Moons ago in college, I took a 1pm class. The combo of dry lectures and it being the time right after lunch was lethal. I craved napping, not learning. It was brutal. I’m particularly prone to the zzzzzs after a heavy lunch, and I’m glad that it’s not just me. What you and I might call “food coma” is referred to scientifically as “post-prandial somnolence.”
Prandial—of or relating to a meal
Somnolence—the quality or state of being drowsy
Basically what happens after a large meal is that the parasympathetic nervous system (PNS) kicks into gear. The PNS is the complement of the sympathetic nervous system (SNS) which is what is large and in charge during stressful times, aka “fight or flight.” The PNS is more “rest and digest.” Energy is low, food is being digested.
It isn’t only the PNS that is responsible for food coma. Circadian rhythms are also involved, as lunchtime is typically a rest part of this 24 hour sleep-wake cycle. Hormones play a role too. Carb-rich foods are often the culprit because when you gouge on a carbohydrate-filled lunch, the bulky amino acid tryptophan goes right up to your brain where it is converted into serotonin and melatonin, equaling sleepy time! Too bad I don’t live in Spain, hello siesta.