Food is delicious and essential to our survival. But what happens at the molecular level if you stopped giving your body food completely? What does starvation do to the body, and how long can the body survive in such a state before giving out?
When the body isn't fed with calories on a regular basis, it starts raiding its own fat supply for energy. The burning of fat for energy is a metabolic process known as ketosis. While this state of fat-burning is a desired outcome for athletes and people looking to shed some pounds, prolonged and persistent ketosis can impair normal brain functions.
After about 72 hours of burning fat, the body will switch to burning proteins, which it gets from muscles. At this stage, the body is essentially "eating" itself to make enough energy to stay alive.
How long can this process go on before death? The answer depends on many individual factors, including body size, activity level, as well as hydration status. That is, a body can survive without food longer than it can survive without water. Generally, without food, death will occur in about three weeks. Without food and water, life expectancy is shortened to about one week.