As someone who grew up in Northern California during the 1970s, I was surrounded by all the fads of the New Age movement: past-life regression, crystals, channeling, EST (or Erhard Seminars Training), macramé, hot tubs, and the nascent organic food movement.
My mother willingly embraced many of these fads, particularly the organic movement. Our school lunch boxes were often filled with granola, yogurt and sandwiches on homemade whole grain bread the color and consistency of the macramé potholders that hung in our patio. It wasn’t until after my mother started working long hours as a real estate agent that we kids finally got the sorts of lunches we craved: PB&J or bologna sandwiches on Wonder® bread, with a Hostess Ho-Ho or Ding Dong as a treat.
If a new study out of the University of Texas MD Anderson Cancer Center is correct, that much-ballyhooed switch from homemade wheat bread to store-bought white bread may have been a bad move, at least with respect to my lung cancer risk. That study looked at the link between diet – specifically a diet rich in high glycemic foods like white bread – and rates of lung cancer among non-smokers.
Lung cancer is one of the most common (and the most preventable) forms of cancer in the US. According to the American Lung Association, about 225,000 Americans are diagnosed and 160,000 die of lung cancer annually. The majority of these cases are directly linked to smoking. An adult male who smokes is 25 times (or 2500%) more likely to get lung cancer than a non-smoker. In fact, nearly a quarter of heavy smokers (defined as smoking more than five cigarettes a day) will be diagnosed with the disease, as compared with less than one percent of people who have never smoked.
However, despite the clear link between smoking and lung cancer, approximately 25,000 non-smokers will be diagnosed with lung cancer in the US this year. Many of these cases can be linked to secondhand smoke, occupational hazards like asbestos or uranium, or exposure to radon (a colorless and odorless radioactive gas that can build up in basements and cellars). But many cases of lung cancer among non-smokers have no clear etiology. That, coupled with mounting evidence that dietary factors can influence an individual’s lifetime cancer risk, led the investigators at MD Anderson to conduct their study.
Nearly 4,500 non-smokers (1,900 lung cancer patients and 2,400 healthy controls) were asked about their dietary habits, including their consumption of sugary and starchy foods like white bread and white rice. The people who ate the most of so-called high glycemic foods – foods that quickly raise blood sugar levels following a meal – were 50% more likely to have cancer than those that ate the fewest of these foods.
So this must mean that the old adage “the whiter the bread the quicker you’re dead” is correct, right? In order to reduce my lifetime risk of developing lung cancer, a non-smoker like myself should eliminate all white bread, bagels, white rice, and potatoes from my diet, right?
Not so fast! Despite all of the television reports and newspaper headlines to the contrary, the results of this study are somewhat suspect. Retrospective studies of dietary habits are notoriously inaccurate; most people can’t even tell you what they had for breakfast that very morning, let alone give you an accurate description of the types of foods they’ve eaten over the past months and years.
In addition, the study failed to control for other lifestyle factors that may also influence cancer risk, including exercise, obesity and consumption of red meats and saturated fats. In fact, the greatest association between starchy foods and lung cancer was seen among patients with fewer than 12 years of formal education, which is often used as a proxy for socioeconomic status, health literacy, and dietary and exercise habits.
The biological mechanism by which starchy foods may increase a non-smoker’s risk of lung cancer are also unclear. One theory is that these high-glycemic foods stimulate the production of insulin, which in turn stimulates the growth of cells. Cancer is essentially the uncontrolled growth of cells, so this insulin-induced stimulation might be fueling the development of tiny tumors. But if that is true, then a diet with a high glycemic index should also be linked with a variety of other cancers. To date, however, studies looking at the consumption of starchy foods and colon, stomach, pancreatic, ovarian and prostate cancers have been inconclusive.
Finally, even if these results turn out to be true, this doesn’t mean that you should eschew your morning bagel. If you are a non-smoker, the likelihood that you will develop lung cancer is slim. Fewer than 1 in 500 people who have never smoked will be diagnosed with this disease, and most of those cases can be linked to non-dietary factors like secondhand smoke, asbestos and radon. A 50% increased lifetime risk is, in absolute terms, but a drop in the bucket. You’re more likely to die of some other dietary or lifestyle-related health issue, such as heart disease or type 2 diabetes.
Eating a diet that limits the consumption of sugary and starchy foods is a good thing to do. Coupled with regular exercise and other healthy choices, it can help reduce your likelihood of developing all sorts of chronic diseases. But to recommend that we avoid eating that bowl of steamed rice because of a putative lung cancer risk? That’s just blowing smoke.
[This blog entry was originally presented as an oral commentary on Northeast Public Radio on March 10, 2016, and is available on the WAMC website.]