percentile is indicative of obesity.
Alternatively, waist circumference can be used to measure overweight and obesity in adults. A measurement of 80cm and over around the narrowest point for women, or 94cm and over around the navel for men, is defined as overweight and increases the risk of metabolic complications (see Table 2).
The cut-off points for both BMI and waist circumference based estimates of excess body weight are lower for Asian populations than for those of European origin.
Table 2. Waist circumference definitions according to the National Health and Medical Research Council
|Risk of metabolic complications||Waist Circumference (cm)|
|Increased||80 and above||94 and above|
|Substantially increased||88 and above||102 and above|
- World Cancer Research Fund, American Institute for Cancer Research. Food, nutrition, physical activity, and the prevention of cancer: a global perspective. Washington DC: AICR; 2007.
- World Cancer Research Fund, American Institute for Cancer Research. Policy and action for cancer prevention. Food, nutrition, and physical activity: a global perspective. Washington DC: AICR; 2009 Available from: http://www.dietandcancerreport.org/cancer_resource_center/downloads/chapters/pr/Introductory%20pages.pdf.
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- World Health Organization, Food and Agriculture Organization. Diet, nutrition and the prevention of chronic diseases. Geneva, Switzerland: WHO; 2003. Report No.: WHO technical report series 916. Available from: http://apps.who.int/iris/bitstream/10665/42665/1/WHO_TRS_916.pdf.
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- National Health and Medical Research Council. Australian dietary guidelines. Canberra: NHMRC; 2013 Available from: http://www.nhmrc.gov.au/_files_nhmrc/publications/attachments/n55_australian_dietary_guidelines_130530.pdf.
- WHO Expert Consultation. Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies. Lancet 2004 Jan 10;363(9403):157-63 Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/14726171.