A new University of Iowa study suggests that digestion of plant-based dietary substances by specific gut bacteria, which are lacking in patients with multiple sclerosis, may provide protection against the disease. The study showed a diet rich in isoflavone, a plant-based compound resembling estrogen, protects against MS-like symptoms in a mouse model of the disease. Importantly, the isoflavone diet was only protective when the mice had gut microbes capable of breaking down the isoflavones. 

Recently, the gut microbiome – the trillions of gut bacteria the live inside human intestines – has emerged as a potential environmental factor contributing to MS. In prior work, researchers demonstrated there are significant differences between the gut microbes of patients with MS and people without MS. Specifically, patients with MS lacked bacteria that are able to metabolize isoflavones. Isoflavones are found in soybeans, peanuts, chickpeas, and other legumes. Although role of gut microbiome in human diseases such as MS is being appreciated, the mechanism used by these gut bacteria to influence the disease is poorly understood.

The study found that mice fed the isoflavone diet have a microbiome that is similar to the microbiome found in healthy people and includes the bacteria that can digest isoflavones. Conversely, a diet lacking isoflavones promotes a microbiome in mice that is similar to one observed in patients with MS and lacks beneficial bacteria capable of metabolizing isoflavone.

While the results of mouse model studies sometimes do not translate to humans and may be years away from being a marketable treatment, in the current study, researchers found the bacteria, which are lacking in patients with MS, are able to suppress inflammation in a mouse model of the disease. The team compared the effects of an isoflavone diet and an isoflavone-free diet on disease in the mouse model of MS. They found that the isoflavone diet led to disease protection. However, when the team placed the mice on the isoflavone diet but removed the isoflavone-metabolizing gut bacteria, the isoflavone diet was no longer able to protect against MS-like symptoms. When the bacteria were reintroduced, the protective effect of the isoflavone diet was restored. Researchers were able to show that a specific isoflavone metabolite called equol, which is produced by the gut bacteria from isoflavone, is also able to provide protection against disease.

The findings were published in the journal Science Advances.