Tryptophan is an essential amino acid, a subunit in protein molecules and a precursor to serotonin. The brain uses tryptophan to produce serotonin, a neurotransmitter largely responsible for feelings of happiness and well-being.
Tryptophan cannot be synthesised by the body and must be obtained through diet.
Tryptophan is a large, neutral amino acid (LNAA) that must compete with the other LNAAs including leucine, isoleucine, valine, phenylalanine, and threonine when crossing the blood-brain barrier. So these LNAAs can prevent tryptophan from entering the brain, resulting in low serotonin production. A high-protein meal, for example, leads to more amino acids in the bloodstream and more competition for tryptophan to enter the brain.
Hence, the Tryptophan/LNAA Ratio governs the amount of serotonin synthesis in the brain.
Lower levels:
– Competition from other amino acids prevents tryptophan from entering the brain, resulting in low serotonin production. A high-protein meal, for example, leads to more amino acids in the bloodstream and more competition for tryptophan to enter the brain.
– Scientists have found meals rich in carbohydrates promote an increase in insulin production, allowing muscle cells to absorb competing amino acids. This makes it easier for tryptophan to cross the blood-brain barrier, increasing serotonin levels in the brain. This may explain the association between depression and carbohydrate cravings.
– While meats such as turkey also contain the amino acid, the body can have a difficult time converting it to serotonin.
– Plant-based sources of tryptophan include leafy greens, sunflower seeds, watercress, soybeans, pumpkin seeds, mushrooms, broccoli, and peas.
– Some studies have reported decreases in the plasma tryptophan concentration and the tryptophan/large neutral amino acid (LNAA) ratio in patients with schizophrenia.
– A diet high in protein and animal foods can limit serotonin production. A healthy approach for ideal levels of tryptophan in the brain is to focus on plant proteins along with generous amounts of complex carbohydrates, such as vegetables, fruits, whole grains, and legumes. With this pattern in place, there is sufficient serotonin produced to maintain feelings of well-being.
Note: We have not come across conservative recommendations to increase or decrease blood tryptophan levels that are supported by scientific studies and there are very few published studies in humans which manipulate plasma tryptophan levels by dietary means or supplementing.
Higher levels:
Elevations in the tryptophan/LNAA ratio could cause manic tendencies by promoting elevated serotonin production.
Note: We have not come across conservative recommendations to increase or decrease blood tryptophan levels that are supported by scientific studies and there are very few published studies in humans which manipulate plasma tryptophan levels by dietary means or supplementing.
References:
– https://www.ncbi.nlm.nih.gov/pubmed/20699195
– https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1601-5215.2010.00508.x
– https://www.ncbi.nlm.nih.gov/pubmed/12499331
– https://www.pcrm.org/good-nutrition/food-and-mood
– https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2077351/
– https://www.ncbi.nlm.nih.gov/pubmed/12499331
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