Protein | Composition of Proteins | Eight Essential Amino Acids | Functions of Proteins | Dietary Sources of Protein

 

Protein: An Overview

Proteins are essential macronutrients composed of amino acids, which are the building blocks of life. They play a critical role in maintaining the structure and function of the body, supporting growth, repair, and overall health.

1. Composition of Proteins

Proteins are made up of smaller units called amino acids, linked together by peptide bonds.

• Amino Acids: There are 20 types of amino acids, categorized as essential, non-essential, and conditionally essential.
• Essential Amino Acids: These cannot be synthesized by the body and must be obtained through the diet.

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2. Eight Essential Amino Acids

Essential amino acids are amino acids that the human body cannot synthesize and must be obtained from dietary sources. They are critical for numerous physiological processes, including protein synthesis, tissue repair, and the production of enzymes and hormones.

1. Isoleucine

• Function:
  • Supports muscle repair and recovery.
  • Involved in hemoglobin production and energy regulation.
  • Helps maintain stable blood sugar levels.
• Sources: Eggs, soy, legumes, fish, chicken, and seeds.

2. Leucine

• Function:
  • Promotes muscle protein synthesis and growth.
  • Plays a role in wound healing and blood sugar regulation.
  • Provides energy during intense physical activity.
• Sources: Meat, dairy products, nuts, soy, and beans.

3. Lysine

• Function:
  • Essential for collagen formation, which supports skin, bones, and connective tissues.
  • Aids calcium absorption and supports bone health.
  • Helps in the production of enzymes and hormones.
• Sources: Fish, eggs, dairy, quinoa, and legumes.

4. Methionine

• Function:
  • Acts as a precursor for cysteine, an important antioxidant.
  • Plays a role in metabolism and detoxification processes.
  • Supports the synthesis of cartilage and healthy hair and nails.
• Sources: Fish, eggs, meat, sesame seeds, and Brazil nuts.

5. Phenylalanine

• Function:
  • Precursor to neurotransmitters such as dopamine, norepinephrine, and epinephrine.
  • Enhances mood, memory, and cognitive function.
  • Supports the production of other amino acids like tyrosine.
• Sources: Milk, eggs, soy products, fish, and meat.

6. Threonine

• Function:
  • Key component of structural proteins like collagen and elastin.
  • Supports immune function by aiding antibody production.
  • Involved in fat metabolism in the liver.
• Sources: Cheese, lentils, fish, poultry, and nuts.

7. Tryptophan

• Function:
  • Precursor to serotonin, which regulates mood, sleep, and appetite.
  • Supports niacin (Vitamin B3) production, which is essential for energy metabolism.
  • Helps maintain a stable nervous system.
• Sources: Turkey, nuts, seeds, tofu, and chocolate.

8. Valine

• Function:
  • Involved in muscle metabolism and energy production.
  • Supports muscle tissue repair and growth.
  • Contributes to maintaining nitrogen balance in the body.
• Sources: Dairy, grains, mushrooms, soy, and peanuts.

3. Functions of Proteins

Proteins are crucial for numerous physiological processes, including:

• Structural Support: Building and maintaining muscles, skin, hair, and nails.
• Enzymes and Hormones: Regulating biochemical reactions and physiological processes.
• Immune Defense: Producing antibodies to fight infections.
• Transport: Carrying molecules like oxygen (via hemoglobin) and nutrients.
• Energy Source: Providing energy when carbohydrates and fats are insufficient.

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4. Dietary Sources of Protein

Proteins are found in both animal and plant-based foods.

• Animal Sources:
  • Meat (chicken, beef, lamb)
  • Fish and seafood
  • Eggs
  • Dairy products (milk, cheese, yogurt)
• Plant Sources:
  • Legumes (lentils, chickpeas, soybeans)
  • Nuts and seeds (almonds, peanuts, sunflower seeds)
  • Whole grains (quinoa, oats)
  • Vegetables like spinach and broccoli (though in smaller amounts).

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5. Protein Daily Requirement

Protein requirements vary based on age, gender, activity level, and physiological conditions like pregnancy or illness.

• General Guidelines:
  • Infants: 1.2–2.0 g/kg of body weight
  • Children: 1.0–1.5 g/kg of body weight
  • Adults: 0.8 g/kg of body weight
  • Pregnant and Lactating Women: 1.1–1.3 g/kg of body weight
  • Athletes or Bodybuilders: 1.2–2.0 g/kg of body weight