|Sadava, David and Orians, Gordon H. Life: The Science of Biology. New York: W. H. Freeman and Co, 2000: 887.||"Fat yields 9.5 kcal/g, cabohydrates 4.2 kcal/g, and proteins about 4.1kcal/g."||17.6 MJ/kg|
|Calories from Fat, Protein, Carbohydrates, Alcohol. NutriStrategy, 2005.||"Carbohydrates: 1 gram = 4 calories"||16.7 MJ/kg|
|"Calories and Meat Products." Readers Digest. (1986): 72.||"A pound of proteins like a pound of carbohydrates contain 1820 calories."||16.8 MJ/kg|
|Carbohydrates-I need more energy. Connecticut Team Nutrition Training Program, 25 May 2007.||"Each gram of carbohydrate povides 4 calories."||16.7 MJ/kg|
Carbohydrates, also known as saccharides, are the most abundant energy providing molecule on the planet. They are made up of very simple molecules and play many major roles in the living world.
A basic unit of carbohydrate is known as a monosaccharide (CH2O). Two examples of monosaccharides are glucose and fructose. Two combined monosaccharides are known as a disaccharide. Example of disaccharides include sucrose and lactose. Carbohydrates which contain three to six monosaccharides are named oligosaccharides; anything larger than that is called a polysaccharide. Some examples of polysaccharides are starch, glycogen and cellulose.
Unlike proteins and fats, carbohydrates are not considered essential nutrients. The body can obtain all its energy by converting fats and proteins. However, fats and proteins are vital building components for tissues and cells. Therefore it is not practical to waste them for the purpose of energy production. Carbohydrates and proteins provide the body with 4 kilocalories per gram while fats provide the body with 9 kilocalories of energy. Therefore in SI units carbohydrates provide the body with 16.7 mega joule of energy for each kilogram. Although it seems like fats provide more kilocalories per gram, it is better to consume carbohydrates for energy production purposes because they are abundantly available. They also require less water to be digested.
Examples of foods that are rich in carbohydrates and cheaply available are cereal, rice, pasta, beans and bread. The Food and Agriculture Organization and World Health Organization recommend that about 55-75% of a person's total energy consumption should come from carbohydrates. In addition, it is also recommended that simple sugars, commonly known as junk food, should only consist of less than 10% of that intake.
There is also a differentiation between "good carbs" and "bad carbs" for diet purposes. In this diet, consumption of good carbs such as vegetables is promoted instead of insulin increasing starches. Since "good carbs" have less energy density compared to "bad carbs," they are more filling and are therefore considered healthier.
Anurag Panda -- 2007