Bioavailability and amino acid profile
Protein quality is partly measured by its bioavailability, or the body’s ability to absorb and utilize it. Highly bioavailable protein, such as that found in eggs or chicken, is quickly absorbed and utilized by the body, unlike some plant or grain proteins, which often have lower bioavailability.
Proteins are composed of about twenty amino acids, nine of which are considered “essential” because the body cannot synthesize them and must obtain them from food. Animal proteins, which contain all the essential amino acids, are often considered “complete.” Plant proteins, on the other hand, are incomplete, sometimes lacking some essential amino acids, which can limit their effectiveness when consumed alone. However, combining several plant protein sources, such as rice and lentils, can achieve a complete amino acid profile.
Measuring Protein Quality: PDCAAS
A key indicator for assessing protein quality is the PDCAAS (Performance Corrected Amino Acid Score), which takes into account the proportion of essential amino acids and protein digestibility. For example, eggs have an index of 1.21, meaning they are very complete and have a high bioavailability of approximately 97%. Rice, on the other hand, has an index of 0.57, which indicates an incomplete amino acid profile, specifically lacking lysine, which reduces its effectiveness in the body.
Antinutrients and Factors Limiting Protein Intake
Some foods, especially those of plant origin, contain antinutritional substances that can hinder nutrient absorption. These molecules, absent from animal proteins, often reduce the bioavailability of plant proteins. Furthermore, protein structure also affects digestibility. Animal proteins, which are more easily digested, are more quickly and fully absorbed by the body, especially whey protein, which is highly valued for its easy digestion and exceptional bioavailability.
