Before an important meeting or when a big decision needs to be made, we often mentally run through various scenarios before settling on the best course of action. But when it comes to our health—be it choosing a treatment for an ailment or even selecting a dietary regimen—it is a lot harder to predict how each choice will affect our bodies and whether it will suit us personally.

Before the Human Genome Project was launched in 1990 to explore the fundamental question of what makes each of us who we are, only a fraction of human genes were known to science. The project led to the identification of tens of thousands of genes that shape our traits, and it revealed the genetic basis of numerous diseases.

Today, however, it is clear that genes alone provide only a partial picture. Many of the characteristics that define us and the diseases that threaten us are linked to environmental factors, the community of microorganisms residing in our bodies (our microbiome), the aging process and other factors.