10% Human : How Your Body's Microbes Hold the Key to Health and Happiness

Once again, we can take instruction from the koala, and other marsupials, this time about the importance of the oligosaccharide content of milk. Most marsupials have two teats, which are inside the pouch. Only one of these is used by the joey for the duration of its suckling life. If two joeys are born in two consecutive seasons, they each have their own teat. Remarkably, the two teats provide milk that is tailored to the age of each joey. The newborn receives milk high in oligosaccharides and low in lactose, whereas the older joey receives a lower dose of oligosaccharides, but far more lactose. Once a joey has left the pouch, the oligosaccharide content of its milk supply drops even further.

Rob Knight and Maria Gloria Dominguez-Bello, an associate professor in the Department of Medicine at New York University, are now running a large clinical trial to establish whether transferring microbes from a woman’s vagina to her newborn might ameliorate some of the short- and long-term effects of C-sections. The experimental technique is simple: a small piece of gauze is inserted into the mother’s vagina an hour before she is due to go into the operating theatre. Just before the first cut is made, the gauze is removed and placed in a sterile pot. A few minutes later, when the baby is out, it is rubbed with the gauze – first in its mouth, then across its face, and then over the remainder of its body.

As it emerges from its mother, it gets another dose of microbes alongside those from the vagina. Disgusting as it may sound, ingesting faeces early in life is not unique to koalas. During human labour and birth, the contraction-inducing hormones and the pressure of the descending baby cause most women to defecate. Babies tend to be born head first and facing towards their mum’s bottom, pausing for a moment with their heads and mouths in prime position whilst their labouring mothers wait for the next contraction to help them ease the rest of the body out. Whatever your instinctive revulsion, it’s an auspicious start. After birth, the mother’s gift of a new coat of microbes, both faecal and vaginal, makes for a simple and safe birthday suit for the newborn.
It’s also probably an ‘adaptive’ start. That is, it’s probably no bad thing that the anus is so close to the vagina, or that the hormones that bring on contractions in the uterus have the same effect on the back passage. Natural selection may have made it that way because it benefits baby, or at the very least causes no more harm than good. Receiving a gift of the microbes, and their genes, that have worked in harmony with your mother’s genome gets you off to a great start.

But if wheat and dairy cause such trouble, why did our ancestors ever start consuming them? In the case of lactose – the sugar found in milk – people in many populations actually evolved what’s known as ‘lactase persistence’. We can all tolerate lactose as babies; it’s in our mother’s milk. We have a gene that makes an enzyme – lactase – specifically to break it down. Before the Neolithic Revolution, that gene would switch ‘off ’ after infancy, when lactase was no longer needed. But during the Neolithic Revolution, some human populations started to herd animals: the ancestors of today’s goats, sheep and cattle. At the same time, these populations began to evolve persistence of the lactase gene. No longer did it switch off after weaning, but instead remained on throughout adulthood.
Natural selection for lactase persistence happened really quickly in an evolutionary sense, which means one thing: if people are able to digest lactose as adults, it really helps them to survive and reproduce. In just a few thousand years, starting in the Near East, humans all across Europe shifted to lactose tolerance. Now, about 95 per cent of North and West Europeans can tolerate milk as adults. Elsewhere, other human populations who herd animals, like the goat-herding Bedouins of Egypt and the cattle-herding Tutsi of Rwanda, independently evolved lactase persistence through a different mutation than in Europeans.

He tried supplementing their high-fat diets with a type of fibre known as oligofructose (sometimes called fructo-oligosaccharide, or FOS), which is found in foods including bananas, onions and asparagus. It made a big difference: the abundance of bifidobacteria rose.

The irony is, then, that in washing with chemicals and using deodorant to ensure that we smell nice, we kick off a vicious cycle. Soap and deodorant kill off our AOBs; no AOBs means disruption to our other skin bacteria; the altered composition means our sweat smells unpleasant; and therefore we must use soap to clean up the mess, and deodorant to mask the smell. What AOBiome suggest is that replenishing our AOBs could break this endless loop.

Think of the vocal and physical tics of Tourette’s syndrome, which may be the result of the basal ganglia’s failure to decide not to suppress the conscious mind’s idea of mischief. Streptococcus infection plays a role here, making children fourteen times more likely to develop Tourette’s if they have suffered multiple infections of a particularly nasty strain of strep in the past year. Parkinson’s, ADHD and anxiety disorders are also linked with strep and damage to the basal ganglia.

Vegetables, though not dosed with antibiotics directly, are often grown in soil fortified with animal manure. Manure is not only a rich source of nutrients, but also of drugs – around 75 per cent of antibiotics given to animals pass straight through them. So much for using nature’s fertiliser to keep things clean and green. For some types of antibiotics, there can be as much as one dose of the antibiotic in every litre of manure. That works out as the equivalent of sprinkling the contents of one or two capsules of antibiotics over every 10 m² of farmland.

Ear infections are also around twice as common in children given a dummy to suck, which is by now practically ubiquitous. These infections are taken seriously by doctors because of two risks – both of which are very small: one, young children with repeated infections can sometimes have difficulty hearing, at a time crucial for them to learn to speak; and two, these infections can turn nasty if they spread deeper and affect the mastoid bone behind the ear. Known as mastoiditis, this bacterial infection can cause permanent hearing damage or even death.

Humans, too, are influenced by sex pheromones. In a now legendary experiment, female students at the University of Bern were given T-shirts worn by male students in bed, and asked to rate them in order of attractiveness. The women preferred the T-shirts of men who had the most different type of immune system from their own. The theory goes that by choosing their genetic opposite, the girls would be providing their offspring with an immune system that can handle twice as many challenges. Through their sense of smell, the girls were scanning the boys’ genomes, looking for the best match to be a father to their children.