Despite being consumed by the majority (>80%) of the global population, relatively little is known about the metabolic effects of milk sugars compared with other carbohydrates. Galactose is the defining monosaccharide of the milk sugar, lactose and is thought to be primarily metabolised by the LeLoir pathway, producing glucose metabolites. However, recent evidence has challenged this understanding, on the basis that galactose ingestion results in several metabolic effects that are more similar to fructose ingestion than to glucose ingestion. In this talk, I will present previous and ongoing research in this area where we are employing several stable isotopic tracer methods to understand the how lactose and galactose affect metabolism across a range of doses. Recent data suggest that there may be several similarities between galactose and fructose metabolism, whilst also retaining some important differences.