The World Cancer Research Fund (WCRF) has provided a global perspective report focusing on Diet, Nutrition, Physical Activity and Cancer. The last report was published over a decade ago. There are still components surrounding our knowledge of cancer that are maintained between then and now, but others have changed.
Cancer claims one in six people worldwide. Smoking is still considered the number one cause of cancer but there are other risk factors and this new report illuminates one of those causative pieces that, in my opinion, we have been reluctant to embrace and accept. Obesity is not just a healthcare concern for disorders like diabetes, heart disease, osteoarthritis, and pulmonary challenges; obesity is a serious risk factor for cancer. Fat cells can produce hormones that promote cell growth. Rapid cell growth can lead to errors in cellular DNA and mutations can lead to cancerous cell types. Now that growth drives cancer cell proliferation. Sugars drive cancer growth by providing endless sources of energy to rapidly replicate and spread. Chronic inflammation and insulin resistance can produce hormone signals that promote cell growth. Again, if this pathway leads to mutated cells because the process is going too rapidly, now that mutated cell population is growing, dividing, and spreading.
It isn’t really just the state of being obese that is the causative agent. It is a combination of factors that leads an individual to that state; therefore it is those combination of factors that contribute to the risk. The WCRF report provides what they call a “blueprint”, or recommendations, for decreasing that risk of obesity and therefore, cancer. The recommendations are as follows: being a healthy weight, being physically active, eating non-processed food (healthily), limiting fast foods, limiting red meat and processed meats, limiting intake of sugary drinks, limiting alcohol, and limiting supplements to make up for missing nutrients. These individual pieces can be tailored to each individual based on their body composition, tendencies, and lifestyle so that they are do-able for nearly everyone.
The WCRF report claims that nearly 40% of cancers are preventable. The National Cancer Institute has linked 13 cancers to obesity:
Endometrial Cancer: risk of endometrial cancer increases with increases in weight in adulthood; obese and overweight women are nearly 4 times as likely to develop this compared to healthy weight women.
Esophageal Adenocarcinoma: adipose tissue acts on tumor progression directly; mechanism not fully understood but the literature has shown that peritumoral adipose tissue secretes paracrine factors which directly affect the progression of this cancer.
Gastric Cardia Cancer: increased BMI positively associated specifically with risk of gastric cardia cancer; obese individuals reported to develop this cancer type twice as often as healthy-weight individuals.
Liver Cancer: an obese individual’s liver is chronically being damaged as it works hard to maintain metabolism and function; the damage can predispose that same individual to development and progression of cancer. Association is stronger in men than women.
Kidney Cancer: Renal Cell Cancer occurs in overweight or obese individuals at two times the occurrence in healthy-weight individuals. Although not fully understood, it is suggested that insulin resistance, insulin-like growth factor, and biochemical markers may be involved.
Multiple Myeloma (MM): monoclonal gammopathy of undetermined significance (MGUS) is a pre-cancerous blood disorder; studies have shown that nearly 40% of overweight and obese individuals may have MGUS and this significantly increases the likelihood of progression to MM for obese patients specifically.
Meningioma: slow growing brain tumor risk is increased by 50% in obese individuals
Pancreatic Cancer: identified in 2007 WCRF report as being a “convincing increased risk” factor; insulin resistance is a risk factor for pancreatic cancer and metabolically active visceral body fat secretes adipokines with a downstream effect on insulin resistance.
Colorectal Cancer (CRC): strong literature to support statistically significant positive association between CRC and obesity.
Gallbladder Cancer: obese individuals have a 60% increased risk of developing gallbladder cancer; risk increase is greater in women than men.
Breast Cancer: most literature separates postmenopausal women from premenopausal women in breast cancer links or associations. Obese postmenopausal women have a 20-40% increased risk of developing breast cancer compared to healthy-weight postmenopausal women. Of note, highest risks are for women who have not used hormone therapy and have tumors that express hormone receptors. There is a 20% decreased risk of hormone receptor expressing breast tumors in premenopausal women.
Ovarian Cancer: slight increased risk for women with higher BMI, however obesity has also been shown to affect overall survival of women with ovarian cancer
Thyroid Cancer: slight increased risk for women with higher BMI; association between these is not well understood. Some studies indicate TSH has been associated with thyroid cancer risk and TSH is thought to promote tumor growth.
These are not the only contributors for cancer risk; individual health factors including genetic makeup, family history, and more also add to the complexity of determining causation for disease states. However, the worldwide supportive literature and recognition that cancer, albiet complex, has a likelihood of continuing to plague our populations and will lead to increased deaths if we don't take steps to make meaningful change.
Sources: National Cancer Institute, World Cancer Research Fund, Cancer Epidemiology, Recent Results in Cancer Research Journal, Journal of the National Cancer Institute, Bioscience Report, Clinical Thyroidology, American Cancer Society,