Aspartic acid is one of twenty amino acids that serve as the building blocks for proteins. It is classified as a “non-essential” amino acid, which refers to the body’s ability to produce it independently. The human system synthesizes aspartic acid from other molecules, meaning it is not strictly necessary to obtain it from dietary sources. It is a common component of nearly all proteins.
The Two Forms of Aspartic Acid
Aspartic acid exists in two distinct forms, known as isomers, which are mirror images of each other. These two forms are L-aspartic acid and D-aspartic acid, and the “L” and “D” designations refer to their molecular configuration. While chemically similar, their roles within biological systems are quite different.
L-aspartic acid is the isomer the body uses in the synthesis of proteins. As one of the proteinogenic amino acids, it is directly incorporated into the polypeptide chains that form proteins. This is the form of aspartic acid naturally present in protein-containing foods.
In contrast, D-aspartic acid is not used to build proteins. Its roles are concentrated in the nervous and endocrine systems, where it acts as a neuromodulator and is involved in hormone regulation. Because of these specific functions, D-aspartic acid is the form most often found in dietary supplements.
Biological Roles in the Body
The functions of aspartic acid are diverse and depend on which of its two forms is involved. L-aspartic acid’s primary role is its participation in protein synthesis. It is integrated into structures for tissues, enzymes, and molecules throughout the body, which is necessary for growth and repair.
Beyond its structural capacity, the ionic form of aspartic acid, known as aspartate, functions as an excitatory neurotransmitter in the brain, helping transmit signals between nerve cells. Aspartate is also a participant in the urea cycle. This cycle assists in the detoxification of ammonia by converting it into urea for safe excretion.
Aspartate contributes to energy production through gluconeogenesis, the process of generating glucose from non-carbohydrate sources, and it aids in cellular respiration. Separately, D-aspartic acid has a targeted role in the endocrine system. It is involved in the synthesis and release of certain hormones, including testosterone.
Aspartic Acid in Your Diet and Supplements
L-aspartic acid is widely available in protein-rich foods. Common dietary sources include:
- Animal products such as beef, poultry, and fish
- Dairy items like milk and cheese
- Plant-based foods like soy products and peanuts
- Vegetables such as asparagus
Since the body can produce aspartic acid and it is present in many common foods, a dietary deficiency is exceptionally rare. For most individuals, normal protein consumption provides an ample supply of L-aspartic acid.
Dietary supplements containing aspartic acid provide the D-aspartic acid (D-AA) form. These products are marketed toward athletes and bodybuilders with claims of enhancing athletic performance and increasing testosterone levels. This is linked to D-aspartic acid’s role in hormone regulation.
The Link to Aspartame
Aspartic acid is related to aspartame, a widely used artificial sweetener. Aspartame is synthesized from two amino acids: aspartic acid and phenylalanine. These two amino acids are joined together, resulting in a compound that is approximately 200 times sweeter than table sugar.
The aspartic acid in aspartame is chemically identical to the L-aspartic acid found in foods. When consumed, aspartame is broken down in the digestive system into its constituent parts: aspartic acid, phenylalanine, and a small amount of methanol. These components are then absorbed and metabolized just as they would be from any other food source.
Concerns are sometimes raised about the safety of the aspartic acid from this source. However, the quantity obtained from consuming foods and beverages sweetened with aspartame is minor compared to the amounts from protein-rich foods. For example, a glass of milk contains significantly more aspartic acid than a diet soda.