Why 30 plants a week? The American Gut Project

What does the research say?

This is where the popular ‘30 plants a week’ idea comes from. People who ate more than 30 different types of plant food a week had more diverse gut bacteria than people who ate 10 or fewer, regardless of whether they followed a vegan, vegetarian or omnivore diet.

The science

Participants sent in stool samples and answered detailed questions about diet and lifestyle. The researchers sequenced the microbes in each sample.

The number of different plant types eaten each week was more strongly linked to gut microbial diversity than the type of diet people followed. Herbs, spices, nuts, seeds, wholegrains and legumes all count as plant types.

Key findings

• More than 30 plant types a week was associated with greater gut microbial diversity.
• Plant variety mattered more than being vegan, vegetarian or omnivore.
• Higher plant variety was also linked to differences in gut bacteria that make short-chain fatty acids.

Limitations

• Observational: people eating more plants may differ in other ways.
• Volunteers were self-selected and diet was self-reported.
• Greater microbial diversity is generally seen as positive, but it isn’t a health outcome in itself.
• ‘30’ was a comparison point in the study, not a proven target.

References

1. McDonald D, Hyde E, Debelius JW, et al. American Gut: an open platform for citizen science microbiome research. mSystems. 2018;3(3):e00031-18. doi.org/10.1128/mSystems.00031-18