Amino acids are the basic building blocks for proteins. Before we dive into the details about amino acids, let’s take a minute to level-set about proteins.
We all know protein is an essential part of the diet, but protein has a slightly different meaning at the biological level. Proteins are large molecules that your body produces to perform specific functions within individual cells.
Here are some of proteins roles within our bodies:
- help form structural components of cells
- digest nutrients or convert one substance into another
- transport substances into or out of cells
As you can see, proteins have many functions and come in many shapes and sizes. As we mentioned earlier, amino acids are the building blocks for proteins, which can be very large.
Each protein is composed of any number of amino acids; the smallest proteins might only contain 20 amino acids,1 while the largest can have thousands.2
Structure of an Amino Acid
The size of a protein alone doesn’t determine its role in the cell; instead, it is the protein’s composition. What do we mean by “composition?” The sequence of amino acids that make up the protein.
There are 20 unique amino acids, but all amino acids are very similar in structure. Amino acids share a basic outline or skeleton with only one unique functional group each. A functional group is a unique part of the amino acid that determines its purpose in a final protein.
Some functional groups bond to each other, creating large three-dimensional structures in the protein. Other functional groups react with substances in the body to digest food. Others still transport nutrients into and out of cells or through the bloodstream. Sometimes multiple amino acids coordinate these complex roles in the body.
Amino Acids and Protein in the Diet
Protein is an integral part of the diet, as you already know. When eaten, proteins are broken down to serve two purposes.
First, proteins can be broken down completely to provide energy for the body. In a healthy diet, 10-20% of all consumed calories come from protein.3 In addition, a little more than half of all consumed protein is converted to energy.
The other half of protein from the diet can be broken down into amino acids. These amino acids are then used by individual cells to create new proteins that humans need to survive. Foreign proteins from the diet are never used “as-is.” They are always broken down into amino acids, and your body creates new proteins from the individual amino acids. This is true even for proteins that are very similar between humans and other animals.
What is an “Essential” Amino Acid?
Of the 20 different amino acids that form all human proteins, nine are considered “essential.” These amino acids cannot be synthesized by the human body and must be consumed in the diet. The remaining 11 amino acids can be synthesized if your other nutritional needs are met.
Also, a handful of amino acids are semi-essential or essential for certain groups of people. Infants and children in particular need to eat almost all 20 amino acids to stay healthy. There are only actually two amino acids that are considered completely nonessential;4 a healthy body will always be able to produce these naturally.
A deficiency in any essential amino acid can cause severe risks to your health.5 Proteins are involved in so many functions throughout the cell, and all nine essential amino acids are needed to produce your body’s many proteins.
A small reduction of essential amino acids in the diet will result in dysfunctional proteins or an insufficient number of proteins in the cell. As you can imagine, the problems can range from digestive to neurological and everything in between.
What Foods Contain Essential Amino Acids?
Most food sources contain all 20 amino acids. This is because all living organisms (both plants and animals) need these same amino acids to produce the proteins they need to survive.
However, every organism needs a different amount of each amino acid. Some plants, for example, use a very high percentage of one or two amino acids. The other amino acids are used but in much smaller quantities. Therefore, some of these foods will be a good source of some amino acids, but not all.
However, if you are eating a vegetarian or vegan diet, don’t worry! Eating a variety of grains, vegetables, legumes, and fruits will supply all your amino acid needs.6 If you’re eating enough protein and a variety of plant-based foods, you’re already supplying yourself with all nine essential amino acids.
Some foods contain all nine essential amino acids in high quantities. These foods include meat, seafood, and poultry. Some whole grains, such as quinoa, also contain adequate amounts of all nine essential amino acids.
Eggs are also an excellent source of essential amino acids. They are high in protein, and the protein in eggs contains a good range of essential and nonessential amino acids. In addition, most protein supplements will provide the complete spectrum of essential, semi-essential, and nonessential amino acids.
- TRP-Cage product details. AnaSpec. https://www.anaspec.com/products/product.asp?id=59018#:~:text=Trp%20Cage%20is%20a%20highly,features%20specific%20to%20this%20miniprotein. Accessed June 13, 2020.
- Sela B. [Titin: Some aspects of the largest protein in the body]. Harefuah. 2002;141(7):631-635.
- Balancing carbs, proteins, and fat. Kaiser Permanente. https://wa.kaiserpermanente.org/healthAndWellness?item=%2Fcommon%2FhealthAndWellness%2Fconditions%2Fdiabetes%2FfoodBalancing.html. Accessed June 13, 2020.
- Reeds PJ. Dispensable and indispensable amino acids for humans. J Nutr. 2000;130(7):1835S-40S. DOI: 10.1093/jn/130.7.1835S.
- Rose WC, Haines WJ, Warner, DT. The amino acid requirements of man. III. The role of isoleucine; additional evidence concerning histidine. J Biol Chem. 1951;193(2):605–612.
- Mariotti F, Gardner CD. Dietary protein and amino acids in vegetarian diets—A review. 2019;11(11):2661. DOI: 10.3390/nu11112661.