The medical community has long recommended eating a diet rich in fruits, vegetables, and whole grains to stay healthy and lower your risk of cancer. But provocative new research suggests the opposite may be true, at least for early-onset lung cancer.
The study found a link between a healthy diet and an increased risk of being diagnosed with lung cancer before age 50.
Understandably, this finding has raised some eyebrows. Here’s what the study revealed and what might be behind this surprising connection.
This study analyzed dietary information of young lung cancer patients
For the study, presented at the annual meeting of the American Association for Cancer Research, researchers launched the Juvenile Lung Cancer Epidemiology Project. The project looked at 187 people diagnosed with lung cancer before age 50.
Most of the patients had never smoked and had a different form of lung cancer than that typically associated with smoking. The researchers asked the participants, all of whom had been diagnosed with cancer, to recall their pre-diagnosis diet. The researchers then analyzed the participants’ diets using the Healthy Eating Index (HEI), a system that ranks the quality of Americans’ diets on a scale of 1 to 100. The researchers then compared that diet to that of the broader American population.
Researchers found that the average score for these young lung cancer patients was 65 out of 100, compared to the national average of 57. Additionally, women’s HEI scores were higher than men’s.
In general, young lung cancer patients ate more fruits, vegetables, and whole grains per day than the general population. That means consuming an average of 4.3 servings of dark green vegetables and legumes and 3.9 servings of whole grains per day. Meanwhile, the average American adult consumes 3.6 servings of dark green vegetables and legumes and 2.6 servings of whole grains per day.
Could pesticide residues on fruits, vegetables, and grains explain this association?
While the discovery is shocking, scientists agree there is likely more to the connection than meets the eye.
“This association may be due to exposure to pesticides, as we see high concentrations of pesticides in the types of foods consumed by this patient population,” Dr. Nieva said. He also points out that people who work in agriculture as pesticide applicators are at higher risk of developing lung cancer.
But other experts say the findings are not strong enough to prove the link. “This is low-level evidence and should be considered hypothesis-generating and not ready for prime time,” says Dr. Katrine Wallace, an epidemiologist and adjunct assistant professor in the department of epidemiology and biostatistics at the University of Illinois School of Public Health in Chicago. She added that this message was problematic because it had the potential to “mislead the public and undermine established dietary guidance.”
Roberto Pili, MD, associate dean of cancer research and integrative oncology at Buffalo Jacobs School of Medicine and Biomedical Sciences, agrees that the results should be interpreted with caution. “The higher healthy eating index reported in this patient population is actually associated with a lower risk of chronic disease and cancer, especially colon cancer,” he says. “Therefore, there is a recognized protective effect of eating more fruits and vegetables.”
Dr. Pili said the theory that exposure to pesticides could be involved is a “reasonable assumption,” but the evidence doesn’t exist. “Unless there is a way to prove that these patients have higher levels of pesticides in their urine or blood, this will remain a mere association,” he says. “There is no documented evidence that these patients were exposed to higher doses of pesticides.”
This study has important limitations to keep in mind.
The study asked patients about their diet before diagnosis, but there is likely recall bias, says Sora Ely, MD, a lung and esophageal cancer researcher and surgeon at George Washington University School of Medicine and Health Sciences in Washington, DC. He is not involved in the new research.
“We’ve all seen patients who are looking for reasons why they might have cancer, even if there’s no reason, especially patients who feel like they’re out of the normal group because of their cancer,” she says. “We often think, ‘If I did something that caused this, maybe I can do something to help with it.'” As a result, many patients make healthier lifestyle changes, such as eating cleaner foods, she says.
However, Dr. Ely points out that it can be difficult for patients to remember what they have eaten in the past, especially if they were diagnosed with lung cancer some time ago. “We’re all human, so our memories can be faulty,” she says. “Certainly, a cancer diagnosis can add a new lens to memory, which is a common problem in these retrospective studies.”
Finally, Ely says it’s also possible that people who were more interested in participating in such studies had healthier behaviors to begin with.
“The results only show that lung cancer patients reported slightly healthier diets than the national average,” Wallace says. “This is an example of ‘correlation does not equal causation’ and is not proof that healthy foods cause cancer.”
The majority of patients in the study had an EGFR mutation, which is associated with an increased risk of lung cancer in young adults, Pili said. “The incidence of smoking was also close to 40%, adding another potential risk factor,” Wallace said.
Finally, Wallace said that interpretation “overstates” the findings. “The results only show that lung cancer patients reported slightly higher Healthy Eating Index scores than the general American population,” she says. “This observation does not support the claim that high intake of fruits, vegetables, or whole grains increases the risk of lung cancer.”
Cancer experts still want people to eat healthier
Professor Ely stresses that doctors still do not understand the causes of lung cancer rates in young people, but says the findings do not suggest that a healthy diet is to blame. “I’m not going to change my diet, and I’m not going to recommend it to my patients, because I think there’s a good chance that stigma is at play,” she says.
However, Pili says further research is needed in larger patient groups to investigate potential links between pesticide exposure, produce consumption, and lung cancer risk. “Whether produce is organic or conventional, washing should always be recommended to reduce contaminants such as chemicals and bacteria,” he says.
Professor Nieva acknowledges that further research is needed to learn more about what is behind the rise in lung cancer in young adults. “We need to stop ignoring the problem and investigate the causes further,” he says.
