At the age of 74, Mahatma Gandhi went 21 day without food during the hunger strike. Despite his age and poor physique, the civil rights activists managed to survive.
According to some reports, some people managed to survive 70 days without food.
What is more fascinating, human bodies are able to develop a defense mechanism to help survive without food for longer period of time, even though the body can die within a few days without water.
6 Hours after Eating
After you eat, your body digests the food and breaks it into glycogen molecules that store energy. This process produces glucose the main source of energy which is quickly absorbed and goes into the bloodstream.
Glucose is used as the primary source of energy if you have a normal diet. It makes you feel well-fed, because glucose goes into your muscles and gallbladder. Glucose fuel is enough for the next 6 hours. After 6 hours, when the body spends its fuel, it creates a feeling of hunger and you become lazy.
Starvation Mode: 3 Days without Food
Our glucose reserves can last up to 24 or 48 hours, although most of them will be spent after 6 hours. Then, you will not only feel hungry, but your body will fall into ketosis, which means increased level of ketones in the body.
Ketone bodies are produced from fatty acids when the glycogen in the gallbladder is completely spent. Ketosis can sometimes be useful, and it uses the body fat as energy, so a ketogenic diet is commonly practiced by people who are trying to lose some weight.
However, your brain can not function using fat as a source of energy, so it continues to use other glucose reserves in the body. The brain uses 120 grams of glucose a day so when the glucose is spent, your body has to think of a backup plan for the brain.
After the third day without food, your brain starts using ketone bodies as an energy source it gets about 30% energy in this way. On the fourth day, the brain will get up to 70% energy from the ketone bodies.
If You Do Not Eat More Than 72 Hours
The hard part comes after 72 hours without food this is known as a state of autophagy. When fat splits up, your body turns to the protein in muscle, which means it starts spending your muscles. At this point, brains need for glucose decreases from 120 to 30 grams.
Now the brain must get energy from the protein. Although the brain can survive on protein, your muscles will slowly disappear. Metabolism slows down and your body starts using the least amount of energy.
At some point, your immune system will weaken due to the lack of vitamins and minerals. Usually two types of diseases appear in the last stages of starvation: marasmus and kwashiorkor.
Marasmus is characterized by muscle loss and edema. Kwashiorkor is the most common form of malnutrition in developing countries, and it is characterized by fatigue, edema and reduced muscular fat.