The association between diet quality, plant-based diets, systemic inflammation, and mortality risk: findings from NHANES

PURPOSE: To our knowledge, no studies have examined the association of diet quality and plant-based diets (PBD) with inflammatory-related mortality in obesity. Therefore, this study aimed to determine the joint associations of Healthy Eating Index-2015 (HEI-2015), plant-based dietary index (PDI), healthy PDI (hPDI), unhealthy PDI (uPDI), pro-vegetarian dietary index (PVD), and systemic inflammation with all-cause, cardiovascular disease (CVD), and cancer mortality risks by obesity status. METHODS: Participants from NHANES were included in cross-sectional (N = 27,915, cycle 1999–2010, 2015–2018) and longitudinal analysis (N = 11,939, cycle 1999–2008). HEI-2015, PDI, hPDI, uPDI, and PVD were constructed based on the 24-h recall dietary interview. The grade of inflammation (low, moderate, and high) was determined based on C-reactive protein (CRP) values and multivariable ordinal logistic regression was used to determine the association. Cox proportional hazard models were used to determine the joint associations of diet and inflammation with mortality. RESULTS: In the fully adjusted model, HEI-2015 (OR(T3vsT1) = 0.76, 95% CI 0.69–0.84; p-trend = < 0.001), PDI (OR(T3vsT1) = 0.83, 95% CI 0.75–0.91; p trend = < 0.001), hPDI (OR(T3vsT1) = 0.79, 95% CI 0.71–0.88; p trend = < 0.001), and PVD (OR(T3vsT1) = 0.85, 95% CI 0.75–0.97; p trend = 0.02) were associated with lower systemic inflammation. In contrast, uPDI was associated with higher systemic inflammation (OR(T3vsT1) = 1.18, 95% CI 1.06–1.31; p-trend = 0.03). Severe inflammation was associated with a 25% increase in all-cause mortality (OR(T3vsT1) = 1.25, 95% CI 1.03–1.53, p trend = 0.02). No association was found between PDI, hPDI, uPDI, and PVD with mortality. The joint association, between HEI-2015, levels of systemic inflammation, and all-cause, CVD and cancer mortality, was not significant. However, a greater reduction in mortality risk with an increase in HEI-2015 scores was observed in individuals with low and moderate inflammation, especially those with obesity. CONCLUSION: Higher scores of HEI-2015 and increased intake of a healthy plant-based diet were associated with lower inflammation, while an unhealthy plant-based diet was associated with higher inflammation. A greater adherence to the 2015 dietary guidelines may reduce the risk of mortality associated with inflammation and may also benefit individuals with obesity who had low and moderate inflammation. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00394-023-03191-z.