Preterm babies are at risk of problems with growth, intelligence, and adult diseases such as obesity and diabetes. We will study how best to feed preterm babies to reduce these risks and whether preterm girls and boys need feeding differently. Our randomised trial will investigate the impact of three feeding approaches on growth and body composition, feed tolerance and the gut microbes (the microbiome) which may influence later risk of obesity. We will assess whether specific nutrients can protect the pancreas in preterm lambs, reducing later risk of diabetes. Systematic reviews of human and experimental data, and analysis of breast-milk composition in mothers of preterm girls and boys, will determine whether feeding strategies should differ by infant sex. Together, these studies of simple interventions will provide the evidence as how best to feed preterm babies to achieve their intellectual potential whilst minimising their risk of metabolic disease.