Insulin resistance and obesity have been linked to conditions like diabetes and heart disease, but too few of us are making the connection with cancer. In my consult practice I see patients at high risk for heart disease, but it's important to understand that the same lifestyle risks that raise heart attack risk are responsible for raising cancer risk as well.
People have very different emotional reactions to heart disease and cancer. Heart attacks are usually an abrupt, instantaneous event that catches individuals completely off guard. The intervention is rapid (some type of bypass procedure) and often patients return quickly to their baseline level of function. A heart attack patient physically looks pretty much the same before, during and after their heart attack. Perhaps a little lighter and fitter after the heart attack if such an event hopefully prompts some healthy lifestyle changes. There is far more certainty to the process of diagnosis, treatment and follow-up.
Cancer has a completely different cadence. There is the process of receiving the news about your diagnosis, absorbing the emotions of that news, the toxicity and side effects of the various treatments, the multiple follow up tests and imaging studies, the uncertainty for the cancer patient regarding survival, the number of experimental treatments and protocols, the emotional and physical deterioration and degeneration….I could go on. I've watched many patients and very close family members go through cancer. Vibrant, energetic, confident individuals reduced rapidly into a state of vulnerability and frailty. Fortunately many previously untreatable cancers have become treatable and in some cases curable. Improved diagnostic testing and early screening are key strategies that prevent and cure cancer in its incipient stages. However, cancer is still the 2nd leading cause of death after heart disease and we are identifying a growing list of modern day lifestyle exposures that are increasing cancer risk in adults and children.
Is Cancer Preventable?
When people discuss cancer prevention, typical topics include sunscreen, smoking cessation, and performing important screening tests like mammograms and colonoscopies. These are important prevention strategies, but too few people discuss the role of nutrition and lifestyle habits in the prevention of cancer. Let me present some basic science on cancer cells and hopefully that understanding will reinforce why a healthy lifestyle is the ultimate weapon in our war against cancer. I also want us to expand our definition of the more traditional carcinogens (smoking, etc.) to an entirely new class of risks I refer to as “lifestyle carcinogens.” These include factors such as diet, stress, sleep, activity and vitamin D. Let's discuss a few of these and how they relate to cancer risk.
Cancer Cells Eat Glucose
Cancer is a disease that results from abnormal cells that multiply rapidly without regulation. Cancer cells are remarkably resilient and able to replicate in harsh environments thanks to some unique metabolic properties. A healthy, non-cancerous cell produces energy by taking glucose and converting it into pyruvate which then enters the mitochondria (power-generating unit inside the cell) which next burns the pyruvate in the presence of oxygen. Cancer cells, however can produce energy directly from glucose without oxygen and without involving the mitochondria. If we were to use a car analogy, cancer cells are significantly more fuel-efficient than non-cancerous cells, using glucose alone to allow rapid replication and growth. Dense tumors often lack an adequate oxygen supply, so the ability to produce energy without oxygen is a major survival advantage for cancer cells. In fact PET/CT scans utilize the cancer cell's appetite for glucose to image tumors. Patients are given an injection of radioactive glucose which travels directly to the site of the tumor, allowing physicians to view the location and size of the cancer.
Key Point: Cancer cells use glucose as their primary energy source
Insulin Resistance and Cancer
If you don't understand the process of insulin resistance, be sure to read this, paying attention to my carb trafficking diagram. Essentially insulin resistance is diverting glucose from carbohydrates away from muscle, the preferred destination, towards the less desirable parking lots, fat and liver. Now look at my modified carb traffic diagram below which has added another highly undesirable parking lot for glucose. If genetics and/or environmental exposures (aka carcinogens like cigarette smoke, air pollution, and those listed here) in some way increase your susceptibility towards cancer, then insulin resistance may be potentially pushing excess glucose towards feeding those cancer cells as shown in the diagram below. In fact, there are several studies showing that the diabetic drug metformin may play a role in inhibiting cancer cell growth. In addition to making glucose more readily available to tumor cells, insulin resistance has another effect on tumor cell growth. Individuals who are insulin resistance tend to have higher levels of circulating insulin. When insulin fails to push glucose into muscle cells, your pancreas responds by pumping out even more insulin. Excess insulin not only triggers fat storage, but may also lead to cancer cell growth. For example, studies show that breast cancer cells contain insulin receptors and excess insulin when attached to these receptors can trigger growth and spread of the tumor.
Key Point: Insulin resistance can increase cancer risk by increasing glucose availability to feed tumor cells and by producing excess insulin which can trigger cancer cell proliferation.
Inflammation and Cancer
Many of the patients I see in my clinic who have already read my book have successfully reduced excess carbohydrates in their diet, but often continue to eat a plant-deficient diet. You can technically reduce insulin resistance measures (glucose, triglycerides ,waistline, etc.) by replacing carbohydrates with highly processed meats and poor quality fats, but now you've traded in high insulin foods with high inflammation foods. Inflammation is the major underlying cause of most chronic health conditions, including cancer. A highly processed diet that is deficient in plants is not going to provide enough anti-inflammatory, anti-cancer phytonutrients (plant-derived nutrients) to further protect you against cancer.
One of the key foods I emphasize in my book is the addition of cruciferous vegetables like cauliflower. Although I've always known about the anti-cancer benefits of eating cruciferous vegetables, I was especially impressed when I met a cancer researcher from a major university describe in detail how chemicals such as isothiocyanates found in cruciferous vegetables destroy cancer cells even more effectively than many chemotherapy drugs. In fact I was disturbed to learn from him that a few companies that produce chemotherapeutic drugs are investing money into blocking anti-cancer nutrition research since it is a threat to sales of anti-cancer drugs. After this eye-opening conversation, rarely a day goes by where I don't consume some form of cruciferous vegetables in my diet. The simple switch from white rice to cauliflower rice which I emphasize during consults and in my book provides a double whammy against cancer by reducing the glucose supply to cancer cells and providing cancer-killing isothiocyanates. Other lifestyle factors that can trigger cancer possibly via inflammation include chronic stress (be sure to read this) and sleep deprivation. In fact, night shift workers are at higher risk for cancers such as breast cancer due to the disruption in normal melatonin release.
Vitamin D and Cancer
Vitamin D deficiency is rampant in the diverse patient population I see in clinic and especially severe in my darker skinned South Asians who spend most of their time indoors. Keep in mind that vitamin D is not just involved in bone health, but is classified as a hormone that plays a key role in multiple metabolic processes. Low vitamin D is also associated with increased insulin resistance and inflammation, which are the two key processes I just tied to cancer. It's tragic that a general public health message to limit sun exposure as a preventive strategy for skin cancer has contributed to severe vitamin D deficiency due to paranoia about sun exposure. Yes our indoor-predominant modern day lifestyles are the main culprit, but demonizing the sun does not help. Vitamin D deficiency is now being tied to several different cancers including colorectal, breast, prostate and pancreatic cancer as shown in this review by the National Cancer Institute. Be sure to read my blog post on Vitamin D for more information on tailoring your sun exposure to your individual risk. Does this mean taking vitamin D supplements will reduce cancer risk? No compelling studies to suggest that yet, but getting safe sun exposure and supplementing to reach target levels might be an effective cancer prevention strategy. More studies are needed on this in the future.
Sitting Time and Cancer
Now that you understand the link between insulin resistance, inflammation and cancer, it should come as no surprise why prolonged sitting is a lifestyle carcinogen. Frequent activity, such as standing and walking, in addition to exercise a few times a week combats insulin resistance and inflammation as I highlight in this post.
What About Our Kids?
Cancer doesn't develop overnight. It takes years for the combination of genes, lifestyle and potential carcinogenic exposures to result in tumor growth. Unfortunately today's modern child is being exposed to the lifestyle carcinogens (excess sugar, increased processed foods, less plants, low vitamin D, inactivity, poor sleep habits, etc.) we just discussed from an earlier age. Just as lung cancer risk goes up the more years you smoke (quantified by doctors as “pack years”), children exposed to lifestyle carcinogens from an earlier age not only increase their future risk of cancer, but may develop cancer earlier in life due to a longer duration of adverse lifetime exposure.
Rising Cancer Incidence in South Asians
Based on everything I've told you so far, it should come as no surprise why this study reveals that cancer incidence is rising in South Asians. All of the lifestyle carcinogens we discussed are global health risks affecting all ethnic groups, but my book cites numerous studies on how South Asians are experiencing these lifestyle carcinogens at a greater dose than virtually every other group on the planet. In comparison to most other ethnic groups, South Asians consume more carbohydrates and less plants (this includes Indian vegetarians), adults and children are more sedentary and get less sleep, and our vitamin D levels are significantly lower than others. Even without ever touching a single cigarette, these other pervasive habits which have come to define Indian culture and lifestyle, are contributing to rising cancer risk.