The Differences Between L-Aspartic Acid & D-Aspartic Acid

Aspartic acid, also known as aspartate, is one of 20 amino acids commonly used in your body. It’s considered a nonessential amino acid because it can be synthesized within your body from oxaloactetate, which is an intermediate of the tricarboxylic acid cycle. Amino acids and most other biologically active molecules are chiral, which means they exist as two molecules that are the mirror image of each other. In other words, they have the same chemical formula and similar properties, but they are oriented differently. Most naturally occurring proteins consist of L-form or “left-handed” amino acids, although the D-form or “right-handed” varieties are used by your body also.

Chiral Molecules

The origin of chirality in biology is the subject of much debate. Scientists are not sure why biologically active molecules such as enzymes and amino acids exist in two forms that mirror each other. Theories involve rotation of the Earth, electromagnetic radiation from the sun and polarized radiation from elsewhere in the universe. In terms of amino acids, the L-form is by far the most predominant. The L-form designation usually refers to the “levorotatory” or counterclockwise rotation of the molecule, but it can also refer to which isomer of glyceraldehyde the amino acid comes from. The D-form represents “dextrorotatory” or clockwise rotation when the molecule is exposed to polarized light.

L-Aspartic Acid

Aspartic acid was first discovered in 1827 by deriving it from asparagine, which in turn had been isolated from asparagus juice about 20 years earlier. Aspartic acid was eventually understood to be an amino acid. Like all amino acids, aspartic acid is a chiral molecule. The L-isomer is one of the 20 amino acids or building blocks of protein-based structures in human beings. Muscle tissue, skin, hair, fingernails and enzymes are all made from amino acids. L-aspartic acid is found in food, but it can also be made in your body, which makes it a nonessential amino acid.

D-Aspartic Acid

While L-aspartic acid is widely used in your body as a building block, the biological role of its counterpart or enantiomer, D-aspartic acid, is much more limited. D-aspartic acid occurs naturally within all animals, but in much lower amounts compared to L-aspartic acid. D-aspartic acid is known to accumulate in the pituitary gland, pineal gland and testes, and is involved in hormone production, according to the “Textbook of Functional Medicine.” More specifically, it stimulates the release of sex hormones from the pituitary gland and testosterone from the testes. Consequently, D-aspartic acid has become a popular supplement among bodybuilders, other serious athletes and elderly men who have low-circulating levels of testosterone.

Dietary Sources

Both forms of aspartic acid are found in food, although your body uses them in different ways as noted above. Exceptional animal-based sources of aspartic acid include beef, wild game, salmon, shrimp and eggs, according to the “Encyclopedia of Human Nutrition.” Good vegetable sources include sprouting seeds, legumes, most nuts, avocados and asparagus.