By Caroline Carney
With summer around the corner, we will soon be basking in the sun, sipping cocktails at backyard cookouts, and scarfing down char-grilled delicacies. These summer rituals are tasty and enjoyable, but it also means our systems will be exposed to more carcinogens: sun, alcohol, and even that delicious char from the grill. Scientists suspect these carcinogens contribute to an overall assault on the body that may increase the risk of developing cancer. The American Institute for Cancer Research estimates that nearly 40% of cancers can be prevented by lifestyle and dietary choices. Eating a diet of whole foods – fruits and vegetables packed with cancer fighting compounds – can help prevent cancer.
Good news, right? Suddenly the waters are muddied again: a recent study threatens to refute the assertion that the intake of fresh fruit and vegetables decreases cancer risk. This study, published in the April issue of the Journal of the National Cancer Institute, tracked the fruit and vegetable consumption of nearly 500,000 Europeans and found that produce does not significantly reduce cancer risk. Science is complicated: competing voices, contradictory findings – all in an unfamiliar language. As nutrition students, one of our roles is to clarify science for the public.
To get to the bottom of this thorny issue, I sat down with Dr. Xiang-Dong Wang, Director and Senior Scientist in the Nutrition and Cancer Biology Laboratory at the Jean Mayer USDA Human Nutrition Research Center on Aging. A veteran cancer researcher, Dr. Wang has been studying food and cancer prevention for over twenty years. We discussed this new article from the Journal of the National Cancer Institute and the larger issue of how to accurately translate scientific findings from the research bench to the public.
Lost in Translation
Dr. Wang believes the skills we’re acquiring as nutrition students are incredibly valuable. He says he and his colleagues are immersed in “data, data, data and we need someone to translate the science for the public.” He can cite many instances when research was either not translated at all or translated so poorly that it caused confusion among the public. The Beta-Carotene and Retinol Efficacy Trial (CARET), a landmark intervention study published in 1996 looking at the effect of beta-carotene on cancer risk among smokers, found that the high dosage actually increased the risk of lung cancer in smokers. People took this to mean that smokers who ate a lot of carrots would actually increase their risk of cancer. Not long after the CARET study was published, Dr. Wang received a call from a concerned young woman who claimed to eat a pound of carrots every day. She asked if she should stop eating carrots because she had read that beta-carotene could cause cancer.
Dr.Wang stresses the importance of knowing who the study population is. In the abovementioned CARET study, beta-carotene was given as a high dosage supplement to smokers. Because smokers are already subject to carcinogens and pro-oxidants (chemicals that cause cell damage either by creating reactive oxygen species or inhibiting antioxidants), the high amounts of beta-carotene actually resulted in an abnormal metabolite (substance produced from metabolism) that intensifies the effects of the carcinogens and inhibit the antioxidant power of the normal beta-carotene metabolites. Dr. Wang confirmed that woman who called her wasn’t a smoker and wasn’t taking a supplement, and then told her she could safely continue her carrot binge.
This story illustrates how easily science can be misinterpreted. The recent fruit and vegetable study that concludes vegetable consumption does not reduce cancer risk is another case of the science getting lost in translation. Dr. Wang explained, “This [finding] is not new. Two years ago a similar paper was published by Walter Willet out of Harvard.” Dr. Wang recalled speaking with Dr. Willet about the findings, and they both agreed that two key points were lost on the press and public. First, the study looked at all cancer types; second, it did not look at specific populations. “When you mix all cancer types and populations together it is very hard to see the difference,” clarified Dr. Wang. This does not necessarily mean that the study is flawed or its findings incorrect, however the results must be framed in the proper context. When The New York Times website has an article on the recent study entitled “Eating Vegetables Doesn’t Stop Cancer,” one can imagine that readers might misinterpret the study.
The Myth of a Silver Bullet
Dr. Wang believes “in an anti-cancer diet” based on whole foods, not supplements. He said “there is no silver bullet,” and no one nutrient that can stop cancer in its tracks. Nutrition research often focuses on the association between single nutrients and cancer prevention. Although helpful in understanding mechanisms of interaction, these studies lack the holistic diet perspective that is needed for behavior change.
Dr. Wang stressed the importance of the “antioxidant network” or how nutrients within a given food interact. This network can be overlooked during clinical trials that look at just one nutrient. Researchers do not always know how this network functions in the body, but it is clear that more forces are at play in carrots, for example, than just vitamin A.
The question of whole food versus single nutrient has recently taken center stage regarding the prevention and treatment of an inflammatory disease: steatohepatitis. Steatohepatitits, a disease usually seen in alcoholics, results from the accumulation of excess fat in liver cells, leading to liver inflammation. Over time, an inflamed liver may scar, harden, and result in liver cancer. Nonalcoholic steatohepatitis (NASH) is liver inflammation not linked to alcohol. Along with the rise in obesity, there has also been an increase in NASH. The high fat diet associated with obesity can lead to a fatty liver, a barrage of inflammatory cytokines (proteins secreted by immune system cells), and ultimately NASH.
Dr. Wang predicts that “in 20 years we will see a rise in liver cancer.” When many of the children who are obese today become obese adults suffering from NASH, they will be at a greatly heightened risk for this cancer.
Health professionals must take action today to prevent this tragedy. Dr. Wang recently published a study investigating the effect of lycopene, an anti-inflammatory compound, compared to tomato extract on cancer risk among obese participants with NASH. He proudly reports that the tomato extract proved to be significantly more effective at reducing liver cancer risk, while lycopene barely made a difference. The whole food, tomato extract, with its lycopene and thousands of other compounds was the victor. Perhaps this should mean tomato salads as a part of every school lunch!
So what should we eat?
Despite the null findings published in the Journal of the National Cancer Institute, the body of evidence supporting the anti-cancer properties of fruits and vegetables is extensive. A review of more than 150 studies of cancer and diet found a statistically significant protective effect of fruit and vegetable consumption in 80% of the studies. People with low fruit and vegetable intake had nearly double the risk of developing cancer compared with those with high intake, after control for confounding factors. A review of over 200 epidemiological studies looking at cancer and fruit and vegetable consumption found protective effects of allium genus vegetables (garlic, onions, leeks), carrots, green vegetables, cruciferous vegetables, and tomatoes.
As we bring our summer clothes out of storage and start filling our calendars with outdoor festivities, let’s remember to protect the health of our cells by eating plenty of fruits and vegetables. As nutrition students, we also must try to educate others on the benefits of these whole foods. There is a lot of good research out there, it just needs a spokesperson.