The passengers in our microbiome contain at least four million genes, and they work constantly on our behalf: they manufacture vitamins and patrol our guts to prevent infections; they help to form and bolster our immune systems, and digest food.

Whole grains help digestion, and vitamins should prevent sickness.

Be sceptical, ask questions, demand proof. Demand evidence. Don't take anything for granted. But here's the thing: When you get proof, you need to accept the proof. And we're not that good at doing that.

There is a major problem with reliance on placebos, like most vitamins and antioxidants. Everyone gets upset about Big Science, Big Pharma, but they love Big Placebo.

We can boost our immune systems by strengthening our social networks and decreasing stress.

We inherit every one of our genes, but we leave the womb without a single microbe. As we pass through our mother's birth canal, we begin to attract entire colonies of bacteria. By the time a child can crawl, he has been blanketed by an enormous, unseen cloud of microorganisms - a hundred trillion or more.