What it does in the body
- Tyrosine and catecholamine neurotransmitter precursor (dopamine, norepinephrine, epinephrine)
- Melanin synthesis for skin/hair pigmentation
- Thyroid hormone precursor (via tyrosine)
- Natural pain modulation (D-phenylalanine inhibits enkephalinase)
- Protein structure (aromatic stacking in protein folding)
How much you need (Daily Value)
| Group | Recommended | Source |
|---|---|---|
| Adult male | 25mg/kg/day combined phe + tyr (~1.75g for 70kg) | WHO/FAO/UNU |
| Adult female | 25mg/kg/day (~1.5g for 60kg) | WHO/FAO/UNU |
| Pregnancy | 31mg/kg/day | WHO |
| Children | 27-54mg/kg/day depending on age | WHO |
| Older adults | 25mg/kg/day | WHO |
Richest food sources
| Food | Amount | Where |
|---|---|---|
| Soybeans (cooked) | 0.8g per 100g | east-asia |
| Chicken breast (cooked) | 1.1g per 100g | global |
| Beef (lean, cooked) | 1.0g per 100g | global |
| Salmon (cooked) | 0.9g per 100g | global |
| Eggs (whole) | 0.7g per 100g | global |
| Almonds | 1.1g per 100g | middle-east |
| Peanuts | 1.4g per 100g | global |
| Mung beans (cooked) | 0.4g per 100g | south-asia |
If you don't get enough
Mild: Low mood, reduced motivation, mild cognitive fog, fatigue
Moderate: Depression, poor memory and concentration, reduced stress tolerance, skin depigmentation
Severe: Severe neurological dysfunction, profound depression, vitiligo-like changes, growth retardation in children
Time to onset: Neurotransmitter effects within days to weeks; visible changes over months
Too much
Upper limit: No UL for healthy adults; toxic in PKU patients at >600 µmol/L plasma. Supplemental doses >5g/day may cause headaches
In PKU: intellectual disability, seizures, behavioral problems, musty odor. In healthy adults: headaches, anxiety, hypertension with high supplementation
How well you absorb it
90-95% across gut epithelium; competes with other large neutral amino acids for brain uptake
Helped by: Carbohydrate co-ingestion (insulin promotes amino acid uptake), Vitamin B6 (cofactor for aromatic amino acid decarboxylase), Iron and BH4 cofactor
Hindered by: Other large neutral amino acids (leucine, isoleucine, valine) compete for BBB transport, BH4 deficiency
Cooking & storage
Stable during normal cooking. Aspartame (containing phenylalanine) degrades at temperatures above 86°C, relevant for PKU patients tracking intake from processed foods.
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