Professor Tim Spector explains the science behind the 30-plant-a-week challenge

Eating around 30 different plants a week is really beneficial to our health. Why 30? That was the optimal number when my research with the combined American and British Gut Project explored the relationship between diet and a helpful gut biome. Optimal both in the sense that the health benefits for eating higher numbers than 30 started to plateau, and also because it was a realistic goal: a significant number of participants were managing to get to 30, or pretty close.

Looking at a subgroup of the 11,000 community science volunteers who completed a food frequency questionnaire and gut microbe analysis, we compared those who reported eating 30-plus different plants per week with those who reported eating 10 or fewer. The 30 plant eaters had on average a much greater diversity of gut microbes (meaning more species) than the low plant group. High diversity is consistently linked to reduced risk of common diseases, from obesity and diabetes to dementia, depression and heart disease, to autoimmune diseases and allergies.

Until fairly recently, plant foods were thought to be beneficial mainly because of their micro-nutrient content, with particular focus on vitamins. But we are now beginning to understand that it is the complex combinations and interactions of fibres, phytochemicals and plant proteins that makes plants unique. And it’s what happens in our gut microbiome when we eat them that makes them beneficial for our health.

Our gut microbes thrive on having a variety of plant fibres to choose from, using each of them to make different chemicals for us like mini personal pharmacies.

Plants also contain polyphenol chemicals that, via gut microbes, give us a strengthened immune system, making us less susceptible to infections. By adding a rich variety of plants to our diets, we are welcoming in as many of the good

guys as possible, and crowding out the baddies at the same time. The beauty of changing the message from ‘five fruit and veg per day’ to ‘30 plants a week’ is that it encourages us to include a much wider variety of foods. Your microbes will love you for it, and the chances are you will rapidly feel the benefits too.

Professor Tim Spector, King’s College London, is co-founder of ZOE, the personalised nutrition company, and author of Food For Life.