What is Romboutsia ilealis, and why is she a ‘good’ bug?

ZOE runs the largest study of nutrition and gut bacteria in the world, with data from over 40,000 people. We publish our research in top scientific journals, including Nature Medicine.

Our scientists have found 15 “good” gut microbes that are associated with indicators of good health and 15 “bad” gut microbes that are linked with worse health. 

Romboutsia ilealis — or “Rumi,” as we call her — is one of the 15 “good” bugs. In this article, you can find out more about Rumi, why she’s a good bug, and what foods she likes and dislikes. 

Fast facts about your gut microbiome

  • Your gut is home to trillions of bacteria and other microbes that make up your gut microbiome.

  • These microbes mainly feed on fiber and chemicals called polyphenols, which give plants their color, and turn these into chemicals that help support your health and weight control. 

  • Your gut microbiome is unique and radically different from everyone else’s, unlike your DNA, which is 99% the same. Even twins only share 34% of the same microbes. 

  • At ZOE, we use the latest and most advanced biotechnology to analyze the bacteria in your gut from a poop sample.

  • Using this technology, the ZOE program tells you your unique microbiome composition — including which of the 15 “good” and 15 “bad” bugs are in your gut — in order to recommend the best foods for you.

Who is Rumi?

Rumi is part of a group of bacteria called Firmicutes. If you looked at her under a microscope, you would see that she’s shaped like a rod. 

Our scientists found Rumi in the guts of over three-quarters of our study participants: 83%, to be precise. 

Other members of the Firmicutes group include Lactobacillus, which you may be familiar with already. They're “good” bugs in foods like yogurt.

Why is Rumi a ‘good’ bug?

Scientists don’t know much about Rumi yet, as she was only recently discovered. 

Some researchers don’t think that she is “good” and are investigating links between higher levels of Rumi in the gut and an increased risk of nonalcoholic fatty liver disease and neurodevelopmental disorders in children.  

However, in our study, we saw links between having Rumi in your gut and higher levels of polyunsaturated — or healthy — fat, as well as lower inflammation levels. 

Lower levels of inflammation are good for your body. Chronic, long-term inflammation can increase your risk of chronic health conditions like type 2 diabetes and heart disease.

What foods does Rumi like and dislike?

Our scientists have found links between specific foods and the 15 “good” and 15 “bad” gut bugs.

In general, Rumi likes fish and broccoli. She doesn’t particularly like beer or vegetable oil.

But the exact foods that will help Rumi thrive in your body depend on the combination of bugs in your gut. Since every person’s gut microbiome is completely unique, there’s no one-size-fits-all diet that’s right for everyone. 

The ZOE program analyzes your entire microbiome and works out your unique “gut booster” and “gut suppressor” foods, so “good” bugs like Rumi can flourish.

If you want to know the best foods for your body and your unique combination of gut bugs, take our free quiz


Gut microbiota dysbiosis associated with altered production of short chain fatty acids in children with neurodevelopmental disorders. Frontiers in Cellular and Infection Microbiology. (2020). https://www.frontiersin.org/articles/10.3389/fcimb.2020.00223/full

Insights from shotgun metagenomics into bacterial species and metabolic pathways associated with NAFLD in obese youth. Hepatology Communications. (2022). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9315112/

Microbiome connections with host metabolism and habitual diet from 1,098 deeply phenotyped individuals. Nature Medicine. (2021). https://www.nature.com/articles/s41591-020-01183-8