BACKGROUND AND OBJECTIVE: To assess longterm feasibility of low saturated fat diet (less than 15 g of saturated fat per day) in patients with relapsing remitting multiple sclerosis (RRMS) and its effect on the course of the disease. MATERIALS AND METHODS: Patients were enrolled into a single arm, prospective study. The eligibility criteria included the diagnosis of RRMS according to the McDonald criteria 2010 and the ability to comply with the diet. Patients were allowed to receive disease modifying therapy (DMT) and to take food supplements. Diet adherence was monitored by food diaries. Number of attacks, brain magnetic resonance imaging (MRI) characteristics, Expanded disability status scale (EDSS) and Body mass index (BMI) were recorded. RESULTS: Twelve patients with RRMS were enrolled. Six patients (50%) continued with the diet for the median duration of 37 months. The high drop-out of patients was caused mainly by patients' inability to strictly adhere to the diet. In six patients who were able to follow the diet - their mean EDSS of 1.30 decreased to 1.17. None of the patients experienced an attack, 5 of 6 patients had stable disease on yearly magnetic resonance imaging (MRI) scans with no new lesions identified. CONCLUSION: The low fat diet is safe and seems to be effective in preventing clinical attacks/new MRI lesions. The main drawback is the problem of adhering to the diet longterm in the western-style diet environment.