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Why 2 hours, not 1 or 3 ? The science behind the rule
Two hours is the precise duration of one digestive hormonal cycle: insulin rises and falls, gastrin and histamine peak, then glucagon and growth hormone reactivate. Eating earlier resets the cycle, eating much later changes nothing.
What happens during minutes 0 to 60
From the first bite, insulin rises sharply within 15 minutes, gastrin acidifies the stomach to digest proteins, histamine triggers digestive enzymes, and serotonin produces the feeling of fullness. Glucagon, growth hormone, testosterone and cortisol all enter standby mode. The body cannot mobilise stored fat during this entire phase ; it is in storage mode, not combustion mode.
What happens between minutes 60 and 120
Insulin gradually drops as glucose is absorbed and stored. Gastrin and histamine recede. The stomach finishes emptying its last batches into the duodenum. The body is winding down the storage phase but has not yet reactivated combustion. This is the intermediate window where eating again would be especially counterproductive: insulin would spike a second time on a still-working digestive system.
Minute 121 : combustion mode opens
At the 2-hour mark, insulin has dropped low enough that glucagon takes over. Stored glycogen is broken down for energy, the liver starts gluconeogenesis to keep blood sugar stable, and after 30-45 minutes of glucagon dominance, lipolysis kicks in and stored fat begins to release fatty acids into the bloodstream. This is the fat-combustion phase. Every additional hour without eating extends and deepens the burn. The 2-hour rule is therefore not arbitrary, it is the precise threshold where the system flips from store to burn.
This article relays the public teachings of Dr. Diaa Al-Awadi for educational and informative purposes. It is not medical advice. Consult your physician before any dietary change. Legal notice.