What can lead to cancer? In many cases, the first things to come to mind are sun exposure, smoking, toxic chemicals, or gene mutations. Did you know there's a strong link between excess body fat and cancer? Yes, excess body fat and body weight may be just as dangerous as any of these other factors in terms of cancer. Many are unaware this link exists and that it's a very strong one.
The New England Journal of Medicine published a review of more than 1,000 epidemiological studies that compare cancer risk with excess body weight.
In 2002, the IARC (International Agency for Research on Cancer) found 5 cancers closely linked to excess body fat. The latest 2016 report found excess body fat to be linked to at least 13 different kinds of cancers, including cancer of the liver, gallbladder, rectum, colon, esophagus, stomach, pancreas, breast, ovaries, kidney, uterus and thyroid. Other cancers with convincing evidence of a link with overweight and obesity include cancer of the blood (multiple myeloma), brain, and prostate.
When we place cancer deaths attributed to smoking and to excess body weight side by side, the statistics can be quite surprising! Of the 572,000 cancer deaths that occur in the US each year, 1/3 can be attributed to exposure to tobacco products. How many can be attributed to diet and exercise habits (including overweight and obesity)? One-third! Yes, it is not a stretch to say excess body fat can be just as dangerous as smoking when it comes to cancer!
Body Fat in THE CANCER PROCESS
How can something as ordinary as body fat be as dangerous as toxic, carcinogenic chemicals found in cigarette smoke? Fat is often perceived to be as lifeless as a storage depot. It is commonly viewed as a layer of inert, dormant tissue that, for the most part, is harmless and, at the most, can sabotage our body image goals. This is a misconception.
That seemingly inactive mass of fat is actually extraordinarily active, dynamic, and complex! Many of its actions can create the perfect environment for cancer development.
GROWTH FACTORS: Excess body fat influences levels of growth factors such as insulin-like growth factor 1 (IGF-1). This can promote cancer cell growth.
INSULIN RESISTANCE: Abdominal fat increases resistance to insulin. The pancreas compensates by boosting insulin production. This increase in blood insulin levels increases risk of colon and endometrium cancers, and possibly pancreatic and kidney cancer.
HORMONES: Obesity can influence the levels of a number of other hormones, including sex steroid hormones (estrogens, androgens, and progesterone) and leptin. When there are increased levels of leptin circulating in theblood, risk increases for colorectal and prostate cancer. Increased levels of sex steroids are very strongly associated with endometrial and breast cancers.
INFLAMMATION: Obesity is a state of chronic low-grade inflammation. Fat cells produce a variety of pro-inflammatory chemicals, such as tumor necrosis factor (TNF), C-reactive protein, interleukin-6, and leptin.
Overall, the studies have shown high-fat diets and diet-induced obesity can promote cancer by influencing:
- early appearance of tumors
- greater frequency of tumors
- accelerated growth
- larger tumor sizes
- and even more frequent metastasis of tumors.
The Good News
In the article "Obesity and Cancer Pathogenesis", the Annals of the New York Academy of Sciences calls obesity "public health issue number one".
What can we do about it? The good news is that excess body fat or body weight is a modifiable risk factor, "modifiable" meaning there is much we can do about it. Cancer is not completely out of our control.
The best way to interfere with obesity-related cancer risks is to prevent obesity in the first place, to achieve and maintain a healthy body weight, or to strive to be as lean as possible without being underweight and undernourished.
Need some motivation? The American Institute for Cancer Research (AICR) published a neat chart estimating how many cancer cases could be prevented by simply staying lean.4 Consider just a few:
- 13% of postmenopausal breast cancer cases in women
- 15% and 17% of colorectal cancers in women and men, respectively
- 28% and 27% of liver cancers in women and men, respectively
- 11% of advanced prostate cancer cases
1. N Engl J Med. 2016;375(8):794-798.
2. World Cancer Research Fund/American Institute for Cancer Research. Food, Nutrition, Physical Activity, and the Prevention of Cancer: A Global Perspective. Washington, DC: World Cancer Research Fund/American Institute for Cancer Research; 2007.
3. Berger, N. A. (2014). Obesity and cancer pathogenesis. Annals of the New York Academy of Sciences, 1311, 57–76. http://doi.org/10.1111/nyas.12416
4. AICR/WRCF, Policy and Action for Cancer Prevention 2009; Continuous Update Project reports; American Cancer Society, Cancer Facts & Figures 2016.