What Tryptophan Really Does, and How It’s Helping Scientists Better Understand Depression

Is it really tryptophan making you sleepy after your holiday meal? The truth about this old myth is no–and the culprit is actually just a lot of food and too much sugar. 

But the exciting news about tryptophan is that it plays a much bigger role in things like mood regulation, digestion, and a lot more. And new research is helping scientists discover a link between this humble amino acid, and influential pathways that might be the key to better understanding the inflammatory component to depression.

What is Tryptophan?

Tryptophan is an essential amino acid, which are the individual building blocks of proteins. Tryptophan is considered “essential” because your body cannot make it in sufficient amounts, so you must consume it from food. 

This essential building block is a precursor for neurotransmitters, other protein messengers, and two critical metabolic pathways that regulate everything from digestion to mood health, which you’ll learn more about in a moment.

And even though turkey is a great source of tryptophan, you can also find this amino acid in other poultry, red meat, eggs, cheese, fish, and some nuts. And it’s a good thing it’s widely available, because it’s a crucial part of your body’s chemistry!

What Does Tryptophan Do?

Tryptophan is the precursor for two incredibly important metabolic pathways in your body. The first involves serotonin synthesis, and the second is a much lesser known pathway, but one that accounts for as much as 90% of tryptophan use. 

We’ll learn more about this second pathway, and why researchers think it might be the key to understanding depression in a moment.

Tryptophan Provides Precursors for Serotonin

Once enzymes get a hold of tryptophan, gut bacteria help convert it first to 5-HTP, and then synthesize serotonin. Serotonin is most well-known for stabilizing mood and creating feelings of well-being, but it also helps regulate appetite, digestion, and body temperature. 

Serotonin is active in the brain, and has an impact on your enteric nervous system, which resides in your gut.

The Brain Within Your Gut

It’s estimated that about 95% of serotonin is produced in the digestive tract, and that it’s also stored there for later use by the brain (1). In the gut, serotonin is responsible for the wave of movements known as peristalsis, which stimulates food to move from one part of the digestive tract to another. 

Researchers believe that the uptake (or lack thereof) of serotonin in the gut could play a role in conditions like IBS, IBD, and other problems where food is delayed moving through the digestive tract (2).

Outside the digestive tract, serotonin goes on to initiate the production of other hormones, as well as impact areas of the nervous system. 

Serotonin for a Stable Mood and Happiness

Serotonin plays a significant role in mental health. While other neurotransmitters like dopamine provide stimulation for our brain’s reward centers, serotonin promotes feelings of wellbeing and happiness.

Low levels of serotonin within the brain have been linked with increased anxiety as well as depression, and some studies also suggest low serotonin may have a negative effect on memory as well (3).

Since tryptophan is a precursor for serotonin, scientists have suggested that the manipulation of tryptophan within the gut can impact serotonin levels to support mood and cognition, but it’s unclear whether increasing tryptophan in the gut has a positive effect on serotonin levels.

If you or a friend or family member is navigating mental health issues, learn more about the integrative approach to anxiety and depression, and don’t hesitate to contact one of our experienced providers today.

Serotonin Is Necessary for Melatonin Production

While many people know that melatonin is essential for falling asleep at night, fewer realize that melatonin is made from serotonin, which means low levels of serotonin can decrease the available melatonin required for adequate rest (4).

Without enough tryptophan (or if it’s being diverted toward other pathways), serotonin availability decreases, and we can experience symptoms like depression and poor sleep.

As crucial and far-reaching as serotonin is, only about 3% of tryptophan is reserved for serotonin production, while about 90% of tryptophan is diverted toward another powerful pathway, known as the kynurenine pathway (5).

Tryptophan and the Kynurenine pathway

The majority of tryptophan is reserved for an essential metabolic pathway called the kynurenine pathway (KP). The KP plays a role in generating cellular energy in the form of NAD+ especially during times of increased immune response. This form of cellular energy is extremely important for protecting cells and fueling mitochondria.

New research, however, finds a link between inflammation and a change in the KP, which could play a significant role in the development of depression and other mood disorders.

Inflammation Limits Serotonin Availability

This change in the KP occurs in the presence of inflammation, and functions a little bit like a railroad switch. 

When the immune system activates proinflammatory cytokines in response to an infection or illness, the KP diverts more tryptophan than usual away from serotonin production and toward a different pathway that increases production of NAD+. This NAD+ is used to provide the large amounts of energy needed for activated immune cells to fight off infection.

This tells us the kynurenine pathway plays a critical role in creating cellular energy in the form of NAD+ for immune function. And because energy requirements are substantially increased during an immune response, the KP is a key regulator of the immune system.

But during this time of increased inflammation, the KP sequesters available tryptophan, limiting it’s availability for serotonin production and therefore reducing serotonin in the brain and gut.

Studies suggest there may be a link between increased inflammation, and the decreased availability of serotonin due to the kynurenine pathway (6). 

10 Anti-Inflammatory Tips

Inflammation is at the root of not only many chronic diseases, but can alter metabolic reactions, such as the kynurenine pathway which negatively impact immune function and depressive symptoms. To reduce inflammation in your body, practice more of the following:

1. Get more omega-3’s.
2. Modulate inflammation with supplements like turmeric, lipoic acid, or resveratrol.
3. Limit inflammatory grains and processed foods.
4. Maintain a healthy blood sugar balance.
5. Support insulin sensitivity.
6. Exercise more.
7. Practice stress relief and regular self-care strategies.
8. Support natural detoxification pathways in the gut.
9. Get adequate sleep.
10. Reduce your toxic burden.

Foods with Tryptophan

To optimize your intake of dietary tryptophan, first make sure you’re consuming adequate quality protein. Then, include foods such as:

• Chicken, or other poultry.
• Grass-fed beef
• Pork
• Fish
• Eggs
• Milk or cheese (if tolerated well)
• Pumpkin seeds
• Sesame seeds
• Oatmeal

Even though tryptophan isn’t directly responsible for our sleepiness after a holiday meal, what’s more interesting is its extensive role in neurotransmitter function and metabolic reactions that impact almost every system within the body.

So at your next meal, don’t hesitate to prioritize your protein intake to capitalize on all the benefits of tryptophan!

Resources

1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2908021/
2. https://www.sciencedirect.com/science/article/abs/pii/S0009898109000576
3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4728667/
4. http://www.vivo.colostate.edu/hbooks/pathphys/endocrine/otherendo/pineal.html
5. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2908021/ 
6. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6790159/