Our bodies are made from the food we have eaten during our lifetime. To survive and grow we need to eat enough of each of the essential building blocks of the human body. How did scientists discover the right mix of nutrients and how does what we eat match up? Is it true that eating fish makes you brainier, carrots help you see in the dark and spinach will make you stronger? John takes us through the maze of diet and health. We uncover the truth behind the claims for different kinds of foods, including organic food, and ask whether we instinctively tend to choose the balance of nutrients our bodies need. In different parts of the world, people eat remarkably different diets, some entirely vegetarian, some largely meat or fish. How do these different populations manage to get the building blocks they need when they eat such different things? Lots of people try to lose weight by dieting. But does it work? And if so, what is the secret of successful dieting?