Calories are ubiquitous across most of the world and have been used to help people manage their weight for more than a century. But have we been counting them wrong all along? In this episode, Emily Thomas finds out how the calorie is a lot more complex than many of us realise. Historian Louise Foxcroft describes how this measure of energy became the darling of scientists and public health experts across the globe, and the unwitting bedfellow of the diet industry. Geneticist Giles Yeo argues that calorie counting can actually be harmful, encouraging us to make unhealthy choices, and Bridget Benelam from the British Nutrition Foundation explains why she thinks that despite all its flaws, the calorie will be with us for a good while yet.