What Determines a Protein’s “Quality”?
Protein is a crucial macronutrient that plays a vital role in various physiological functions within our bodies. Whether you're an athlete, a fitness enthusiast, or simply aiming to lead a healthy lifestyle, understanding protein quality and its impact on muscle protein synthesis (MPS) is of utmost importance.
In this blog post, we will delve into how protein quality is measured, focusing on essential amino acids, leucine content, and bioavailability. We will also discuss why high-quality protein is essential for MPS post-exercise.
Protein quality refers to the nutritional value and composition of a protein source. Several factors help determine the quality of a protein, including essential amino acid content, leucine content, and bioavailability.
1. Essential Amino Acid Content: Proteins are made up of amino acids, some of which are essential, meaning they must be obtained from the diet as our bodies cannot produce them. The essential amino acids include histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. One way to easily measure protein quality would be by assessing the presence and proportion of these essential amino acids. A protein source that contains all essential amino acids in the right proportions is considered “complete” and of higher quality. Specifically to maximise MPS, it is believed that 10g of EAA are required in a single dose.
2. Leucine Content: Leucine, an essential amino acid, holds particular significance in protein quality measurement. Leucine plays a crucial role in stimulating muscle protein synthesis. It activates the mTOR pathway, a signalling pathway responsible for initiating MPS. It is believed that c3g of leucine is required to optimally stimulate MPS. Sources of 3g of leucine include; 25g Whey Isolate, 5 medium eggs, a small steak (160g), 180g peas!
3. Bioavailability: Bioavailability refers to the extent to which our bodies can digest, absorb, and utilise the amino acids present in a protein source. Proteins that are highly bioavailable are more efficiently utilised by the body. Factors such as protein structure, processing methods, and food matrix influence the bioavailability of protein.
There are two widely recognised methods for measuring protein quality, these are the Protein Digestibility-Corrected Amino Acid Score (PDCAAS) and the Digestible Indispensable Amino Acid Score (DIAAS).
1. PDCAAS measures protein quality by evaluating both the essential amino acid composition and digestibility of a protein source. It rates protein quality on a scale from 0 to 1, with 1 being the highest quality. PDCAAS has been the standard method for protein quality assessment for many years, but it has limitations. For instance, it does not account for factors like bioavailability or the specific amino acid requirements of different age groups.
2. DIAAS is a more advanced method for measuring protein quality. It considers the amino acid composition as well as the true ileal digestibility, which reflects the absorption of amino acids in the small intestine. DIAAS provides a more accurate assessment of protein quality, accounting for the differences in digestibility between protein sources. This method rates protein quality above 1, allowing for a better distinction between high-quality proteins.
Importance of High-Quality Protein for MPS Post-Exercise
Muscle protein synthesis is a critical process for muscle growth, repair, and maintenance. Consuming high-quality protein after exercise is essential to stimulate MPS effectively. Protein sources rich in essential amino acids, especially leucine, provide the necessary building blocks for muscle repair and growth. Leucine acts as a trigger for MPS, initiating the process that leads to muscle adaptation. Therefore, consuming protein sources with optimal essential amino acid content, high leucine content, and good bioavailability helps maximize the MPS response, aiding in muscle recovery and development.
Conclusion:
Understanding how to measure protein quality through essential amino acid content, leucine content, and bioavailability is crucial for selecting the right protein sources to support optimal health and muscle growth. While PDCAAS has been widely used, the more advanced DIAAS method offers a more accurate assessment. Consuming high-quality protein post-exercise, rich in essential amino acids and leucine, facilitates effective muscle protein synthesis, enabling better recovery and muscle development. By prioritizing high-quality protein sources, we can ensure that our bodies receive the necessary nutrients for optimal physical performance and overall well-being.