Tryptophan

 

Tryptophan Introduction

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.

Additionally, vitamin B6, vitamin C, folic acid, and magnesium are needed by the body for tryptophan metabolism.

Tryptophan Food Sources

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-.

FoodServing SizeKCalsAmount (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
Garlic 1 oz-wt 42.2 0.02 6.3
Green Peas-Boiled 1 cup 134.4 0.06 18.8
Barley 1 cup 270.0 0.12 37.5
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

[1]

Tryptophan Uses

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. [2]

Supplemental tryptophan, and its impact on serotonin levels in the human brain, has been a topic of ongoing research for the past thirty years. [3] “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. [4] 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. [5] 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. [6]

Positive tryptophan blood levels have been shown to regulate appetite behavior and overall food consumption in clinical settings. [7] 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.

Tryptophan Dosages

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 acidInfant 3 - 6 mo.Child 10 - 12 yr. Adults
Histidine 33 not known not known
Isoleucine 80 28 12
Leucine 128 42 16
Lysine 97 44 12
S-containing amino acids 45 22 10
Aromatic amino acids 132 22 16
Threonine 63 28 8
Tryptophan 19 4 3
Valine 89 25 14

[8]

Tryptophan Deficiencies and Toxicities

Tryptophan Deficiencies

Deficiencies of tryptophan are often paralleled to an inadequacy in the production of serotonin and may ultimately impact the transmission of certain nerve impulses. [9] 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)

Tryptophan Toxicities

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
  • Headaches
  • Muscle incoordination
  • Nausea

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. [10]

References

1. Source: “Tryptophan.” World’s Healthiest Foods. 2002-2005, George Mateljan Foundation. 12 Feb. 2005. http://www.whfoods.com/genpage.php?tname=nutrient&dbid=103

2. Maurizi CP, “The therapeutic potential for tryptophan and melatonin.” Med Hypoth. 1990; 31:233-242.

3. Van Praag HM et al. “Therapeutic indications for serotonin potentiating compounds, a hypothesis.” Biol Psychiat. 1987; 22:433-40.

4. Robertson J, Monte T. “Natural Prozac.” San Francisco, Harper 1997.

5. Shaw K, Turner J, Del Mar C. Tryptophan and 5-Hydroxytryptophan for depression. The Cochrane Database of Systematic Reviews 2002, Issue 1. Art. No: CD003198. DOI: 10.1002/14651858.CD003198.

6. Sandyk R. “L-Tryptophan in neuro psychiatric disorders, a review.” Int. J. Neuroscience. 1992. 67: 24-144.

7. Z Ernahrungswiss. “The effect of tryptophan on the regulation of food intake in normal and overweight persons.” [In German] 1994 Sep; 33(3):167-84.

8. Zest for life information page. “RDA of amino acids.” (1999-2003) http://www.pdrhealth.com/drug_info/nmdrugprofiles/herbaldrugs/101840.shtml (14 Sept. 2004).

9. Balch, Phyllis A., James F. “Amino Acids.” Prescription for Nutritional Healing. Ed. Amy C. Tecklenberg. New York, NY: Penguin Putnam Inc., 3rd Ed. 2000. 42-53.

10. EMS and Tryptophan Production: A Cautionary Tale, Trends in Biotech 12 346-352, September 1994.