The human gastrointestinal tract is inhabited by myriad microbes, which collectively form the gut microbiome. The interaction between the members of this internal 'ecosystem' can help us understand their organisation, growth, and how they react to what we eat. In summary, this tiny ecosystem in our gut determines our health. In a recent study, published in the journal Science, an international collaboration of researchers has investigated if these microbes hold a clue to the health of malnourished children.