 The purpose of this work is to investigate the influence of dietary salt intake on immune function in MS subjects and healthy controls. This study primarily tests the hypothesis that higher dietary salt intake will be associated with a higher frequency of pathogenic Th17 cells and impaired function of protective regulatory T cells. If a relationship between dietary salt intake and immune function is observed, this study will also test: a whether this relationship is unique to MS subjects or whether it is also present in healthy controls, and b whether healthier immune function can be restored by restricting dietary salt intake. This is a 5-week pilot study of a dietary intervention of 25 subjects with MS or Clinically Isolated Syndrome CIS by 2010 Diagnostic Criteria who will be identified and recruited from the Yale MS Center andor referred from outside MS centers. 25 age-matched healthy controls will be recruited from friends, family members, spouses and the patient waiting room at the Yale MS Center. 