High-protein diets take a page from the low-carb craze. The goal is to lose weight by eating more protein-packed foods, which often means consuming fewer carbohydrates. The portion of total calories derived from protein is what defines a high-protein diet. In a typical diet, 10%-15% of daily calories come from protein. In a high-protein diet, this number can be as high as 30%-50%. Besides curbing appetites, high-protein diets may also change a person’s metabolism. When carbohydrates are severely restricted, the body begins burning its own fat for fuel – a state called ketosis. Ketosis may shed weight, but it’s also associated with headaches, irritability, nausea, kidney trouble, and heart palpitations. High-protein diets come in many forms, and not all are created equal. The most nutritious high-protein plans are low in fat and moderate in carbohydrates, rather than high in fat and low in carbohydrates.