A calorie is actually a measure of heat, and heat is a measure of energy. So in this topic when we speak about calories, we are talking about amounts of energy in a food, or the energy required to burn a calorie of heat or create a calorie of heat. It is important that an appreciation is developed for this concept because weight gain and weight loss are directly associated with the amount of energy (calories) consumed in relation to the amount of energy burned. The body is usually exceptionally efficient and will store energy at every opportunity it is given. These energy stores occur because more energy (calories) is consumed than is required to maintain the body's ‘machinery' running and functioning. It is only when less energy is consumed than is required that the body will give up some of its energy reserves to keep the ‘machine' running and functioning properly.
The amount of energy a particular body needs to maintain a weight or to avoid a weight loss can be difficult to accurately predict, and varies with every person and their genetic makeup. In order to predict how much energy a body will need, mathematical formulas have been developed. These energy requirement prediction formulas have been estimated by over 200 complicated equations that will use a patient's weight, and height. These equations are designed to determine the minimum amount of energy that a body needs to maintain a weight, thereby preventing a weight loss. So if someone wants to loose weight, they need to consume less than what their body needs. The differences between formulas and their many uses is beyond the scope of this section, but health care professionals are familiar with these equations and use them when necessary to assist in developing recommendations for nutritional management. The take home message is that these equations are helpful and have been used to assess metabolic needs of a person. In short, health care professionals are not just guessing at the calorie requirements of an individual. Although they may not be able to give you 100% certainty of your requirements, they will be able to guide you better than a random guess.