Histidine, Methionine, Phenylalanine, Threonine and Valine: Roles, Food Sources and Supplements

Food sources and official figures

Amino acids come from animal foods such as meat, milk, fish and eggs and from plant foods such as soy, beans, legumes, nut butters and some grains. [4] Methionine and threonine generally occur in low amounts in plant products and are enriched in animal products. [5] Phenylalanine is found in all proteins. [2]

Verified daily requirements for these five amino acids from NIH ODS, EFSA, the NHS, MedlinePlus or Health Canada were not found, so none is quoted. Health Canada does give a scoring pattern for judging food protein (people aged 1 year and over, mg of amino acid per gram of protein): histidine 18, methionine plus cysteine 25, phenylalanine plus tyrosine 47, threonine 27, valine 32. [6] It is a yardstick for food protein, not a target for any person. A 2025 systematic review found limited requirement studies across life stages, especially pregnancy, infancy and childhood. [7]

Histidine

Histidine is required to make proteins, and the body uses it as the starting material for carnosine (in muscle and parts of the brain) and histamine (in the stomach, immune cells and parts of the brain). [8]

Methionine

Methionine is the other building block, with lysine, that the body uses to make carnitine. [9] It is also linked to homocysteine, an amino acid the body normally breaks down quickly using vitamin B12, vitamin B6 and folate; a high level can be a sign that this process is not working right or that B vitamins are lacking. [10] In homocystinuria, an inherited disorder, homocysteine and methionine build up in the blood. [11]

Methionine is not a treatment for high homocysteine; a clinician interprets homocysteine tests and decides on any treatment. Methionine supplements for any health goal: Proper evidence not found in the sources read (searched PubMed for methionine supplementation trials in humans; no systematic review of methionine supplements was read). See methionine, homocysteine and sulfur amino acids and vitamin B12.

Phenylalanine

Phenylalanine is found in all proteins. [2] PKU is an inherited disorder in which the body cannot break phenylalanine down; untreated, it can build up to harmful levels and cause intellectual disability and other serious problems. [2] The PKU diet limits high-protein foods because phenylalanine is in all protein. [2] In the US, the FDA says people with PKU should avoid or restrict aspartame, a sweetener that contains phenylalanine, and that newborns are routinely tested for PKU with a heel-prick test. [12] Full detail is on phenylalanine, PKU and aspartame. Phenylalanine supplements for mood, skin or pain: Proper evidence not found in the sources read.

Threonine

Threonine is on MedlinePlus's list of essential amino acids. [1] Threonine supplements: Proper evidence not found (searched PubMed for threonine supplementation trials in humans; no systematic review was read). Threonine in food generally follows the pattern above: richer in animal products. [5]

Valine

Valine is one of the three branched-chain amino acids and is found in many foods, particularly protein-rich foods such as milk, meat and eggs. [3] A meta-analysis found higher plasma levels of valine, leucine and isoleucine associated with later type 2 diabetes. [13] That is an association with blood levels, not proof that food or supplements cause diabetes. Valine on its own as a supplement: Proper evidence not found; see the BCAA guide for products that contain it with leucine and isoleucine.

Upper limits

No national agency has set upper intake levels for individual amino acids, according to a 2023 review. [14] Under an initiative of a nonprofit amino acid science council, researchers reported these values from clinical studies of relatively healthy adults.

Threonine and valine were not among the amino acids in that review's value list. These are research estimates, not official limits, not advice and not for people with metabolic disorders or kidney or liver disease.

Product quality, medicines and surgery

Single amino acid products vary in what they contain; see quality testing and certifications. For medicine questions, see medication interactions and amino acid supplements and medicines. Tell the surgical team about every supplement (supplements before surgery).