Calories - Basic Facts

What is calorie

Calorie is the unit of energy commonly used in studying human nutrition. Calorie is the amount of heat energy required to raise temperature of 1 ml of water at 15°C by 1°C. Since the amounts of energy involved in the metabolism of foodstuffs are fairly large, the kilocalorie (kcal) equal to 1000 calories is commonly used.

Calories are needed for maintenance of body tissues & body temperature for growth & also for physical & mental activity as well as for reproduction. The number of calorie obtained from a food is its calorific value. Every food varies in its calorific value. The variation in calorific value of foods is due to the amount of carbohydrates, fats & proteins in each of them eg. - A paratha made of 30 gms of wheat flour & 1 tsp oil gives about 145 calories while one fruit gives about 60 calories (on an average / serving of 100 gms).

This is because the former contains a large amount of carbohydrates, fair amounts of protein & some fat while the latter contains negligible quantity of proteins & fats & some amounts of carbohydrates.

Calorific value of some common foods.

Each food has a specific calorie value i.e. a given amount of food will yield a certain number of calories when it is metabolized in the body & the calorie yield depends on the composition of the food in terms of protein, fat, carbohydrate & alcohol.

Substance (1g)                   Calorie yield

Protein                              4 kcals

Carbohydrate                              4 kcals

Fat                                    9 kcals

Alcohol                              7 kcals

Calorie requirement of various groups

The three main factors that determine the total energy requirement of an adult are

1)    Basal metabolism

2)    Physical activity

3)    Specific dynamic action of food

In addition, other factors such as growth, pregnancy, lactation, and recovery from illness & temperature regulation.

Physical activity is the greatest single factor influencing the energy needs of an individual. It may be as little as 10% of the total energy requirement, as in a bedridden person to as much as 50% in a very active person. A man doing heavy work may need 4800 or more kcals/day, while an individual of the same body build & age and height living in the same climate but doing sedentary work may require only 2500 kcals.

The   following table gives the calorie requirements for various age, groups; as per their age, sex & physical activity:

·        Physical activity and calorie

The body expends energy for voluntary actions such as running, walking, talking etc.

The energy requirements of different activities are given in the table below: -

Besides the energy required for physical activity / voluntary actions the body also expands energy for involuntary bodily functions such as expansion & contraction of the heart, respiration & digestion. This minimum energy required for the basic internal functioning of the body is known as basal metabolic rate (BMR). This is influence by factors such as body size, body composition, age, diet, climate etc.

Foods when ingested in the body release the nutrients contained in them, for the sake of giving energy for the various body processes, maintenance of body tissue or reproduction. The entire process that the food undergoes from the time it is eaten to its excretion is known as metabolism of food. Metabolism is a combination of two important processes that take place in the body, namely Anabolism - process of building up of body substance. Catabolism - process of breaking down of body substance.

Metabolism of food is a 3-step process, which includes digestion, absorption & assimilation. The final stage is where the body uses the calories provided form food for various energy needs & the remaining is stored away in the form of glycogen in the liver. Another form in which the body stores energy is in the form of fatty tissues. Thereby there is a direct relation to weight gain & excess of calorie intakes. When the deposition of fatty issues exceeds the normal limits it results in obesity.