Is it possible for diet to play a role in the development of lung cancer among never-smokers? According to the results of a new analysis, the answer seems to be a resounding yes. 

An international, multi-center team of researchers concluded that after adjusting for known risk factors, consumption of dietary fiber and yogurt was associated with a reduced risk of lung cancer in these individuals. 

Food. Source: Getty Images

Reporting in JAMA Oncology, the investigators noted that dietary fiber is a primary source of prebiotics, while yogurt is a well-known probiotic. As such, these two foods confer a variety of health benefits, primarily via modulating the gut microbiota and metabolic pathways. 

“However,” the researchers wrote, “their associations with lung cancer risk have not been well investigated.”

To help answer these questions, the investigators -- led by Jae Jeong Yang, Ph.D, a Research Fellow at Vanderbilt University Medical Center in Nashville, Tennessee — set out to evaluate the individual and joint associations of dietary fiber and yogurt consumption with lung cancer risk. They also sought to assess the potential effect modification of the associations by lifestyle and other dietary factors.

The pooled analysis included 10 prospective cohorts comprising 1,445,850 adults from studies conducted in the United States, Europe, and Asia. Data analyses were performed between November 2017 and February 2019. 

The researchers used harmonized individual participant data to estimate hazard ratios and 95% confidence intervals for lung cancer risk associated with dietary fiber and yogurt intakes for each cohort. The analysis excluded individuals with a history of cancer at enrollment or those developed any cancer, died, or were lost to follow-up within two years of enrollment.

Validated instruments were used to measure dietary fiber intake and yogurt consumption. The trial’s primary outcome was incident lung cancer, which was subclassified according to histologic type, such as adenocarcinoma, squamous cell carcinoma, and small cell carcinoma.

The final study sample included 627,988 men (mean age 57.9 years) and 817,862 women (mean age of 54.8 years). Among this group, 18,822 cases of incident lung cancer were documented, over a median follow-up period of 8.6 years.

After adjusting for a variety of risk factors, it was found that intake of both fiber and yogurt was inversely associated with lung cancer risk. Indeed, the highest quintile of fiber intake yielded a hazard ratio of 0.83 (95% confidence interval 0.76-0.91) when compared with the lowest quintile of fiber intake. 

Similarly, high yogurt consumption yielded a hazard ratio of 0.81 for the development of lung cancer (95% CI: 0.76-0.87) when compared with no yogurt consumption. 

Furthermore, the associations between fiber or yogurt and lung cancer were found to be significant in never smokers, and were consistently observed across sex, race/ethnicity, and tumor histologic type. 

When considered jointly among the entire total study population, the combination of high yogurt consumption and the highest quintile of fiber intake showed a reduction in lung-cancer risk 33% when compared with non-yogurt consumption and the lowest quintile of fiber intake (HR 0.67; 95% CI: 0.61-0.73). This, the researchers said, suggests a potential synergistic association between fiber and yogurt consumption with lung cancer risk.

The association was similar among never smokers (HR 0.69; 95% CI: 0.54-0.89). 

The results of the analysis demonstrate that dietary fiber and yogurt may be individually and jointly associated with reduced risk of lung cancer. “Our findings,”  the authors wrote, “suggest a potential protective role of prebiotics and probiotics against lung carcinogenesis.”