MS can cause impaired gut transit times, usually resulting in easy bloating and fullness and constipation. My doctor would like me to lose weight but even at 1200 calories a day combined with 40 minutes on a treadmill, I have been unable to lose any weight. MS has no impact on metabolism directly. Many patients are relatively inactive physically, so daily caloric expenditures and requirements drop down markedly. This usually results in weight gain that is hard to shed.
Metabolism also becomes more efficient, another reason it is harder to lose weight.
An occasional patient has marked loss of appetite and cannot lose weight. It would be wonderful if an infectious organism could be linked to MS and we could eradicate the disorder with a course of antibiotics. Thus far, that dream has not been realized. He reported a 20 year follow up several years ago in the Lancet, indicating some benefit in his diet in retarding disease worsening. It would be tough to do a blinded study.