1 · reactive hypoglycemia
Fast-digesting high-glycemic-index food pushes glucose up and insulin runs high, and in some people glucose drops below its pre-meal level around 2 hours later, bringing sleepiness.Explanation one · Glucose shoots up, then falls back (reactive post-meal hypoglycemia)Typical scenario: a lunch of white rice + a sugary drink + white bread
· Half an hour to an hour after eating, fast-digesting high-glycemic-index food pushes glucose fairly high
· Insulin release runs on the high side — this happens in healthy people too, and is often more marked with insulin resistance
· In some people, around 2 hours later, glucose drops below its pre-meal level; in people without diabetes, falling to true hypoglycemia is uncommon
· As it drops, people feel sleepy, irritable and want something sweet (the classic craving for bubble tea at 3 PM)
On a : a spike and a steep drop, not a gentle wave.
Why low glucose makes you sleepy: the brain runs almost entirely on glucose (except in prolonged ketosis); as glucose falls, the body also sounds a sympathetic alarm — palpitations, sweating, craving sweets — as it corrects. In healthy people this usually recovers on its own; it just feels bad.
Type of evidence: it makes physiological sense and shows up on a glucose monitor, but nobody has directly measured how much of post-meal sleepiness it explains. Post-meal sleepiness is mostly normal physiology, amplified by certain ways of eating.