What is threonine?
Threonine abbreviation (symbol): Thr
Threonine Functions in the Human Body
Threonine is [1,2]:
- A building block of proteins
- A precursor of the amino acids serine and glycine; the later acts as an inhibitory neurotransmitter in the brain, which reduces spasticity
- A glucogenic amino acid — it can be converted into glucose 
- A ketogenic amino acid — it can be converted into ketones 
Threonine Rich Foods
- ANIMAL FOODS: meat, fish, cheese 
- PLANT FOODS: beans, lentils, wheat germ, seeds, baker’s yeast, spirulina 
Foods low in threonine include cereals (except wheat germ), fruits and vegetables .
Threonine deficiency in humans seems to be rare.
Oral L-threonine supplements without prescription (over-the-counter) are available.
Threonine Health Benefits
Threonine supplements are POSSIBLY EFFECTIVE in the treatment of spinal spasticity , phenylketonuria  and tyrosinemia type I .
Threonine supplements are POSSIBLY INEFFECTIVE in the treatment of amyotrophic lateral sclerosis (Lou Gehrig’s disease) .
There is INSUFFICIENT EVIDENCE about the effectiveness of threonine supplements in the prevention or treatment of anxiety, depression, multiple sclerosis and familial spastic paraparesis or in boosting immune system .
Threonine Safety: Side Effects, Toxicity
Threonine in doses up to 4 g/day for 12 months is POSSIBLY SAFE .
Side effects may include nausea, stomach upset, headache, skin rash .
Not enough studies have been done about the safety of threonine supplements during pregnancy and breastfeeding, so women in these periods should better avoid them .
Threonine supplements may reduce the effectiveness of memantime–a drug used in Alzheimer’s disease .
Who should avoid threonine?
Individuals with the following conditions may need to limit their threonine intake from foods and supplements:
- Methylmalonic acidemia 
- Propionic acidemia