Suppression

Tryptophan

Category: Natural chemicals

Type

Voluntary

Introduction and description

 

Tryptophan (IUPAC-IUBMB abbreviation: Trp or W; IUPAC abbreviation: L-Trp or D-Trp;) is one of the 22 standard amino acids.

For many organisms (including humans), tryptophan is an essential amino acid. This means that it cannot be synthesized by the organism, it is needed to prevent illness or death, and it therefore must be part of their diet.

Amino acids, including tryptophan, act as building blocks in protein biosynthesis, and proteins are required to sustain life. In addition, tryptophan functions as a biochemical precursor for the following compounds in humans:

  • Serotonin (a neurotransmitter) -  Serotonin, in turn, can be converted to melatonin (a neurohormone).  Low Serotonin affects mood and produces aggression, whilst melatonin affects the sleep wake cycle.
  • Niacin – an essential vitamin, is synthesized from tryptophan via kynurenine and quinolinic acids as key biosynthetic intermediates.

Tryptophan Imbalance

Deprivation

Niacin deprivation is covered in the section on Niacin as a Vitamin, if we thus look more at serotonin, the main effects of deprivation are as follows

 

Aggression - Serotonin plays a role in the regulation of aggression in many invertebrates, although the effects are not always consistent between species and may depend on context. For example, serotonin modulates aggression in lobsters!  But the exact effect depends on factors such as the relative dominance of the animals involved. However, in many situations, low serotonin promotes aggression, whereas increased serotonin promotes prosocial behaviours. For example, increased serotonin levels are involved in the transformation in locusts from being solitary to collecting together in swarms. 

A wealth of data support the idea that low serotonin promotes aggression in mammals. There appears to be an additional factor in some mammals that is played by protein.  High poor quality protein, coupled with low tryptophan results in aggression, for example:

For dogs with dominance aggression, the addition of tryptophan to high-protein diets or change to a low-protein diet may reduce aggression. For dogs with territorial aggression, tryptophan supplementation of a low-protein diet may be helpful in reducing aggression.  PMID:  10953712

In one of two small clinical trials comparing tryptophan supplementation with placebo for the treatment of aggression, 12 aggressive patients with schizophrenia, whose aggression was not treated adequately with antipsychotic drugs, were given tryptophan and placebo for 4 weeks in a cross-over study. Tryptophan, relative to placebo, decreased incidents on the ward requiring intervention. In the second study on 20 aggressive psychiatric inpatients, tryptophan, relative to placebo, decreased the need for antipsychotics and sedatives.

 

Depression - Numerous studies have looked at the effect of acute tryptophan depletion (ATD) on mood in healthy participants, in healthy participants with a family history of depression, in patients with depression, in newly recovered patients on antidepressants and in recovered depressed patients off antidepressants. A number of reviews have summarized these studies. Results are somewhat variable, but some important patterns emerge.

  • In healthy individuals, there is little or no lowering of mood, although results can be quite variable between studies, with some lowering of mood seen more often in women than in men.
  • In healthy participants with a family history of depression, there is a lowering of mood.

The results of ATD studies suggest that lowering serotonin synthesis can lower mood in some circumstances, and that the magnitude of the effect tends to be greater in people with a greater susceptibility for depression. Low serotonin by itself is not enough to cause depressed mood, but of course it would be surprising if it did, given that the number of serotonin neurons in the brain is small. But what does affect the results is possibly the number of serotonin receptors, which can of course be destroyed by various factors including drugs

Insomnia -  Tryptophan is used to create melatonin and melatonin affects the sleep wake cycle, thus low melatonin levels may cause insomnia

Insomnia is a general sleep disorder and functional foods are known to play a key role in the prevention of insomnia. A number of studies have demonstrated that major insomnia risk factors in human being are less ‘functional foods’ in the diet…. Functional components in functional foods promoting sleep include tryptophan, GABA, calcium, potassium, melatonin, pyridoxine, L-ornithine and hexadecanoic acid.   PMID:  26005400

Melatonin is also involved in energy metabolism and body weight control in small animals, as well as libido, so there may be other knock on effects of tryptophan deprivation as yet unidentified.

As an interesting extra, in 1912 Felix Ehrlich demonstrated that yeast attacks the natural amino acids essentially by splitting off carbon dioxide and replacing the amino group with hydroxyl. By this reaction, tryptophan gives rise to tryptophol.  Tryptophol is an aromatic alcohol that induces sleep in humans. It is found in wine as a secondary product of alcoholic fermentation, but there is the possibility that the yeasts in our intestine may have a somewhat similar effect.

Overdose

 

Interestingly it appears that the effects of overdosing on tryptophan  are identical to those for deprivation.

In bacteria that synthesize tryptophan, for example, high cellular levels of this amino acid activate a repressor protein, which binds to the trp operon. Binding of this repressor to the tryptophan operon prevents transcription of downstream DNA that codes for the enzymes involved in the biosynthesis of tryptophan. So high levels of tryptophan prevent tryptophan synthesis through a negative feedback loop and, when the cell's tryptophan levels are reduced, transcription from the trp operon resumes. The genetic organisation of the trp operon thus permits tightly regulated and rapid responses to changes in the cell's internal and external tryptophan levels.

Overdosing is usually caused by using supplements, and cases have appeared which show additional risks exist with supplements:

a large outbreak of eosinophilia-myalgia syndrome (EMS) occurred in the U.S. in 1989, which caused 1,500 cases of permanent disability and at least thirty-seven deaths. After preliminary investigation revealed that the outbreak was linked to intake of tryptophan [supplements] …...  It was later found that the manufacturer had used genetically engineered bacteria to produce the contaminated batches of L-tryptophan

 Dietary sources

It is totally pointless and indeed, because of the risk of overdose undesirable, to use supplements.  Tryptophan is a routine constituent of most protein-based foods or dietary proteins.

It is particularly plentiful in chocolate, oats, dried dates, milk, yogurt, cottage cheese, red meat, eggs, fish, poultry, sesame, chickpeas, almonds, sunflower seeds, pumpkin seeds, spirulina, bananas, and peanuts.

Contrary to the popular belief that turkey has a particularly high amount of tryptophan, the amount of tryptophan in turkey is typical of most poultry. There is also a myth that plant protein lacks tryptophan; in fact, tryptophan is present in significant amounts in almost all forms of plant protein, and abundant in some”.

Tryptophan (Trp) Content of Various Foods

Food

Tryptophan
[g/100 g of food]

Protein
[g/100 g of food]

Tryptophan/Protein [%]

egg white, dried

1.00

81.10

1.23

spirulina, dried

0.93

57.47

1.62

cod, atlantic, dried

0.70

62.82

1.11

soybeans, raw

0.59

36.49

1.62

cheese, Parmesan

0.56

37.90

1.47

sesame seed

0.37

17.00

2.17

cheese, cheddar

0.32

24.90

1.29

sunflower seed

0.30

17.20

1.74

pork, chop

0.25

19.27

1.27

turkey

0.24

21.89

1.11

chicken

0.24

20.85

1.14

beef

0.23

20.13

1.12

oats

0.23

16.89

1.39

salmon

0.22

19.84

1.12

lamb, chop

0.21

18.33

1.17

perch, Atlantic

0.21

18.62

1.12

chickpeas, raw

0.19

19.30

0.96

egg

0.17

12.58

1.33

wheat flour, white

0.13

10.33

1.23

baking chocolate, unsweetened

0.13

12.9

1.23

milk

0.08

3.22

2.34

Rice, white, medium-grain, cooked

0.028

2.38

1.18

Quinoa, uncooked

0.167

14.12

1.2

Quinoa, cooked

0.052

4.40

1.1

potatoes, russet

0.02

2.14

0.84

tamarind

0.018

2.80

0.64

banana

0.01

1.03

0.87

 

 

References and further reading

see also

Soh NL, Walter GT (2011). "Tryptophan and depression: can diet alone be the answer?". Acta Neuropsychiatrica VL 23 (1): 1601–5215;. doi:10.1111/j.1601-5215.2010.00508.x.

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