A healthy diet rich in fruits, vegetables, and whole grains has long been associated with a lower risk of many chronic diseases, including several types of cancer. However, new preliminary research suggests an unexpected pattern among younger adults who have never smoked. The study found that people with lung cancer in this group tended to consume more plant-based foods than the average American, raising questions about whether long-term exposure to pesticide residues could play a role.
The findings were presented at the American Association for Cancer Research (AACR) Annual Meeting. Lead investigator Jorge Nieva, MD, a lung cancer specialist at the USC Norris Comprehensive Cancer Center, emphasized that the research does not suggest fruits and vegetables are harmful. Instead, the team is investigating whether pesticide exposure associated with conventionally grown produce may contribute to lung cancer risk in younger adults who have never smoked.
Why Researchers Are Investigating Pesticides
The researchers believe any potential risk would likely stem from pesticide residues rather than from fruits, vegetables, or whole grains themselves.
Conventionally grown produce and grains generally contain higher levels of pesticide residues than meat, dairy products, and many processed foods, according to previous food monitoring programs.
Nieva noted that agricultural workers with prolonged occupational exposure to pesticides have been shown in previous studies to experience higher rates of lung cancer, even after accounting for smoking. This observation prompted researchers to investigate whether chronic low-level dietary exposure might also contribute to cancer risk in people who have never smoked.
At present, however, this remains a hypothesis rather than a proven explanation.
Importantly, the researchers did not directly measure pesticide exposure in individual participants. Instead, they estimated likely exposure using publicly available data describing average pesticide residue levels across different food categories. Individual pesticides were not analyzed separately, and no direct testing of participants’ diets was performed.
Lung Cancer Is Increasing Among Younger Never-Smokers
Although lung cancer has traditionally been associated with older adults and cigarette smoking, cases among younger people who have never smoked have been increasing in recent years, particularly among women.
The average age of lung cancer diagnosis in the United States remains about 71 years, and overall lung cancer rates have declined substantially since smoking became less common during the 1980s.
To better understand the rising number of younger patients, researchers launched the Epidemiology of Young Lung Cancer Project.
The current analysis included 187 adults diagnosed with lung cancer at age 50 or younger, most of whom had never smoked. Many developed tumor types that differ biologically from cancers typically associated with long-term tobacco use, suggesting different underlying causes.
Earlier findings from the broader Genomics of Young Lung Cancer Project, published in 2021, also showed that lung cancers diagnosed before age 40 often represent distinct genetic subtypes driven by specific mutations that may respond to targeted therapies.
Participants Reported Healthier Diets Than Average
Researchers assessed participants’ diets using the Healthy Eating Index, which measures how closely eating habits align with U.S. dietary guidelines on a scale from 1 to 100.
The younger lung cancer patients achieved an average score of 65, compared with the national adult average of 57. Women generally scored higher than men.
Participants also reported eating more fruits, vegetables, and whole grains than the average American. On average, they consumed 4.3 daily servings of dark green vegetables and legumes and 3.9 servings of whole grains. By comparison, the average U.S. adult consumes approximately 3.6 servings of dark green vegetables and legumes and 2.6 servings of whole grains each day.
Within the study population, women younger than 50 who had never smoked were diagnosed with lung cancer more frequently than men. Women also tended to consume more plant-based foods, although the researchers caution that numerous biological and environmental factors could contribute to this pattern.
Important Limitations
The researchers stress that the findings should not discourage people from eating fruits and vegetables.
Extensive evidence accumulated over decades has consistently linked diets rich in plant-based foods with lower risks of cardiovascular disease, several forms of cancer, and premature death. Any new hypothesis regarding pesticide exposure must therefore be considered alongside these well-established health benefits.
The current study also has important limitations.
Because it was observational, it can identify associations but cannot establish cause and effect. Dietary information was based on participants’ own recollections, which may not always be accurate. In addition, pesticide exposure was estimated using average food residue data rather than direct biological measurements.
Other factors—including air pollution, inherited genetic susceptibility, previous respiratory infections, occupational exposures, and other environmental influences—could also contribute to lung cancer risk.
Previous research has shown that lung cancer among never-smokers occurs more frequently in women and people of East Asian ancestry and is often associated with genetic alterations such as EGFR mutations, which can be treated using targeted therapies. These cancers are increasingly recognized as a distinct subtype that may require different prevention and screening approaches.
Next Steps
The USC research team plans to directly measure pesticide exposure by analyzing blood and urine samples from future participants.
They also hope to identify whether particular classes of pesticides show stronger associations with lung cancer than others while controlling more carefully for diet, occupation, and environmental exposures.
Future studies may combine these exposure measurements with genetic analyses of tumors to determine whether certain environmental exposures leave characteristic patterns of DNA damage. If consistent associations are eventually confirmed, the findings could inform future regulations governing pesticide use, food residue limits, or recommendations for preparing produce.
For now, clinicians emphasize that younger adults—particularly women who have never smoked—should not ignore persistent symptoms such as a chronic cough, unexplained shortness of breath, chest pain, or coughing up blood. Early diagnosis remains especially important because lung cancer is often detected only after it has reached a more advanced stage, when treatment becomes more challenging.
