Drug Medical Information

CARBOHYDRATES - PERFECT FUEL FOR BODY

Unlike proteins, carbohydrates burn "clean." After the body breaks them down into usable units (molecules of sugar, or glucose), only carbon dioxide and water remain - perfectly harmless end products that we excrete easily through our lungs when we breathe. Any carbohydrates not utilized for fuel are stored in the liver and muscles in the form of glycogen. If a diet is very low in carbohydrates, the body is forced to rely more on fat and protein for energy. But fats burn inefficiently on very-low-carbohydrate diets and leave behind potentially toxic residues called ketones that turn the blood more acidic and interfere with normal body functions. Protein is less undesirable as an energy source, too, since it leaves behind potentially hazardous nitrogen and sulfur wastes that put extra stress on the kidneys as they perform their disposal function.
Protein is the body's major building and repair material, a chief constituent of everything from our muscles and bones to the enzymes that control all our chemical reactions. Protein is present in all our cells, but we need to eat only a moderate amount of it. (For one thing, some amino acids - they're the building blocks of proteins - are converted into body fat more readily than carbohydrates, so you might gain weight more quickly from eating excess amounts of certain proteins than excess amounts of carbohydrates.) But our bodies need to have carbohydrates replenished in greater quantities and more often.
Fats are the most calorically concentrated foods you can eat, supplying at least 9 calories per gram. We say "at least" 9 calories since a recent animal study by Dr. Mark Hegsted, a noted Harvard University nutritionist, found that fat is in fact "worth" about 11 calories per gram inside the body.2 (That would make fat, in terms of calories, nearly three times as concentrated as protein or carbohydrates, each of which provides 4 calories per gram.) According to Dr. Hegsted and other researchers, because dietary fat's chemical structure is essentially the same as body fat's, it is far easier (because it takes less energy) for the body to convert dietary fat into body fat than to change either carbohydrates or protein into body fat.
While fat is readily stored as fuel in our fat cells, the same is not true of carbohydrates or protein: The body has to work harder and use up more energy to store an equivalent number of calories from carbohydrates or protein as fat. If excess carbohydrates are eaten, the liver will convert them into fat, which is sent through the blood as VLDL triglycerides and stored in fat cells. But about 25 percent of these carbohydrate calories never get converted into fat - they're burned in the conversion process.
Carbohydrates also provide the brain with its primary fuel. Unlike muscles, the brain does not burn either protein or fat for energy (except after prolonged fasting): Under normal circumstances glucose (blood sugar) is its primary food. This blood glucose comes mostly from glycogen stored in the liver.
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