Tryptophan and Mood: Why Turkey — and Supplements — Aren’t a Simple Fix

Every Thanksgiving the old claim resurfaces: turkey makes you sleepy because it contains tryptophan, an amino acid that the body converts into serotonin and then melatonin. That neat chain — tryptophan → serotonin → melatonin → sleep — is appealing, but it oversimplifies a complicated story.

The turkey myth

Tryptophan is present in many protein sources and even in plant foods; turkey is not uniquely loaded with it. Moreover, the grams of tryptophan in a typical meal are unlikely on their own to change brain chemistry enough to cause the post-feast drowsiness most people notice. Factors such as large meals, alcohol, social relaxation and reduced activity after eating are far more plausible contributors.

What the research shows

There is evidence that tryptophan availability can influence mood under specific conditions. For example, a 2000 study reported that participants who consumed an isolated protein very high in tryptophan reported less stress during a math task. Early animal studies from the 1970s also showed that tryptophan supplements can raise brain serotonin in rodents.

However, randomized placebo-controlled trials in people have generally produced mixed or weak results. Several clinical trials found little to no consistent benefit from pure tryptophan supplements for depression, and experimental tryptophan depletion often produced minimal mood changes. These inconsistent findings make it difficult to conclude that dietary tryptophan or simple supplementation is an effective, general treatment for mood disorders.

Serotonin is not a single switch

Part of the complexity comes from serotonin itself. The brain has at least 14 serotonin receptor subtypes distributed across many regions, and each receptor can have different — sometimes opposing — effects. Drugs that alter serotonin levels, such as selective serotonin reuptake inhibitors (SSRIs) like Prozac, act broadly rather than selectively targeting particular receptors or brain areas. That lack of specificity helps explain why outcomes vary: a global increase in serotonin can help some symptoms or people, have no effect for others, and even cause side effects.

Implications for research and treatment

Contemporary neuroscience increasingly favors more precise approaches — identifying specific circuits, receptor subtypes, and individual differences — over simplistic chemical explanations. While boosting tryptophan availability can affect serotonin levels, changing one part of a broad, interacting system is unlikely to be a universal remedy for depression or emotional disorders. Researchers and clinicians should be cautious about elevating tryptophan as a straightforward solution.

Bottom line

A hearty turkey dinner — even one containing tryptophan — is unlikely to be the neurochemical driver of how you feel on Thanksgiving. Tryptophan can influence serotonin under particular conditions, but evidence from clinical trials is mixed, and serotonin’s role in emotion is complex. For lasting progress in mental health, more nuanced and targeted approaches are needed.

By Andrew Neff, Rochester University