Obesity has reached alarming levels in the UK. According to a government report, one in four adults are obese in the UK. Medical and dietary interventions are often ineffective at inducing weight loss and the best outcomes are obtained after weight loss surgery (also known as bariatric surgery). These surgical procedures were initially thought to work mechanistically through stomach restriction and lower calorie absorption through the shortened intestine. However, recent evidence has challenged this concept and it has been suggested that changes in the gut microbial flora could affect metabolism contributing to weight loss and increased insulin response. Gut flora is beneficial to the host in many ways, contributing to for example, nutrient absorption and a healthy immune system. Abnormalities in the composition of the gut microbes are thought to contribute to the pathology of certain diseases, including obesity and diabetes.