Health Explained: What is a calorie?
23 December 2011 Last updated at 01:12 GMT
BBC health correspondent Branwen Jeffreys explains what calories are, as she prepares for Christmas.
She explains why we need calories, how we use them, and how reducing or increasing our intake of calories affects our weight.
After the cooking is done, she also heads out to the garden to explain how we can burn off a few calories.