Fat vs sugar.

Over the course of a month, twin doctors Chris and Xand van Tulleken explore whether high-fat or high-sugar diets are nutritionally worse for us. Chris looks at how fat has traditionally been seen as bad by British doctors and goes on a high-sugar diet. In America, Xand considers how sugar is seen to be at fault and goes on a high-fat diet. Nutritionist, Amanda Ursell, helps them to get their diets right. The sugar diet includes all food that breaks down into blood sugars including bread, pasta and vegetables, whereas the fat diet has meat, cheese and cream with no fruit or vegetables. Along with Dr. Richard Mackenzie, from the University of Westminster, they consider how food is converted into energy in their bodies, and what the risks from fat and sugar are in the form of cholesterol and insulin. Two weeks into the diet they measure how sugar and fat are affecting their bodies. They look at brain function and become city stock traders for a day to see how they cope. They are watched by Professor Robin Kanarek, from Tufts University, who studies diet and cognition, and who talks about the dietary requirements needed for good brain function. In America, doctors consider simple sugar carbohydrates, such as fructose and glucose, to be particularly bad. Dr. Robert Lustig, from the University of California, talks about how sugar works in our bodies, particularly with regard to insulin. The twins then consider how fat and sugar work to give us energy and, with the help of Nigel Mitchell from Team Sky, undergo a series of cycling tests. At the end of their month long diets they return to see Richard Mackenzie at the University of Westminster to learn about the results which include a loss in muscle mass, insulin and blood glucose changes, but some of the outcomes are the opposite of what they expected. They look further at wider dietary studies on nutrition and obesity with nutritionist, Professor Susan Jebb of Oxford University. The twins then consider the psychology of food preferences and speak to Professor Paul Kenny about his work on obesity and addiction in rodents. His studies also look at diets combining fat and sugar in relation to weight gain and lifestyle. Susan Jebb gives some tips about overall balance in diet.