The prevalence of obesity has increased substantially over recent decades and interventions to halt the epidemic have been unsuccessful. Although the causes of obesity are complex, key drivers include the over-consumption of highly palatable energy-dense and nutrient-poor foods. These dietary changes have had a profound impact on our gut microbiome, which comprises the bacterial community of the bowel. Tantalising new evidence suggests that microbial complexity and functionality in the gut may play a crucial role in obesity. In the proposed study we will characterise the gut microbiome in two populations with markedly different metabolic disease risk (Pacific and European women) and different body fat profiles (normal and obese). We will test whether diet, taste perception, sleep and physical activity are key pathways that modify the gut microbiome and its impact on obesity. This new knowledge will help us understand obesity and how best to prevent it.