Excess calories are the number of calories you consume above the amount you need to fuel daily activities, resting metabolism and exercise. Your body prefers to use certain calorie sources in specific ways. Carbohydrates, for example, are converted to glucose and used to meet immediate energy needs or are stored as glycogen in your liver and muscles to be used at a later time. Fat and protein each have their preferred pathways, as well, which affects how these macronutrients are used or stored.
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Dietary fat primarily exists in food and in your body as triglycerides. Both stored fat and fat circulating in the bloodstream can be used as a source of energy. Although excess dietary fat is stored as triglycerides, these fat stores can be broken down into fatty acids and glycerol to provide energy between meals, to fuel low-intensity exercise and to support high-intensity activities by assisting in the release of glycogen.
Although excess calories from fat, protein and even carbohydrates get stored as fat, the body prefers to use protein and carbs elsewhere. Protein is the last resource tapped when your body needs energy for everyday activities or exercise. Likewise, protein resists conversion to fat because your body uses this nutrient for other functions, such as repairing muscle tissue following exercise, building muscle and delivering oxygen to working muscles. Taking in more calories than you need, however, can result in excess body fat, regardless of your primary source of calories.
The recommended intake of dietary fat is 20 percent to 35 percent of overall calories. The typical American diet provides around 12 percent of calories from protein, while athletes commonly get 25 percent to 30 percent of calories from protein. The recommended range for protein intake is 10 percent to 35 percent of overall calories. While these percentages can serve as general guidelines to help you plan a balanced diet, the total number of calories you need depends on factors such as your age, gender and lifestyle.
Excess calories generally translate into stored body fat, regardless of the source of your calories. Although protein, fat and carbohydrates each have preferred jobs in your body's healthy function, excess calories in general lead to weight gain. Protein doesn't convert fat to muscle and can even contribute to additional body fat if you consume more calories than you need. Adopting a balanced diet that limits refined carbs and includes lean proteins, healthy fats, whole grains, fruits and vegetables -– while limiting caloric intake to less than expenditure -– is an effective strategy for healthy weight management.