Scientists have discovered the keto diet makes the gut and its microbes produce two factors that reduce symptoms of multiple sclerosis in mice. If the study translates to humans, it points toward a new way of treating MS and other autoimmune disorders with supplements.

Scientists have long suspected the keto diet might be able to calm an overactive immune system and help some people with diseases such as MS. Now, they have reason to believe it could be true.

The keto diet severely restricts carbohydrate-rich foods such as bread, pasta, fruit, and sugar, but allows unlimited fat consumption. Without carbohydrates to use as fuel, the body breaks down fat instead, producing compounds called ketone bodies. Ketone bodies provide energy for cells to burn and can also change the immune system.

Working with a mouse model of MS, the researchers at the University of California – San Francisco found that mice who produced more of a particular ketone body, called β-hydroxybutyrate, had a less severe disease. The additional βHB also prompted the gut bacterium Lactobacillus murinus to produce a metabolite called indole lactic acid. This blocked the activation of T helper 17 immune cells, which are involved in MS.

Earlier, researchers had shown that when secreted by the gut, βHB counteracts immune activation. This prompted other researchers to see if the compound could ease the symptoms of MS in mice. The researchers looked at how the ketone body-rich diet affected mice that were unable to produce βHB in their intestines, and found their inflammation was more severe. But when the researchers supplemented their diets with βHB, the mice got better.

To find out how βHB affects the gut microbiome, the team isolated bacteria from the guts of three groups of mice that were fed either the keto diet, a high-fat diet, or the βHB supplemented high-fat diet.

Then, they screened the metabolic products of each group’s distinct microbes in an immune analysis and determined the positive effects of the diet were coming from a member of the Lactobacillus genus: L. murinus. Two other techniques, genome sequencing and mass spectrometry, confirmed the L. murinus they found produced indole lactic acid, which is known to affect the immune system.

Finally, the researchers treated the MS mice with either ILA or L. murinus, and their symptoms improved.

The study’s authors cautioned the supplement approach still needs to be tested in people with autoimmune disorders. Results of mouse model studies sometimes do not translate to humans and may be years away from being a marketable treatment. However, they said these results provide hope for the development of a more tolerable alternative to helping those people than asking them stick to a challenging restrictive diet.

The study appears in the journal Cell Reports.