The claim that eating 30 different plant foods a week is essential for a healthy gut microbiome has gained traction, but the scientific basis is weaker than many believe. The idea originates from a 2018 study involving more than 10,000 participants in the US, UK, and Australia, which found that those who consumed over 30 plant foods weekly had a more diverse gut microbiome than those eating fewer than 10. However, experts caution that 30 is not a magic number.
The Arbitrary Nature of the 30-Plant Target
Prof Daniel M Davis, head of life sciences at Imperial College London and author of Immune Health: A Myth-Busting Guide, states: “Thirty is pretty arbitrary. It’s not as though researchers compared 10 plants, 20 plants, 30 plants and 35 plants and found a clear cut-off point.” The study does not prove that eating 30 plants directly improves health; it only shows an association between higher plant diversity and a more diverse microbiome.
No Proven Direct Health Benefits
While a diverse microbiome has been linked to a lower risk of some diseases, scientists still do not know what a truly healthy gut microbiome looks like. Davis adds: “People eating more than 30 plants a week are probably doing a gazillion other things differently as well.” Factors such as exercise, sleep, and stress also influence the microbiome, making it difficult to isolate the effect of plant diversity alone.
Beware of Commercial Exploitation
Davis warns against the growing supplements market capitalizing on the 30-plants message. Expensive products promise to help people hit the target, but there is little independent evidence they work. “It hasn’t been proven that reaching 30 plants a week will prevent illness or lead to specific health benefits,” he says. Instead, he emphasizes that eating a variety of fruits, vegetables, legumes, nuts, and wholegrains is generally beneficial for health.
