In Australia today two thirds of adults and one in four children are either overweight or obese. Many research studies over the past 15-20 years have shown that being overweight or obese – that is having a BMI (Body Mass Index) of over 29.9 - is a risk factor for many diseases, including colorectal (bowel) cancer.
According to 2018 figures from the Australian Institute of Health and Welfare*, colorectal cancer is the third most common cancer diagnosis in the country behind breast cancer and prostate cancer, and globally the incidence of colorectal cancer is increasing, with the World Cancer Research Fund reporting strong evidence that lifestyle factors, including food choices and 'greater body fatness' are contributing to this increase**.
A number of research studies around the world, mainly cohort studies (which are research studies carried out over long periods of time with groups of people who share one or more characteristics), show that higher amounts of body fat are correlated with increased risks for at least thirteen different types of cancer, including colorectal cancer. A 2013 study*** has shown that obesity increases the risk of contracting colorectal cancer by a factor of 30% over the risk for normal weight individuals.
So far, medical science has not shown a direct causative link between increased body fat and increased risk of developing cancer, however there are a number of possible factors which have been identified as being responsible for the increased risk. These include…
- Increased prevalence of low level inflammation in obese people, which has been linked to the DNA damage which may be a precursor to cancer
- Increased levels of insulin and 'insulin-like growth factor' often present in obese people may promote the development of colorectal cancer
- A type of protein/hormone known as adipokines that are produced by fat tissue and are linked to stimulation and inhibition of cell growth. One adipokine – leptin – promotes cell proliferation (which is essentially what cancer is, when uncontrolled) and is present in larger amounts where more body fat is present; adiponectin – another adipokine which is associated with cell growth inhibition, is present in smaller amounts in obese people
- Fat tissue may impact other growth regulators such as mTOR and AMP-activated protein kinase
Although medical science may not yet have found the precise interrelations between disease – including colorectal cancer – and obesity, it has certainly identified many correlations between the condition and many disease types.
Dr Renaut has outlined in his theory, called the Renaut Hypothesis, the close correlation between the body not being at its 'biological optimum function' and the negative influence of insulin resistance, which can in turn lead to weight gain.
*https://bowel-cancer.canceraustralia.gov.au/statistics
**https://www.wcrf.org/dietandcancer/colorectal-cancer
***https://www.ncbi.nlm.nih.gov/pubmed/23349764