What is a Limiting Amino Acid of a Food? And why is this concept important for meal planning?

What is a Limiting Amino Acid of a Food? And why is this concept important for meal planning?

In this ongoing series on protein nutrition, I have been highlighting the importance of amino acids. At a fundamental level, our bodies don’t require whole proteins from our diets; we simply need sufficient amounts of the nine essential amino acids. As protein researcher Don Layman, PhD contends we don’t have a protein requirement – we have a requirement for the essential amino acids. That does not mean we should not be eating whole foods – there are benefits to whole foods beyond supplying amino acids – just that if we need to make sure that we are getting enough of the right amino acids.

When we consume food, our digestive system breaks down proteins into individual amino acids and small peptides, which are then actively transported into the cells lining the gut wall. We don’t take in whole proteins – just the individual amino acids.

The proteins found in our diet contain varying amounts of each of the nine essential amino acids. Some sources provide more than enough of all the essential amino acids, while others may be deficient in one or more.

To create the myriad proteins necessary for our bodies to function optimally, we must have an adequate supply of each essential amino acid. Our proteins consist of specific chains of amino acids linked together. If an amino acid is unavailable during protein synthesis, that particular protein cannot be formed, regardless of the availability of other amino acids. This missing amino acid is referred to as the first limiting amino acid of that protein source. There may also be subsequent limiting amino acids as the supply of those amino acids is depleted.

It can be argued that every protein source has a limiting amino acid since, eventually, one will run out during synthesis. However, from a practical perspective, many protein sources such as meats, eggs, and dairy typically do not have a limiting amino acid as long as they are consumed in adequate quantities.

Conversely, most plant protein sources tend to have one or more limiting amino acids. This does not imply that a plant-based diet cannot provide all the necessary amino acids. Different plant protein sources exhibit various limiting amino acids. For instance, protein researcher Don Layman notes that plant proteins are often low in lysine, methionine, tryptophan, and leucine. He further states that grains are generally deficient in lysine, while legumes are lacking in methionine and sulfur-containing amino acids.
By combining a variety of plant-based protein sources, you can meet your essential amino acid requirements.

Before delving into how this can be achieved, it’s crucial to discuss two additional concepts: the digestibility of different protein sources and their varying biological effects. In the next article in this series, I will introduce these concepts.

Thanks for reading and please share,

Russ

See also the latest article in the Training 4 Life series. I just posted “9 Adaptations : Resistance Training for Muscle Mass, Function AND Quality of Life” and the second article in the Exercise Planning and Programing series “Planning and Logging Your Fitness”.