BACKGROUND: An inconsistent yet notable relationship between dietary habits and the risk of amyotrophic lateral sclerosis (ALS) has been previously established, with the causative nature of this relationship remaining uncertain. This study aims to explore the causal connections at a genetic level. METHODS: A two-sample Mendelian Randomization (MR) based analysis was conducted utilizing a comprehensive, publicly assessable Genome-wide association study (GWAS) database. Fourteen dietary variables were examined as potential exposure factors, and the ALS outcome data was statistically analyzed. The inverse-variance weighted (IVW) approach was used as the primary analytical method, supplemented by sensitivity analyses to assess the reliability of our findings. RESULTS: Our analysis identified significant protective effects against ALS from increased intake of water (fixed-effects IVW: OR = 0.700, 95 % CI: 0.524-0.935, P = 0.016), fresh fruit (random-effects IVW: OR = 0.561, 95 % CI: 0.361-0.871, P = 0.010), and cooked vegetable (fixed-effects IVW: OR = 0.200, 95 % CI: 0.090-0.445, P = 0.000). No significant associations were found for the other 11 dietary factors examined. CONCLUSION: The study highlights the protective association of cooked vegetables and fresh fruit intake with ALS risk reduction. Additionally, an intriguing association between water intake and ALS was observed, warranting further investigation to elucidate the underlying mechanisms.