A Sulfur-Heavy Diet Pattern Linked to 25% Higher Lung Cancer Risk in Women

If you've been told to keep an eye on your gut for skin, mood, or digestive trouble, here's a less obvious one to add to the list: your lungs. A new study following more than 114,000 women for up to 18 years found that a dietary pattern linked to sulfur-processing gut bacteria was tied to a meaningfully higher risk of developing lung cancer, independent of smoking. The finding builds on years of research connecting this same "sulfur microbial diet" to colorectal cancer, and it's the first time anyone has tested whether it reaches beyond the gut to a distant organ like the lungs.

Key takeaways

• Women who ate the most sulfur-microbial-diet-promoting foods (processed meat, low-calorie soft drinks, less vegetables and legumes) had a 25% higher risk of lung cancer than women who ate the least, in a study of 114,981 women.
• Risk rose in a steady, dose-dependent way as adherence to the diet increased, and swapping vegetables in for processed meat trended toward lower risk, though that swap did not reach statistical significance.
• The catch: researchers measured diet, not gut bacteria or hydrogen sulfide directly, so this is an observational proxy, not proof that the microbiome itself is driving the extra risk.

Sulfur Microbial Diet Score Tied to a 25% Higher Lung Cancer Risk

Women who scored highest on the sulfur microbial diet (SMD), a dietary pattern built to reflect the abundance of sulfur-metabolizing gut bacteria, had a 25% higher risk of lung cancer than women who scored lowest, according to a prospective cohort study of 114,981 women published in the International Journal of Women's Health. The SMD isn't a diet anyone follows on purpose. It's a score built from eight food and drink categories, including processed meat, alcohol, low-calorie drinks, fruit juice, legumes, vegetables, and sweets, that researchers designed to track how much a person's habitual diet feeds bacteria that convert dietary sulfur into hydrogen sulfide, a gas that's toxic to the cells lining the gut. Women in the highest quarter (quartile 4) of the score had a hazard ratio (HR, a measure of relative risk over time) of 1.25 (95% confidence interval 1.02 to 1.54) for developing lung cancer, after researchers statistically adjusted for age, smoking status, body weight, income, physical activity, and several other factors. The risk climbed step by step from the lowest to the highest quartile, and every one-standard-deviation increase in the score was tied to an additional 8% higher risk (HR 1.08), though that finer-grained estimate sat right at the edge of statistical significance.

Why This Matters for Women, Including Those Who Have Never Smoked

Lung cancer is the leading cause of cancer death worldwide, and its toll on women specifically has been rising even among those who have never smoked, a group the researchers note makes up roughly 15% to 25% of female lung cancer cases. Smoking is still by far the dominant cause of lung cancer, but that leaves a real slice of cases that smoking alone can't explain, which is why researchers are hunting for other modifiable risk factors, especially ones tied to something as changeable as diet. This particular study matters to that search because it adds lung cancer to a list of cancers already linked to the SMD, joining earlier research tying the same diet pattern to colorectal cancer, precancerous colon growths, and higher all-cause and cancer mortality. In this new analysis, the positive association held up across women of different ages, ethnic backgrounds, smoking histories, and drinking habits, with no single subgroup driving the result.

How Researchers Tracked Diet and Cancer Risk Over 18 Years

The findings come from a large UK prospective cohort that originally enrolled close to 500,000 adults between 2006 and 2010. For this analysis, researchers restricted the sample to women, excluded anyone with lung cancer at enrollment or missing follow-up data, and were left with 114,981 women. Diet was measured using a web-based 24-hour recall tool completed up to five times per person, then averaged to estimate habitual intake, and each woman's answers were converted into an SMD score and sorted into quartiles. Cancer cases were tracked through national cancer registry records, and over a follow-up period stretching up to 18 years, researchers documented 802 incident lung cancer cases. To make sure the result wasn't a statistical fluke, they ran it through several checks: a spline model confirmed the risk rose in a smooth, straight-line pattern rather than jumping at some threshold; excluding cancer cases diagnosed in the first two years (to rule out reverse causation, where an early undetected cancer changes a person's eating habits) softened the link slightly to an HR of 1.22 but kept the same direction; and excluding women with diabetes or heart disease at the start actually strengthened it, to an HR of 1.44.

What This Means If You're Watching Your Gut Health

If you're already trying to eat less processed meat and more vegetables and legumes for your gut, heart, or colon, this study gives you one more reason, but not proof that changing your diet will lower your lung cancer risk specifically. In a substitution analysis, the researchers modeled what would happen if women swapped an equivalent amount of processed meat for vegetables, and found a trend toward lower risk (HR 0.93) that landed just short of statistical significance. Notably, when the researchers checked whether standard blood markers, cholesterol, blood sugar, blood pressure, and C-reactive protein (a marker of inflammation), could explain the diet-cancer link, they came up mostly empty. The biggest single contributor, triglycerides, accounted for less than 2% of the association, and several markers actually worked in the opposite direction. That's worth knowing if you or your doctor are trying to make sense of routine bloodwork: normal cholesterol or inflammation markers do not rule out this pathway, because the study suggests it likely isn't running through those numbers at all. The association also held up among never-smokers specifically, though the researchers caution that this subgroup had few cancer cases, so that particular result deserves a healthy dose of caution.

The Study Measured Diet, Not Gut Bacteria or Hydrogen Sulfide Directly

The biggest limitation is baked into the method: researchers never measured anyone's actual gut microbiome or hydrogen sulfide levels. The SMD score is a diet-based proxy, originally built from a separate group of study participants whose stool samples were analyzed for sulfur-processing gut bacteria, then applied here based on food intake alone. That means the proposed mechanism, that this diet raises hydrogen sulfide, which then travels beyond the gut to affect the lungs, remains a hypothesis rather than something this study directly demonstrated. It's also an observational study, so it can show an association but can't prove the diet causes lung cancer; residual confounding from unmeasured factors like air pollution, secondhand smoke, occupational exposures, or family history, none of which were collected in this dataset, can't be ruled out. The participants were also overwhelmingly white, generally healthier and less economically deprived than the broader population, which may limit how far the specific numbers generalize elsewhere, and the per-standard-deviation risk estimate landed just at the edge of statistical significance (P = 0.054).

What Researchers Want to Test Next

The authors are explicit about what would settle this: cohort studies that directly measure gut microbiome composition and hydrogen sulfide levels alongside diet, rather than relying on diet as a stand-in for both. They also call for replication in more diverse, multi-ethnic populations with better data on air pollution and occupational exposures, and for actual dietary intervention trials to test whether replacing processed meat with vegetables lowers lung cancer risk in practice, not just on paper. Given the gut-lung axis, the idea that gut bacteria can influence immune activity and inflammation in the lungs, a distant organ, has picked up mainstream research interest in recent years, and the authors suggest sex-specific studies on hormones and the microbiome as a next step given the distinct biology of lung cancer in women.

Common Questions

What exactly is the sulfur microbial diet?

It's a dietary pattern score, not a diet people intentionally follow, built from eight food and drink categories (including processed meat, alcohol, low-calorie drinks, and vegetables) that was originally shown to correlate with higher levels of sulfur-processing gut bacteria in earlier research on colorectal cancer.

Does this mean processed meat causes lung cancer?

Not on its own, and not according to this study. The researchers found only a non-significant trend toward lower risk when modeling a swap of vegetables for processed meat, so this study shows an association with an overall dietary pattern, not proof that any single food causes cancer. Processed meat has separately been classified as a carcinogen linked to colorectal cancer by international health authorities, which is part of why researchers wanted to test its broader effects.

Were the women in this study smokers?

The cohort included never-smokers, former smokers, and current smokers, and the diet-cancer link held up across all three groups, with no single smoking-status group driving the overall result.

How many women actually got lung cancer in this study?

Out of 114,981 women followed for up to 18 years, 802 developed lung cancer, a small fraction overall, which is why even a real 25% relative increase in risk translates to a modest number of additional cases at the individual level.

References

1. Gaofeng Liang, Hongyan Yu, Chengbin Lin, Jinxian He, Hui Tian (2026). Association of Sulfur Microbial Diet and the Risk of Lung Cancer in Women. International Journal of Women's Health. https://doi.org/10.2147/ijwh.s628503
2. Yumeng Ding, Huanqing Tao, Chen Zhu, et al. (2026). Lung cancer in never-smoking females: epidemiology, risk factors and screening. Frontiers in Public Health. https://doi.org/10.3389/fpubh.2026.1834538
3. Ji-Yeon Moon, Bong-Hyeon Kye, Seung-Hyun Ko, Ri Na Yoo (2023). Sulfur Metabolism of the Gut Microbiome and Colorectal Cancer: The Threat to the Younger Generation. Nutrients. https://doi.org/10.3390/nu15081966
4. The Role of Gut Microbiota in Lung Cancer: From Carcinogenesis to Immunotherapy. NIH. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8417127/