A diet filled with fruits, vegetables, and whole grains has long been celebrated as one of the simplest paths to better health, linked to lower risks of heart disease, diabetes, and many cancers. But new research is adding an unexpected layer of complexity to that message, especially for younger non-smokers in the United States.
Findings from USC Norris Comprehensive Cancer Center, part of Keck Medicine of USC, presented at the annual meeting of the American Association for Cancer Research, suggest that this traditionally “healthy” diet may be associated with a higher risk of lung cancer in Americans under 50 who do not smoke.
“Our research shows that younger non-smokers who eat a higher quantity of healthy foods than the general population are more likely to develop lung cancer,” said Jorge Nieva, MD, a medical oncologist and lung cancer specialist with USC Norris and lead investigator of the study. “These counterintuitive findings raise important questions about an unknown environmental risk factor for lung cancer related to otherwise beneficial food that needs to be addressed.”
Rather than pointing to the foods themselves, researchers are cautiously exploring what comes with them. Nieva and his team speculate that pesticide exposure may be a contributing factor, since commercially grown fruits, vegetables, and whole grains are more likely to carry pesticide residues than animal products or processed foods. The idea is further supported by observations that agricultural workers exposed to pesticides often show higher rates of lung cancer.
The study also uncovered a striking gender pattern: young non-smoking women appear to have higher lung cancer rates than men, and they also tend to consume more produce and whole grains.
Lung cancer has historically been associated with older adults; the average age at diagnosis is 71, along with smoking and a higher incidence in men. But that pattern is changing. As smoking rates have steadily declined since the mid-1980s, overall lung cancer cases have dropped, except among one unexpected group: non-smokers under 50, particularly women.
To better understand this shift, researchers launched the Epidemiology of Young Lung Cancer Project, surveying 187 patients diagnosed with lung cancer at or before age 50. Participants provided detailed information about their diet, lifestyle, and medical history.
Most had never smoked. Many also had lung cancer types that differ biologically from those typically caused by smoking. A related 2021 study from the project found that lung cancer subtypes in people under 40 are distinct from those seen in older adults.
When researchers examined diet quality using the Healthy Eating Index (HEI), a 1-100 scale measuring overall diet quality, the results added another layer of surprise. Young non-smoking lung cancer patients scored an average of 65, compared with the U.S. national average of 57. Women in the study had higher scores than men.
On average, these patients consumed more fruits, vegetables, and whole grains than the general population. They reported eating 4.3 servings of dark green vegetables and legumes per day and 3.9 servings of whole grains, compared with 3.6 and 2.6 servings, respectively, in the average U.S. adult.
Despite the unexpected pattern, researchers stress that the findings do not prove cause and effect. Instead, they point to a potential environmental link worth deeper investigation.
“In the study, researchers did not test specific foods for pesticides. Instead, they used published data on average pesticide levels for food categories such as fruits, vegetables, and grains to estimate exposure. The next step, said Nieva, is to confirm the link by directly measuring pesticide levels in blood or urine samples from patients. This could also help reveal whether or not some pesticides increase lung cancer risk more than others.”
“This work represents a critical step toward identifying modifiable environmental factors that may contribute to lung cancer in young adults,” said Nieva. “Our hope is that these insights can guide both public health recommendations and future investigation into lung cancer prevention.”
The research was supported by the Addario Lung Cancer Medical Institute, AstraZeneca, the Beth Longwell Foundation, Genentech, GO2 for Lung Cancer, and Upstage Lung Cancer, underscoring growing interest in understanding why lung cancer is appearing in unexpected populations, and what modern environmental exposures may be quietly contributing to it.
