In a recent study published in Nutrients, researchers performed a meta-analysis to evaluate the association between different “a posteriori” (data-driven) diets and the risk of lung cancer.
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Background
Lung cancer remains a leading cause of cancer mortality worldwide, with smoking being the primary risk factor. Although smoking prevalence has reduced, non-smokers are witnessing increased lung cancer incidence.
Vegetables, fruits, nuts, polyunsaturated fatty acids, and fish can considerably lower the risk of pulmonary cancer, whereas red and processed meats increase the risk.
Nutritional epidemiology has switched to assessing the effects of varied diets on chronic diseases such as cancer to improve understanding of the influence of dietary patterns. Healthy diets, such as the Mediterranean diet, minimize the risk of pulmonary cancer, whereas the Western diet has the opposite effects.
Further research into the dietary modification of lung cancer may aid in developing interventions to enhance care for affected individuals and reduce the healthcare burden.
About the study
In the present meta-analysis, researchers evaluated the impact of diet on lung cancer risk.
The PubMed, Scopus, and Web of Science databases were searched through February 2023. Random-effects modeling was performed for the meta-analysis. The Population, Intervention, Comparison, and Outcome (PICO) method was used for study eligibility.
Only prospective and case-control-type studies evaluating the relationship between data-driven diets and the risk of lung cancer and presenting results as odds ratios (ORs), relative risk (RRs), or hazard ratios (HRs) were included. The references to the included studies were searched to identify additional studies.
In vitro studies, pooled analyses, reviews, intervention studies, case studies, molecular studies, animal studies, meta-analyses, commentaries, and ecological evaluations were excluded. Two researchers independently screened the data, and a third researcher resolved disagreements. The Newcastle-Ottawa Scale (NOS) was used to assess the quality of the included studies.
The Begg-Mazumdar-Egger method was used to assess publication bias. Subgroup analysis was performed, stratifying by smoking status.
In addition, a sensitivity analysis was performed by excluding one study at a time to assess the robustness of the results. The I2 statistic was used to determine the level of heterogeneity in the included studies.
Results
Initially, 1,048 articles were identified, of which 12 studies, including eight and four case-control and cohort studies, respectively, were selected for the meta-analysis. The case-control studies included 6,011 cases and 8,263 controls; seven studies were hospital-based, and one was population-based. The cohort studies included 505,665 individuals, of whom 3,638 were diagnosed with lung cancer. The food frequency questionnaire (FFQ) was used for dietary evaluation in all included studies.
Of the 12 included studies, one used cluster analysis (CA) to determine the data-driven diets, whereas 11 used principal component analysis (PCA). Seven case-control studies and three cohort studies were high quality.
Two diets were identified, i.e., “healthy/prudent” and western/meat”; the Western diet was characterized by increased consumption of red and processed meat, eggs, refined grains, and sweets, whereas the healthy diet had an increased factor loading for fruits, vegetables, whole grains, fish, and poultry.
There was no evidence of publication bias in the included studies considering pooled information and funnel plot symmetry for the diets; however, Begg’s test indicated publication bias among cohort studies for the healthy diet with statistical significance.
Western dietary adherence significantly elevated the risk of lung cancer (OR, 1.4), whereas that to a healthy diet reduced the risk (OR, 0.7).
The relationship between the diets and the risk of pulmonary cancer was linear; however, the relationship was direct but non-significant for the Western diet and inverse and significant for the healthy diet.
Further, the Western diet significantly enhanced the risk of lung cancer among current smokers (seven individuals, OR, 1.4) and former smokers (four individuals, OR, 1.9), whereas a healthy diet conferred protection to current smokers (eight individuals, OR, 0.6) and former smokers (four individuals, OR, 0.6). However, none of the diets exerted significant effects on non-smokers. The sensitivity analysis yielded similar findings as the primary analysis.
The high levels of heme iron and saturated fat in processed and red meats elevate the risk of pulmonary cancer by causing deoxyribonucleic acid (DNA) damage. The Western diet, which includes refined grains, reduces fiber intake, which may prevent lung cancer development.
On the contrary, a healthy diet, which includes vegetables, unrefined grains, and fruits, is rich in fiber, antioxidants (carotenoids, polyphenols, and flavonoids), and anti-inflammatory compounds that reduce oxidative stress and inhibit carcinogenesis.
Smoking, which contributes to lung cancer, can also cause DNA damage, and thus, a healthy diet may be more effective in preventing lung cancer among smokers than non-smokers.
Conclusion
Overall, the study findings highlighted the influence of Western and healthy diets on pulmonary cancer risk, particularly among current and former smokers. The Western diet was linked to a 39% elevation in the risk of lung cancer, while the healthy diet led to a 35% reduction.
The healthy diet showed a linear but inverse dose-dependent association with pulmonary cancer risk, while the Western diet had a positive but non-significant association.
Further research, including more prospective studies with larger sample sizes and diverse populations concerning age, gender, ethnicity, and different histological types of pulmonary cancer, is required to understand the interactions of diets with gut microbes and genetic polymorphisms associated with the risk of pulmonary cancer.
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