Whether fasting or not, the body demands energy, which is mostly derived from glucose, a sugar.
Glucose is primarily derived from carbohydrates found in grains, dairy, fruits, vegetables, legumes, and even sweets.
When the body’s immediate energy requirements are met, the liver and muscles store any surplus glucose as glycogen.
These glycogen stores can be released into the bloodstream as necessary to produce energy.
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However, while fasting, the body’s process changes. After about 18 to 24 hours of fasting, the liver depletes its glycogen stores.
At this point, the body enters a condition known as gluconeogenesis, in which it begins to produce glucose from fat storage, signalling the body’s transition to fasting mode.
As the fasting continues and carbohydrate sources become unavailable, the body finally depletes its fat reserves.
At this point, the body enters starvation mode, a more serious state in which the metabolism slows and muscle tissue is broken down for energy.
Although “starvation mode” is a common concept in diet culture, genuine starvation usually occurs after several days or weeks without eating.
Individuals fasting for up to 24 hours are normally safe to go without eating for a day, as long as they have no underlying health issues that make fasting dangerous.