Pro-inflammatory dietary patterns and physical fitness in Spanish adolescents: a cross-sectional analysis from the...

Chronic low-grade inflammation has been implicated in diminished physical fitness, with diet being a key modulator of inflammatory status. The dietary inflammatory index (DII) literature quantifies the inflammatory potential of habitual diet; however, evidence linking pro-inflammatory dietary patterns (when operationalized using DII-type scores) to physical fitness during adolescence remains scarce. This study aims to characterize the distribution of a pro-inflammatory dietary pattern score (DII-informed food frequency questionnaire [FFQ]-derived inflammatory score) and examine its cross-sectional associations with multiple physical fitness components in adolescents, accounting for relevant confounders.

We conducted a cross-sectional analysis including Spanish adolescents aged 12-17 years from the Eating Healthy and Daily Life Activities (EHDLA) study. Dietary inflammatory potential was operationalized using a DII-informed FFQ-derived inflammatory score based on 45 food items (higher scores indicate more pro-inflammatory dietary patterns). Physical fitness was assessed with the 20 m shuttle run test, standing long jump, 4 × 10 m shuttle run, sit-and-reach, handgrip strength, and an age- and sex-standardized overall fitness score. Associations were examined using robust linear regression models (lmrob function, robustbase package, KS2014 setting in RStudio), with adjustment for energy intake, age, sex, socioeconomic status, sleep duration, physical activity, sedentary behavior, and body mass index z-score. We additionally performed Benjamini-Hochberg false discovery rate (FDR) correction across the six primary outcomes and sensitivity analyses.

The analytical sample included 909 adolescents (median age: 14.0 years [interquartile range (IQR): 2.0]; 55.1% girls). In adjusted models, higher pro-inflammatory dietary pattern scores were associated with lower overall physical fitness (unstandardized beta coefficient [B] = -0.007 z-score units per 1-point increase; 95% confidence interval [CI]: -0.012 to -0.002; p-adjusted = 0.003), lower cardiorespiratory fitness (20 m shuttle run: B = -0.137; 95% CI: -0.243 to -0.031; p-adjusted = 0.011), and lower handgrip strength (B = -0.048; 95% CI: -0.092 to -0.005; p-adjusted = 0.029). Flexibility showed an inverse association that did not remain significant after FDR correction (p-adjusted = 0.173). Effect sizes were trivial to small.

A more pro-inflammatory dietary pattern (DII-informed score) was associated with lower physical fitness indicators in Spanish adolescents, although effect sizes were modest. Findings should be interpreted within a multifactorial framework of physical fitness, where diet represents one modifiable contributor among behavioral, biological, and social determinants.