2.3 Protein

Proteins help the body build tissues, provide energy, and maintain fluid balance. They make up muscles, organs, and enzymes that catalyze metabolic reactions.

Getting enough protein supports health across the lifespan. The recommended daily intake for adults is 0.8 g/kg body weight. Protein quality matters too, with complete proteins containing all amino acids the body cannot make. Adequate protein intake can also help prevent chronic diseases.

Protein in Human Nutrition and Health

Roles of proteins in nutrition

• Builds and repairs tissues
  • Constructs muscles, organs, skin, hair, and nails
  • Produces enzymes catalyzing metabolic reactions
  • Synthesizes hormones regulating bodily functions (insulin)
  • Creates antibodies defending the immune system
• Provides energy
  • Supplies 4 calories per gram of protein
  • Enables gluconeogenesis converting amino acids to glucose during prolonged fasting or starvation
• Maintains fluid balance
  • Balances albumin and globulins in blood plasma
  • Regulates osmotic pressure
• Transports nutrients and molecules
  • Carries oxygen via hemoglobin
  • Moves lipids using lipoproteins
  • Delivers iron with transferrin

Protein intake for health

• Requires adequate protein intake for optimal health
  • Recommends Dietary Allowance (RDA) of 0.8 g/kg body weight/day for adults
  • Increases requirements for growth, pregnancy, lactation, and recovery from illness or injury
• Considers protein quality and digestibility
  • Contains amino acids the body cannot make: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine
  • Classifies complete proteins containing all amino acids the body cannot make in sufficient amounts (animal-based proteins, quinoa, soy)
  • Identifies incomplete proteins lacking one or more amino acids the body cannot make (most plant-based proteins)
  • Measures protein quality using Protein Digestibility Corrected Amino Acid Score (PDCAAS) based on amino acid composition and digestibility
  • Evaluates biological value to determine protein quality based on amino acid content and digestibility
• Links protein intake to chronic disease prevention
  1. Supports cardiovascular health by replacing saturated fats with plant-based proteins reducing heart disease risk
  2. Promotes weight management as high-protein diets increase satiety and weight loss
  3. Maintains bone health with adequate protein intake supporting bone mineral density and reducing osteoporosis risk
• Cautions against risks of excessive protein intake
  • Strains kidneys, especially in individuals with pre-existing kidney disease
  • Potentially increases certain cancer risks (colorectal cancer) with high consumption of red and processed meats

Protein Structure and Metabolism

• Explains protein structure
  • Describes amino acids as building blocks of proteins
  • Illustrates how amino acids are joined by peptide bonds to form protein chains
• Discusses protein metabolism
  • Explains nitrogen balance as the difference between nitrogen intake and excretion
  • Describes protein denaturation as the alteration of protein structure due to heat, acid, or other factors
• Explores protein combinations
  • Defines complementary proteins as combinations of incomplete protein sources that together provide all amino acids the body cannot make

Addressing protein deficiency

• Identifies at-risk groups
  • Recognizes children in developing countries
  • Includes elderly individuals with reduced appetite or impaired digestion
  • Considers vegetarians and vegans without proper meal planning
  • Encompasses individuals with eating disorders or chronic illnesses
• Provides nutrition education and counseling
  • Emphasizes the importance of protein in the diet
  • Teaches meal planning and food combination strategies ensuring adequate intake of amino acids the body cannot make
  • Encourages consumption of high-quality protein sources (lean meats, legumes)
• Implements food fortification and supplementation
  • Fortifies staple foods with amino acids the body cannot make (lysine-fortified wheat)
  • Provides protein-rich food supplements (peanut butter, milk powder)
  • Considers using amino acid supplements in severe deficiency cases
• Addresses underlying socioeconomic factors
  • Improves access to affordable, high-quality protein sources
  • Supports sustainable agriculture and livestock production
  • Implements poverty reduction strategies improving overall nutrition status