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How Long Can You Live Off The Fat In Your Body?

How Long Can You Survive Off Body Fat?


How Long Can You Live Off The Fat In Your Body?

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.Grim Reaper

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.

L. Flemming & W.K Stewart – University Department of Medicine, Scotland – “Features of a successful therapeutic fast of 382 days’ duration
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



  1. disqus_hw3CIpv33L

    August 5, 2015 at 7:41 pm

    I’m quite tempted to do this if it weren’t for the nerve/brain destroying bit. I’d stop at day 30 though, definitely wouldn’t last a year with current energy stores.

  2. Jane Smith

    September 3, 2015 at 10:48 am

    Starvation is when you no longer have any body fat reserves to call upon, fasting is not starvation unless you have no reserves. Fasting should always be done with appropriate knowledge and if longer than a week, with knowledgeable supervision. That does not usually mean your physician as they know next to nothing about the process. The medical literature and medical profession have notoriously been uneducated in the fasting process as well as proper nutrition. You have to educate yourself. I am on a 3-day fast at the moment and feel fantastic but I took the time to LEARN.

  3. hugh munhus

    November 5, 2016 at 8:30 pm

    I like how they ended this article with a showcase of a successful attempt at self starvation. I understand that he had doctors monitoring him but obviously it can work.

  4. Brent

    November 11, 2016 at 5:30 pm

    I once fasted for about 20 days drinking only water and coffee. The first week is rough (headaches, dizziness, fatigue) because your body has to adjust to using a new source of energy (body fat vs carbohydrates) while detoxing at the same time. This “adjustment period” is different for each individual depending on your overall health and body type. This is why some experts claim fasting is dangerous or not healthy etc. You really have to know your body and be confident that you can endure the process of fasting. For example, if you are on medication or have some health issues then it may not be a good idea. This is why they say it should be done under the supervision of a doctor. During this time is when meditating, yoga etc really help until you get used to fasting. Week two, you really start to notice the benefits of fasting as you experience periodic bursts of energy and a heightened state of awareness. You no longer generally crave food but you may miss the routine of cooking or the social aspect of eating etc. Week three, you’ll notice the weight loss, lighter on your feet, more energy etc as most foreign substances and chemicals are no longer slowing down your body’s natural systems. You’ll also notice something quite profound- and that is how quickly the body was able to heal itself. Scratches and scabs were gone. Athletes foot, jock itch etc disappear. No more headaches, bloating, soreness, insomnia, fatigue, etc. Week 4 you start to think about the negative impact of continuing to fast, losing muscle etc and you’ll also miss the social (cultural) aspects of food. This is when you should ease back into it with salads and drinking juice etc…

  5. Felipe Blue

    December 8, 2016 at 12:11 pm

    Do you have a website that you can recommend regarding the process?

  6. bob russell

    June 27, 2017 at 12:24 am

    You have to be out in the wet, cold and wind, because you gotta get firewood. You can’t just sit around at room temp. even getting water is an ordeal, because you have to boil all of it.

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