BackgroundA proinflammatory diet has been associated with a risk of individual chronic diseases, however, evidence on the association between inflammatory dietary patterns and the trajectory of chronic disease multimorbidity is sparse. ObjectivesWe aimed to investigate the associations of a low-inflammatory diet with the multimorbidity trajectory. MethodsWithin the UK Biobank, 102,424 chronic disease-free participants (mean age 54.7 ± 7.9 y, 54.8% female) were followed up to detect multimorbidity trajectory (annual change in the number of 59 chronic diseases). Baseline inflammatory diet index (IDI) and empirical dietary inflammatory pattern (EDIP) were separately calculated from the weighted sum of 32 posteriori-derived (15 anti-inflammatory) and 18 prior-defined (9 anti-inflammatory) food groups, and tertiled as low-, moderate-, and high-inflammatory diet. Data were analyzed using linear mixed effects model, Cox model, and Laplace regression with adjustment for potential confounders. ResultsDuring the follow-up (median 10.23 y), 15,672 and 35,801 participants developed 1 and 2+ chronic conditions, respectively. Adherence to a low-inflammatory diet was associated with decreased multimorbidity risk (hazard ratio [HRIDI] = 0.84, 95% confidence interval [CI]: 0.81, 0.86; HREDIP = 0.91, 95% CI: 0.89, 0.94) and a slower multimorbidity accumulation (βIDI = −0.033, 95% CI: −0.036, −0.029; βEDIP = −0.006, 95% CI: −0.010, −0.003) compared with a high-inflammatory diet, especially in participants aged > 60 y (βIDI = −0.051, 95% CI: −0.059, −0.042; βEDIP = −0.020, 95% CI: −0.029, −0.012; both P-interactions < 0.05). The 50th percentile difference (95% CI) of chronic disease-free survival time was prolonged by 0.81 (0.64, 0.97) and 0.49 (0.34, 0.64) y for participants with a low IDI and EDIP, respectively. Higher IDI and EDIP were associated with the development of 4 and 3 multimorbidity clusters (especially for cardiometabolic diseases), respectively. ConclusionsA low-inflammatory diet is associated with a lower risk and slower accumulation of multimorbidity (especially in participants aged > 60 y). A low-inflammatory diet may prolong chronic disease-free survival time.