Food provides the raw material required for life. Yet most of us don't have a clue about how our bodies use it. How do we get energy from our food while at the same time extracting the physical materials we need to make and maintain our bodies? How does the food we eat affect the way our bodies function? What's distinct about the way we metabolise highly-processed food? Food and nutrition are overrun by myth and pseudoscience. The reality is that millions of years of evolution have structured human physiology so that it is macronutrient agnostic. Protein, carbohydrate: the body has evolved so that it extracts the same amount of energy from each, and retains the same amount of fat. There are countless theories about the efficacy and health benefits of certain macronutrients - proteins versus carbs versus fat... but biology simply doesn't work that way. The problem is that while diet gurus are busy prescribing what to eat, they haven't bothered to explain why we eat in the first place. Why We Eat is a definitive look at the science of food and metabolism. It will explain why we're hungry at particular moments in our days and our lives, why diets almost never work, why exercise doesn't benefit you in the ways you probably think it does, and how ultra-processed food fools and alters our metabolisms.