Geneticist Giles Yeo and his team assess five overweight volunteers, before putting them on personalised diets tailored to their bodies and brains.

Your skinny best friend seems to eat twice as much as you. But you’re still overweight. Why?

For decades, experts thought they had the answer: too many calories and not enough exercise. But the latest scientific research is turning those assumptions on their head. Differences in our individual biology – our genetics, hormones or psychology – all play a crucial role.

In this BBC documentary, five volunteers are going on diets tailored to their bodies and brains and guided by geneticist and obesity expert Dr. Giles Yeo. They’re just like you – normal people who spend their lives going up and down in weight. Combining rock-solid science with engaging personal stories, this experiment will revolutionize how we think about diet.

Think long-term weight loss is impossible? Think again.