Supposedly carbohydrates are a precursor to serotonin, so getting sleepy from carbs could be expected. The neuroscientist Andrew Huberman talks about this in hi

Supposedly carbohydrates are a precursor to serotonin, so getting sleepy from carbs could be expected. The neuroscientist Andrew Huberman talks about this in his podcast, eating low carb during the day can maintain alertness, while eating carbs at night are useful to prepare for sleep.