AIM: To assess if a healthy diet might attenuate the positive sedentary-inflammation relation, whereas an unhealthy diet may increase the effect of sedentary behaviors on inflammatory biomarkers. METHODS: In 618 adolescents (13-17 years) of the European HELENA study, data were available on body composition, a set of inflammation markers, and food intake assessed by a self-administered computerized 24 h dietary recall for 2 days. A 9-point Mediterranean diet score and an antioxidant-rich diet z-score were used as dietary indices and tested as moderators. A set of low-grade inflammatory characteristics was used as outcome: several cytokines in an inflammatory ratio (IL-6, IL-10, TNF-alpha, TGFbeta-1), C-reactive protein, three cell-adhesion molecules (sVCAM-1, sICAM-1, sE-selectin), three cardiovascular risk markers (GGT, ALT, homocysteine) and three immune cell types (white blood cells, lymphocytes, CD3). Sedentary behaviors were self-reported and analyzed as total screen time. Multiple linear regression analyses tested moderation by diet in the sedentary behaviors-inflammation association adjusted for age, sex, country, adiposity (sum of six skinfolds), parental education, and socio-economic status. RESULTS: Both diet scores, Mediterranean and antioxidant-rich diet, were significant protective moderators in the effect of sedentary behaviors on alanine-transaminase enzyme (P = 0.014; P = 0.027), and on the pro/anti-inflammatory cytokine ratio (P = 0.001; P = 0.004), but not on other inflammatory parameters. CONCLUSION: A higher adherence to the Mediterranean diet or an antioxidant-rich diet may attenuate the onset of oxidative stress signs associated by sedentary behaviors, whereas a poor diet seems to increase inflammation.