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The benefits of a diet anchored in an abundance of plants is clear to see. The healthiest and longest-lived societies are scattered across the globe, whether it be the mountain villages of Sardinia, the forests of Costa Rica or the Japanese island of Okinawa, but they have one thing in common: a diversity of plants in their diet. The Hadza people of Tanzania are among the last hunter-gatherers on Earth, and they probably consume a diet closest to that which humans have adapted to eat. They forage wild berries, honey and fibre-rich tubers, and eat lean, wild meat. This consumption of between 100g and 150g of varied fibre a day results in a beautifully diverse and robust gut microbiome.4 This could not be more different from the industrialized West. Americans, on average, eat around 15g of fibre a day – half of the recommended amount and ten times less than the Hadza – resulting in poor microbial diversity.5 The so-called Standard American Diet (with the apt acronym SAD) has replaced fibre-filled plants with refined grains (plants stripped of their fibre), processed meats, sugar-sweetened drinks and deep-fried food. We all know that the modern Western diet is not good for physical and mental health, but the reason is that it’s essentially an anti-biotic diet. Without providing the food for healthy microbes, we end up overfed yet undernourished. Add to this mix an overuse of pharmaceutical antibiotics and a lack of exposure to a variety of environmental microbes due to home-cleaning products and urban living, and no wonder the industrialized world is a desert for microbes. A diet low in plant-based fibre results in a vulnerable microbiome.6 This increases the likelihood that the defence system loses balance, resulting in chronic inflammation and, eventually, a host of physical and mental health conditions.7 If it’s clear that a variety of plant fibre is the key to a microbiome-friendly diet, how do we practically implement this? The American Gut Project is a large citizen science project in which individuals across the world volunteer to send stool samples for analysis by a team at University of California San Diego School of Medicine. In 2018, they published the results of over 10,000 participants, finding that eating thirty different plants a week was associated with increased microbiome diversity.8 This was regardless of whether you were vegetarian or vegan. Most of us in the West manage only around ten plants a week. While not a necessary requirement for good health, thirty a week is a sensible, evidence-based target. It’s important to remember that plant foods aren’t restricted to fruit and vegetables; nuts, seeds, herbs, spices, grains and legumes also count. While you can add as many layers of complexity as you wish, getting a diverse, healthy microbiome is really as simple as aiming for thirty types of plant a week.
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Monty Lyman (The Immune Mind: The Hidden Dialogue Between Your Brain and Immune System)