Our digestive system converts the food we eat into energy which our body uses to keep itself going.
The surplus or extra energy which we don’t use gets converted to body fat. Our body fat can then be converted into glucose by the liver at a later time when it is needed. This raised the question for one reader:
How long can we live off the fat in our bodies?
How Long Can You Survive On Body Fat?
The general consensus in medical literature is that a person dying from hunger will succumb to death when one of two things happen; either half of the body’s protein is used up, or all of their body fat – whichever comes first.
The internal systems in your body become severely weakened and its muscles (including the heart) are susceptible to atrophy as it starves. Your body is not only converting its reserve fuel (body fat) into usable energy, it’s also breaking down muscles for the glucose and protein it cannot get from body fat alone.
Eventually, the damage to your organs and heart from your body cannibalizing itself is what finally kills you. A lack of sufficient protein to the heart causes the heart muscles to breakdown which causes murmurs and arrhythmias until the heart stops beating completely. Without a heart to keep pumping blood and oxygen to your brain, you slip into unconsciousness and die.
If you have access to water but no food, then the entire process will take between 2 to 8 weeks depending on how much body fat is stored up. For obese individuals, this estimate can swing wildly but we’ll talk more about that at the bottom of the article.
The Starving Process
- Stage 1 – You haven’t consumed any food for an extended length of time and now you are starving. Luckily, you have a reserve of glycogen in your skeletal muscles and liver. Glycogen can be broken down into glucoses which your body can use as extra fuel. This extra “gas” will last you roughly 10-14 hours.
- Stage 2 – When that supply runs out, your body turns to body fat to keep itself going. Body fat is broken down into fatty acids and glycerol in a process called gluconeogenesis. The fatty acids themselves get broken down into ketones which enter the citric acid cycle and are converted into useable energy. When people are fasting or on a hunger strike, this is the energy their body is using to survive.
- Stage 3 – The human brain cannot survive on ketones alone. A maximum of 75% of its fuel can be ketones, but the remaining 25% must be glucose. The body then begins breaking down the glycerol into glucose, which was left over from the body fat conversion in stage 2.
- Stage 4 – Because the glucose isn’t enough to make up the full 25% required by the brain, your body begins to convert amino acids into glucose. It does this by breaking down your body’s protein. Since you haven’t consumed any protein recently, your body turns to the next available source of protein – the protein in your muscles.
- Stage 5 – The body isn’t particularly picky about which muscles it targets and begins to target several organs and intestinal muscles. The now damaged intestinal muscles are the reason why complications occur when trying to feed someone who has been starving for an extended period of time. Worse still, the body begins attacking the heart muscles.
- Stage 6 – Your body is now near a complete shutdown. Your nervous system is severely compromised, your electrolyte levels are causing arrhythmia in your already weakened heart, and your other organs have begun to shut down or are severely impaired. Your body is now fully cannibalizing itself. Eventually, your atrophied, arrhythmic heart can’t take anymore and stops beating. With no oxygen or blood pumping to your organs and brain, you finally succumb to death.
Fun Fact: In 1965, a severely obese man starved himself and survived off his body fat for 1 year and 17 days. He was continually monitored by University of Dundee medical staff in Scotland who only fed him yeast, multi-vitamins and occasionally potassium for his heart. They kept their eye on his condition and took routine blood tests. After all was said and done, he had dropped from 456 pounds to 180 pounds. He was weighed again 5 years later and had only put on 15 pounds.
We strongly recommend that you do not attempt to starve yourself without the help of a medical professional. Numerous complications can occur from fasting, including complete heart failure and lactic acidosis which occurs after the fast and can be fatal.
Silva, Pedro. “The Chemical Logic Behind Gluconeogenesis”
Widmaier, Eric (2006). Vander’s Human Physiology – McGraw Hill p. 96
“The Physiology and Treatment of Starvation” – US National Library of Medicine.
Mary K. Campbell, Shawn O. Farrell (2006). Biochemistry (5th ed.) – Cengage Learning. p. 579
Richard A. Paselk. (2001) Fat Metabolism 2: Ketone Bodies at Humboldt State University