You may have heard experts like ZOE Co-Founder Prof. Tim Spector recommending that you eat 30 different plants a week. Or, you’ve seen it mentioned as a “challenge” on social media. But where did this number come from?

In 2018, scientists published results from the American Gut Project, a collaboration of researchers and more than 10,000 “citizen scientists” from the United States, the United Kingdom, and Australia.

Tim led the U.K. arm of the research, called the British Gut Project.

The volunteers shared detailed information about their eating habits. They also provided samples of their poop. The researchers analyzed these to find out which gut bugs they contained.

Participants who ate 30 or more different plants per week were more likely to have certain “good” gut bugs than those who ate just 10 and had a more diverse microbiome. This was irrespective of whether they were vegan, vegetarian etc. Their poop samples also contained higher levels of healthy chemicals produced by the gut bacteria. Interestingly, the bacteria in their guts had fewer selected antibiotic resistance genes!

Dietary fibers are very heterogeneous in their chemical composition and physicochemical properties, which will influence how they are fermented and processed by microbial community. Therefore, diets rich in diverse plant-based foods likely supports a more diverse microbiota composition.

Figure from the American Gut Project comparing the abundance of gut bacteria in participants who ate 10 versus 30 plants a day. Note, the plot shows the family name.