“It is a predisposition of human nature to consider an unpleasant idea untrue, and then it is easy to find arguments against it.” Sigmund Freud
Almost everyone knows that smoking causes cancer and obesity increases the risk of heart disease and diabetes. Most of us don’t know, however, that obesity is also associated with the risk of cancer. That’s the case especially with common cancers like breast cancer, prostate cancer, colon, kidney and endometrium cancer. Data also shows that people who are obese when they are diagnosed with cancer seem to have a higher risk of developing recurrence and dying from their disease.
Obesity causes one in five cancer deaths. One epidemiological study estimated that the continuation of current trends in obesity will lead to more than 500,000 additional number of cancers in the States alone by 2030. This data also suggested that if every adult reduced their body mass index by 1%, which is equivalent to a weight loss of 1kg (2.2 lbs), this would prevent about 100,000 new cases of cancer a year.
Cancer risk associated with obesity is an overlooked problem. The statistics say that one in two men and one in three women will have any kind of cancer in their lifetime. That's a lot of cancers!
As we live longer, age slower, and have better access to health care and screening methods it appears natural that more people will develop cancer during their lifetime than ever before. However, it’s not a coincident that over the last 20 years our waistlines have continued to grow and so has cancer. We now have convincing evidence that obesity is strongly associated with many common types of cancer.
Let's look at the mechanisms that explain the link between obesity and cancer.
Obesity is a condition where a person has an abnormally high and unhealthy proportion of body fat. Large fat cells are not sitting around passively. Every fat cell is as active organism secreting high levels of more than fifty chemicals like cytokines, hormones and markers of inflammation. These molecules first contribute to developing chronic metabolic diseases like diabetes and heart disease, but they also create a cosy environment for cancer cells to grow.
Obese people often have increased levels of insulin and so-called Insulin-like growth factor-1 (IGF-1) in the blood that is the first sign of insulin resistance. The problem is that insulin not only regulates the metabolism but it can also act as a growth-stimulating hormone that promotes cell division and tumour growth. High blood sugar levels promote certain types of cancer, in particular, liver and pancreatic cancer. In other words, diabetes is closely related to tumour growth and increased risk of cancer.
Fat cells produce hormones, called adipokines, which either stimulate or inhibit cell growth, for example, leptin, promotes cell proliferation, whereas adiponectin, has antiproliferative effects. Fat cells may also have direct and indirect effects on other tumour growth regulators, like AMP-activated protein kinase. Most obese people have high levels of chronic inflammation markers that have also been associated with increased cancer risk.
What does research say about weight and cancer?
Researchers at Vienna University were looking at how obesity may be associated with breast and endometrial cancer in postmenopausal women. They measured blood levels of so-called osteopontin, a prognostic marker in breast cancer progression. The scientists found an interesting pathway. They noticed that obesity-induced osteopontin in fat cells might contribute to estradiol production and consequently to the association of obesity with oestrogen-dependent cancers like breast cancer or endometrial cancer.
A research team at the University of Washington found that black men who are obese with a body-mass index of 35 or higher had a 122% higher risk of low-grade and an 81% higher risk of high-grade prostate cancer compared to those who were of normal weight (with a BMI of 25 or lower). In contrast, among white men, those who were obese had a 20% lower risk of low-grade and only a 33% increased risk of high-grade prostate cancer compared to those of normal weight.
How about people with diagnosed cancer?
Although we don’t know for sure whether modifying weight after diagnosis will have an effect, knowing that there is a link between obesity and cancer is important in oncology. Many patients turn attention after completing their active cancer treatment to survivorship, and this often can include a focus on healthy eating, losing weight and increased physical activity. We also know that it’s safe for most people with cancer to exercise all through the cancer trajectory as remaining physically active has been shown to prevent from gaining weight during cancer therapy.
Are the genes responsible for our weight?
Maintaining healthy weight is in our hands and within our control. It’s at the core of keeping in check both metabolic chronic illnesses and cancer as all those conditions are interconnected. Like a spider web.
Genes do influence obesity, the way they influence every aspect of human physiology, development, and adaptation. So far, there is no evidence regarding the specific genes that may contribute to obesity.
One study published last year found that eating fried food has an effect on genes related to obesity showing that some people may be more predisposed to obesity than others. The research talks about predisposition, not causation or association. In other words, genes are our predisposition, but genes are not our faith.
Genes express themselves differently depending on the environment. Our lifestyle choices pretty much predict how our genes behave. We have the power to either down-regulate gene expression to suppress their response to the stimulus, or we can up-regulate the genes, so they express themselves more actively.
The link between cancer and weight is part of a broader problem of general health. Obesity is a modifiable risk factor, which means that we have an opportunity and responsibility right now to do something about it. For those who are obese, there are myriad of clear reasons to lose weight that go beyond the fear of cancer.