It probably comes as little surprise that fiber—a prebiotic, and yogurt—a probiotic, protect against heart disease and gastrointestinal cancers. However, researchers have now found that this two-fer could also protect against lung cancer. Their results are published in JAMA Oncology.
“Our study provides strong evidence supporting the US 2015-2020 Dietary Guideline recommending a high fiber and yogurt diet,” said senior author Xiao-Ou Shu, MD, PhD, MPH, Ingram Professor of Cancer Research, associate director for Global Health, and co-leader of the Cancer Epidemiology Research Program, Vanderbilt-Ingram Cancer Center, Vanderbilt University Medical Center, Nashville, TN.
Although experts have identified an association of dietary fiber intake with improved lung function in previous studies, as well as a nonsignificant inverse association between yogurt intake and lung cancer risk, no studies have directly assessed the link between fiber and yogurt consumption and the risk of lung cancer. Thus, Dr. Shu and colleagues performed a pooled analysis of 10 prospective cohort studies in over 1.44 million adults from the United States, Asia, and Europe to evaluate the independent and joint associations of fiber and yogurt intake with lung cancer risk.
They also investigated how dietary and lifestyle factors (eg, smoking) might affect these potential associations. The primary outcome was the incidence of lung cancer by subtype—adenocarcinoma, small cell carcinoma, and squamous cell carcinoma. Levels of yogurt and fiber intake were stratified into quintiles.
Participants were followed-up for a median of 8.6 years. After accounting for smoking and other lung cancer risk factors, Dr. Shu and fellow researchers found that fiber and yogurt consumption was negatively related to lung cancer risk, with an HR of 0.83 (95% CI: 0.76-0.91) in those in the highest vs lowest quintiles of fiber intake. For those in the highest quintile of yogurt intake vs those eating no yogurt, the HR was 0.81 (95% CI: 0.76-0.87).
When the highest quintiles of yogurt and fiber intakes were assessed jointly, the relative risk of lung cancer dropped by more than 30% (HR: 69; 95% CI: 0.54-0.89), compared with non-yogurt consumption and the lowest quintile of fiber intake. Individually, the highest intake levels of fiber were linked to a 15% drop in lung cancer risk, and the highest levels of yogurt intake were tied to a 19% drop.
Importantly, the associations of fiber and yogurt intake with the risk of lung cancer were significant only in those with no smoking history, and were sustained regardless of sex, race/ethnicity, and tumor time.
“The inverse association of lung cancer risk with dietary fiber and yogurt consumption was more evident for squamous cell carcinoma and among participants with proinflammatory conditions (eg, heavy consumers of alcohol), suggesting that fiber and yogurt may exert beneficial effects on lung carcinogenesis via anti-inflammatory mechanisms,” wrote the authors.
While some researchers have shown no association between fiber intake and the risk of lung cancer (ie, the UK Million Women Study), others have demonstrated that a high-fiber diet may be related to better lung functions in US populations. Furthermore, in the Nurses’ Health Study (NHS) and Health Professionals Follow-Up Study (HPFS)—which were both included in the current pooled analysis—a high-fiber diet decreased the risk of chronic obstructive pulmonary disease (COPD) by 33%. Findings from Dr. Shu et al are in line with those from these previous studies on COPD and lung function.
They suggest that the observed beneficial health effects of fiber and yogurt consumption may be regulated by changes to the gut microbiome. Although dietary fiber can’t be digested, it is fermented in the body to form short-chain fatty acids. These may enhance host immunity and metabolism, proffering benefit that extends beyond the gut and to far-flung organs—such as the lungs.
“For the first time to our knowledge, a potential synergistic association between fiber and yogurt intakes on lung cancer risk was observed. Although further investigation is needed to replicate these findings and disentangle the underlying mechanisms, our study suggests a potential novel health benefit of increasing dietary fiber and yogurt intakes in lung cancer prevention,” the authors concluded.