The American Gut Project analysed the microbiomes of over 10,000 participants from 45 countries. Researchers found that people who ate 30 or more different plant species per week had significantly more diverse gut microbiomes than those eating fewer than 10. This held true regardless of whether they identified as vegan, vegetarian, or omnivore.
Microbiome diversity matters because different bacterial species perform different functions: some produce short-chain fatty acids, others synthesise vitamins, regulate immune function, or produce neurotransmitters. A diverse microbiome is more resilient (less likely to be disrupted by stress, illness, or antibiotics) and more functional (performing a wider range of health-supporting activities).
Each plant species contains a unique combination of fibres, polyphenols, and phytochemicals that feed different bacterial populations. An apple feeds different bacteria than a carrot, which feeds different bacteria than lentils. When you eat the same 5-10 foods every week, you starve the bacterial species that depend on other plant nutrients.
Think of your gut microbiome as a rainforest: the more species present, the healthier and more resilient the ecosystem. Low-diversity microbiomes — like monoculture farms — are vulnerable to disruption and associated with obesity, autoimmune disease, allergies, inflammatory bowel disease, and mental health disorders.
Thirty sounds intimidating but it's easier than you think. Every unique plant counts: fruits, vegetables, grains, legumes, nuts, seeds, herbs, and spices. Add basil to your pasta — that's one. Sprinkle mixed seeds on your yoghurt — that's 3-4. Use a mixed salad bag — that's 4-5. It adds up fast.
Practical tips: buy pre-mixed bags (stir-fry mix, mixed salad, frozen mixed berries). Rotate your choices weekly — don't buy the same vegetables every shop. Add herbs and spices liberally to cooking. Keep a jar of mixed nuts and seeds for snacking. Eat bean-based soups and stews with multiple vegetables. Most people find they can comfortably hit 30+ within a week or two of paying attention, without dramatically changing their diet.
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