Scientists have only recently started to understand the importance of fat in insulin resistance and how people unable to store fat very well can have insulin resistance despite not being obese. The investigators have also recently discovered that small changes in a person's genetic code (their body's instruction manual) may also affect their ability to store fat and would like to explore this in more detail. To do this, they will recruit volunteers from the Exeter 10,000 study who gave permission to contact them about further research. The investigators will collect detailed body size measures and blood samples taken before and after a special drink that is high in fat (similar to a thick milk shake), then compare the results between people with and without the particular genetic changes of interest.