Hint: tryptophan is only part of the equation.
Tryptophan is an essential amino acid that is a precursor to serotonin. The primary source of tryptophan is meats such as turkey. The truth however lies not only with how much turkey you eat but also what else you eat. Carbohydrates lead us into feeling great because they remove molecules that would otherwise limit our production rate of this happy neurotransmitter. High carbohydrate meals increase the availability of tryptophan in your brain leading to a flood of serotonin which accounts for why we feel so good after Thanksgiving dinner!
“The mechanism of the rise in brain serotonin [from carbohydrates] involves the secretion of insulin, and the decrease that the hormone produces in plasma levels of certain amino acids that compete with tryptophan, serotonin’s precursor, for transport across the blood-brain barrier. The rise in serotonin can thus be produced by any carbohydrate that elicits insulin secretion, independent of its sweetness.” (Wurtman, 1988)
In other words, it is not the turkey that is making you sleepy, it’s the potatoes and pie!
Feeling drowsy after any carbohydrate-rich meal is the effect of serotonin being released. Serotonin can improve one’s mood and provide feelings of satiation. It also relaxes the nervous system resulting in sleepiness. Once these effects fade, you are left craving more carbohydrates.
To learn more about how this serotonin feedback loop can result in cravings (and how to overcome it!) read our white paper:
Wurtman, RJ., Wurtman, JJ. (1988) Do carbohydrates affect food intake via neurotransmitter activity? Appetite.
Retrieved from: https://www.ncbi.nlm.nih.gov/pubmed/2903717