CALORIFIC VALUE OF FOOD

CALORIFIC VALUE OF FOOD

The energy needs of the body are calculated in terms of calories (sometimes called the kilocalorie or kcal) or in the metric system, the joule.

One calorie is equal to 4.184 joules which may be rounded off to 4.2 joules.

A calorie is the amount of heat needed to raise the temperature of one kilogram of water through one degree at 15⁰ Celsius (15⁰ C).

The number of calories obtained from a food is its calorific value. Every food varies in its calorific value. The average calorific value of some common foods are as follows:

Table: Calorific value of some common foods

Food	Average Protein	Quantity	Calories
Milk (Buffalo’s)	1 cup	5 oz	200
Tea	1 cup	5 oz	60
Coffee	1 cup	5 oz	75
Bread	1 slice	30 g	75
Butter	1 tsp	5 g	35
Cheese	1 piece	28 g	110
Biscuit	1 piece	8 g	30
Jam	1 tsp	20 g	55
Cornflakes	1 cup	25 g	100
Cake, plain	1 piece	75 g	220
Chapati	1 thin	15 g	40
Puri	1 piece	16 g	70
Paratha	1 piece	70 g	250
Dal	1 cup	6 oz	200
Green vegetables	1 cup	6 oz	75
Potato	1 piece	100 g	80
Potato chips	10 pieces	20 g	100
Rice khichdi	1 cup	210 g	250
Rice (puffed)	1 cup	15 g	50
Oil, ghee	1 tsp	5 g	45
Cream	1 tsp	½ oz	50
Fruit	1 piece	100 g	60
Coconut water	1 glass	8 oz	45
Lemon juice	1 glass	8 oz	75
Coca cola, Gold spot	1 bottle	6 oz	80
Pie (apple)	1 serving	160 g	380
Jelly (plain)	1 tsp	65 g	65
Sugar	1 tsp	5 g	20
Tomato ketchup	1 tsp	15 g	15
Idii	1	75 g	75
Dosa (plain)	1	50 g	110
Dosa (masala)	1	100 g	190
Almonds	15	30 g	170
Chashewnuts	15	30 g	170
Groundnuts	1 tsp	15 g	90
Egg	1 piece	50 g	210
Omelette	1 piece	40 g	210
Chicken/mutton soup	1 serving	7 oz	35
Meat (cooked)	1 slice	30 g	80
Chicken, roast	1 serving	100 g	200
Meat	1 serving	150 g	350
Fish fry	1 serving	100 g	220
Beer	1 glass	8 oz	100
Whisky, gin/rum	1 measure	1 ½ oz	110

The variation in calorific value of foods is due to the amount of carbohydrates, fats and proteins in each of them e.g., one paratha made of wheat flour and oil gives about 250 calories while a glass of coconut  water gives only 45. This is because the former contains a large amount of carbohydrates, fair amount of proteins and some fat, while the latter contains negligible quantity of carbohydrates, proteins and fats.

The contribution of calories from carbohydrates, fats, proteins, and alcohol  are given in the following table.

Table: Energy Values of Food and Alcohol.

	In Bomb Calorimeter	In Human Body
Substance (1 gram)	kcal	kcal	kJ
Protein	6.65	4	17
Carbohydrates	4.1	4	17
Fat	9.45	9	38
Alcohol (Absolute ethanol)	7.1	7	29

• The values are rounded off for easy reference.

These values are derived with the help of an instrument called Bomb Calorimeter. This  instrument consist of the following parts:

Thermometer, Electric wires, Oxygen chamber, and insulator.

In this instrument a small electric spark ignites the sample in the presence of oxygen catalyst such as platinum. The amount of heat energy released by the complete oxidation of the sample raises the temperature of the surrounding water.

   Catalyst           

Carbohydrate, protein or fat + oxygen                                                        Heat energy + Water

                                                                                                                      + Carbon dioxide

A similar process takes place in every cell of the human body but with a difference. The human body always derives less energy than the bomb calorimeter from a given amount of food. This is due to the body’s efficiency for utilization of proteins, fats and carbohydrates. This is more true in case of protein proteins which is not oxidized completely in the body, a fact that limits the energy released and leads to the formation of by products such as urea and uric acid.

From this we can understand that in the body:

1 g of carbohydrate yields 4.0 cal or 17 J

1 g of protein also yield 4.0 cal or 17 J

1 g of fat yields 9.0 cal or 38 J

Fats are a more concentrated source of energy than carbohydrates and proteins and limiting fats in the diet while cutting down on calories helps weight loss and restricts weight gain.