Antioxidant intake has been suggested to be associated with the prognosis of amyotrophic lateral sclerosis (ALS). This study aimed to investigate whether dietary total antioxidant capacity (DTAC) and that of major food groups are related to disease progression rate (ΔFS) and survival time in ALS patients. A total of 301 participants diagnosed with sporadic ALS according to the revised El Escorial criteria were recruited from March 2011 and followed up to the event occurrence, or the end of October 2021. Events included percutaneous endoscopic gastrostomy, tracheostomy, and death. DTAC was estimated using task automation and an algorithm based on 24 h dietary recall. ΔFS was negatively correlated with the vegetable and legume DTAC, and event-free survival was different among the tertiles of vegetables and legumes DTAC. Consistently, the risk of events was negatively associated with DTAC from vegetables and legumes. These results suggest that the intake of antioxidants, especially those derived from vegetables and legumes, has a beneficial effect on delaying disease progression and prolonging survival in patients with ALS. Further studies with large prospective cohorts and clinical trials are needed to determine whether the consumption of foods with high DTAC improves the prognosis of ALS.