What Is Tryptophan?
Tryptophan is an amino acid. Amino acids are molecules that your body uses to make proteins, which help you to:
- Break down food
- Grow and repair your tissues
- Make hormones and brain chemicals (neurotransmitters)
- Build muscles
- Maintain your skin, hair, and nails
- Have a healthy digestive system
Tryptophan is one of the nine essential amino acids. Essential amino acids can't be made by your body, so you have to get them from your food. The nine essential amino acids are:
Tryptophan plays a part in many aspects of your health. For instance, it helps keep your nitrogen levels in balance and also helps make a few brain chemicals, like serotonin and melatonin. Serotonin is a hormone that helps regulate mood, sleep patterns, and appetite. Melatonin is a hormone that helps keep your body clock regular, so, for instance, you feel sleepy when it's time to sleep.
Tryptophan was discovered in the early 1900s after it was isolated from casein, a protein found in milk. Its molecular structures were determined a few years later. In nature, the same molecule can be arranged in different forms, called isomers. Tryptophan has two isomers: L-tryptophan and D-tryptophan.
L-tryptophan is the form that your body uses to make proteins. The structure of D-tryptophan is the mirror image of L-tryptophan, but this small change makes it so that your body doesn't usually use it. Studies in mice, pigs, chickens, and dogs show that the body can use D-tryptophan if it doesn't have any L-tryptophan to use. But D-tryptophan doesn't work as well for the body as L-tryptophan. For instance, mice who eat food with D-tryptophan and no L-tryptophan weigh about 20% less than mice who eat regular food sources.
Benefits of Tryptophan
Tryptophan is vital for a wide variety of your body's functions, such as processes that affect your mood, thinking, and behavior. Tryptophan has an impact on:
- Mood, such as whether you have anxiety or depression or feel aggressive
- Sleep and regulation of your body clock
- Pain sensations
- Learning, memory skills, and visual thinking
How much tryptophan per day?
Tryptophan is found in both plant and animal proteins, although animal proteins tend to have more and it's easier for your body to break it down and use it. Animal-based proteins like meat, poultry, fish, eggs, cheese, and yogurt are called complete proteins because they have all nine of the essential amino acids, including tryptophan. Some plant-based proteins like quinoa, soy, and buckwheat (groats) are also complete proteins that have tryptophan.
Only small amounts are necessary for healthy nutrition in most people. In the U.S., the average person takes in about 826 milligrams a day of tryptophan, while the estimated average requirement (EAR) for most adults is 4-5 milligrams per kilogram of body weight per day. For a 70-kilogram (154-pound) adult, that's about 280-350 milligrams a day. The EAR for infants and children up to about 2 years old is 13-17 milligrams per kilogram of body weight per day.
Many foods that you probably eat are good sources of tryptophan. Here are some examples, with the serving size of the food and the estimated amount per serving:
Legumes and tofu
- Tofu, 1/2 cup, 296 milligrams
- Soybeans (edamame), 1 cup, 270 milligrams
Fish and seafood
- Tilapia, 3 ounces, 231 milligrams
- Tuna (canned white), 3 ounces, 252 milligrams
- Snapper, 3 ounces, 250 milligrams
- Salmon (farmed, Atlantic), 3 ounces, 211 milligrams
- Lobster, 3 ounces, 248 milligrams
- Crab (blue), 3 ounces, 192 milligrams
- Oysters (Pacific), 3 ounces, 90 milligrams
Meat and poultry
- Pork roast, 3 ounces, 238 milligrams
- Turkey (light meat), 3 ounces, 214 milligrams
- Beef roast, 3 ounces, 229 milligrams
- Chicken breast, 3 ounces, 77 milligrams
Dairy and eggs
- 2% milk, 1 cup, 120 milligrams
- Mozzarella cheese, 1 ounce, 146 milligrams
- Whole milk, 1 cup, 107 milligrams
- Cheddar cheese, 1 ounce, 90 milligrams
- Yogurt (low fat), 8 ounce, 68 milligrams
- Egg (whole), 1 large, 83 milligrams
- Quinoa, 1 cup, 284 milligrams
- Oats, 1 cup, 147 milligrams
- Buckwheat (groats), 1 cup, 82 milligrams
- Bread (wheat), 1 slice, 19 milligrams
- Bread (white), 1 slice, 22 milligrams
Nuts and seeds
- Black walnuts, 1 ounce, 90 milligrams
- Cashews, 1 ounce, 81 milligrams
- Pistachios, 1 ounce, 71 milligrams
- Peanuts, 1 ounce, 65 milligrams
- Almonds, 1 ounce, 60 milligrams
- Pumpkin and squash seeds, 1 ounce, 163 milligrams
- Chia seeds, 1 ounce, 124 milligrams
- Flax seeds, 1 tablespoon, 31 milligrams
Vegetables and fruits
- Potatoes (white), 4 ounces, 29 milligrams
- String beans, 3 ounces, 17 milligrams
- Prunes, 1/4 cup, 12 milligrams
- Banana, 1 medium, 11 milligrams
- Apple, 1 medium, 2 milligrams
- Semisweet chocolate, 1 ounce, 18 milligrams
- Sweet chocolate, 1 ounce, 16 milligrams
You may find tryptophan supplements labeled as tryptophan, L-tryptophan, or 5-Hydroxytryptophan (5-HTP).
Some people take tryptophan supplements to help with:
- Migraine and other headaches
- Severe premenstrual syndrome (PMS)
Keep your supplements out of the reach of children and pets.
Don't take supplements without talking to your doctor first. Some supplements, including tryptophan, can interact with your medicines or any other supplements you take. Don't take tryptophan supplements if you take a monoamine oxidase inhibitor (MAOI), such as isocarboxazid (Marplan), phenelzine (Nardil), or tranylcypromine (Parnate). Tell your doctor all the medicines, herbs, nonprescription drugs, and supplements you use so they can check for interactions.
The FDA banned all tryptophan supplements in 1989 because of an outbreak of eosinophilic myalgia syndrome (EMS). EMS is a potentially fatal disorder of the skin, blood, muscles, and organs. The FDA traced this outbreak to a contaminant in one brand of supplements. Tryptophan supplements are back on the market, but it's still possible for them to have contamination.
You might not get enough tryptophan if you don't eat enough protein, but it's rare. Most Americans get more than twice as much as they need every day. Researchers have done experiments where they intentionally kept people from getting enough tryptophan. They found that the following may be signs you need to eat more foods high in tryptophan:
- Increased pain sensitivity
- Sensitivity to noise
Tryptophan Side Effects
Possible side effects of tryptophan supplements are generally mild, but may include:
- Nausea or vomiting
- Feeling of fullness or loss of appetite
- Stomach rumbling or upset
- Blurry vision
High doses may cause serotonin syndrome, which is caused by having too much serotonin in your body. Serotonin syndrome is dangerous and potentially fatal. Serotonin syndrome can cause mental changes, hot flashes, fast changes in your blood pressure and heart rate, and possibly coma and death. Talk to your doctor before you take more than the recommended amount.
If you have diabetes or high blood pressure, talk to your doctor before taking 5-HTP.
Does tryptophan make you sleepy?
It's a common belief that tryptophan causes drowsiness. This has been associated with the U.S. holiday, Thanksgiving, and the stereotype of eating a huge meal with turkey as the centerpiece, followed by a need to nap.
But there's uncertainty about whether tryptophan causes the drowsiness. Large amounts of carbohydrates from Thanksgiving staples like potatoes and bread, and the extra insulin your body makes to process a big meal, can also cause it.