Your body switches to “fat-burning mode” after about 12–24 hours
When you stop eating, your body first uses stored sugar (glycogen). After that, it begins burning stored fat for energy through a process called ketosis. This is why some people lose weight during fasting.
You may feel more mentally alert after the first difficult phase
Many people think fasting makes you weak and confused, but after the initial hunger and headache phase, some experience clearer thinking and better focus. This happens because ketones can be an efficient fuel for the brain.
Water fasting can reduce sodium, potassium, and other electrolytes in the body. This can cause dizziness, weakness, or cramps—so prolonged fasting without medical guidance can be risky.
Your body does a “clean-up” process called autophagy
During fasting, the body starts recycling damaged cells and proteins. This process, called autophagy, is linked to cell repair and may support healthy aging (though research is still ongoing).
Hunger usually comes in waves, not continuously
Hunger is often strongest at normal meal times and then fades. This is because hunger hormones like ghrelin rise and fall in cycles. So you might feel very hungry at noon but okay again an hour later.
