Understanding Dietary Protein Quality and Requirements

Posted on Mar 7, 2025 in Human Nutrition and Dietetics

Quality of Dietary Proteins

Complete Proteins (Balanced): Contain all essential amino acids in sufficient concentrations to meet an individual’s protein requirements.

Incomplete Proteins (Unbalanced): Deficient in one or more essential amino acids.

Complementary Proteins

You can obtain the daily requirement of protein and essential amino acids in different ways:

  • By consuming adequate amounts of foods containing complete proteins.
  • By consuming a variety of foods containing complementary proteins. Combining complete and incomplete protein foods can provide all essential amino acids throughout the day.

Evaluation of Protein Quality

  • Amino Acid Content: The types and amounts of amino acids in food.
  • Digestibility: How well the protein is broken down and absorbed.
  • Requirements: Based on the standard requirements for a population of a particular age. Requirements for children aged 2 to 5 years are considered suitable for children up to one year.

Factors Affecting Amino Acid Bioavailability

Egg Proteins:

  • The three-dimensional structure of egg white proteins can be difficult to digest.
  • Egg white contains protease inhibitors.
  • Glycoproteins and egg lipids can hinder proteolysis.
  • Avidin (in raw egg white) binds biotin and prevents its absorption; it is denatured by heat.

Methods for Assessing Protein Quality

Old methods were based on:

  • Biological Value (BV): Ability to provide essential amino acids.
  • Net Protein Utilization (NPU): Nitrogen retained / Nitrogen ingested.
  • Protein Efficiency Ratio (PER): Weight gain / Protein intake.

New methodology is based on protein digestibility, corrected for the value of the most limiting amino acid (PDCAAS).

Protein Digestibility Corrected Amino Acid Score (PDCAAS)

PDCAAS takes into account:

  • The content of essential amino acids in the food.
  • Digestibility.
  • Ability to provide essential amino acids in adequate amounts for human requirements.

Requirements for children aged 2 to 5 years are considered, as they are the most demanding group (except for infants). The maximum possible PDCAAS value is 1.0.

PDCAAS Calculation

  1. Analyze the nitrogen content to estimate the protein (N x 6.25).
  2. Determine the levels of essential amino acids.
  3. Calculate the amino acid score:
    (mg of essential amino acid in 1g of sample protein) / (mg of essential amino acid in 1g of reference protein)
  4. Determine the overall protein digestibility.
  5. Calculate PDCAAS: The lowest essential amino acid score x protein digestibility.

Protein Requirements

  • Adults: 0.8 g/kg/day (FAO/WHO recommends 0.7-1 g protein/kg body weight daily).
  • Children: ~1.5 g protein/kg body weight/day.

These requirements are to meet nutritional needs (growth, pregnancy, etc.) and protein turnover. Approximately 15% of total kcal should come from protein.

Choosing Proteins Wisely

  • Eating more protein does not necessarily mean eating better.
  • Select 1/3 or less of dietary protein from animal sources.
  • Include legumes such as chickpeas, beans, and lentils.
  • Choose quality protein foods that are low in fat and high in fiber.

Effects of Deficient Protein Intake

  • Protein-Calorie Malnutrition:
    • Kwashiorkor: Caused by inadequate protein intake with adequate caloric intake.
    • Marasmus: Caused by a deficiency in both protein and calories (starvation).

Hypoproteic Diets

Hypoproteic diets are not effective for weight loss. Weight loss occurs at the expense of muscle mass and visceral protein. These diets can lead to low blood pressure and, in some cases, intractable cardiac arrhythmias.