There is a widespread belief, that being overweight or obese is a question of failing willpower, fuelled in no small part by food, fitness and beauty industries. But if we look at the issue of obesity through a scientific spyglass, a very different picture emerges. Genes, for example, exert a large influence on our tendency to become obese often by influencing behaviour – a case of nature via nurture. But it’s not just our own genes that are important.

In terms of processing food, humans are hardly self-sufficient. Our guts are the home of trillions of bacteria that help to break down foodstuffs that our own cells cannot cope with. Together the genes expressed by these intestinal comrades outnumber our