Beginning in the 1970s many doctors and nutritionists advised against eating fatty foods. Such advice led to a significant rise in carbohydrate-based meals—that is, meals with a high content of glucose (sugars) like bread and pasta. The human body can either run on carbohydrates (glucose) or ketones (metabolized fat). The process whereby the body runs on fats as opposed to sugars is called ketosis. This happens when carbohydrates are severely restricted, causing the body to rely on fat intake or existing fat stores already present.