Dr Maneendra - Consultant and Head of Critical Care Medicine, Gleneagles Hospital (Lakdi Ka Pul, Hyderabad, India) - said that when you fast, your body goes through some physiological changes over time to adapt.
Here's what happens to the body, broken down by time frame by Dr. Maneendra:
0 - 4 hours: Immediately after eating, the body focuses on digestion and absorption of nutrients. Blood sugar and insulin levels increase, providing energy.
4-8 hours: Once digestion is complete, blood sugar and insulin levels drop. The body uses glycogen (stored glucose) in the liver and muscles for energy, says Dr. Maneendra.
8 - 12 hours: When glycogen stores are depleted, the body uses fat for energy. This is called ketosis, when fatty acids are converted into ketones, which provide energy for the brain and muscles, according to Dr. Maneendra.
12-16 hours: The body continues to burn fat and ketone levels increase. “Growth hormone production may increase, which aids in fat breakdown and muscle preservation,” shares Dr. Maneendra.
16 - 24 hours: Autophagy begins as cells begin to repair themselves by breaking down and recycling damaged components.
Inflammation is reduced and the body focuses on maintaining cells, explains Dr. Maneendra.
Parmeet Kaur, a nutritionist at Marengo Asia Hospital (Gurugram, India), said that autophagy is the body's way of cleaning out damaged cells, to regenerate newer, healthier cells. Reducing your daily calorie intake by 10-40% can trigger the autophagy process.
Nutritionist Kaur added that autophagy can increase when there is stress on cells, such as nutrient deprivation during a two- to three-day fast.
24 hours or more: During this time, ketosis (a metabolic state) deepens and autophagy increases.
Dr. Maneendra shares that insulin levels are significantly reduced, promoting fat loss and enhancing the body's ability to control blood sugar levels.
However, fasting for more than 24 hours should be done under medical supervision as it can lead to nutrient deficiencies and other complications, says Dr. Maneendra.
