Ask a friend who is on a diet what kind of food she eats. Most probably, she would say her meals consist of low-calorie food.

What exactly is a calorie? A calorie is a unit of measurement of energy. In the past, it has been the unit used in all forms of energy. Now, it is replaced by the joule, the SI unit of energy. In food, however, the calorie remains the unit of measurement used to measure the amount of food energy. It was Prof. Nicolas Clement in 1824 who first defined calorie as a kilogram-calorie. The definition was incorporated into French and English dictionaries between 1842 and 1867.

By definition, a small or gram calorie has energy need to increase the temperature of one gram of water to one degree Celsius. This is equal to about 4.184 joules. A kilogram calorie, which is equal to one thousand calories, increases the temperature of one kilogram of water by one degree Celsius.

The difference is useful for measurements in physics and medical science. In nutrition however, there is no practical relevance between gram calorie and kilogram calorie. That’s because they are not measured as amounts of energy but are calculated from food consumption.

The fat in the human body contains eighty-seven percent of lipids. That means one kilogram of body fat tissue has roughly eight hundred seventy grams of pure fat. That is equal to seven thousand eight hundred kilocalories.

For those who are exercise buffs and on a diet, they believe that taking meals with low calories would help them lose weight or prevent the unnecessary gain of weight. However, low-calorie diets may not be helpful in certain situations.

Let’s look at the facts. Low-calorie diets, as the name implies, has a low calorie intake. The theory states, on principle, that the body will burn excess fat off if the necessary energy to maintain that fat is not provided by the diet.

However, this may not work on everybody due to the simple fact that everybody is different. It is impossible to establish precisely the limit for the normal functioning of the body since the metabolism of each person varies greatly to another person. It also varies according to age, gender, physical condition, and the type of activity the person does.

Also, calorie intake may have to be adjusted to the amount of food available. When food is eaten in lower quantities, for example, metabolism will slow down and burn a fewer number of calories.

As a general guide, men need two thousand two hundred calories in a day. Women, on the other hand, need about one thousand eight hundred calories a day. Low-calorie diets often have one thousand calories in the meal, far lower than the general daily requirement. There are also super-low-calorie diets that contain around eight hundred or less calories.

These diets are not recommended for someone who is living a very active life or for someone who is exercising regularly. Since physically strenuous activities require a great amount of energy to be used, the person would have to take in a meal with a large caloric intake. 

Low-calorie diets are not recommended for pregnant and breastfeeding women. They would need enough calories for themselves and for the infant that they’re carrying in their wombs or they’re breastfeeding with. Low-calorie diets are not also recommended for old people and active children and adolescents.

Low-calorie diets are not necessarily bad as this article would suggest. However, they should be balanced—not too low—as not to restrain a person’s body. Also, the diet must have all the essential nutrients to maintain good health.