The American Gut Project was one of the largest citizen science studies of the human microbiome, analysing stool samples from over 10,000 participants. Participants who ate 30 or more different plant foods per week had significantly more diverse gut microbiomes than those who ate fewer than 10 per week. This was the single strongest dietary predictor of microbiome diversity in the study, more significant than whether participants were vegan, vegetarian, or omnivores.
What Counts as a Plant Food
Plant foods include vegetables, fruits, whole grains, legumes, nuts, seeds, herbs, and spices. A clove of garlic counts. A pinch of cumin counts. A handful of mixed nuts counts as two or three plant foods if they contain different species. The principle is diversity rather than quantity. Eating large amounts of the same five vegetables is nutritionally inferior to eating moderate amounts of twenty different plant foods, because different plant species provide different fibres, phytonutrients, and polyphenols that feed and diversify different gut bacterial species.
Practical Ways to Reach Thirty
- Choose mixed salad leaves over single-leaf options: a bag of mixed leaves might contain six to eight different plant species
- Use a spice blend in cooking: a curry powder containing turmeric, cumin, coriander, cardamom, and fenugreek contributes five plant species in a single teaspoon
- Eat mixed nuts rather than a single nut variety
- Add a tablespoon of mixed seeds to yoghurt or porridge
- Use mixed beans rather than a single legume in soups and stews
- Rotate your fruit choices weekly rather than buying the same two varieties