A unit measuring the energy value of foods, calibrated by the quantity of heat required to raise the temperature of 1 gram of water by one degree celsius at a pressure of one atmosphere. The four sources from which calories are obtained are alcohol, carbohydrates, fats and proteins; however, all these sources are not equal. For example, fat packs a hefty 9 calories per gram, over twice as much as the 4 calories per gram carried by both carbohydrates and proteins. Alcohol has 7 calories per gram, almost as many as fat. Clearly, fats and alcohol have a much higher caloric density than carbohydrates and protein, so it's obvious that a 6-ounce serving of steak will be much more expensive calorically than 6 ounces of cauliflower.
From The Food Lover's Companion, Fourth edition by Sharon Tyler Herbst and Ron Herbst. Copyright © 2007, 2001, 1995, 1990 by Barron's Educational Series, Inc.