The human body cannot make threonine and must obtain it from the diet. This amino acid may play a role in immune system function and a severe deficiency causes neurological symptoms in experimental animals.
Vegetarian sources: Weight for weight, soya protein concentrate, soya flour, tofu, peanuts and almonds are as rich in threonine as animal proteins.
Tryptophan cannot be made by the human body and must be obtained from the diet. It is best known for its role in the production of serotonin, a brain neurotransmitter involved in sleep promotion. The concentration of serotonin in the brain has been shown to be directly proportional to the concentration of tryptophan. Carbohydrate ingestion encourages the uptake of tryptophan into the brain. Tryptophan can also be converted to vitamin B3 within the body, and it is the precursor of the antioxidant and ‘anti-jet lag’ substance melatonin produced by the gut and the pineal gland.
Tryptophan metabolism is highly dependent on vitamin B6. Due to the tryptophan-lowering effects of oestrogen, it has been estimated that women on the contraceptive pill need a minimum of 20 mg vitamin B6 per day (10 times the RDA) to metabolize tryptophan normally.
One of the most important uses of tryptophan supplements by natural medicine and orthodox medical practitioners is as an anti-depressant. Suicidal patients often show a significant decrease in serotonin levels. It is often said that supplements of tyrosine in the morning and tryptophan at night can probably mimic the effects of most pharmaceutical antidepressants.
Suggested dosage to aid sleep: 500 mg 30 minutes before bed-time. At the time of writing a doctor’s prescription may be required to obtain tryptophan supplements since these were withdrawn from general sale in the UK and US in 1990 after supplies which were produced using genetically engineered bacteria led to cases of eosinophilia myalgia syndrome. (See Genetic engineering)
Vegetarian sources: Weight for weight, soya protein concentrate, soya flour, tofu, almonds, peanuts, pumpkin seeds, sesame seeds, tahini, almonds and sunflower seeds are as rich in tryptophan as animal proteins.
Tyrosine is made in the body from the amino acid phenylalanine and is the raw material of the three catecholamines: adrenaline (epinephrine), noradrenaline (norepinephrine) and dopamine. These are involved in alertness, concentration and coping with stress. Tyrosine is also used to make thyroid hormone, which is needed for growth and energy metabolism.
Some researchers have used tyrosine supplements in parkinsonism, and claim to have obtained better clinical results with fewer side effects than conventional treatments.
Low levels of catecholamines can lead to mental apathy, low blood pressure and depression. If these low levels are due to a tyrosine deficiency, tyrosine supplementation can increase them, thus improving all these symptoms. Suggested dose: 1 gram on rising in the morning.
Tyrosine supplements should not be taken by people on MAO inhibitor drugs or individuals with schizophrenia or malignant melanoma.
Vegetarian sources: Weight for weight, soya protein concentrate, soya flour, tofu, peanuts, almonds, pumpkin seeds, peanuts and peanut butter are as rich in tyrosine as animal proteins.
Valine is one of the branched chain amino acids. It cannot be made by the human body, and is particularly involved in stress, energy and muscle metabolism.
Supplements of this amino acid may help to reverse hepatic coma, in which patients with cirrhosis of the liver are suffering from increased amounts of ammonia and tryptophan or tyrosine in the brain. Valine competes with tryptophan and tyrosine for entry into the brain, and, because it can be converted to glucose, also acts as a fuel in brain metabolism.
Branched chain amino acids (BCAAs) decrease the rate of breakdown and utilization of other amino acids.
Vegetarian sources: Weight for weight, soya protein concentrate, soya flour, tofu, pumpkin seeds and peanuts are as rich in valine as animal proteins.