If I told you that you were only 10% human, you’d probably be insulted. What was I suggesting? Obviously, on a psychological level, you’re a whole person. No-one is suggestingyou’re an alien from the Planet Zog, an android, or a chimp. But, physically, it happens to be true. Only 10% of the cells in your body are human cells. The rest are mostly bacteria. (Most people have some fungal cells too, mostly yeasts.) Before you rush to your GP for a course of antibiotics, let me reassure you that this is entirely as it’s meant to be. Those bacteria – almost all of whom live in your gut – are meant to be there. In fact, they’re doing you a power of good.

They help to regulate your weight, power up your immune system and safeguard your mental health. There’s even scientific evidence that they may be helping to protect you from cancer. If this seems like a lot to be getting from a bunch of bugs, don’t forget thathumans have had a million years or so to evolve some powerful win/win partnerships with the friendly bacteria that live in our guts. So, how come you never learnt this in school? If yourschool Biology lessons even mentioned that you had ‘tame’ bacteria in your gut, their rolewas usually described as helping to break down the cellulose walls of plants so that you gotmore nutrition from the fruit and vegetables you ate. And possibly, that they were ‘thought to be involved’ with making some vitamins. The reason your Biology teacher didn’t tell you morethan this, is that almost all of the ground-breaking research into gut bacteria has only happened in the last 15 years or so.

It turns out that they are absolutely crucial to our wellbeing. How do we know? There’s a striking correlation between the very sudden rise in conditions such as autism (so rare in the 1940s, there wasn’t even a word for it), depression, auto-immune illnesses and allergies, obesity, and cancer – and the rise since the 1960s of processed, chemically treated, nutrient- stripped food, which has caused a big shift in the kinds of bacteria most people have in their guts. We (mostly) eat way less vegetables than our grandparents, and what we eat tends to have been treated with chemicals that didn’t exist back then. (And which are not, generally, bug-friendly) Which means that the vegetable fibre that our friendly bacteria live on has been in short supply. And some of it has been rendered toxic to bacteria.

And then there are antibiotics, which kill friendly bugs alongside their intended targets. All of which can mean that for many of us, our guts are populated with a lot of unfriendly bugs. Not to mention yeasts (which the friendly bacteria keep down) As well as causing us to crave unhealthy foods such as sugar, the unfriendly bugs add insult to injury by then producing all kinds of very unhelpful chemicals as a by-product of their digestion. Chemicals like methanol, for example – otherwise known as methylated spirit. Not something you want in your gut!Scientists have found that many people with depression also have inflammatory bowel conditions. And that many people with autism have food sensitivities and are prone to diarrhoea.

The evidence is growing that unfriendly bacteria may be implicated in some mental health conditions by subtly changing our brain chemistry. If you’d like to know more,a good place to start is the book GRAIN BRAIN, by Doctor David Perlmutter. (It’s on Amazon) But meanwhile, cutting right down on sugar and consuming a lot more vegetables could have even more beneficial results than a slimmer waist – you might find yourself becoming saner!