This evening, as you enter into a food coma from way too much turkey, mashed potatoes and utterly fruitless political ranting courtesy of your uncle Gary, you might wonder why you are so sleepy. For a long time many believed that Tryptophan, an α-amino acid that is used in the biosynthesis of proteins, was the cause of the post-Thanksgiving stupor. Now a new study published on the life-sciences reserach site eLife suggests that the abundant proteins and salts present in the food are responsible.

The study was done on a series of fruit flies fed a high concentration of either sugar, salt or proteins. Only the flies fed with a high concentration of salt or protein had a noticeable increase in sleep.

The next step is to figure out the neural pathways that connect sleepiness and these food-based stimuli. A trickier aspect of the study showed that protein can promote both sleep and wakefulness. The ingestion of food stimulates certain neurons, called leucokinin receptor neurons, and protein in high amounts can stimulate this release. Protein provides vital fuel for the body, but the size of ingestion can trigger the sleepiness response. So depending on the amount of protein, it could be either an energy booster or energy inhibitor.

So as you sit across the table at Thanksgiving, after your ne'er-do-well cousin has just finished his third rum and coke and your brother in-law has finished asking you for money, share with your whole family the reason you are all so very tired. It’s guaranteed to at least get a “That’s nice, dear” from your grandma.