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Balanced Diet : Unit 5 – Biology notes for Class 11

Balanced Diet : Unit 5 - Biology class 11

Nutrients and Balanced Diet  Unit 5 Biology Class 11

Balanced Diet : The chemical reactions in our body cause the complex molecules present in food to be broken down into simple molecules. These simple molecules are absorbed by the walls of the small intestine. They enter the bloodstream and are then transported to the cells of various parts of the body. These simple molecules are then burnt by the cells to provide energy.

The food contains a number of basic components such as carbohydrates, proteins, and fats. These components produce different quantities of energy when burnt. The amount of energy produced when one gram of any of these components is burned known as its calorific value.

Balanced Diet: A diet is said to be balanced when various nutritional materials i.e., proteins, carbohydrates, fats, minerals, vitamins, roughage, and water are present in proper amount.

Various constituents of the balanced diet provide energy, growth, repair, replacement of cells, and physiological regulation. Our food should contain the various nutrients in such proportions as can satisfy all the needs of the body. A balanced diet of each individual can be determined according to his or her body requirements.

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The different components of food (nutrients) can be classified as following-

 

(i)Energy-yielding nutrients:

  • Carbohydrates: They are the main source of energy for the human body. When they are broken down they form glucose. Glucose is essential as a source of energy and is also important for maintaining tissue protein. The brain and central nervous system depend solely on glucose for their energy requirements.

Carbohydrates are obtained from foods such as whole-grain cereals and bread, pasta, corn, beans, peas, potatoes, fruit, vegetables, and milk products. These food groups together normally constitute more than 50 percent of the calorie requirement of the human body. It is recommended that carbohydrates should contribute 60-70 percent of the total calories in a day’s diet.

The carbohydrates that are found in such foods are called complex carbohydrates. They are slowly broken down into glucose and absorbed by the body. This ensures that healthy levels of glucose are always maintained in the body.

  • Fats: Fats are the most concentrated source of energy in our diet. They also impart flavor to the food, Fat plays several important roles in the diet.
  1. It is important for the absorption of fat-soluble vitamins such as Vitamin A, D, E and K.
  2. Fats also provide essential fatty acids, which are important for the structure and function of cells.
  3. Fat also cushions the vital organs and protects the body from extremes of cold and heat.

The body requires approximately forty grams of fat in a day.

(ii) Body-building nutrients: Proteins are chief bodybuilding nutrients. They also form antibodies, hemoglobin, enzymes, and hormones. The protein that is absorbed through food is used to perform these vital functions. Proteins are made up of amino acids. Most of these amino acids are not synthesized by the body, but must be obtained from food. These essential amino acids are obtained from eggs, milk, meat, fish, and poultry. Plants, by themselves, do not provide all the essential amino acids, but they may do so in combination with other vegetarian sources of food. For example, when cereals are combined with pulses, they provide most of the essential amino acids.  Vegetarians must take special care to ensure that their body’s requirement of protein is sufficiently met by their diet.

The body’s daily requirement of protein is between 10 to 15 percent of the daily calorie requirement. The body’s protein requirement varies with factors such as age, physiology, and stress. Pregnancy greatly increases the protein requirement of the body. These additional requirements are normally accomplished by the intake of protein supplements.

(iii) Metabolic regulators/ protective food

They are vitamins, water, and mineral salts. Vitamins and minerals are considered essential nutrient. They perform hundreds of roles in the body. They help in building up bones, heal wounds, and bolster your immune system. They also convert food into energy and repair cellular damage.

Besides carbohydrates, proteins, fats, vitamins, minerals, and water, roughage (fiber) is also essential in the diet.

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Calorific Value of Carbohydrate, Protein, and Fat:

Carbohydrates, proteins, and fats serve as the chief sources of energy in humans. These are oxidized and transformed into ATP, the chemical energy form used by cells for their various activities.

Because heat is the ultimate form of all energy, the energy value of food (or any fuel) is expressed in terms of a measure of heat energy it produces on combustion. The heat energy released by combustion of one gram of food is usually known as its gross calorific value.

It is defined as the amount of heat produced in calories (cal) or in joules (J) from the complete combustion of 1 gram food in a bomb calorimeter (a closed metal chamber filled with O2). The calorific value is usually expressed in terms of kcal per gram or kilojoules per gram.

(1kcal = 4.184kJ)One kilocalorie is the amount of heat energy needed to raise the temperature of one kilogram of water through 1°C (1.8°F). It is referred to kcal as the Calorie or to kJ as Joules (always capitalized).

The calorific values of carbohydrates, proteins, and fats are 4.1 kcal/g, 5.65 kcal/g and 9.45 kcal/g, respectively.

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Physiologic Value of Carbohydrate, Protein, and Fat:

The actual amount of energy liberated in the human body due to combustion of 1g of food is the physiologic value of food. It is always less than the gross calorific value calculated by bomb calorimeter.

The Physiologic Value of food is defined as the actual amount of energy liberated in the human body due to combustion of 1 g of food. It is always less than the gross calorific value calculated by bomb calorimeter. The physiologic values of carbohydrates, proteins, and fats are 4.0 Kcal/g, 4.0 Kcal/g and 9.0 Kcal/g respectively.

Calorific Value and Physiologic Value of Carbohydrate, Protein, and Fats

1 Kilocalorie (Kcal) = 1000 calories

Calorific Value and Physiologic value of Carbohydrate, Protein and Fat
Sr. No Macronutrient Gross calorific value Kcal/g Physiologic value Kcal/g
1 Carbohydrate 4.1 4
2 Protein 5.65 4
3 Fat 9.45 9

For more notes click Chemistry notes for Class 11.

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