Diet in multiple sclerosis: Science takes a seat at the table
author info: https://www.ncbi.nlm.nih.gov/pubmed/29212826
Let food be your medicine and medicine be your food.
Attributed to Hippocrates
Persons with multiple sclerosis (MS) are often proactive in their quest to delay or avoid disability. They frequently seek guidance from their physicians on modifiable lifestyle factors that may slow MS disease progression. Questions about exercise, dietary supplements, and various natural remedies are common, but dietary concerns are among the most common inquiries from patients. Low-fat, Paleolithic, gluten-free, vegan, Mediterranean, and ketogenic diets all have their advocates. Despite multiple self-help books and Internet sites advising specific diets for persons with MS, there is little high-level evidence in the scientific literature to inform clinical recommendations. Patients often ask for specific guidance that goes beyond “eat a healthy diet,” and, most importantly, information on whether or not dietary changes can reduce their risk of long-term disability. Thus far, we have had little basis for making any recommendations based on scientific data.
In this issue of Neurology®, Fitzgerald et al.1 provide epidemiologic evidence for an independent link between patient-reported healthier diets and lower disability. They describe self-reported data obtained from a questionnaire completed by 6,989 persons with MS registered in the North American Research Committee on MS (NARCOMS; a large registry of patient-reported disability and quality of life outcomes, health care utilization and comorbidities, and other health-related variables, such as diet, which is updated and expanded with biannual surveys). In their analysis, a healthy diet was quantified, in quintiles, as consumption of (1) more fruits, vegetables, legumes (fifth quintile = most), (2) more whole grains (fifth quintile = most), (3) less sugar from desserts and beverages (fifth quintile = least), and (4) less red and processed meats (fifth quintile = least). Persons with MS in the highest quintile for diet quality (sum of quintiles across the 4 food categories) vs lowest quintile were at 20% lower risk for severe vs mild self-reported physical disability, even after controlling for several other health-related factors (age, disease duration, body mass index, income, smoking). When examined separately, higher intake of whole grains was the only component of the diet score reliably linked to lower disability. These data from a large cohort of persons with MS provide a convincing observational link between diet and disability. The field of diet in MS has served up courses of a priori opinions garnished with anecdotes and small samples, to which Fitzgerald et al. add substantive and robust empirical data. This sets the table for subsequent work on mechanisms of action and causal relationships.
Fitzgerald et al. acknowledge limitations, including inability to draw causal inferences and to perform fine-grained dietary analyses (e.g., various fats) due to brevity of their diet survey. Fish intake, with the interesting link to vitamin D, is a potentially important dietary factor that was not investigated in this study. Like survey research generally, there was potential selection bias (68% response rate from an already active responder subgroup, one-third of the overall NARCOMS database: responders were older with longer disease duration and more likely to be Caucasian, married, and of higher income) and potential response bias may have occurred, since all variables were self-reported.
This study does not identify mechanisms of action. How might a healthy diet, as defined by Fitzgerald and colleagues, reduce disability among people with MS? It is unknown whether diet is linked to disability through relationships with inflammatory disease activity, disease-related degeneration, brain aging independent of MS disease, or interactions among these or other factors. Vascular disease risk factor comorbidities, such as hypercholesterolemia, may be a mechanism linking diet and MS disability,2 perhaps through increased disease activity 3 or cerebral atrophy.4 Another mechanism may relate to influences of diet on the gut microbiome, which is linked to inflammatory processes in MS.5 How much is it simply an issue of better symptom control, such as less fatigue or constipation? Might certain diets influence the absorption and metabolism of disease-modifying therapies, resulting in altered efficacy? Unrelated to MS, a Mediterranean diet is linked to lower risks for mortality,6 incident dementia,7 and cerebral atrophy 8 in non-neurologic cohorts, thereby also protecting patients against comorbidities that are associated with increased disability in MS. Consistent with the notion of brain reserve against disability in MS,9 lifestyle factors, such as diets, which contribute to preservation of brain health and structure could reduce risk for disability. Indeed, Fitzgerald et al. also reported that a composite healthy lifestyle (body mass index <25, physical activity, no smoking, better than average diet) was robustly related to lower risk for disability, ostensibly mediated through preserved brain health and maintenance of brain reserve.
The next important but challenging steps are to perform randomized controlled trials of diet to yield causal evidence for dietary interventions. Pilot studies have been completed 10 or are underway (e.g., NCT02986893, NCT02647502). Isolating specific dietary factors and mechanisms of action driving protective effects against disability and disease progression would help advance the field. Ideally such studies should be longitudinal, include patients with early disease, and involve multimodal objective assessments, including relapse rates, MRI, and postulated MS biomarkers.
Motivated by the current work of Fitzgerald and colleagues, future rigorous experiments and multidisciplinary collaborations on diet may someday yield empirically validated dietary recommendations for our patients. Until then, encouraging a healthy lifestyle (healthy eating, a normal weight, routine physical activity or exercise, and avoiding smoking) should be a fundamental message we give to all newly diagnosed patients with MS.
pursue optimal self care at least as actively as a diagnosis
ask for referrals to preventive health care specialists eg dietitians
don't let suboptimal self care muddy any underlying diagnostic picture!
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