Alanna Collen

If this bacterium could boost the thickness of the mucus layer, Cani thought, perhaps it could reduce LPS levels and prevent weight gain too. He tried supplementing the diets of a group of mice with Akkermansia, and sure enough, their LPS levels dropped, their fat tissue began creating healthy new cells again, and, most importantly, they lost weight. The mice given Akkermansia had also become more sensitive to leptin, meaning their appetites decreased.

Take the case of a Belgian girl, Miss A, who had, up to the age of eighteen, been happy and healthy, and working towards her college exams. Over the course of a few days, she became aggressive, refused to communicate and lost her sexual inhibitions. She was sent to a psychiatric hospital, where she was prescribed anti-psychotic medication and discharged. Three months later, Miss A returned to the hospital with worsening behaviour and uncontrollable vomiting and diarrhoea. Her doctors decided to take a biopsy of her brain, which revealed the source of her psychiatric condition – a microbe. She had Whipple’s disease – a rare infection caused by a bacterium which occasionally announces its presence through the behaviour of its host.

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.