When most people think of tryptophan, they think of the Thanksgiving myth we’ve been told about why we get sleepy after eating turkey. The truth of the matter is, we don’t get sleepy due to tryptophan from turkey (you’d need to eat pounds of turkey to make you sleepy). What makes you sleepy is the sheer quantity of food and the excessive sugar and carbohydrates.
This tryptophan myth is interesting not because it’s incorrect, but because it touches on an important metabolic pathway — called the kynurenine pathway — that’s proving to be essential to happiness and good health.
What is tryptophan?
Tryptophan is an amino acid used in the synthesis of proteins. It’s an essential amino acid, meaning your body can’t create it and it must come from your diet. Tryptophan is a precursor to serotonin and melatonin — your body needs sufficient tryptophan to create both of these.
Tryptophan is an amino acid that converts to 5-hydroxytryptophan (5-HTP), which then becomes serotonin. Because of this, tryptophan is considered a natural mood regulator. Eating more tryptophan-rich foods and/or taking supplements has been shown to balance mood, induce sleepiness, alleviate depression, and calm anxiety.
What is the kynurenine pathway?
If you haven’t heard of the kynurenine pathway yet, you’re about to start reading about it more. As research grows, I’m sure you’ll be hearing about the promising implications of treatments involving your kynurenine pathway that are being uncovered. This important metabolic pathway has been linked to depression and suicide.
The kynurenine pathway revolves around tryptophan degradation and results in NAD+. This process is started when inflammatory cytokines are present. These cytokines then trigger an enzyme called, indoleamine 2,3-dioxygenases (IDO). IDO takes your calming tryptophan – which should be on it’s way to creating your serotonin – and instead diverts it down the degrading kynurenine pathway.
Your IDO enzyme is like a railroad switch, when inflammatory cytokines are present it diverts the tryptophan amino acid from a potentially beneficial railroad to the kynurenine pathway — a harmful runaway train. This switch can cause low serotonin levels, neurotoxic metabolites, and consequently, depression.
Tryptophan degradation in the kynurenine pathway causes depression
I don’t mean to be a Debbie downer talking about depression, especially during the holidays — but I see this research as promising.
When we can identify pathways associated with depression and suicide, we can begin research on treatments targeting these pathways. This is good news.
Numerous studies have linked inflammation to depression, but the mechanism behind this association wasn’t initially clear. Recent research has found that when the kynurenine pathway is activated (often by inflammation) it can result in a degradation of tryptophan and consequently lower serotonin levels. On top of lower serotonin levels, this activated kynurenine pathway creates multiple metabolites such as 3-hydroxykynurenine acid (3-HAA) and quinolinic acid, which are neurotoxic (some linked to suicide). This process also impairs neuroprotection.
There are a whole host of negative side effects from an activated kynurenine pathway — this is what I mean by a runaway train.
Kynurenine pathway depression and treatments
Kynurenine pathway depression is a relatively new concept, but treatments which target this process are promising. The first report of the kynurenine pathway’s impact on suicide only first came out in 2011. This study found that kynurenine pathways were strongly implicated in suicidal behavior. Treatments focusing on this process could be groundbreaking.
While we know the kynurenine pathway is an important place to look in depressed patients, testing is still bears some difficulties. For example, the typical blood samples a doctor might run of the kynurenine pathway metabolites might not be reflective of the concentrations in the brain. Still, these results offer some insight and as research progresses these tests could give us detailed information on depression and other neuropsychiatric diseases.
At this point you’re probably wondering…
Should you eat more foods high in tryptophan?
Interestingly, foods high in tryptophan don’t appear to raise tryptophan blood levels dramatically, whereas supplements do. But due to the nature of the kynurenine pathway, it seems reducing inflammation and the inflammatory cytokines that set it off in the first place is best. Though you should still ensure your body has enough tryptophan.
- Add anti-inflammatory spices to your foods – turmeric, rosemary, and ginger to name a few.
- Check for food sensitivities and avoid them – or avoid major culprits including gluten, dairy, peanuts, tree nuts, and eggs.
- Eat more probiotic foods or take supplements
- Get high quality sleep to help detox your body
- Reduce your daily toxin exposure
- Sweat more – through exercise and infrared saunas
- Add gut detoxifying supplements to your routine
A word of caution about tryptophan supplements: They can interact with antidepressants and mood-altering drugs, so make sure you talk with your doctor first before significantly increasing you tryptophan intake (minus the Thanksgiving turkey, of course).