unit five - proteins

Protein

Proteins form a fundamental part of the body’s structure.

• Essential components of the body:

• Active, versatile, and functional molecules responsible for complex cellular tasks.

• Constitute 15–20% of an adult’s body weight:

• 40% in muscle tissue.

• 30% in skin and blood.

• The rest in other tissues and fluids (not found in bile or urine under normal conditions).

Derived from Greek 'proteos'

Meaning 'the first,' indicating the fundamental role of proteins in the body.

chemical composition

Building blocks of proteins; over 200 exist, but only 20 are part of human proteins.

• Polymers of simpler substances: amino acids (AA).

• Composed of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N).

• Energy yield: 4 kcal/g when oxidized.

Amino Acids (AA):

• Over 200 types of amino acids exist in nature.

• Only 20 amino acids form part of human body proteins.

• 9 Essential Amino Acids:

• Leucine, Isoleucine, Valine, Lysine, Methionine, Threonine, Phenylalanine, Tryptophan, Histidine.

• Branched-chain amino acids (leucine, isoleucine, valine):

• Vital for protein synthesis.

• Comprise one-third of skeletal muscle.

Essential Amino Acids

9 amino acids that must be obtained from the diet: Leucine, Isoleucine, Valine, Lysine, Methionine, Threonine, Phenylalanine, Tryptophan, Histidine.

Protein sources

Can be classified as animal-based (higher quality and digestibility) or plant-based (often lower quality but can be complemented).

Limiting Amino Acid

The amino acid present in the lowest proportion in a protein source, affecting its overall quality.

Protein Complementation

Combining different foods to balance amino acid deficiencies and enhance protein quality.

Protein Quality

Definition:

• Protein quality refers to the ability of a protein source to meet an individual’s nitrogen and amino acid requirements.

Factors Influencing Protein Quality:

1. Digestibility:

• Refers to how easily a protein is broken down and absorbed.

2. Chemical Integrity:

• The balance and completeness of amino acids in the protein.

3. Antinutritional Factors:

• Can reduce protein availability by up to 50%.

• Examples:

• Natural Antinutrients: Tannins, phytates, etc.

• Storage or Processing Effects: Formation of compounds during food storage or cooking.

PDCAAS

Protein Digestibility Corrected Amino Acid Score; a method to assess protein quality based on amino acid content and digestibility.

2. PDCAAS (Protein Digestibility Corrected Amino Acid Score):

• Adjusts protein score based on digestibility.

• Calculated by multiplying protein score by digestibility percentage.

3. Applications:

• PDCAAS values are useful for selecting protein sources in dietary planning based on their quality.

Daily Protein Requirements

General recommendation of 0.8 g/kg body weight, with increased needs in specific conditions like activity or aging.

Protein Turnover

Process where approximately 200–300 g of proteins are degraded and synthesized daily for tissue maintenance.

Energy Function of Proteins

Proteins can be oxidized for energy (4 kcal/g) when other energy sources are insufficient.

• When energy sources (carbohydrates and fats) are insufficient, or protein intake exceeds requirements, proteins are oxidized for energy (4 kcal/g).

• This process is less efficient than lipid or carbohydrate oxidation.

• Results in nitrogen waste, requiring energy for urea formation.

Structural Function of Proteins

Provide essential amino acids necessary for tissue synthesis and repair.

1. Structural (Plastic) Function:

• Provides essential amino acids for tissue synthesis.

• Protein turnover:

• Approximately 200–300 g of proteins are degraded and synthesized daily, maintaining a dynamic balance.

• Daily protein intake is essential to repair wear and tear.

Functional Molecules

Proteins are active and versatile, playing critical roles in various cellular functions.

Antinutritional Factors

Substances that reduce protein availability, such as tannins and phytates.

Digestibility

How easily a protein is broken down and absorbed in the body.

Serum Albumin

A protein that maintains osmotic balance and transports various substances in the blood.

Immunoglobulins

Antibodies that protect the body against foreign organisms and particles.

Nitrogen Waste

Byproduct of protein oxidation that requires energy for urea formation.

Protein Sources Comparison

Animal proteins are generally more efficient and digestible than plant proteins.

• Animal Proteins:

• Higher efficiency and digestibility.

• Examples: Meat, fish, eggs, dairy.

• Plant Proteins:

• Generally less efficient due to lower digestibility and being encased in carbohydrates.

Branched-Chain Amino Acids

Amino acids including leucine, isoleucine, and valine, vital for protein synthesis.

Protein Score

A method comparing the amino acid content of a test protein to a reference protein.

1. Protein Score:

• Compares the amino acid content of a test protein to that of a reference protein.

• Formula:

Protein Score = mg of amino acid in test protein/mg of amino acid in reference protein

Food Protein Content

Quantitative measurement of protein in various foods; important for dietary planning.

Animal-Based Protein Sources

Food Protein per 100g Carbohydrates

Meat 20–25 g <0.5 g

Fatty Fish 20–25 g <0.5 g

Lean Fish 15–20 g <0.5 g

Egg (1 unit) ~6 g <0.5 g

Plant-Based Protein Sources

Food Protein per 100g Carbohydrates

Firm Tofu 15 g <2 g

Soy Tempeh 18 g <2 g

Textured Soy Protein 50 g 25 g

Legumes (dry) 20–25 g 50 g

Legumes (cooked) 6–8 g 15 g

Canned Legumes 5–6 g 10 g

Legume Pasta (dry) 20–25 g 50 g

Dynamic Balance

The ongoing process of protein synthesis and degradation in the body.

Energy Yield of Proteins

Proteins yield 4 kcal/g when oxidized, but this is less efficient than carbohydrates or fats.

Legumes

Plant-based protein sources that vary in protein content; can be complemented with other foods.

Osmotic Balance

Maintained by proteins that transport substances and regulate fluid levels in the body.

General Protein Intake Guideline

Recommended daily protein intake of 0.8 g/kg for the average adult.

Canned Legumes Protein Content

Contain 5–6 g of protein per 100g, providing a source of plant protein.

Protein Essentials for Health

High-quality protein sources are crucial for maintaining health and physiological functions.

Diverse Protein Sources

Incorporating both animal and plant proteins ensures a well-rounded amino acid intake.

classification by nutritional value

• Protein Quality:

• Foods contain proteins of varying quality, depending on their essential amino acid content and digestibility.

• The limiting amino acid is the one present in the lowest proportion compared to cellular demand.

• Protein Complementation:

• Combining different foods can balance the deficiencies of amino acids, enhancing overall protein quality.

protein requirements

• General recommendations: 0.8 g/kg body weight.

• Increased needs: 1.0–1.2 g/kg, up to 2.0 g/kg in specific conditions.

• Protein efficiency decreases with:

• Sedentary lifestyle.

• Obesity.

• Aging.

• Restrictive diets.

• Poor sleep quality.

functions of proteins

1. Structural (Plastic) Function:

• Provides essential amino acids for tissue synthesis.

• Protein turnover:

• Approximately 200–300 g of proteins are degraded and synthesized daily, maintaining a dynamic balance.

• Daily protein intake is essential to repair wear and tear.

2. Energy Function:

• When energy sources (carbohydrates and fats) are insufficient, or protein intake exceeds requirements, proteins are oxidized for energy (4 kcal/g).

• This process is less efficient than lipid or carbohydrate oxidation.

• Results in nitrogen waste, requiring energy for urea formation.

3. Regulatory Function:

• Involves the regulation of cellular activities through:

• Hormones (e.g., insulin, growth hormone).

• Enzymes that catalyze metabolic reactions.

• Neurotransmitters that facilitate nerve impulses.

4. Transport Function:

• Maintains osmotic balance by transporting substances:

• Gases (e.g., hemoglobin transports oxygen).

• Lipids (e.g., serum albumin).

5. Defensive Function:

• Protects against foreign organisms and particles:

• Antibodies (immunoglobulins).

• Blood clotting factors (e.g., fibrinogen, thrombin) prevent blood loss when vessels are damaged.

measuring protein quality

1. Protein Score:

• Compares the amino acid content of a test protein to that of a reference protein.

• Formula:

Protein Score = mg of amino acid in test protein/mg of amino acid in reference protein

2. PDCAAS (Protein Digestibility Corrected Amino Acid Score):

• Adjusts protein score based on digestibility.

• Calculated by multiplying protein score by digestibility percentage.

3. Applications:

• PDCAAS values are useful for selecting protein sources in dietary planning based on their quality.

overview

• Proteins are essential macronutrients that serve critical roles in the body.

• Protein sources vary in quality and digestibility, with animal proteins generally having higher efficiency.

• Combining plant-based proteins can ensure adequate amino acid intake in vegetarian and vegan diets.

• A balanced intake of diverse protein sources is key to maintaining health and supporting physiological functions.

functions overview

1. Structural Function:

• Provides the building blocks for tissue growth and repair.

2. Energy Function:

• Secondary energy source, yielding 4 kcal/g when oxidized.

3. Regulatory Function:

• Hormones (e.g., insulin, growth hormone) and enzymes regulate metabolic processes.

4. Transport Function:

• Proteins like hemoglobin and albumin transport oxygen, lipids, and other substances.

5. Defensive Function:

• Antibodies protect against infections, and clotting factors prevent blood loss.

protein quality and evaluation overview

1. PDCAAS (Protein Digestibility Corrected Amino Acid Score):

• Assesses protein quality by measuring amino acid content and digestibility.

2. Limiting Amino Acids:

• Plant proteins often lack one or more essential amino acids but can be complemented by combining food sources.

dietary protein sources

Animal-Based Sources:

• High in quality, providing all essential amino acids.

• Examples: Meat, fish, eggs, and dairy.

Plant-Based Sources:

• Often incomplete in amino acids but can be combined to achieve complete protein intake.

• Examples: Legumes, tofu, tempeh, and soy products.

protein intake guidelines

1. General Recommendations:

• 0.8 g/kg body weight for adults.

2. Increased Needs:

• 1.2–2.0 g/kg for athletes, elderly individuals, or during recovery from illness.

key points

• Proteins are indispensable for maintaining and repairing body tissues, energy production, and metabolic regulation.

• A balanced intake of high-quality proteins supports optimal health.

• Plant-based proteins can achieve equivalent nutritional value to animal proteins when combined appropriately.