OBESITY + CANCER
If you live in the UK, you might have seen the Cancer Research Society’s latest campaign plastered on bus shelters and billboards.
It specifically targets obesity as a “cause of cancer”, and states that obesity is the “UK’s second biggest preventable cause of cancer after smoking”.
Now, while I’m very glad to see this issue being highlighted (as it is too often tiptoed around and not truly given the exposure it deserves) it is worth noting that correlation and causation are very different things. It is thought that more than 1 in 20 cancers in the UK are linked to being overweight or obese (1), however to be accurate and true to the science, it is still not exactly understood how obesity causes cancer. Research has shown that many specific cancers are more common in those overweight and obese including cancers of the breast (in women after the menopause), bowel, womb, oesophageal (food pipe), pancreatic, kidney, liver, upper stomach (gastric cardia), gallbladder, ovarian, thyroid, myeloma (a type of blood cancer), and meningioma (a type of brain tumour).
The strong links between cancer and excess fat should not be ignored and here are some of the key processes that research suggests could be responsible for this significantly increased risk in overweight and obese people.
FAT AS A MESSENGER
Fat tissue isn’t just dormant, sitting there harmless like a lot of people think. It is regulated by, and regulates, various hormones and is active – sending information to the body and cells in the form of chemical messages.
Fat cells can actually initiate inflammatory responses in the body as well as perpetuate them through the activation of the immune system (as if they are infected or sick) and the release of inflammatory chemicals. (2) Higher levels of inflammation in the body leads to cellular damage and breakdown as well as increased cell turnover which may increase the risk of cancerous changes and premature ageing.
INSULIN + GROWTH HORMONES
Fat tissue and insulin have a close relationship. High insulin drives fat storage and high fat tissue levels perpetuate high insulin levels into a vicious cycle. Chronically high insulin can lead to insulin resistance and diabetes. This combined with insulin’s growth promoting effects can lead to increased cell turnover again and joined with the inflammatory process, this leaves potential for cancerous changes again.
As we age, changes in hormone levels can have an effect both directly on cells, and also on the factors above. Mice who had their ovaries removed and therefore stopped producing estrogen, gained a lot of weight, and gained it fast (3). A similar, more gradual effect can happen in menopausal women. In men as they age, testosterone levels drop and estrogen levels rise, leading to changes in hormone regulation, fat regulation and cell growth. Hormones and fat tissue are closely linked and fat tissue can in fact secrete estrogen and other hormones. Any changes above or below normal levels, combined with the right mix of other factors, may contribute to cancerous changes in various hormonally sensitive tissues such as breasts, ovaries and the uterus.
LOCATION, LOCATION, LOCATION
The location and distribution of fat tissue also contributes to its effects. Excess fat tissue carried on the lower body or backside tends to be less harmful than that carried around the abdomen or upper body. The closer the fat is to sensitive organs, the more at risk they are, possibly due to being bathed in the inflammatory chemicals and hormones being produced, and due to the fat tissue’s potential to infiltrate other tissue (which occurs in fatty liver disease).
So while direct causality of cancer by obesity is still yet to be firmly established, we can be sure that there is a very strong link between the two leading to a firmly increased risk of many cancers.
Obtaining and maintaining a healthy weight is vitally important for health and longevity, but it is worth remembering that even people who look thin, can still be carrying excess fat tissue – they’re often called “skinny fat” or TOFI (thin outside, fat inside).
Optimal body composition goes beyond “thin” and if you need to lose weight, adopting a healthy lifestyle that you can sustain for life should be your #1 priority.
2. Tuo Deng, Christopher J. Lyon, Laurie J. Minze, Jianxin Lin, Jia Zou, Joey Z. Liu, Yuelan Ren, Zheng Yin, Dale J. Hamilton, Patrick R. Reardon, Vadim Sherman, Helen Y. Wang, Kevin J. Phillips, Paul Webb, Stephen T.C. Wong, Rong-fu Wang, Willa A. Hsueh. Class II Major Histocompatibility Complex Plays an Essential Role in Obesity-Induced Adipose Inflammation. Cell Metabolism, Volume 17, Issue 3, 5 March 2013, Pages 411-422 DOI: 10.1016/j.cmet.2013.02.009
3. G. Wade, J. McElroy Short- and long-term effects of ovariectomy on food intake, body weight, carcass composition, and brown adipose tissue in rats. Physiology & Behaviour Volume 39, Issue 3, 1987, Pages 361-365 https://doi.org/10.1016/0031-9384(87)90235-6