A clear, direct link between obesity and colorectal cancer, the second most common form of cancer in Australia with more than 12,000 new cases each year, has been shown in a new analysis by The George Institute for International Health in Sydney, Australia.

The report shows that obese individuals (Body Mass Index* (BMI) >30 kg/m2) have a 20% greater risk of developing colorectal cancer compared with those of normal weight (BMI < 25 kg/m2). The analyses also indicated that obese men are at 30% greater risk of developing the cancer compared with obese women. Findings from the study also showed that carrying even a few excess kilos substantially increases the risk of colorectal cancer; for every 5 kg weight gain the risk of developing the cancer increases by 7%.

Dr Rachel Huxley and co-authors at The George Institute reviewed over 70,000 patients in an analysis that included studies all across the globe: "Approximately, one in twenty Australians will develop colorectal cancer in their lifetime and our data clearly indicate that the risk of developing the cancer can be substantially reduced by maintaining a healthy weight" said Dr Huxley.

The new report carries links with the latest report from the World Cancer Research Fund Report, which provides further support regarding the link between obesity and cancer. Importantly, the primary recommendation of the report is; "Be as lean as possible within the normal range of body weight", supported by a public health goal of 'Median adult body mass index (BMI) to be between 21 and 23'. All eight recommendations made in the report were focused on healthyeating, drinking and physical activity, creating a sincere message of the relationship between diet and cancer risk. "Although the mechanisms that explain the link between excess weight and cancer remain to be elucidated, substantial evidence supports an important role for diet and physical activity" added Dr Huxley.

Both the international and George Institute report stress the increasing levels of obesity in both high income and developing countries. "Currently, around 300 million people across the world are obese. This figure is expected to rise up toward 700 million by 2015. Considering that obesity increases the threat of colorectal cancer by 20%, this means that 10,000 cases each year are due to severe excess weight. The number of cases of colorectal cancer alone, caused by obesity, is likely rise to at least 25,000 by 2015," added Dr Huxley.

Body Mass Index (BMI) is measured by dividing your body weight in kilograms by height in meters squared. An individual's BMI is associated with their body fat and health risk, a high BMI is >30kg/m2 and normal BMI is 25kg/m2."

The authors conclude by stating, while 20% is a considerable risk, previous reviews have suggested that obesity may be associated with up to 30-60% greater risk of colorectal cancer. However, according to Dr Huxley, "this over-estimation is most likely due to the impact of publication bias in medical and scientific journals. Regardless, a 20% greater risk is still considerable and sends a clear message about watching what you eat and being more physically active."

This research was published in the journal Cancer Epidemiology, Biomarkers and Prevention.

*The BMI equation is = body weight in kilograms/height in meters squared.

For more information on the George Institute, visit www.thegeorgeinstitute.org.