The medical community has long recommended eating a diet high in fruits, vegetables, and whole grains to stay healthy and lower the risk of cancer. But provocative new research suggests the opposite may be true — for early-onset lung cancer, at least.
The study found a link between a healthy diet and a higher risk of being diagnosed with lung cancer before the age of 50.
“There is an epidemic of lung cancer in young, nonsmoking people in the United States, and we need to make efforts to understand what is causing it,” says Jorge Nieva, MD, the lead study author, a medical oncologist, and a lung cancer specialist with USC Norris Comprehensive Cancer Center in Los Angeles. “Something about their diet might be contributing to it.”
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Naturally, the findings are raising eyebrows. Here’s what the research uncovered, plus what could be behind this surprising link.
The Study Analyzed Dietary Information From Young Lung Cancer Patients
For the study, which was presented at the American Association for Cancer Research’s annual meeting, researchers launched the Epidemiology of Young Lung Cancer Project. This project surveyed 187 people who were diagnosed with lung cancer by age 50.
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Most of the patients had never smoked, and had a form of lung cancer that was different from those typically linked to smoking. The researchers asked the participants, all of whom were diagnosed with cancer, to recall their diet before their diagnosis. The researchers then analyzed the participants’ diets using the Healthy Eating Index (HEI), a system that ranks the quality of Americans’ diet on a scale of 1 to 100. Investigators then compared the diets with those of the wider American population.
The researchers discovered that these young lung cancer patients had an average score of 65 out of 100, compared with the national average of 57. Women also had higher HEI scores than men.
In general, young lung cancer patients ate more servings of fruit, vegetables, and whole grains per day than the general population. That was broken down as averaging 4.3 servings of dark green vegetables and legumes and 3.9 servings of whole grains per day, compared with average American adults, who ate 3.6 servings of dark green vegetables and legumes and 2.6 servings of whole grains per day.
Could Pesticide Residue on Fruits, Vegetables, and Grains Explain This Link?
The findings are shocking, but scientists agree there’s likely more to this association than it seems at first glance.
Dr. Nieva says the link may be due to pesticide exposure, “as these are seen at higher concentrations in the types of foods eaten by our patient population.” He also points out that people who work in agriculture as pesticide sprayers have a higher risk of developing lung cancer.
But other experts say the findings aren’t strong enough to make that connection. “This is low-level evidence that should be considered hypothesis-generation and not ready for prime time,” says Katrine Wallace, PhD, an epidemiologist and an adjunct assistant professor in the division of epidemiology and biostatistics at the University of Illinois School of Public Health in Chicago. She adds that the message is problematic because it could “mislead the public and undermine well-established dietary guidance.”
Roberto Pili, MD, an associate dean for cancer research and integrative oncology at the University at Buffalo Jacobs School of Medicine and Biomedical Sciences, agrees that the results should be interpreted with caution. “A higher Healthy Eating Index reported in this patient population, actually, has been associated with reduced risk of chronic diseases and cancer, in particular colon cancer,” he says. “Thus, there is a recognized protective impact of eating more fruits and vegetables.”
While Dr. Pili says the theory that pesticide exposure may be involved is a “reasonable assumption,” there is no proof of this. “Unless there is a way to demonstrate higher levels of these pesticides in the urine or blood of these patients, this will remain just an association,” he says. “There is no documented evidence that these patients were exposed to greater levels of pesticides.”
The Study Has Important Limitations to Keep in Mind
While the study asked patients about what their diet was like before their diagnosis, there is likely a recall bias, says Sora Ely, MD, a lung and esophageal cancer researcher and a surgeon at George Washington University School of Medicine and Health Sciences in Washington, DC, who wasn’t involved in the new study.
“We have all seen patients — particularly those who feel they are out of the normal demographic for a form of cancer — who are searching for reasons they may have gotten cancer, even if there is no reason,” she says. “The thought is often, ‘If I did something that caused this, there may be something I can do to help the outcome.’” As a result, many patients will change to a healthier lifestyle, including eating a cleaner diet, she says.
But Dr. Ely points out that it can be difficult for patients to remember what they ate in the past, especially if they were diagnosed with lung cancer a while ago. “We’re all human and subject to errors in memory,” she says. “Certainly, a cancer diagnosis can add a new lens to the memory. That’s a common issue we see in these retrospective surveys.”
Finally, Ely says that it may also be that people who are willing and interested in participating in a study like this may have had healthier behaviors to begin with.
“The results only show that lung cancer patients reported slightly healthier diets than national averages,” Wallace says. “That is an example of ‘correlation doesn’t equal causation’ and is not evidence that healthy food causes cancer.”
The majority of patients in the study were carrying an EGFR mutation, which is linked with a higher risk of lung cancer in younger adults, Pili says. “Also, the incidence of smoking was close to 40 percent, adding another potential risk factor,” Wallace says.
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Finally, Wallace says that the interpretation “overstates” the findings. “The results show only that lung cancer patients reported slightly higher Healthy Eating Index scores than the general U.S. population,” she says. “This observation does not support the claim that higher consumption of fruits, vegetables, or whole grains increases lung cancer risk.”
Cancer Experts Still Want People to Follow a Healthy Diet
Ely stresses that doctors still don’t understand what is driving rates of lung cancer in younger adults, but says the findings don’t suggest a healthy diet is a culprit. “The possibility of bias playing a role is enough that I’m not going to change my diet, and I’m not going to recommend that my patients do either,” she says.
But Pili says that more research with a larger group of patients is needed to explore a potential link between pesticide exposure, produce consumption, and lung cancer risk. “Regardless of whether the produce is organic or conventional, washing should always be recommended to reduce contaminants such as chemicals and bacteria,” he says.
Nieva acknowledges that more work is needed to learn more about what’s behind rising rates of lung cancer in younger adults. “We need to stop ignoring the problem and conduct more research into the cause,” he says.
