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.

Of the four elements, air is the most elusive because we can't see it. There's something very magical about it. One of the ways we transform food is by getting air into it. Think of the soufflé, think of the loaf of bread. These things are elevated by the fact that they now contain air. They're ethereal. Visit food labs and Moroccan fields as Michael Pollan delves into the science of bread-making and the nature of gluten.