Dr Michael Mosley - The Clever Guts Diet: How to revolutionise your body from the inside out

Although this book has diet in its title, it is not really about losing weight. That may well happen, if you eat the foods and do the things I recommend, but thats not its primary purpose. The Clever Guts Diet is a diet in the same way you might talk about being on a vegetarian diet or a Mediterranean diet. Its not about calories or restriction; its about the sort of food and lifestyle changes you should make if you have gut problems, or simply want to keep yours in good condition.

The gut is not a glamorous organ. When I was at medical school many of my fellow students wanted to study the brain, by training as neurosurgeons, or become cardiologists, experts in the heart. I never heard anyone say they wanted to dedicate their life to the gut. And yet it is extraordinary a part of the body, hitherto relatively unexplored, with which I have recently become rather obsessed. Thanks to a huge amount of new research, probing the world within our guts is changing our understanding of the way our bodies work.

As well as extracting energy from our food, the gut accounts for most of our immune system and produces more than two dozen hormones that influence everything from our appetite to our mood.

I also love the fact that, buried in our intestines, deep inside its tissue, is a very thin layer of brain. Its called the enteric system and it is made up of the same cells, neurons, which are found in the brain. There are over 100 million neurons in the gut, as many as you would find in the brain of a cat. Except, instead of being in one big lump, like the brain on top of your neck, the neurons in your gut are spread out in a thin mesh that extends all the way from your throat to your rectum. This second brain doesnt do much geometry or worry about tax returns, but it does orchestrate digestion and moderate gut pain.

When we talk about having gut feelings or gut instincts we are reflecting the reality of how closely our guts and are brains are entwined. In this book I am going to be talking a lot about the gutbrain axis and the new science that surrounds it.

Your gut is a wonderful piece of engineering and I hope, after you have read this, you will share my enthusiasm for it. But in many ways the star of the digestive show is not actually part of the human body at all it is the one to two kilos of microbes that live in your gut and make up the microbiome.

Until recently the world of the microbiome was a dark, dank and private one. Down there live creatures that have never seen the light of day, more than 50 trillion of them, at least 1000 different species, a richer diversity of life than you would find in a rainforest.

As is often the case with new scientific discoveries, a lot of

In fact, according to one of the researchers who helped explode this myth, the proportions are so similar that each defecation may flip the ratio to favour human cells over bacteria.

More importantly, while there are foods that will help your microbiome thrive (and thats why this book contains recipes), few of the products that are sold on this basis have credible science behind them. When it comes to prebiotics, probiotics and supplements, I will show you what works, and what doesnt.

Our widespread ignorance about the microbiome arises from the fact that, until quite recently, its inhabitants, microbes, were impossible to study. We knew they helped protect the gut from dangerous invaders; that they synthesised a few vitamins; and that they gobbled up fibre that our bodies cant digest.

Now we know they do far more than that:

1. They help regulate our body weight. As well see in later chapters the microbes in your gut can decide how much energy your body extracts from the food you eat; they control hunger signals; they help decide which foods you crave; and they determine how much your blood sugar spikes in response to a meal. Can your microbiome make you fat? It certainly can. Can you change your microbiome so it works with you rather than against you? You certainly can, and I will show you how.

2. The microbiome not only protects our guts from invaders, it teaches and regulates our entire immune system. Over the last half-century we have seen a massive rise in allergic diseases, such as asthma and eczema, caused by an overactive immune system. We have also seen a huge surge in autoimmune diseases, ranging from inflammatory bowel disease to type 1 diabetes, which again are primarily caused by an immune system that has got out of control. I will show you how changing the mix of bacteria in your gut can reduce the impact of these diseases.

3. The microbiome takes the bits of food our body cant digest and converts them into a wide range of hormones and chemicals. These, it seems, can control our mood, as well as our appetite and general health. Changing your biome may reduce anxiety and lessen depression.

The tragedy is that, in our ignorance, we have been laying waste to our microbiome and its population of microbes, or Old Friends. Theyve been given that name because they have evolved with us over millions of years, and also because so many of them are essential to our health. Just as we have ravaged the rainforests and consigned numerous animal species to oblivion, so we have decimated the populations that live inside us. Fortunately we can help these Old Friends bounce back. I will show you how.

I will also be looking into the latest treatments for a number of gut problems, ranging from gluten intolerance to irritable bowel syndrome. These are diseases that many people struggle with, in part because doctors are often bad at both diagnosing and treating them. They are frequently dismissed as psychosomatic that is, the product of anxiety or depression.

The same used to be said of stomach ulcers. Also known as gastric ulcers, these are open sores that develop on the lining of the stomach and small intestine.

Back in 1994, when I made a television programme about ulcers (which I unimaginatively called Ulcer Wars), they were common and considered incurable. It was widely believed that they were caused by stress, which made your stomach produce too much acid, and that was what did the damage. The standard medical advice was to eat bland food, change your stressful lifestyle and take a drug to reduce acid production. If that didnt work, and it often didnt, you might find yourself in the hands of surgeons having parts of your stomach and small bowel removed.

But in Perth, Western Australia, there were a couple of doctors who did not think that stress was the real cause of ulcers. They argued that most ulcers are the result of infection by a previously unknown bacterium that they had identified and named Helicobacter Pylori.

To make his point, in 1984 one of the scientists, Dr Barry Marshall, brewed up a flask of Helicobacter and swallowed it. A few days later, as he smilingly told me, he started vomiting. He had himself endoscoped; a small tube was passed down his throat and into his stomach. Samples of his now inflamed stomach lining were removed. These showed that his stomach had been colonised by Helicobacter.