How Long Can You Survive Without Food?

Food is important. You can find people sitting down with friends to enjoy a delicious meal all over the globe. We bond, build relationships, and enjoy company while satisfying our taste buds. Nevertheless, food is more important than that. You need food to survive.

Well, that makes sense- food is a biological necessity. But what happens if we take food off your table for a day? Three days? A month? Your life would unravel quickly- and we’ve been asked a few times to address just how quick that would be. The answer to this question lets us be more prepared and allow us to improve our survivability. So, this week we’ll dive in for the answers to a great question: how long can you survive without food?

Contents (Jump to a Section)

Survival Rule of Three

The Survival Rule of Three is a well-known rule of thumb that describes the basic survival rules using the number three. The rule states that you can survive:

  • 3 minutes without air
  • 3 hours without shelter
  • 3 days without water
  • 3 weeks without food

We go into much more detail in our breakdown of the Survival Rule of 3.

The threes make the rule easy to remember, but as you may have guessed- it isn’t exact:

  • A German diver held his breath for 22 minutes and 22 seconds
  • Shelter requirements depend on the weather and the environment
  • An Austrian man survived for 18 days without water
  • A hunger strike participant lasted 74 days without food, verified by a doctor

These anecdotes blow up the idea that the survival rule of three is consistent for everyone in any situation. To get a better understanding, we’ll need to turn to another source: the medical community.

Medical Opinions

Dr. Alan Lieberson has quite a lot to say on the subject of starvation and fasting. He states that total sustenance (food combined with hydration) is much easier to study and that they have much more effective data.

The grim example provided talks of people in a persistent vegetative state (PVS), and how long they last after the feeding tube is turned off. Almost all patients die between 10 and 14 days. This, however, is an example of how severe dehydration is the survival-limiting factor and not necessarily the lack of food.

Besides incapacitated patients with feeding tubes, doctors also encounter starvation in patients with anorexia nervosa, malignant tumors, or participating in ‘starvation diets’. In these patients, doctors see organ failure and myocardial infarctions commonly. Even still, patients admitted and exhibiting starvation symptoms typically do not last beyond 14 days from their last meal.

Trial and Error

The University of Minnesota gave us a better look at how food impacts our survivability with an experiment conducted in 1945. It was named the Minnesota Starvation Experiment, and it surprisingly had over 200 volunteers. They selected 36 males to participate in the trials and they were tasked with losing 25% of their body weight. Most of these men were selected from the Civilian Public Service (CPS)- an alternative to military combat service for conscientious objectors.

It sounds crazy, but the University of Minnesota was not just putting on a spectacle- they were conducting this research to assist in the war effort. The test helped researchers and scientists understand what the body goes through during starvation.

The results were published in a two-book set “The Biology of Human Starvation”, which is still considered a landmark reference on human starvation. The research leaders, Dr. Keys and Dr. Brozek would go on to become a recognized psychology historians and a proponent of the Mediterranean diet and popularizing the body mass index (BMI).

How Your Body Reacts

There is an enormous amount going on physiologically and psychologically when your body is deprived of food. A few of the important transformations include:

  • At the six-hour mark, your body may run low on glucose. A process called Ketosis will start to crop up in order to find much-needed energy. Your body will start to break down fat to use as energy, leaving behind acid buildup. This will lead to impaired cognitive function.
  • At the three-day mark, your brain gives the command to break down protein stored in your body to find further glucose reserves. This breakdown releases more acid: in the form of amino acids. The amino acid can be converted into glucose.
  • Now that the brain is receiving elevated levels of glucose from amino acids, cognitive function is restored but your muscle mass begins to steadily deteriorate.
  • During this period, menstrual cycles will likely stop for women and your bone density will begin to weaken.
  • After one week of not eating, your body’s immune system will no longer be supported leaving you at high risk of bacteria and viruses.
  • At two weeks, your respiratory quotient (RQ) will show that your body has adapted to starvation with minimal protein oxidation with a 0.6 reading. This indicates that fat oxidation has been your main source of glucose production. You are almost fully converted to running on tissue reserves and food intake would need to be gradually reintroduced to reverse this.
  • Each day brings you successively closer to death, with no nutrients coming in and your body self-cannibalizing to produce glucose energy until complete organ failure, starting with the kidneys.

Dr. Lieberson, from earlier, states that the “duration of survival without food is greatly influenced by factors such as body weight, genetic variation, other health considerations, and, most importantly, the presence or absence of dehydration.”

How Long Can a Fat Person Live Without Food?

The answer is a surprisingly long time.

One man went from 456 pounds down to 180 by not eating for 382 days, losing about 11 1/2 ounces per day.

This was an obesity treatment out of Scotland in 1971, but it was well documented and his conditions were monitored in a clinical setting. He was also provided nutrients intravenously to maintain critical vitamin and mineral levels.

Surroundings and Environment

Your surroundings and environment can impact how long you can survive without food just as much as your own physiology.

Energy is what your body needs to survive, and any environment that requires you to work harder or use more energy to survive will shorten your survivability. In many disaster and emergency situations, your caloric intake has to increase to match your increased activity. This makes it much easier to start starving.

One of the harshest environments you could find yourself in is the desert. A desert is a barren area of land: without water and vegetation. You can still find food in a desert, but it is much harder than in any other area on earth. 33% of the world is covered in desert, and if you find yourself without food in a desert your survival timeline can be drastically shorter.

Fasting vs. Starving

Sometimes confused for each other, fasting and starving are not the same.

Fasting is not eating or drinking (except water) for a set period of time.

Starving is when you severely miss nutrients required to survive. If you fail to eat adequate amounts of protein, carbs, fats, vitamins, and minerals- you are also considered to be starving.

Both fasting and starvation can be voluntary or involuntary. Protestors often resort to fasting as a non-violent protest tactic. You may be required to fast before a medical procedure. Starvation happens in more severe cases, and if fasting gets out of hand it can become starvation.

The main difference between fasting and starvation is the severity of the symptoms. Fasting may leave you with hunger, dizziness, lightheadedness, headaches, and general fatigue. However, starvation will lead to brain dysfunction, convulsions, and heart failure- just to name a few.

Fasting has been a popular diet technique for some time, and is sometimes called a ‘starvation diet’. This accounts for many of the cases that medical practitioners encounter for starvation. These diets can be dangerous and can lead to acute myocardial infarctions for those that take them too far.

Many types of animals are known to fast. Bears, penguins, and seals fast without both food and water for several months at a time. It is important to know that they do not starve during these periods. They have biochemical adaptations in how they metabolize proteins that allow them to survive.

Everyone’s body chemistry is different, but the steps that follow your last meal as you approach and enter starvation are similar for everyone.

What is the Longest Any Person Has Survived Without Food?

A 27-year-old man set the record for the longest fast at 382 days without food in 1971.

They called him Mr. A.B. in the study as they administered the obesity fasting treatment in Scotland. He was monitored closely by doctors and scientists and given supplements to keep his vital nutrients in balance.

His actual name is Angus Barbieri and he still holds the Guinness World Record for this achievement.

How Long Can You Survive Without Food?

After reviewing survival rules of thumb, medical observations, statistical observations, and how other factors can affect survivability, experts agree that fourteen days is the best approximation for how long you can survive without food.

You can caveat this with the fact that there is a high degree of variance and an emphasis on how dehydration speeds up starvation drastically. It never hurts to stay hydrated, and most demonstrated starvation cases that go well beyond the two-week mark were people that were very well hydrated.

References and Sources

Sharing information about survival science would be pretty useless without research and sources. Here is where we sourced our information to verify our facts:

Baker, D., et al. (2013). The Psychology of Hunger. American Psychological Association. Volume 44. Issue 9. Page 56. (Source)

Castellini, M., et al. (1992). The Biochemistry of Natural Fasting at its Limits. Experientia. Volume 48. Pages 575–582. (Source)

Keys, A., et al. (1950). The Biology of Human Starvation. The University of Minnesota Press. Volume 1. (Source)

Lieberson, A. (2004). How Long Can a Person Survive Without Food? Scientific American. (Source)

Stewart, W., et al. (1973). Features of a successful therapeutic fast of 382 days’ duration. Postgraduate Medical Journal. Volume 49. Issue 569. Pages 203-209. (Source)

The Final Word

Food is important. We don’t eat it just because it tastes good- it is required for our survival. It may be the last bullet point in the survival rule of threes, but it is still one of the most important elements of survival. Without food, you will quickly lose energy for other survival activities, and slowly waste away as your body consumes itself.

This is why food storage is a priority for prepping and survival. Everyone should have a food stockpile to last through a small regional disaster or emergency. The target for this is typically three months of food storage. You can use a mix of canned goods and pre-packed food storage kits to get there easily and relatively cheaply.

Here are some other guides our subscribers have found useful:

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How Long Can You Survive Without Food?

Rusty Collins

I am an engineer, Air Force veteran, emergency manager, husband, dad, and experienced prepper. I developed emergency and disaster plans around the globe and responded to many attacks and accidents as a HAZMAT technician. I have been exposed to deadly chemical agents, responded to biological incidents, and dealt with natural disasters. Check out my full story here: Rusty's Story

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