Notes on Protein in the Human Diet

Importance of Protein

• Essential part of the human diet.
• Found in foods like:
  • Eggs
  • Dairy
  • Seafood
  • Legumes
  • Meats
  • Nuts
  • Seeds
• Functions include:
  • Fighting infections
  • Helping cells divide
  • Various other biological processes

Structure of Proteins

• Proteins are chains of amino acids linked by peptide bonds.
• Structure:
  • Resembles a string of beads.
  • Twisted and folded into a specific shape.
• When ingested, proteins are broken down into amino acids.

Amino Acids

• Basic structure:
  • Central carbon atom
  • Amino (nitrogen-containing) group
  • Carboxylic acid group
  • Hydrogen atom
  • Unique side chain (R group)
• Types of amino acids:
  • Non-essential (5): Can be made by the body
    • Alanine, asparagine, aspartic acid, glutamic acid, serine
  • Conditionally essential (6): Can be made under normal circumstances but not during certain conditions
    • Arginine, cysteine, glutamine, glycine, proline, tyrosine
  • Essential (9): Must be obtained from food
    • Histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine

Protein Digestion

• Process called Proteolysis:
  • Begins in the stomach when protein-containing food is ingested.
  • Hydrochloric acid denatures protein, making it more accessible.
  • Pepsin, an enzyme, cleaves proteins into oligopeptides.
  • Oligopeptides are further broken down in the duodenum by pancreatic enzymes into:
    • Tripeptides
    • Dipeptides
    • Individual amino acids
• Absorption:
  • Amino acids absorbed by intestinal cells
  • Some used to synthesize enzymes and new cells
  • Most enter the bloodstream

Sources of Protein

• Animal-based foods:
  • Eggs, dairy, seafood, meat (provide all essential amino acids)
• Soy foods:
  • Unique plant-based source of all essential amino acids
• Plant-based foods:
  • Often contain high amounts of some amino acids and low amounts of others
  • Eating a variety ensures adequate intake of essential amino acids
  • Examples of pairings:
    • Rice and beans
    • Hummus and pita bread
    • Oatmeal topped with almond butter

Daily Protein Requirements

• Estimated minimum requirement: 0.8 grams per kilogram of body weight (WHO and US RDA)
• Recommended daily intake by age:
  • 1-3 years: 13 grams
  • 4-8 years: 19 grams
  • 9-13 years: 34 grams
  • Females (14+ years): 46 grams
  • Males (14-18 years): 52 grams
  • Males (19+ years): 56 grams
• Special groups (pregnant women, breastfeeding, athletes, older adults) may have increased needs

Achieving Protein Intake

• Sample meal plans for about 64 grams of protein:
  • Omnivorous: Greek yogurt, chicken salad, fish at dinner
  • Plant-based: Tofu scramble, edamame, lentils with brown rice

Health Considerations

• Individuals at risk of protein deficiency:
  • Malnutrition
  • Trauma/burn injuries
  • Digestive conditions (e.g., inflammatory bowel disease)
• Generally safe to consume high amounts of protein, except in cases like kidney disease.

Recap

• Protein is crucial for health and bodily functions.
• Different types of amino acids: non-essential, conditionally essential, and essential.
• Protein needs vary by life stage, activity level, and health status.
• Adequate protein can be achieved through a diverse diet regardless of dietary preferences (omnivorous, vegetarian, or vegan).