Turn to Turkey’s Tryptophan to Boost Mood? Not so fast

Every Thanksgiving, myths about tryptophan’s quasi-magical powers resurface.

There’s the turkey/drowsiness myth: Eating a lot of juicy turkey meat makes people feel tired because it contains an amino acid called tryptophan. This molecule travels to the brain, where it is converted into a neurotransmitter called serotonin, which in turn is converted into a hormone called melatonin. Voila! Drowsiness.

But science and the internet agree: It’s not the turkey’s tryptophan that’s responsible for your post-feast nap. All protein sources, and even vegetables, contain some tryptophan; Turkey is not special at all in this respect.

So the turkey sleepiness myth may be fading, but other legends about tryptophan’s effects on the brain are gaining traction. Some people consider tryptophan supplements as an unconventional treatment for depression. Others are curious whether eating foods high or low in tryptophan could be helpful for influencing mood. Recently, some scientists have even proposed that gut bacteria cause changes in emotions by producing or breaking down tryptophan.

This connection between tryptophan and mood is an area of ​​ongoing research. And while some are fascinated by tryptophan’s potential, it’s not clear whether the excitement is justified.

Looking for a link between tryptophan and mood

There is scientific evidence that eating tryptophan can change your mood.

For example, in 2000, researchers found that when people ate an isolated protein that had very high levels of tryptophan, they felt less stress while doing math problems.

However, placebo-controlled clinical trials have generally not shown much of an association. Some studies have found that supplementing with pure tryptophan provided little to no benefit for people with depression. Some studies have even looked at what happens when you remove tryptophan from people’s diets, but also found little to no effect.

So what explains the mixed results?

Serotonin itself still harbors mysteries

In addition to human studies, the biology of tryptophan has been well studied in rodents. Research in the early 1970s showed that taking tryptophan supplements can boost levels of serotonin, a neurotransmitter traditionally associated with feelings of well-being and happiness.

Since then, scientists have learned many interesting facts about serotonin. For example, there are fourteen separate receptors for serotonin, and these are found throughout the brain.

SSRIs block the ability of neurons to reabsorb serotonin, leaving more of the neurotransmitter in the brain to affect other receptors. Blamb/Shutterstock.com

Researchers have learned how to influence this system with drugs, but not with much precision. Drugs such as the antidepressants, selective serotonin reuptake inhibitors – better known as SSRIs – do not target individual receptors and are not limited to certain areas of the brain. Instead, SSRIs, the best known of which are Prozac, bluntly boost serotonin everywhere.

This non-specificity is why, in my opinion, it is hard to believe that SSRIs work at all. Here’s an analogy: Suppose you’re Jeff Bezos and you want to increase Amazon’s revenue by speeding up your deliveries. So you decide to increase the speed of all vans. From now on, every truck will increase its speed by 5%. It could be a feat of logistical genius, or, perhaps more likely, it could end in chaos. Like boosting serotonin in the brain, this blunt approach may not be ideal.

Analogies aside, the question of whether SSRIs affect people’s mood is an experimental question, and some research has supported the idea that these drugs work. However, especially recently, its effectiveness has been intensively investigated. Some recent analyzes cite three decades of research and question the clinical value of SSRIs, while others claim that these drugs improve symptoms of depression.

It’s complicated and there is still some disagreement, but most psychiatrists agree that SSRIs are not effective for everyone. These medications are not a psychiatric panacea.

More chemical tuning of mood

In light of all this, I’ve often wondered whether psychiatric researchers needed 73 studies to investigate whether tryptophan depletion affects mood.

When it comes to understanding the connections between gut bacteria and the brain, or the larger challenge of understanding and treating mental illness, should researchers really still be thinking about tryptophan?

It seems true that, as with SSRIs, boosting tryptophan has a broad impact on serotonin. It’s certainly possible that increasing serotonin could affect mood, and therefore boosting tryptophan could do the same. But it’s also possible that manipulating something as complex as human emotions requires a little more nuance.

Psychiatric research has long moved away from the idea that your brain is a bag of chemicals; modern neuroscientists are asking for a little more specificity. From this perspective, I am skeptical of the idea that tryptophan is the anti-depression drug that psychiatry needs. Not only has experimental research produced fairly weak results, but the theory itself is not very convincing.

Serotonin, apparently full of psychiatric potential, has long fascinated psychiatric researchers. But what the past half century seems to have shown is that the neuroscience of human emotions is not simple. To promote lasting changes in mental health, scientists may need a little more respect for the complex emotional beings that we all are.

So no, a big turkey dinner, no matter how filled with delicious tryptophan, probably won’t be the neurochemical driver of your Thanksgiving mood.

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This article is republished from The Conversation, an independent nonprofit organization providing facts and trusted analysis to help you understand our complex world. It was written by: Andrew Neff, Rochester University

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Andrew Neff does not work for, consult with, own shares in, or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond his academic appointment.