What did the researchers do?
Participants, mainly from the United States, United Kingdom and Australia, contributed stool samples and diet and lifestyle questionnaires. More than 10,000 samples were analyzed with standardized methods to examine associations with gut-microbiome features.
What was found?
People reporting more than 30 different plant foods in the previous week had higher gut microbial diversity than those reporting ten or fewer. “Plants” included more than vegetables—also fruits, grains, legumes, nuts, seeds and spices.
This finding helped popularize the “30 per week” idea. Thirty is not an established medical threshold or required dose; it was a comparison category in this study.
Why might variety matter?
Plants differ in fibers, polyphenols and other compounds, providing different substrates for gut microbes. A varied diet may be associated with an environment supporting different organisms, but this study alone does not establish the mechanism or a health outcome.
Important limitations
This citizen-science sample was self-selected and does not perfectly represent the general population. Diet was self-reported, and the largely cross-sectional observational design cannot prove that adding plant types directly caused greater microbial diversity.
A careful practical takeaway
Use 30 as a playful prompt to try one more plant than last week, not as an obligation. If you have a medical condition, allergy, digestive symptoms or relevant medication, consult a qualified professional before major dietary changes.