Cancer, diet, and lifestyle (part I)
Cancer. Utter the word and it may send a chill down your spine—and with good reason. Despite the nearly 50 year-long “War on cancer,” the enemy keeps on winning, claiming lives, and leaving a trail of confused scientists in its wake. More than any other disease, cancer invokes fear—partially because we’ve all seen it swiftly seize both life and dignity, but also because its tendency to lurk silently without warning before exacting its painful toll. Although today we have many weapons against cancer that we merely dreamed of 10 years ago, it remains the #2 killer in the US today. But for a moment, let’s set aside the ever more optimistic discussion of how we can treat cancer and focus on a profoundly more important topic: how can we avoid cancer in the first place?
For starters, we know unequivocally that lifestyle habits—smoking chief among them—can lead to cancer. We know that environmental exposures to toxins, hazards, and pollutants (lead, benzene, radioactive materials, asbestos, radon, and many others) can cause cancer. We also know that certain sexual behaviors that expose/transmit HPV are causative in many urogenital cancers as well as responsible for the surprising rise in HPV-related oral pharyngeal/head and neck cancer (of which I treat quite a bit as a radiation oncologist). There is almost as certain a connection between alcohol and certain liver and esophageal cancers. Thus, by avoiding tobacco, alcohol, toxins/carcinogens, and HPV (or getting vaccinated against HPV at the appropriate age), we can avoid some of the most common cancers.
Unfortunately that is not good enough. Cancer remains a deadly, devastating, and common problem. Although lung cancer is the leading cancer killer in the US and worldwide, it is outpaced in incidence (meaning the number of people diagnosed) by breast cancer; colorectal cancer and prostate cancer are a close 3rd and 4th in incidence. While we have excellent screening programs now for all of these conditions (mammogram for breast cancer, PSA blood test for prostate cancer, colonoscopy/stool testing for colon cancer, and now CT screening for lung cancer), avoidance of these cancers in the first place still remains elusive.
With this background, the boundless interest in the connection—if any—between cancer and controllable risk factors such as diet and lifestyle is not surprising. Much has been written, blogged about, and podcasted about regarding potential links between diet, lifestyle, and cancer. We here at OHH are no exception. In fact I have even written about and talked about this on podcast before. Despite the energy, effort, and advocacy, the unknowns far outweigh what we do know about cancer, diet, and lifestyle.
But the uncertainly does not discount the importance of this topic. “What can I do to prevent cancer” is almost always the first question any of my patients ask me. For many of them it is already too late; but for the readers—and authors of this blog—the question of how we can avoid cancer is of paramount importance. What follows is my honest attempt to tackle this towering, complex question. In this series, we will explore several modifiable diet and lifestyle related topics that can impact the risk of many common cancers. It goes without saying that what follows does not constitute medical advice and is simply the amalgamation of my understanding of the literature and science, integrated with my own experience as an oncologist
Obesity
Apart from smoking, there is probably no modifiable risk factor more strongly associated* with cancer than obesity. The CDC, NCI, and WHO now list obesity as a risk factor for cancers right alongside things like smoking and alcohol. Dishearteningly, one look at national statistics will tell you that as a nation and as a world we are only getting more obese. The 2014 NHANES study data reports that upwards of 70% of American adults are overweight or obese (a number that was only 56% some 20 years ago). Given these data, it is no surprise that cancer is on the rise. According to the NCI, obesity doubles the risk of certain cancers including endometrial (uterine), esophageal, stomach, liver, and kidney cancer. For others including breast, colorectal, and pancreas, the risk is 30-50% higher. See the full list of cancers known to be associated with obesity below in pictorial form courtesy of the NCI.
The most likely mechanism by which obesity causes cancer is related to hormones and cellular signaling. This theory is most apparent in hormonally-driven cancers, such as post-menopausal breast cancer and endometrial cancer, where excess adipose tissues (fat cells) produce excess estrogen, which in turn acts as a chemical promoter of tumor growth.
Additionally, obesity is known to promote chronic inflammation, which has independently been shown to increase cancer risk (see Barrett’s esophagus). Nutrient availability is a strong stimulant for cellular growth and division (central to cancer biology) via mTOR and other cellular signaling pathways; it goes without saying that obese individuals are more likely to have prolonged and excessive levels of nutrient availability that may upregulate mTOR and support cancer development (and may be excellent targets for metabolic therapies such as fasting). The more we learn and understand about the metabolism of cancer it becomes clear that obesity and dys-regulated metabolism is perhaps a more universal risk factor for cancer. Although the link between obesity and other specific types of cancers is not as clearly established, few experts would disagree that maintaining a healthy body weight—via whatever means necessary—will lead to better overall health and less cancer related mortality.
Ketosis
The means by which one achieves optimal bodyweight, however, is subject to more nuanced debate and scientific scrutiny. There has been immense interest of late in the ketogenic diet, both in the mainstream media and the scientific literature. As I have discussed on previous podcast appearances, ketosis may have unique biochemical properties leading to anti-cancer effects. It’s been shown in mouse studies to have an effect on reducing tumor growth and there have been preliminary results of similar success in small, uncontrolled human trials.
How could ketosis prevent cancer? The logic goes something like this: cancer cells preferentially use glucose for metabolism (a phenomenon know as the Warburg effect). Obese patients and patients with type II diabetes/metabolic syndrome have high blood glucose levels, and often subsist on a conventional high carbohydrate diet which promotes continued hyperglycemia. This state of high blood sugar provides just what the cancer wants: more glucose to fuel its metabolism and agenda of unregulated growth and proliferation. By limiting/eliminating glucose in a ketogenic diet, one could “starve” a tumor of its preferred fuel. Seems simple, right?
Unfortunately human physiology is far more complex. Small studies have been done looking at ketogenic diet for aggressive glucose metabolizing tumors such as glioblastomas and effects have been marginal at best. Ketogenic diets may have benefits in terms of making cancer cells more susceptible to chemotherapy while protecting normal cells, but much investigation in this domain still needs to be performed and is currently on going in clinical trials. In a recent mouse study, a pioneering cancer drug (PI3k inhibitor) was only effective when taken in conjunction with a ketogenic diet. although this is very exciting for future study, this does not mean that ketogenic diets are the “cure” for cancer. It also doesn’t prove that keto is good for all cancers in all patients. For now, I see ketosis as a potentially useful adjunct to the current available therapies. It is certainly not for everybody and I think effects will be modest. The best results will undoubtedly be seen with ketosis as part of a comprehensive approach incorporating the diet (and/or the presence of ketones themselves as signaling molecules) with current and future medical therapies.
*its important here to note that many of the items mentioned above are definitively known to cause cancer. Obesity and many of the other topics addressed are merely associated with obesity in observational studies. Correlation does not equal causation.