Reduced fibre-fermenting capacity of gut microbes in multiple sclerosis may result in prebiotic dietary fibre β-fructan promoting inflammation and CNS damage.

Background: Some people with multiple sclerosis display changes in their gut microbiota with separate evidence suggesting that symptoms may worsen following a high-fibre diet. We hypothesised that in people with multiple sclerosis whose gut microbiota are less able to efficiently ferment dietary fibres, unfermented β-fructans induce inflammation. Methods: Diet data (n=48 individuals with multiple sclerosis, n=78 unaffected controls) and stool microbiome data (n=31 individuals with multiple sclerosis, n=61 unaffected controls) were previously collected from participants. Daily fibre subtype intakes were calculated and compared with faecal shotgun metagenomic sequencing in paediatric onset multiple sclerosis and unaffected persons. Response to unfermented β-fructans was examined in a germ-free experimental autoimmune encephalomyelitis (EAE) mouse model (unable to ferment fibres). Mice were fed β-fructans or control fibre diet beginning at symptom onset (day 14). EAE scores and weights were recorded daily. Intestinal and central nervous system tissues were collected at two endpoints to examine inflammatory responses and demyelinating lesions. Results: Individuals with paediatric onset multiple sclerosis consumed less β-fructans (2.4 g/day±0.3 SD; p<0.05) than unaffected participants (3.6 g/day±0.4), which coincided with differences in the gut microbiota including lower fibre fermenting enzymes. Mice exposed to unfermented β-fructans sustained worsened EAE symptoms (day 20-28; p<0.05), immune activation in the gut and immune activation plus demyelinating lesions in the spinal cord compared with mice on control diet. Conclusions: The gut microbiota of individuals with paediatric-onset multiple sclerosis showed reduced fibre fermenting properties, and our animal findings suggest that unfermented β-fructans can worsen demyelination and promote gut-brain axis immune activation. Lower β-fructan consumption was observed among participants with paediatric-onset multiple sclerosis. Future longitudinal studies are warranted to confirm the findings uncovered in this manuscript.