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What Happens When You are Hungry, Thirsty and Tired

When the world ended, you were fortunate enough to get yourself and your family into the SUV along with your bug-out gear and hit the road before your little suburb descended into hell. It has been a long rough two weeks. Now it seems there is trouble in paradise.

The lack of food, water and sleep in a survival situation quickly makes a bad situation worse. Understanding how our bodies react to these stressful circumstances can make us more capable in a crisis.

There are five of you total, but only you, your wife, and your 16-year-old son are up to standing watch. That means everybody is sleep-deprived. Additionally, you didn’t really expect this to be an open-ended affair, so food and water are necessarily rationed.

With each passing day, your stash of supplies grows smaller and those you encounter want it worse. It’s time to apply a little science to the problem.


Nobody knows when or under what circumstances you might be called upon to show a little self-reliance. Our connection to what we perceive as civilization is tenuous at best. If you didn’t believe that at least a little bit, you would not be clutching this hallowed tome.

Many to most survival situations will see their resolution in a day or three tops. The storm will pass, the fire will go out, the power will come back on, or Uncle Sam will roll in with trucks and tents and make everything whole again. However, what if that’s not the case?

“Nobody knows when or under what circumstances you might be called upon to show a little self-reliance. Our connection to what we perceive as civilization is tenuous at best.”

It doesn’t take a whole lot of imagination to conjure some scenario that might demand that you keep your brood above the daisies for a protracted period in the face of dire circumstances.

To best prepare for such sordid eventualities, one should understand how these wonderful machines we live in respond to hardship. The three major players are food, water, and sleep.


So long as he or she has plenty of water, a typical healthy adult human can indeed survive 30 to 45 days or more without food.

However, that oft-reported statistic is terribly misleading. There is a broad gulf between life and quality of life. Going without food for a protracted period will make that difference patently obvious.

The body’s metabolic response to a lack of food goes through several predictable stages. In the near term, the body switches from carbohydrate metabolism to fat metabolism.

While this transition is the desirable end state for anybody who has ever tried to diet, as we all know that is a fairly unpleasant state of affairs.

Once those initial glycogen stores are depleted, your body starts feeding on glycerol and amino acids.

Nature is beautiful, but if you cannot sustain yourself appropriately, it can also be extremely dangerous.

Eventually, decreased insulin levels along with effects from stress hormones like cortisol and catecholamines drive the body into a state of ketogenesis. In this period, the body’s fuel needs are derived from ketone bodies and free fatty acids. When that tank runs dry things get fairly dark.

We think of starvation as something that happens across the ocean in some third-world country. However, we are never more than a few days away from a significant degradation in performance when deprived of sustenance.

At this point in the starvation process protein catabolism occurs. This means that your body’s fuel necessarily comes from degradation of structurally critical proteins like muscle. This final metabolic gasp ultimately causes organ dysfunction and death.

Each stage is unique to the individual. Some of us obviously have more fat reserves than others. However, the process is biologically predictable.


The doctor word is “inanition.” Initial symptoms are irritability (Who saw that coming?), impulsivity, and hyperactivity. As the stomach atrophies, the sensation of hunger actually diminishes.

The lack of metabolic fuel then results in fatigue and lethargy along with a predictable apathy. Apathy can have obvious dire effects on the long-term survivor. This means your innate will to live takes a hit.

Eventually the body grows so weak that it fails to sense thirst, and dehydration ensues. Vitamin deficiencies are frequently concomitant with starvation and result in such stuff as beriberi, pellagra and scurvy.

The most common food-related problem we have in America is that we eat too much of it. Some folks start a survival situation with more fat reserves than others.

Decreased caloric intake results in slowed reaction times and impaired judgment. Cold weather demands significantly greater caloric intake to maintain core body temperature, so the manifestations of food deprivation can be seen faster when it is chilly out.

For a typical person the state of starvation is defined as the loss of 30 percent of one’s normal body weight. A loss of 40 percent is almost always fatal.


While the typical adult human may indeed survive weeks without food, you won’t make it more than a few days without water.

Adults range from 55 percent to 60 percent water by weight, while children are about 65 percent and infants closer to 75 percent. Water is a critical component of all of the body’s metabolic processes.

We think of thirst as being a problem only in arid desert areas. However, dehydration can be a consideration anyplace there is an inadequate source of drinkable water available.

Minimum water intake varies greatly depending upon weight, environment, exertion, nutritional state and genetics. Most people will tolerate a 3 percent to 4 percent decrease in total body water fairly well.

A 5 percent to 8 percent decrease will precipitate significant symptoms. More than 10 percent results in serious impairment, while loss of 15 percent to 25 percent of total body water is usually fatal.


The initial symptoms of mild dehydration are fatigue and dizziness. These effects are compounded by other insults like food and sleep deprivation. Early dehydration also tends to cause headache, decreased appetite, and a general grouchiness.

As the degree of dehydration progresses, urine output will drop, and confusion and fatigue worsen. A person who is severely dehydrated will eventually develop purple fingernails. Once the water loss becomes critical an imbalance in sodium will typically precipitate seizures.

The Camelbak is one of mankind’s greatest survival tools. This inspired device allows you to comfortably carry a decent quantity of potable water that remains easily accessible

In a hostile environment a total body water loss as low as one to two percent can potentially result in demonstrable cognitive impairment. As dehydration is a function of stress, exertion, and environment this can be insidious.

While it is typically presumed that dehydration is a major concern in hot climates, failure to drink adequately in arctic areas can be just as dangerous.

Plan your water requirements in advance. Take into account environmental, fitness and exertional factors.

Diarrhea and vomiting make these problems exponentially worse. While fluid replacement drinks offer some theoretical benefit, consumption of excessively sugary or salty foods can exacerbate the problem. Oral rehydration will reverse the effects of mild dehydration rapidly.


There is an entire discipline of medicine dedicated to studying sleep, but we still don’t understand it well. Different people have different sleep requirements, but getting inadequate sleep over time results in a cumulative sleep debt. This is not something that you can really train for.

The way to beat dehydration is to stay ahead of the hydration curve. Drink water regularly when stressed. Exertion or a hot environment demands greater intake.

There are four recognized stages of sleep. These four stages comprise a sleep cycle that typically lasts 90 to 110 minutes. Each stage lasts between 5 and 15 minutes. This four-stage cycle repeats over and over throughout the night.

Stage 1 is light and easily aroused. This is the phase wherein you might experience those hypnic jerks or the sensation of falling.

Stage 2 sleep is a deeper sleep state wherein everything calms down. Your body temperature drops a bit and heart rate decreases.

Stage 3 non-REM sleep is the good stuff. This is the most restorative phase of sleep. It can be difficult to arouse people from Stage 3 sleep. This is the type of sleep that spawns sleepwalking, sleep talking, bedwetting and night terrors. Stage 3 non-REM sleep involves the release of human growth hormone and several restorative processes for the immune system.

REM, or Rapid Eye Movement, sleep makes up about a quarter of your sleep cycle but is necessary for cementing memory and rejuvenating the body. Awakening is easier from REM sleep than from Stage 3 non-REM sleep but can result in a more pronounced sense of grogginess afterward. REM sleep is when we dream.


The initial manifestations of a sleep deficit are yawning, fatigue, irritability and moodiness. With a cumulative sleep deficit comes a depressed mood, forgetfulness, an inability to concentrate and a lack of motivation. As REM sleep is required to cement memories, a sleep deficit can result in difficulty learning new concepts. Eventually the sleep-deprived person becomes clumsy and can develop an increased appetite.

“As the degree of dehydration progresses, urine output will drop and confusion and fatigue worsen. A person who is severely dehydrated will eventually develop purple fingernails.”

Sleep deprivation is an easy and safe way to increase stress in a training environment, so the military makes widespread use of it.

On two occasions when I was a soldier, I went four days without sleep. In both cases I began to hallucinate. Once a sleep deficit is properly repaid, the sundry negative symptoms of sleep deprivation should abate.

It doesn’t take the zombie apocalypse to create a survival situation. An auto accident or even an injury while on a long run can unexpectedly test your survival skills.

When significantly deprived of sleep, the body compensates by stealing brief periods of microsleep. Such episodes can exhibit very sudden onset and result in accidents. Forcing the body into abnormal sleep cycles due to shift work, standing watch or air travel can exacerbate the manifestations of sleep deprivation.

A fun fact is that death results faster from sleep deprivation than food deprivation. The longest anyone has ever gone without sleep and lived is 11 days.


The human body is a most remarkable machine. To operate at peak efficiency, this machine requires fuel, water and rest. Deprive the machine of any of these critical components and performance predictably deteriorates.

In a scenario wherein performance is critical to survival, attention to these three vital commodities can make the difference between life and death.

It can be tough to prioritize enough sleep when you are fighting to stay alive, but it needs to be a consideration in your planning. A lack of sleep can adversely affect your judgment and precipitate disaster.

A modest amount of the right kinds of foods can keep the human machine operating effectively for long periods. Eat small quantities at regular intervals when supplies are tight. Plan your survival load-out to include sensible shelf stable foods that require a minimum of preparation.

If time and facilities allow, then freeze-dried Mountain House meals provide a nice mix of protein, carbs and fat in a form that will last 25 years if left unopened in a cool dry place.

Water is bulky and heavy, but a proper water filter is not. I have gone weeks living in the Alaskan bush with nothing more than a water filter and natural sources for hydration and thrived.

Drink in modest quantities throughout the day and be mindful of environmental concerns. In hot weather you need more water. In cold weather you still need plenty of water even if you don’t feel thirsty. A Camelbak water carrier is the best piece of survival gear since the match.

Just because it is cold out doesn’t mean that your water requirements have dropped. It is hard to get excited about drinking cold water when you are already chilly, but the symptoms of dehydration can be insidious in cold areas.

It is easy to prioritize sleep out of your schedule when life goes sideways, but you will have to pay that sleep deficit back eventually. Sleep deprivation is not something you can just bulldoze through.

Be mindful of your body’s cyclical sleep requirements and try to devote at least 90 minutes to each sleep break if at all possible.

Maintain the machine properly and it will perform at peak efficiency. Understanding the science and physiology behind how our bodies respond to chronic stress can better prepare us for survival. Plan, perform and survive.


  • No caffeine after lunch
  • Nothing to drink after supper
  • Try to devote at least 90 to 110 minutes to a nap to take best advantage of your natural sleep cycle.
  • Try to work either days or nights if possible. When swapping from one sleep cycle to another, expect decreased performance for a few days until your body acclimates.
  • You cannot train to resist the effects of sleep deprivation.
  • When badly sleep-deprived, expect momentary unexpected periods of micro-sleep.


Physiological manifestations of the lack of food, water, and sleep:

“There is a broad gulf between life and quality of life. Going without food for a protracted period will make that difference patently obvious.”

Day 2  Dehydration causes headache, fatigue and irritability. Decreased attention and speech impairments stem from sleep deprivation.

Day 3  Urine output decreases, and confusion ensues due to lack of water. Sleep deprivation causes forgetfulness, depression and lack of motivation.

Day 4  Expect seizures due to sodium imbalance and possible death secondary to dehydration. Unexpected micro-sleeps, paranoia, psychosis and hallucinations ensue due to a lack of sleep.

Day 5  The urge to sleep can become irresistible.

Day 6  Glycogen stores are gone. The body is breaking down fats as its primary energy source.

Day X Fat reserves are depleted. This obviously is driven by how much fat you started with. The body starts breaking down critical proteins to meet its metabolic demands. This third phase of starvation is characterized by withdrawal, apathy and listlessness. Disease susceptibility skyrockets.

Day 21-70  Starvation severely impairs our immune systems. Most people die of opportunistic disease before they actually starve. The mechanism of death of true starvation is usually heart failure.

Note: These are generalizations. Actual timelines are driven by fitness, nutritional status, exertion, environment and genetics.


Editor’s note: A version of this article first appeared in the October, 2019 print issue of American Survival Guide.