Protein

Protein deficiency is rare in Canada.
Majority of Canadians consumed protein above the Acceptable Macronutrient Distribution Range (AMDR).
Dietary protein represents approximately 15% of caloric intake for the average Canadian.
Globally, many rely on plant proteins, primarily from grains and vegetables.
As a country’s economy improves, the proportion of animal foods in the diet typically increases.
In Canada, a significant portion of protein intake comes from meat, poultry, fish, eggs, and dairy products.

Proteins are chains of amino acids linked together.
Components of proteins include:
- Carbon
- Hydrogen
- Oxygen
- Nitrogen
Structures of proteins:
- Primary: Sequence of amino acids.
- Secondary: Folding patterns (e.g., alpha-helix, beta-sheet).
- Tertiary: Three-dimensional shape.

Each amino acid contains:
- A central carbon atom
- A hydrogen atom
- An amino group
- An acid group
- A side chain (R group)
Types of amino acids:
- Essential (indispensable): Cannot be synthesized by the human body in sufficient amounts.
- Non-essential (dispensable): Can be synthesized by the body in adequate amounts.
- Some non-essential amino acids can be conditionally essential.

Transamination: A process of synthesizing amino acids in the body when not available from the diet.

Amino acid pool: The collection of amino acids in body tissues and fluids available for use.
Approximately half of the amino acids in the pool are derived from recycled proteins, while the other half are from dietary sources.

Muscle Turnover:
- MPS (Muscle Protein Synthesis)
- MPB (Muscle Protein Breakdown)
Protein turnover refers to the continuous cycle of protein synthesis and breakdown in the body.

Amino acids undergo deamination to be used for energy.
In the absence of glycogen, amino acids may serve as a substrate for energy production.
Converted into acetyl-CoA or citric acid cycle intermediates as needed.

Deamination: The removal of an amino group from amino acids.
Produces ammonia, which is converted to urea—a nitrogenous waste product excreted in urine.
Urea is filtered by the kidneys.

Protein-energy malnutrition (PEM) covers conditions of protein deficiency, which may be isolated or accompanied by energy deficiency.
Common types of PEM:
- Kwashiorkor: Nutritional deficiency characterized by difficulty in growth, impaired immune function, low skin elasticity, and liver abnormalities.
- Marasmus: A severe condition resulting from inadequate intake of protein, fat, and carbohydrates, leading to significant body wasting.

Food allergies can arise when dietary proteins are absorbed without complete digestion.
Common allergens include proteins from:
- Milk
- Eggs
- Nuts
- Wheat
- Soy
- Fish and Shellfish
- Peanuts
Symptoms may include gastrointestinal distress, skin rashes, respiratory issues, or anaphylaxis.
Individuals with GI diseases are more prone to allergies due to malabsorption of proteins.

Protein quality assesses how effectively dietary protein can be utilized to synthesize body proteins.
Types of proteins:
- Complete Dietary Protein: Contains all essential amino acids in necessary proportions.
- Incomplete Dietary Protein: Lacks one or more essential amino acids.
Protein synthesis ceases if a required amino acid is unavailable.

High-Quality Protein:
- Complete, with adequate extra amino acids.
- Good digestibility, often from animal sources (with soy as an exception).
Low-Quality Protein:
- Incomplete with limiting amino acids, often from plant sources.

Complements are foods that, when combined, provide all essential amino acids:
- Example: Grains, nuts, and seeds combined with legumes.
- Grains: Often deficient in lysine, while legumes lack methionine.
This combination leads to a complete protein profile.

Nitrogen Balance: Evaluates if protein intake is sufficient.
- Positive Nitrogen balance: occurs in growing children, athletes, or pregnant women.
- Nitrogen equilibrium: normal individuals.
- Negative Nitrogen balance: seen in surgical patients or astronauts.

Indicator Amino Acid Oxidation (IAAO) method:
- Suggests current Dietary Reference Intake (DRI) for proteins may underestimate needs.

Athletes typically require more protein: 1.2-2.0g/kg BW daily.
Recovery proteins and branched-chain amino acids (BCAAs) play significant roles in muscle protein synthesis.

Supplements often come in forms such as powders or bars containing proteins, BCAAs, or individual amino acids.
Concerns regarding supplementation:
- Cost
- Quality
- Nutrient density issues
- Individual amino acids might interfere with the absorption of other essential amino acids due to shared transport systems.