Weight loss typically involves the loss of fat, water and muscle. A dieter can lose weight without losing much fat. Ideally, overweight people should seek to lose fat and preserve muscle, since muscle burns more calories than fat. Generally, the more muscle mass one has, the higher one's metabolism is, resulting in more calories being burned. Approximately 14 kilocalories of fat are burned per pound of muscle at rest. Since muscles are more dense than fat, muscle loss results in little loss of physical bulk compared with fat loss. To determine whether weight loss is due to fat, various methods of measuring body fat percentage have been developed.

Muscle loss during weight loss can be restricted by regularly lifting weights (or doing push-ups and other strength-oriented calisthenics) and by maintaining sufficient protein intake. According to the National Academy of Sciences, the Dietary Reference Intake for protein is "0.8 grams per kilogram of body weight for adults."

Those on low-carbohydrate diets, and those doing particularly strenuous exercise, may wish to increase their protein intake which is necessary. However, there may be risks involved. According to the American Heart Association, excessive protein intake may cause liver and kidney problems and may be a risk factor for heart disease. There is no conclusive evidence that moderately high protein diets in healthy individuals are dangerous, however; it has only been shown that these diets are dangerous in individuals who already have kidney and liver problems.

All body processes require energy to run properly. When the body is expending more energy than it is taking in (e.g. when exercising), the body's cells rely on internally stored energy sources, like complex carbohydrates and fats, for energy. The first source the body turns to is glycogen (by glycogenolysis). Glycogen is a complex carbohydrate (in total about 2000 kcal). 65% is stored in skeletal muscles and the rest in the liver. It is created from the excess of ingested macronutrients, mainly carbohydrates. When those sources are nearly depleted, the body begins lipolysis, the mobilization and catabolism of fat stores for energy. In this process, fats, obtained from adipose tissue, or fat cells, are broken down into glycerol and fatty acids, which can be used to make energy. The primary by-products of metabolism are carbon dioxide and water; carbon dioxide is expelled through the respiratory system.

Fats are also secreted by the sebaceous glands (in the skin). When losing weight one must be careful as to not begin to burn muscle. When the body runs of out of fats and carbohydrates to burn, it will begin to burn muscle which will be harmful for the body.

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Author's Bio: 

This definition is part of a series that covers the topic of Fat Loss. The Official Guide to Fat Loss is Yuri Elkaim.

Yuri Elkaim is regarded as one of the North America's leading fitness and nutrition authorities. He is the author of the groundbreaking book (and e-book) Eating for Energy, and is the creator of the industry-leading Fitter U and Treadmill Trainer iPod workouts.

Yuri graduated summa cum laude with a Bachelors of Physical Education and Health from the University of Toronto and is also a Certified Kinesiologist, a Registered Holistic Nutritionist, a former professional soccer player in Canada and France, and the current Head Strength and Conditioning & Nutrition Coach for the nationally ranked University of Toronto Men's Soccer program.

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