Not to be confused with 5-hydroxy-tryptophan (5-HTP), tryptophan remains among the most popular of all amino acids. This is due, in large part, to its relative abundance in turkey, coupled with the popular assumption that this essential amino acid is the cause of Thanksgiving Day drowsiness. But this speculation is often refuted by experts. Although tryptophan does provide for neurotransmitters responsible for sleep, excessive carbohydrate and alcohol consumption are usually the culprits of Thanksgiving lethargy. Research has indicated that food sources of tryptophan only work as a sleep-inducing agent when consumed on an empty stomach.
Tryptophan is classified as having the lowest biological value of all essential amino acids. Due to this characteristic, the dietary intake of tryptophan is lower than any other amino acid. A typical American diet provides anywhere from 1 - 1.5 grams per day. Other amino acids, mainly phenylalanine and tyrosine, compete for individual absorption privileges with tryptophan. Supplemental tryptophan is often the only accurate method of increasing one’s blood levels of this essential amino acid.
Tryptophan may exist freely in the blood and can be carried via protein to various binding sites. This is a unique trait not seen in other essential or nonessential amino acids. Tryptophan also serves as the precursor to the nutrients niacin (B3) and picolinic acid. Picolinic acid exists as the body’s prime chelator of many of the most vital minerals found in human anatomy. Serotonin, a vital neurotransmitter influential in the regulation of mood and sleep, is equally dependant on the adequate intake of tryptophan.
Being the least abundant amino acid found in foods, most dietary foods possess an uneven distribution of tryptophan. The best dietary sources of this essential amino acid include cottage cheese, brown rice, meat, peanuts, and soy protein. Food sources below represent the highest biological valued foods containing the essential amino acid tryptophan-.
|Food||Serving Size||KCals||Amount (g)||(%) DV|
|Shrimp, MixedSpecies, Steamed, Boiled||4 oz-wt||112.3||0.33||103.1|
|Tamari (Soy Sauce)||1 tbs||10.8||0.03||9.4|
|Mushrooms, Crimini, Raw||5 oz-wt||31.2||0.08||25.0|
|Cod, Pacific, Fillet, Baked, Broiled||4 oz-wt||119.1||0.29||90.6|
|Tuna, Yellowfin, Baked/Broiled||4 oz-wt||157.6||0.38||118.8|
|Snapper, Baked||4 oz-wt||145.2||0.33||103.1|
|Halibut, Baked/Broiled||4 oz-wt||158.8||0.34||106.3|
|Greens, Mustard, Boiled||1 cup||21.0||0.04||12.5|
|Chicken Breast, Roasted||4 oz-wt||223.4||0.39||121.9|
|Scallops, Baked, Broiled||4 oz-wt||151.7||0.26||81.3|
|Spinach (boiled, with salt)||1 cup||41.4||0.07||21.9|
|Turkey Breast, Roasted||4 oz-wt||214.3||0.35||109.4|
|Tofu, Raw||4 oz-wt||86.2||0.14||43.8|
|Lamb, loin, roasted||4 oz-wt||229.1||0.35||109.4|
|Beef Tenderloin, Lean Broiled||4 oz-wt||240.4||0.36||112.5|
|Liver, Calf||4 oz-wt||187.1||0.25||78.1|
|Chinook Salmon Fillet-Baked/Broiled||4 oz-wt||261.9||0.33||103.1|
|Soybeans, Cooked||1 cup||297.6||0.37||115.6|
|Asparagus, Boiled||1 cup||43.2||0.05||15.6|
|Broccoli (pieces, steamed)||1 cup||43.7||0.05||15.6|
|Seeds, Mustard||2 tsp||35.0||0.04||12.5|
|Mozzarella Cheese, Part Skim, Shredded||1 oz-wt||72.1||0.08||25.0|
|Cauliflower (boiled, drained)||1 cup||28.5||0.03||9.4|
|Greens, Turnip, Cooked||1 cup||28.8||0.03||9.4|
|Egg, Hen, Whole, Boiled||1 each||68.2||0.07||21.9|
|Collard Greens, Boiled, Drained||1 cup||49.4||0.05||15.6|
|Peppermint Leaves, Fresh||1 oz-wt||19.9||0.02||6.3|
|Parsley, Fresh||1 oz-wt||10.2||0.01||3.1|
|Chard, Boiled||1 cup||35.0||0.03||9.4|
|Milk, Cow, 2%||1 cup||121.2||0.10||31.3|
|Kale, Fresh, Boiled||1 cup||36.4||0.03||9.4|
|Beans, Kidney, Cooked||1 cup||224.8||0.18||56.3|
|Beans, Black, Boiled||1 cup||227.0||0.18||56.3|
|Beans, Lima, Cooked||1 cup||216.2||0.17||53.1|
|Split Peas, Boiled||1 cup||231.3||0.18||56.3|
|Cucumber, Raw||1 cup||13.5||0.01||3.1|
|Beans, Navy, Cooked||1 cup||258.4||0.19||59.4|
|Beans, Pinto, Cooked||1 cup||234.3||0.17||53.1|
|Miso (Soybean)||1 oz||70.8||0.05||15.6|
|Lentils, Boiled||1 cup||229.7||0.16||50.0|
|Green Snap/String Beans, Boiled||1 cup||43.8||0.03||9.4|
|Brussels Sprouts, Boiled||1 cup||60.8||0.04||12.5|
|Milk, Goat||1 cup||167.9||0.11||34.4|
|Lettuce, Romaine||2 cup||15.7||0.01||3.1|
|Wheat, Bulgur, Cooked||1 cup||151.1||0.09||28.1|
|Apricots, Raw||1 each||16.8||0.01||3.1|
|Pumpkin Seeds, Dried||0.25 cup||186.7||0.11||34.4|
|Seeds, Sesame||0.25 cup||206.3||0.12||37.5|
|Oats, Whole Grain||1 cup||145.1||0.08||25.0|
|Spelt WholeGrain Flour||2 oz-wt||189.0||0.10||31.3|
|Celery, Raw||1 cup||19.2||0.01||3.1|
|Beans, Garbanzo, Cooked||1 cup||269.0||0.14||43.8|
|Buckwheat Groats, Cooked||1 cup||154.6||0.08||25.0|
|Onions, Raw||1 cup||60.8||0.03||9.4|
|Sunflower Seeds, Dried||0.25 cup||205.2||0.10||31.3|
|Green Peas-Boiled||1 cup||134.4||0.06||18.8|
|Peanuts, Raw||0.25 cup||207.0||0.09||28.1|
|Red Bell Peppers (sliced, raw)||1 cup||24.8||0.01||3.1|
|Beets, Boiled||1 cup||74.8||0.03||9.4|
|Yogurt, Cow Milk, Low Fat||1 cup||155.1||0.06||18.8|
|Quinoa, Dry||0.25 cup||158.9||0.06||18.8|
|Squash, Winter, All Varieties||1 cup||80.0||0.03||9.4|
|Eggplant, Boiled||1 cup||27.7||0.01||3.1|
|Nuts, Cashews, Raw||0.25 cup||196.6||0.07||21.9|
|Millet, Cooked||1 cup||285.6||0.10||31.3|
|Nuts, Walnuts||0.25 cup||163.5||0.05||15.6|
|Cabbage (shredded, boiled)||1 cup||33.0||0.01||3.1|
|Potato, Baked, with Skin||1 cup||133.0||0.04||12.5|
|Almonds, whole, natural||0.25 cup||212.7||0.06||18.8|
|Squash, Summer, All Varieties||1 cup||36.0||0.01||3.1|
|Rice, Long Grain Brown, Cooked||1 cup||216.4||0.06||18.8|
|Rye Cereal, Cream of, Cooked||1 cup||108.6||0.03||9.4|
|Tomato, Red, Raw, Ripe||1 cup||37.8||0.01||3.1|
Tryptophan’s most popular mode of action in human physiology may be its beneficial sleep-inducing properties. Although supplemental tryptophan is often deemed ineffective when taken alone, its synergism with melatonin cannot be ignored. This combination has proven extremely effective in double-blind clinical trials. Results indicate that low dose melatonin (0.5 - 1 milligram), when taken in conjunction with L-tryptophan (500 - 1000 milligrams), may prove effective for persons suffering from acute insomnia rather than chronic sleep disorders. 
Supplemental tryptophan, and its impact on serotonin levels in the human brain, has been a topic of ongoing research for the past thirty years.  “Serotonin Deficiency Syndrome,” in particular, is a condition which has received a great deal of attention by biochemists. “Serotonin Deficiency (Shortage) Syndrome,” or SDS, is characterized by various emotional and behavioral disorders. Signs of SDS include depression, PMS, anxiety, insomnia, aggression, suicidal behavior, and obsessive-compulsive tendencies.
It is theorized that this deficiency is often coupled with inadequate plasma levels of tryptophan. Supplemental tryptophan may help to alleviate this chronic deficiency, allowing the brain’s neural circuits to function more effectively.  This is of great interest to mental health, as studies continually highlight serotonin’s ability to initiate feelings of well being, calmness, relaxation, confidence, and concentration.
Because of their mood elevating effects, 5-HTP and tryptophan are classified as natural alternatives to traditional antidepressants. Both 5-HTP and L-tryptophan proved significantly better at alleviating certain types of depression in nearly 108 various clinical trials.  Trials were randomized and included patients suffering from unipolar depression or dysthymia. Tryptophan in its varying forms appears to be a safe and beneficial treatment of depressive disorders in adults when administered by a medical practitioner.
Other neurological disorders, such as Parkinson's Disease and Alzheimer's disease, may also derive benefit from supplemental tryptophan. Recent studies have indicated that inadequate serotonin levels may be directly responsible for the depression that often accompanies the movement disorders in certain Parkinsonian patients. L-tryptophan may be useful in correlation with the standard L-Dopa/deprenyl treatment for Parkinson’s. The heightened irritability, aggression, and mental decline of Alzheimer’s patients (often referenced as dementia), may also be improved by this essential amino acid. 
Positive tryptophan blood levels have been shown to regulate appetite behavior and overall food consumption in clinical settings.  Again, this finding is directly associated with tryptophan’s direct impact upon serotonin uptake within the brain. An increased the brain’s serotonin levels/output is attributed to the lowering of anxiety, and with promoting a sense of well-being; a result often found in comfort eating. Ironically, the only diet that is beneficial for improving brain tryptophan levels is a high carbohydrate low protein diet. Below is an example of this paradox:
Sufficient levels of tryptophan = a positive release of serotonin and carbohydrates assist in the release of insulin and insulin enhances serotonin levels. This additional serotonin promotes the storage of body fat by enhancing the conversion of fats, carbohydrates, and amino acids.
Areas of ongoing study into the benefits of monitored tryptophan supplementation include: hyperactivity in children, alleviating stress, migraine headaches, eating disorders, schizophrenia, and pain syndromes.
The Recommended Daily Allowance (RDA) of tryptophan is set at 200 milligrams per day and has been established as the minimal amount required per day to ward of deficiencies of this nutrient. Dosages, however, often vary and are dependant upon the type and severity of a particular condition.
The U.S. National Academy of Sciences recommends that healthy people achieve .36 grams of highly bioavailable protein for each pound of bodyweight - equaling 0.8 grams of protein, per kilogram of bodyweight. Listed below are the Recommended Daily Allowances (RDAs) for the majority of amino acids, including Tryptophan.
|Requirement - mg. per kg. of body weight|
|Amino acid||Infant 3 - 6 mo.||Child 10 - 12 yr.||Adults|
|Histidine||33||not known||not known|
|S-containing amino acids||45||22||10|
|Aromatic amino acids||132||22||16|
Deficiencies of tryptophan are often paralleled to an inadequacy in the production of serotonin and may ultimately impact the transmission of certain nerve impulses.  Insufficient tryptophan levels are also attributed to pellagra, depression, insomnia, and even suicidal behaviors. The metabolic disturbances carcinoid syndrome and Hartnups disease are also attributed to a prolonged deficiency of this particular amino acid.
When this deficiency is coupled with a deficiency of niacin, symptoms referred to as the Four “Ds” may arise and include the symptoms of dermatitis, diarrhea, dementia, and death. (See Vitamin B3)
Historically, tryptophan has had a low occurrence of reported toxicity. Side effects resulting from acute toxicity include gastrointestinal distress, headache, and anxiety. Prolonged toxicities may result in the following symptoms:
- Blurry vision
- Daytime drowsiness
- Dry mouth
- Muscle incoordination
Eosinophilia-Myalgia Syndrome (EMS) was an allergic reaction caused by the toxic by-products of a specific bacterial strain used to synthesize tryptophan into a supplemental form. This condition was caused by the bacteria rather than the actual amino acid L-tryptophan. For this reason, EMS has been omitted from the toxicities section. 
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