What causes afternoon energy crashes after lunch?

Afternoon energy crashes after lunch are caused by a combination of factors. The biggest contributor is your natural circadian rhythm, which programs a dip in alertness between roughly 1 and 3 PM regardless of whether you ate. However, lunch amplifies this by triggering increased blood flow to the digestive system and releasing hormones like cholecystokinin that promote drowsiness. High-carbohydrate or high-sugar meals spike blood glucose quickly, prompting an insulin surge that then drops blood sugar below baseline, leaving you fatigued. Large meal portions also worsen the effect. Mild dehydration and accumulated sleep debt from the previous night make the crash significantly worse. Eating smaller, protein-rich meals with fiber and staying hydrated can substantially reduce the afternoon slump.