Unit 5: The Macronutrients – Proteins and Fats |DECE2|IGNOU|

Unit 5: The Macronutrients – Proteins and Fats

5.1 Introduction: In this unit, the focus shifts from carbohydrates and water to proteins and fats. The discussion encompasses the nature, functions, and food sources of proteins and fats. Additionally, the processes of digestion, absorption, and utilization of these macronutrients in the body are explored.

Objectives: After completing this unit, learners should be able to list the food sources of proteins and fats, state the roles of these macronutrients in the body, and describe the processes of digestion, absorption, and utilization.

5.2 Proteins: Proteins, the subject of this section, are composed of amino acids, with 22 being their basic building blocks. Eight amino acids are deemed essential, requiring dietary intake, while the rest are non-essential and can be produced by the body. The quality of food proteins is determined by the presence and proportion of essential amino acids. Animal proteins generally provide good quality since they contain all essential amino acids. In contrast, plant proteins may lack one or two essential amino acids, but their quality can be enhanced by combining different plant foods. Traditional Indian diets often incorporate such combinations.

Food Sources: Rich sources of proteins include milk, milk products, flesh foods (meat, fish, poultry), eggs, nuts, oilseeds, and pulses. While animal foods can be costly, milk and eggs are relatively more affordable and provide high-quality protein. Pulses, nuts, and oilseeds from plant sources are also protein-rich but can be expensive. Combining cereals with pulses and incorporating small amounts of milk can improve the overall quality of protein in the diet.

5.3 Fats: This section delves into the topic of fats, providing insights into their nature, functions, and food sources. It discusses the different types of fats, their role in the body, and the importance of maintaining a balance between various fatty acids. Emphasis is placed on distinguishing between saturated and unsaturated fats and understanding the significance of essential fatty acids.

5.4 Summing Up: This section likely consolidates the key points discussed in the unit, emphasizing the importance of proteins and fats, their sources, and the significance of a balanced diet.

5.5 Glossary: This section may provide definitions of key terms used throughout the unit, ensuring a clear understanding of the terminology related to macronutrients.

Check Your Progress Exercise 1:

  1. How can we improve the protein quality of cereals?
    • The protein quality of cereals can be enhanced by combining them with pulses. This combination ensures a more balanced amino acid profile, as pulses complement the amino acids lacking in cereals. Additionally, incorporating small amounts of milk in the diet can further improve the overall quality of cereal proteins.
  2. List the sources of animal and vegetable proteins in your diet and compare their cost.
    • Sources of Animal Proteins:
      • Meat
      • Fish
      • Poultry
      • Eggs
      • Milk and dairy products
    • Sources of Vegetable Proteins:
      • Pulses (e.g., lentils, green gram, rajmah, soybean)
      • Nuts and oilseeds (e.g., groundnuts, almonds, cashewnuts, walnuts)
    • Comparison of Cost:
      • Animal proteins, such as meat, fish, and poultry, are often more expensive compared to plant-based proteins.
      • Milk and eggs, among animal proteins, are relatively more affordable options.
      • Pulses, nuts, and oilseeds from plant sources can also be expensive but are major protein sources in Indian diets.
    • Consideration:
      • While animal proteins may be costlier, they often provide high-quality protein with all essential amino acids.
      • Plant proteins can be more economical but may lack certain essential amino acids, emphasizing the importance of combining different plant foods for a balanced amino acid profile.

Summary: Functions of Proteins and Protein Metabolism

Functions of Proteins:

  1. Body Building:
  • Proteins provide amino acids necessary for building and repairing body tissues.
  • Essential for growth from birth to adulthood and continuous maintenance of the body.
  1. Regulatory and Protective Substances:
  • Enzymes, vital for digestion, are proteins.
  • Hormones, regulating metabolism, include proteins like insulin.
  • Antibodies, essential for immune function, are also proteins.
  1. Carriers:
  • Certain proteins, like hemoglobin in the blood, act as carriers.
  • Hemoglobin transports oxygen from the lungs to body tissues and carbon dioxide from tissues to the lungs.
  1. Energy-Giving Function:
  • Proteins can be broken down for energy, yielding about 4 Kcal per gram.
  • Not the primary function, occurs when carbohydrates and fats are insufficient.

Digestion, Absorption, and Utilization:

  1. Digestion of Proteins:
  • Dietary proteins consist of amino acid chains.
  • Digestion begins in the stomach with pepsin breaking down proteins into smaller amino acid chains.
  • In the small intestine, further breakdown occurs to convert proteins into amino acids.
  1. Protein Metabolism:
  • Metabolism of proteins essentially involves the metabolism of amino acids.
  • Amino acids, the end products of protein digestion, are transported to the liver.
  • In the liver, amino acids are used for building blood proteins, retained, or enter the bloodstream.
  • Amino acids circulate, some remain in circulation, and others are taken up by body tissues for protein synthesis.
  • Emphasis on the maximized utilization of high-quality proteins for the synthesis of the body’s own proteins.

Key Takeaways:

  • Proteins are crucial for body growth, maintenance, and various regulatory functions.
  • Enzymes, hormones, and antibodies are examples of proteins with regulatory and protective roles.
  • Hemoglobin serves as a carrier protein for oxygen and carbon dioxide.
  • While proteins can provide energy, their primary role is in tissue building and maintenance.
  • Protein digestion involves breaking down amino acid chains in the stomach and small intestine.
  • Protein metabolism revolves around the utilization of amino acids for various bodily functions, highlighting the importance of high-quality proteins.

Check Your Progress Exercise 2:

1) Fill in the blanks:
a) Amino acids are the building blocks of all proteins.
b) Cereals and pulses both lack certain amino acids but when combined, the protein quality improves.
c) A good quality protein has the right proportion and combination of all essential amino acids.

2) List four functions of proteins:

  1. Body Building:
    • Proteins provide amino acids for the construction and repair of body tissues, supporting growth and maintenance.
  2. Regulatory and Protective Functions:
    • Enzymes, which are proteins, play a crucial role in the digestion of food.
    • Hormones, including protein-based ones like insulin, regulate metabolism and other body processes.
    • Antibodies, also proteins, contribute to the body’s immune system, protecting against illness.
  3. Carrying Substances:
    • Certain proteins, like hemoglobin, act as carriers, transporting substances such as oxygen and carbon dioxide in the blood.
  4. Energy-Giving Function:
    • While not the primary role, proteins can be broken down to provide energy when carbohydrates and fats are insufficient.

Summary: Fats and Their Functions

Fats and Oils:

  • The term “fats” encompasses both fats and oils, characterized by a greasy feel and insolubility in water.
  • Besides fats and oils, cholesterol, a fat-like substance, is important in the body.

Composition and Differences:

  • Fats and oils are composed of fatty acids and are essential for the diet due to the supply of essential fatty acids.
  • Fats are solid at room temperature (e.g., ghee, butter), while oils are liquid (e.g., mustard oil, groundnut oil).
  • Common sources of fats and oils include ghee, vanaspati, mustard oil, groundnut oil, soya oil, and coconut oil, all containing nearly 100% fat.

Food Sources:

  • Fats are present in fat-rich foods like milk, milk products (curd, paneer, khoa), nuts, oilseeds (almond, groundnut, coconut, mustard seeds), eggs, and flesh foods.
  • Even foods like cereals, pulses, and fruits contain small amounts of fats, contributing significantly to Indian diets due to their consumption in large quantities.

Functions of Fats:

  1. Source of Energy:
  • Fat is a concentrated source of energy, providing around 9 Kcal per gram.
  • Excess fat is stored in adipose tissue, mainly under the skin and in the abdominal region.
  1. Satiety Value:
  • Fat-rich diets induce a feeling of fullness and satiety, as fats take longer to digest and remain in the stomach.
  1. Insulation and Padding:
  • Stored fat under the skin acts as an insulator, keeping the body warm.
  • Fat around vital organs, like the kidney and heart, serves as padding, protecting against injury.
  1. Source of Essential Fatty Acids:
  • Fats provide essential fatty acids crucial for various bodily functions.
  1. Carrier of Fat-Soluble Vitamins:
  • Fats act as carriers for fat-soluble vitamins, aiding in their absorption in the body.

Digestion, Absorption, and Utilization:

  • During digestion, fats are broken down to fatty acids, facilitated by enzymes present in gastric juice and pancreatic secretions.
  • Bile from the liver helps disperse fats in water for enzyme action, crucial for fat digestion in the small intestine.
  • End products (glycerol and fatty acids) move into intestinal cells, aided by bile salts.
  • Bile salts disperse fatty acids into small, water-soluble units for absorption into intestinal cells.
  • Fatty acids and glycerol are transported through the lymph vessels to the bloodstream, where they are either stored in adipose tissue or used for energy, similar to glucose and amino acids.

In conclusion, while excess fat intake may pose health risks, fats play vital roles in energy provision, satiety, insulation, essential fatty acid supply, and vitamin absorption. Balancing fat consumption is key to reaping these benefits without adverse effects.

Check Your Progress Exercise 3:

1) List the steps involved in digestion, absorption, and utilization of fats:

  • a) Digestion: Breakdown of fats to fatty acids and glycerol in the stomach and small intestine, facilitated by enzymes and bile.
  • b) Absorption: Fatty acids and glycerol move into intestinal cells with the help of bile salts, then into blood circulation via lymph vessels.
  • c) Utilization: Fatty acids and glycerol are transported through the bloodstream, either stored in adipose tissue for energy or broken down in cells for energy production.

2) Fill in the blanks:
a) All fats and oils are made up of fatty acids and glycerol.
b) Each gram of fat provides approximately 9 Kcal.
c) The amount of energy supplied by a gram of fat is more than double the amount of energy supplied by a gram of carbohydrate or protein.
d) Bile is essential for the digestion and absorption of fats and oils.

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