Researchers have long believed that the keto diet could help reduce an overactive immune system and benefit individuals with conditions such as multiple sclerosis.

Now, they have reason to believe it could be true.

Scientists at UC San Francisco have discovered that the diet makes the gut and its microbes produce two factors that attenuated symptoms of MS in mice.

If the study translates to humans, it points toward a new way of treating MS and other autoimmune disorders with supplements.

The keto diet severely restricts carbohydrate-rich foods like 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 change the immune system.

Working with a mouse model of MS, the researchers found that mice who produced more of a particular ketone body, called β-hydroxybutyrate (βHB), had less severe disease.

The additional βHB also prompted the gut bacterium Lactobacillus murinus to produce an indole lactic acid (ILA) metabolite. This blocked the activation of T helper 17 immune cells involved in MS and other autoimmune disorders.

“What was exciting was discovering that we could protect these mice from inflammatory diseases simply by putting them on a diet supplemented with these compounds,” said Peter Turnbaugh, PhD, of the Benioff Center for Microbiome Medicine.

Earlier, Turnbaugh had shown that when secreted by the gut, βHB counteracts immune activation. This prompted a postdoctoral scholar working in his lab, Margaret Alexander, PhD, to see if the compound could ease the symptoms of MS in mice.

In the new study, which appears Nov. 4 in Cell Reports, the team examined how the ketone body-rich diet affected mice unable to produce βHB in their intestines and found that their inflammation was more severe.

However, 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 mice 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 assay and determined that the diet’s positive effects were coming from a member of the Lactobacillus genus: L. murinus.

Two other techniques, genome sequencing and mass spectrometry, confirmed that 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, improving their symptoms.

Turnbaugh cautioned that the supplement approach still needs to be tested in people with autoimmune disorders.

“The big question now is how much of this will translate into actual patients,” he said. “But I think these results provide hope for the development of a more tolerable alternative to helping those people than asking them to stick to a challenging restrictive diet.”