The World Health Organization defines overweight and obesity as “abnormal or excessive fat accumulation that may impair health.”
Body mass index (BMI) is a common method for determining overweight and obesity and is defined as a person’s weight in kilograms divided by the square of their height in metres(kg/m2).
For adults, WHO defines overweight and obesity as follows:
• overweight is a BMI greater than or equal to 25; and
• obesity is a BMI greater than or equal to 30.
While useful, BMI should be considered only as a rough guide because it does not correspond to the same degree of fatness in different people.
Cancer and obesity
Cancer develops due to alterations in gene expression that result from changes to the DNA.
These changes can be caused by a range of factors including inherited mutations, DNA damage, inflammation, hormones, and external factors such as tobacco use, infections, radiation, chemicals, and carcinogens in food.
Obesity contributes to increased inflammation in the body, increased release of oestrogens, and a reduction in sensitivity to insulin. The hormones insulin, “insulin-like growth factor-1” (IGF1) and leptin are all elevated in people who are obese and can promote the growth of cancer cells.
Insulin-like growth factors (IGFs) control cell growth, differentiation and death and leptin is a hormone associated with hunger and fullness, which has the ability to stimulate the production of many pre-cancer and cancer cells.
When functioning normally, our body’s sugar regulation processes tightly control the secretion of insulin; however, in those with obesity-related pre-diabetes or diabetes due to insulin resistance, insulin levels can rise to dangerous levels.
Elevated insulin levels in the body can signal tumour cells to grow, increasing the risk of cancer in the bowel, the lining of the uterus, the kidney, and pancreas. IGF-1 has been connected with prostate, breast and bowel cancers and increased leptin levels in obese people are associated with bowel and prostate cancers.
Although sex steroid hormones such as oestrogens, testosterone, and progesterone are critical for healthy body development and sexual function, they may also play a role in obesity and cancer.
There is a strong relationship between increased levels of sex steroids and endometrial and postmenopausal breast cancers, and suggestion they may also increase bowel cancer risk.
Oestrogen production within the body of men and postmenopausal women occurs primarily in fat tissue. In premenopausal women, the ovaries are the main producer of oestrogen.
Because obesity leads to inflammation in the body, the immune system in obese people is consistently more active than in people who maintain a normal weight.
Obesity and cancer treatment
Not only can obesity contribute to cancer, it can also impact cancer treatment.
Research shows that obese patients are much more likely to have a heart attack following surgery, and are also at greater risk of wound infection, nerve injury, and urinary infection.
Obesity alone increases the risk of poorer health outcomes following surgery, and morbid obesity increases the risk of death. One study revealed morbid obesity led to significantly increased surgical complications and prolonged hospital stays for patients with bowel cancer.
By 2025, it is estimated more Australians will be obese than normal weight.
Cancer is a leading contributor to early deaths and disability in Australia and the major cause of years lost from people’s lifespans.
Fortunately, there is evidence to suggest weight loss may reduce or reverse many of the above processes and their associated risks.
What can be done?
Relatively small changes have the potential to make a significant impact in reducing risk related to overweight and obesity.
According to the Australian Institute of Health and Welfare (AIHW), if all Australians at risk of disease due to overweight or obesity reduced their body mass index (BMI) by just one point - equating to around 3 kilograms for a person of average height - the overall health impact of obesity would drop substantially.
The report, Impact of overweight and obesity as a risk factor for chronic conditions: Australian Burden of Disease Study, looked at those who were overweight or obese in 2011, and showed that if this group reduced their weight by just one BMI point, the overall health impact of excess weight would be reduced by 14% in 2020.
If you or someone you know is struggling with overweight or obesity, speak with your GP about options that may assist you in addressing this serious health issue. You can also check out our Nutrition and Lifestyle Challenge and find a range of healthy, bowel friendly recipes on our website, or speak with one of our Bowel Care Nurses about options that might work best.