Have you ever wondered how the humble spud is turned into the unusual shapes in your favourite bag of crisps? Jimmy Doherty visits Germany to learn the secret behind the twists, twirls and curls of this much-loved snack. Dr Helen Lawal investigates whether carb-restrictive diets really burn fat quicker, and uncovers an astonishing medical use for this popular weight-loss tool. And Matt Tebbutt finds out the surprising reason why smoked fish is dyed yellow.