- Health Library
- Research a Disease or Condition
- Lookup a Symptom
- Learn About a Test
- Prepare for a Surgery or Procedure
- What to do After Being Discharged
- Self-Care Instructions
- Questions to Ask Your Doctor
- Nutrition, Vitamins & Special Diets
Amino acids are organic compounds that combine to form proteins. Amino acids and proteins are the building blocks of life.
When proteins are digested or broken down, amino acids are left. The human body needs a number of amino acids to:
- Break down food
- Repair body tissue
- Perform many other body functions
Amino acids are classified into three groups:
- Essential amino acids
- Nonessential amino acids
- Conditional amino acids
Essential amino acids
- Essential amino acids cannot be made by the body. As a result, they must come from food.
- The nine essential amino acids are: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.
Nonessential amino acids
- "Nonessential" means that our bodies produce an amino acid, even if we don't get it from the food we eat.
- They include: alanine, asparagine, aspartic acid, and glutamic acid.
Conditional amino acids
- Conditional amino acids are usually not essential, except in times of illness and stress.
- They include: arginine, cysteine, glutamine, tyrosine, glycine, ornithine, proline, and serine.
You do not need to eat essential and nonessential amino acids at every meal, but getting a balance of them over the whole day is important.
Trumbo P, Schlicker S, Yates AA, Poos M; Food and Nutrition Board of the Institute of Medicine, The National Academies. Dietary reference intakes for energy, carbohydrate, fiber, fat, fatty acids, cholesterol, protein and amino acids. J Am Diet Assoc. 2002;102(11):1621-1630.
Escott-Stump S, eds. Nutrition and Diagnosis-Related Care. 6th ed. Philadelphia Pa: Lippincott Williams & Wilkins; 2008.
Reviewed By: A.D.A.M. Editorial Team: David Zieve, MD, MHA, and David R. Eltz. Previously reviewed by Alison Evert, MS, RD, CDE, Nutritionist, University of Washington Medical Center, Diabetes Care Center, Seattle, Washington (2/8/2011).