Aspartic acid supplements are considered safe for everyone except pregnant women and infants. While you shouldn't need to worry about the aspartic acid in a protein shake, remember that it's only one source of this amino acid in your diet. If you follow a high-protein diet, you take other supplements that contain aspartic acid or your protein shake is fortified with extra aspartic acid, you could consume an unhealthy amount. Aspartic acid becomes toxic to nerves if its levels get too high, so talk to your doctor before using supplements to be sure they’re safe for you.
Aspartic Acid Overview
Aspartic acid exists in two forms: L-aspartic acid and D-aspartic acid. The two forms share the same chemical components, but the individual particles are attached differently. As a result, L- and D-aspartic acid form mirror images of one another. This change in structure determines the jobs each performs.
Your body uses L-aspartic acid to build proteins, produce energy and help detoxify ammonia byproducts left over from protein metabolism. D-aspartic acid helps stimulate specific nerve impulses that influence learning and memory. It also triggers the release of hormones, such as growth hormone and testosterone.
Some neurotransmitters in your central nervous system inhibit nerve impulses. Other neurotransmitters, including D-aspartic acid, enhance or trigger nerve impulses. If levels of these excitatory neurotransmitters get too high and out of balance, they can become toxic and damage nerves.
Protein shakes may contain the artificial sweetener aspartame, which is made from aspartic acid. Consuming a large amount of aspartame at one time will temporarily boost blood levels of aspartic acid. However, the amount of aspartame most people consume shouldn’t contribute enough aspartic acid to increase the risk of problems, according to a 2007 report in Critical Reviews in Toxicology.
The safety of aspartic acid has been studied more than many other amino acids due to concerns over aspartame. Aspartic acid did not cause any health problems in doses that were two to four times higher than the amount found in a typical dose of pure L- and D-aspartic acid supplements, according to studies cited by the Institute of Medicine.
Infants and pregnant women should avoid all supplemental forms of aspartic acid. Research has produced conflicting results, but some studies using animals found that aspartic acid damaged nerves in the brains of infants.
Aspartic Acid in Protein Shakes
If your protein shake is fortified with aspartic acid, the amount added will be on the label, but this doesn't reflect the total content. Any aspartic acid from casein, whey or soy protein in the supplement isn't reported separately in the nutrition facts.
The U.S. Department of Agriculture reports that generic, soy-based protein powder has 3 grams of aspartic acid in one scoop. A cup of pure, dried whey supplies 2 grams of aspartic acid.
While the USDA doesn't report isolated casein protein, you can get an idea of the amount of aspartic acid it may contain based on regular milk. An entire quart of low-fat milk fortified with extra protein only has 3 grams of aspartic acid. By comparison, the Institute of Medicine noted that 8 grams of aspartic acid daily didn’t cause any adverse effects.