VITAMINS & SUPPLEMENTS · GUIDE
Protein and Amino Acid Glossary: Terms From Anabolic to Zwitterion
Plain-language definitions of protein and amino acid terms, from anabolic and BCAA to PKU and zwitterion, each with a link to the page that covers it in depth.
Content last updated . This page has not been medically reviewed.
Back to Amino Acids & ProteinHow to use this glossary
Protein and amino acid writing is full of short technical words. This page defines the ones you are most likely to meet on labels, in articles and at a clinic visit, in alphabetical order. Each entry is short on purpose and points to the page that covers the topic properly. It is general information, not advice for any one person. For personal questions, talk to a clinician, pharmacist or registered dietitian. The overview page, Amino Acids & Protein, shows how the whole library fits together.Numbers appear only where a named source gave them, with the country or body and the year. Where our sources did not describe something, we say so.
Terms from A to Z
| Term | Plain meaning | Read more |
|---|---|---|
| Amino acid | A molecule that combines with others to form proteins. [1] | More about Amino acid → |
| AMDR (Acceptable Macronutrient Distribution Range) | A range for the share of daily energy that comes from a nutrient. Health Canada's 2005-based table lists 10 to 35 percent of energy from protein for people 19 years and over. [2] | More about AMDR (Acceptable Macronutrient Distribution Range) → |
| Anabolic | Describes anabolism, the building-up side of metabolism; one review says it supports the synthesis of organic matter using energy-carrier molecules. [3] | More about Anabolic → |
| "Anabolic window" | A popular phrase for a claimed short period after exercise when protein is said to matter most. It is a marketing-style claim, so it has its own claim check. | More about "Anabolic window" → |
| Anaphylaxis | A rare, life-threatening allergic reaction. MedlinePlus says it is a medical emergency and to call 911 if someone has its symptoms. [4] | More about Anaphylaxis → |
| Aspartame | An artificial sweetener that contains phenylalanine; MedlinePlus says people with PKU should avoid products containing it. [5] | More about Aspartame → |
| BCAA (branched-chain amino acids) | Leucine, isoleucine and valine, the three amino acids that get this name. One review notes whey protein is a rich source of them. [6] | More about BCAA (branched-chain amino acids) → |
| Catabolic | Describes catabolism, the breaking-down side of metabolism, which one review says breaks down organic matter to obtain energy. [3] | More about Catabolic → |
| Complete protein | An everyday phrase, not a formal score, for a protein source with all the essential amino acids. The British Heart Foundation says other plant sources lack some of them, and that eating a variety of plant protein each day will supply all you need. [7] | More about Complete protein → |
| Conditionally essential amino acid | One that is usually not essential, except in times of illness and stress. MedlinePlus lists arginine, cysteine, glutamine, tyrosine, glycine, proline and serine. [1] | More about Conditionally essential amino acid → |
| DIAAS (Digestible Indispensable Amino Acid Score) | A protein quality score that takes digestibility of each essential amino acid into account. One 2020 paper (authors employed by a food ingredient company) calculated it for animal and plant proteins and rated whey and soy as high quality (average 75 or more). [8] | More about DIAAS (Digestible Indispensable Amino Acid Score) → |
| Digestive enzyme | A protein your body makes to break food down. NIDDK says the pancreas makes a digestive juice with enzymes that break down carbohydrates, fats and proteins. [9] | More about Digestive enzyme → |
| Essential amino acid | One the body cannot make, so it must come from food. MedlinePlus names nine: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. [1] | More about Essential amino acid → |
| 5-HTP | A compound made from tryptophan on the way to serotonin and melatonin, sold as a supplement. Memorial Sloan Kettering says people taking SSRIs, MAOIs or tricyclic antidepressants should avoid it without a physician's supervision. [10] | More about 5-HTP → |
| Hepatic encephalopathy | Loss of full brain function when the liver cannot remove toxins from the blood. [11] | More about Hepatic encephalopathy → |
| Homocysteine | An amino acid measured in a blood test. [12] | More about Homocysteine → |
| Hydrolysate (whey) | Whey protein that has been partly digested in advance; one review describes it as partially digested for ease of metabolism and hypo-allergenicity. [6] | More about Hydrolysate (whey) → |
| Isolate and concentrate (whey) | One review describes whey concentrate as having fat and lactose along with 29 to 89 percent protein, and whey isolate as 90 percent protein. [6] | More about Isolate and concentrate (whey) → |
| Kwashiorkor | A form of malnutrition that occurs when there is not enough protein in the diet. [13] | More about Kwashiorkor → |
| Lactose | The sugar in milk. The NHS says it is found in foods containing animal milk (dairy products). [14] | More about Lactose → |
| Maple syrup urine disease | An inherited disorder in which the body cannot process certain amino acids properly. [15] | More about Maple syrup urine disease → |
| NAC (N-acetylcysteine) | A cysteine-related compound. The FDA has determined it is excluded from the dietary supplement definition in the US, and has described enforcement discretion for certain products. [16] | More about NAC (N-acetylcysteine) → |
| Nonessential amino acid | One the body can produce even if food does not supply it. [1] | More about Nonessential amino acid → |
| Peptide | A short chain of amino acids, typically 2 to 50, joined by peptide bonds, according to NHGRI. [17] | More about Peptide → |
| PKU (phenylketonuria) | A rare inherited condition in which a baby is born without the ability to break down the amino acid phenylalanine. MedlinePlus says treatment needs close supervision by a registered dietitian or health care provider. [5] | More about PKU (phenylketonuria) → |
| PRI (Population Reference Intake) | The European term for a protein intake level. EFSA's 2012 value for healthy adults, as reproduced by the European Commission, is 0.83 g per kg of body weight per day. [18] | More about PRI (Population Reference Intake) → |
| Protein | MedlinePlus describes proteins as the building blocks of life, with a basic structure that is a chain of amino acids. [19] | More about Protein → |
| RDA (Recommended Dietary Allowance) | A reference intake level. In Health Canada's table, RDAs are shown in bold and Adequate Intakes in ordinary type; for adults 19 to 30 the protein RDA/AI is 0.80 g/kg/day, which is 56 g/day for males and 46 g/day for females. These are published reference values for groups, not personal targets. [2] | More about RDA (Recommended Dietary Allowance) → |
| Sarcopenia | Age-related muscle loss, as the British Heart Foundation puts it. [7] | More about Sarcopenia → |
| Serotonin syndrome | A potentially life-threatening reaction to certain medicines. [20] | More about Serotonin syndrome → |
| Standardized ileal digestibility | The digestibility measure used with DIAAS in the 2020 paper above. [8] | More about Standardized ileal digestibility → |
| UL (Tolerable Upper Intake Level) | The highest intake not expected to cause harm. A 2023 review stated that national health agencies had not set a UL for amino acids because of a lack of well-conducted human dose-response trials. [21] Health Canada's protein UL is listed as "ND" (not determined). [2] | More about UL (Tolerable Upper Intake Level) → |
| Zwitterion | A molecule with equal numbers of positively and negatively charged groups; amino acids are a particularly important family of them. [22] | More about Zwitterion → |
Terms not defined here
We did not read a suitable source for a few terms, such as PDCAAS and nitrogen balance, so they are not defined on this page rather than defined from memory. The page on how protein requirements are set covers how requirements are worked out.Frequently asked questions
Is this glossary medical advice?
No. It explains words in plain language. Whether a protein or amino acid product is suitable for you depends on your health, your medicines and your diet, so ask a clinician, pharmacist or dietitian. [23]
What is the difference between a protein, a peptide and an amino acid?
Amino acids are molecules that combine to form proteins. [1] NHGRI describes a peptide as a short chain of amino acids, typically 2 to 50. [17] See Protein vs amino acids vs peptides.
Which amino acids are essential?
MedlinePlus lists nine: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. [1]
Is "complete protein" an official score?
No. It is an everyday phrase. Formal scores such as DIAAS exist; one 2020 paper rated whey and soy as high quality on that score. [8]
Where do I find official protein intake levels?
Health Canada lists a protein RDA/AI of 0.80 g/kg/day for adults 19 and over (its 2005-based table), [2] and EFSA's 2012 PRI for healthy adults is 0.83 g per kg per day. [18] Details are on the intake levels page.
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
A word on safety
Several terms above point to real safety issues: kidney and liver disease, PKU, allergy and medicine interactions. NCCIH notes that supplements may interact with medications or pose risks if you have certain medical problems or are going to have surgery. [23] The Safety Quick Reference collects these points on one page. Never stop or change a prescribed medicine on the basis of a glossary; ask the prescriber or a pharmacist first.
Education, not medical advice. This page is for general information. It does not diagnose or treat any condition and is not a substitute for care from a qualified health professional. Natural does not automatically mean safe. Ask a clinician or pharmacist before changing your care, especially if you take medication, are pregnant or breastfeeding, or have a health condition.