10% Human

Obesity, autism, mental health problems, IBS, allergies, auto-immunity, cancer. Does the answer to the modern epidemic of ‘Western’ diseases lie in our gut?

You are 10% human. For every one of your cells, there are nine impostors hitching a ride. You are not just flesh and bone, but also bacteria and fungi. And you are more ‘them’ than you are ‘you’.

Your gut alone hosts 100 trillion of them and until recently we thought that our microbes didn’t matter. This is all set to change as the latest scientific research tells a very different story, one where microbes run our bodies and being healthy is impossible without them.

In this ground-breaking book, biologist Alanna Collen reveals how our personal colony of microbes influence our weight, immune system, mental health and even our choice of partner. This is a new way of understanding modern diseases – obesity, autism, mental health problems, gut disorders, allergies, auto-immunity and even cancer – as she argues they have their root in our failure to cherish our most fundamental and enduring relationship: that with our microbes.

Illuminating many of the questions still unanswered by the human genome project 10% Human completely changes our understanding of diet, modern disease and medicine. The good news is that unlike our human cells, we can change our microbes for the better and this book shows you how. A revelatory and indispensable guide: life – and your body – will never seem the same again.

Praise for 10% Human:

‘A fascinating study of the intertwined lives of microbes and humans’


‘Seminal … a mind-blowing look into the concept that suggests we are more bacteria than human. Collen recounts her own up-close and personal experiences, and looks at our bacteria from birth and what manipulates our development thereafter. A truly fascinating and thought-provoking read’


‘A welcome antidote to the simplistic “boost your health with probiotics” books and articles posing as science (but serving mostly commerce), Collen dares to tell the messy truth about what science knows – and doesn’t know – about the microbes that live in us, live with us, and in some ways even become us … [Collen] is clearly an expert in the field … fascinating … Everything you wanted to know about microbes but were afraid to ask’

Kirkus, Starred Review for books of exceptional merit. 

‘A fascinating subject to consider … A beginner’s guide to microbiota …There’s value in Collen’s point about reconsidering what is truly healthy at a time when healthy living is so in vogue’

Philadelphia Inquirer

‘Collen argues convincingly that our enthusiasm for killing human bacteria is playing a leading role in ailments ranging from immune problems and obesity to autism’

The Listener, the 100 Best Books of the 2015

‘Compelling…Packed with extensive research and interviews, with insights hidden like gems in the text… Adept at explaining complex topics like the workings of immune system cells, Collen is strong on biological and historical context for each point’

Gut Microbiota Worldwatch

‘Collen’s book satisfies on every level… 10% Human is a page-turner that will leave science-loving readers wishing for more’

The ASCO Post

‘This book was a mind-changer for me, but it has a moderate tone that will appeal to skeptics and believers alike. Please, please read this book. It will make you smarter about your own health, your children’s health and the sociology of human illness’


‘Fascinating… I like 10% Human because while talking to an incredibly specific topic, it highlights the wholeness of the whole. It reminds me that no matter how specific we get with anything-it’s always part of a bigger picture’

Actionable Books (Top books of 2015)

‘A fascinating look into the world of the microbiological hitchhikers that travel with us throughout our lives…Recommended for all readers, particularly those contending with the diseases listed and parents making health choices for their children that may have far-reaching consequences’

Library Journal (starred review)

‘Collen’s evidence for how each person’s microbiota, or personal community of microbes, impacts his or her health is undeniably powerful. She creates compelling connections between microbes and the “twenty-first-century illnesses” that affect all of us in some way…’


Editions and Translations

10% Human has been translated into 16 further languages. It is currently published in English by William Collins (HarperCollins) in the UK and Australia, and by Harper (HarperCollins) in the United States and Canada. It is published in Germany by Riemann Verlag (Random House) under the title Die stille Macht der Mikroben (The Silent Power of Microbes), in France by JC Lattès under the title Nos Amies les Bactéries, in Korea by Sigongsa, in Brazil by Sextante, in Portugal by Objectiva (Penguin Random House), in the Czech Republic by Dobrovsky, in Taiwan by Suncolor, in Finland by Alligaattori, in Japan by Kawadeshobo, in Poland by Wydawnictwo Bukowy Las, and in Slovenia by Mladinska Knjiga.

10% Human will be available soon in Italy, Russia, Serbia, Spain, and Turkey. For further foreign rights enquiries, please contact Jake Smith-Bosanquet  at Conville & Walsh Literary Agency.