Objective This study employs Mendelian randomization analysis to explore the causal relationship between dietary habits and systemic lupus erythematosus (SLE). MethodsWe obtained data from the MRC-IEU database on five dietary habits as instrumental variables for exposure “never eating dairy products” “never eating eggs or foods containing eggs” “never eating sugar or foods/drinks containing sugar” “never eating wheat products” and “I eat all of the above”. Summary data related to SLE were retrieved from the MRC-IEU database for the discovery cohort (designated as MSLE) and from a Finnish database for the validation cohort (recorded as FSLE). Two-sample Mendelian randomization analyses were conducted using inverse variance weighting (IVW), MR-Egger, weighted median, Simple Mode, and Weighted Mode methods to investigate the causal relationship between dietary habits and SLE. The MR-Egger intercept test was performed to assess the presence of horizontal pleiotropy, while the leave-one-out method was employed to verify the stability of the results, with Cochran’s Q test and funnel plots used to evaluate heterogeneity. ResultsMendelian randomization analysis indicated that never eating wheat products increases the risk of developing SLE (IVW P<0.05). In contrast, there was no significant causal relationship between the consumption of dairy products, eggs or foods containing eggs, or the consumption of all of the above with SLE (IVW P>0.05). Additionally, there was no significant causal relationship between never sugar or foods/drinks containing sugar and MSLE (IVW P=0.877), although a potential causal association with FSLE was suggested (IVW P=0.016). The MR-Egger intercept test indicated no evidence of horizontal pleiotropy (P>0.05). ConclusionNever eating wheat products may be an independent risk factor for SLE. However, the causal relationship between never sugar or foods/drinks containing sugar and SLE remains indeterminate.