Researchers never tested participants' gut bacteria; their exposure measure came from a food questionnaire. After the team accounted for overall diet quality, the diet pattern's association with lung cancer was no longer statistically significant. The study cannot show that the pattern causes cancer. Smoking remains the dominant established risk factor.
The findings came from 95,612 U.S. adults in a study published Oct. 12, 2026, in Nutrition Journal. Authors Yi Xiao and Hongtao Tie analyzed data from the National Cancer Institute's Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial (PLCO). The trial enrolled about 155,000 people ages 55 to 74 at 10 U.S. screening centers between 1993 and 2001. The diet analysis covered a subset of 95,612 participants.
Participants completed a 124-item food-frequency questionnaire, on average about three years after randomization. Researchers used it to calculate a score from 25 food groups. The score represented a dietary pattern previously associated with gut microbes involved in sulfur metabolism. It was a food-based proxy, not a direct measurement of gut bacteria or sulfur compounds.
People in the highest fifth of pattern scores ate red and processed meat more often. They also ate french fries and high-fat dairy more often. Fruit and yellow vegetables were less common in their diets, as were whole grains. Through 2009, researchers recorded 1,561 lung cancer diagnoses. They tracked lung cancer deaths through 2018 and counted 2,109. Compared with participants in the lowest fifth, those in the highest fifth had a 23% higher risk of lung cancer and a 19% higher risk of lung cancer death in adjusted analyses.
Those figures describe an association, not a cause. The association weakened when researchers added overall diet quality to their models. Continuous measures also failed to reach statistical significance after that adjustment. Unadjusted lung cancer rates ranged from 1.20 to 3.03 per 1,000 person-years between the lowest and highest score groups. Adjusted differences were much smaller.
The score reflected foods associated with a microbial pattern. It did not show that a particular bacterium or hydrogen sulfide caused cancer. Researchers did not directly measure participants' gut microbes or sulfur metabolites. A review in the Journal of Gastroenterology and Hepatology describes roles for mucus and bile acids in sulfur metabolism. It also discusses interactions between microbes. The review says a universal low-sulfur diet is not supported.
Participants in the highest-score group were more often male, and their body mass index was higher. Smoking rates were higher in that group. Diabetes and high blood pressure were also more common. The authors noted that smoking may not have been fully accounted for. The association with lung cancer deaths was strongest among heavy smokers, including people with more than 20 pack-years of smoking.
Several limits narrow what the study can establish. Participants reported their diet only once, most were white, and the data came from an older U.S. cohort. After correction for multiple tests, only yellow vegetable intake remained associated with lower lung cancer mortality.
Readers assessing nutrition headlines can compare this uncertainty with our earlier evidence review, which examined how claims can outpace what the available evidence confirms.
The study gives people no reason to change their eating habits specifically to prevent lung cancer or to eliminate sulfur-containing foods. A balanced diet rich in vegetables and fruit supports overall health; whole grains are also part of that pattern. The researchers called for future studies that repeatedly measure diet. They also said future work should directly assess gut bacteria and sulfur compounds.
Established risk-reduction steps remain more relevant. Avoid smoking, quit if you smoke, and limit secondhand smoke exposure. The CDC also identifies radon and some workplace exposures as risks. Adults ages 50 to 80 with a significant smoking history may qualify for yearly low-dose CT screening under U.S. Preventive Services Task Force guidelines. Free help quitting is available by calling 1-800-QUIT-NOW. Some state health departments offer low- or no-cost home radon test kits.
