Horizon investigates the idea that the best way to lose weight successfully is a personalised approach, diets tailored to our individual biology and psychology. In a groundbreaking experiment, Dr Chris van Tulleken and Tanya Byron join a team of experts to put 75 overweight volunteers on diets designed to tackle the specific reasons why they eat too much. The volunteers are put through a series of tests at a residential clinic to understand how their genes, hormones and psychology influence their eating behaviour. They are then put on the diets the experts believe are best suited to them. Can science succeed where other diets have failed?

Half of the population in Western society suffers from being overweight. Cardio-vascular diseases, diabetes and cancer are epidemic. Our meat consumption has quintupled over the past 50 years. 65 billion land animals are being slaughtered every year for food consumption. One third of the global grain production is fed to animals for fattening while 1.8 billion people worldwide suffer from hunger and starvation. Can there really be a solution to all these problems?
H.O.P.E. is a life-changing documentary uncovering and revealing the effects of our typical Western diet high in animal-based foods. It contrasts the limited interests of the pharmaceutical and agricultural industry with the all-encompassing interests of living beings on this planet and with the power of responsible consumer action. H.O.P.E. is an urgent call to action to all of us to commit to a change towards sustainability and safeguarding our living environment.

It is time to see if personalised dieting will work in normal life. The volunteers have been given one of three diets to follow - based on their genes, their hormones and their psychology. But now they are back at home, trying to stick to their personalised diets with all the stresses and temptations of real life. Dr Chris van Tulleken and Professor Tanya Byron discover how our genetic makeup can make temptation difficult to resist, how understanding the brain reveals what makes us comfort eat and what science can tell us about why we make disastrous food choices.