A quarter of New Zealanders have prediabetes which is a condition that can progress to type 2 diabetes and cause significant long term health problems. There is now exciting research demonstrating that the microbes in our gut affect our health in many ways, including how our bodies process foods and sugars. We can modify our gut microbes by taking supplements of probiotics (which contain live bacteria that give health benefits) and prebiotics (substances from foods which support the gut microbes). This study is a blinded randomised placebo-controlled trial to see if in adults with prediabetes taking a probiotic supplement with either a standard cereal or a cereal enriched with a specific prebiotic called beta glucan for six months can improve glucose and fat levels in the blood. In addition this work will evaluate the cost effectiveness of the interventions, and how to translate the study findings into practice.