Working in the emergency preparedness industry, we spend a lot of time thinking about how long we need to be prepared for to survive a disaster. But what about once the supplies run out? How long can you survive without food? Without water? Without air? Without shelter? In this article we will be looking at how long a human can survive without the basics of survival. We will also cover the effects of missing crucial supplies.
In all these cases we will be providing an average. Timelines can vary a lot based on the individual’s situation, physical state and history.
How long can you survive without food?
According to the Journal of Nutrition, there seems to be a set parameter for healthy BMI, with a minimum BMI (body mass index) at which humans stop being able to sustain life. For men this is a BMI of 13 and for women, 11. How long can you survive without food with those minimums? On average, you can survive for up to two months without food. However, humans need adequate water supplies to achieve that timeline. It goes without saying that it’s illegal to study starvation in humans. Therefore, these numbers are derived from studying voluntary hunger strikes that ended with the participants experiencing life-threatening symptoms.
What happens when you don’t eat enough?
Over the first 72 hours of starvation, our bodies make adjustments to how they create energy. Once there is no food left in our systems to turn into glucose (AKA: body fuel), we begin to convert glycogen from our livers and muscles. From there, our bodies begin to use amino acids for energy. Between these three fuel sources, we can usually go for 3 days without food before our metabolisms have to undergo some major changes.
To prevent too much muscle loss, the body begins to burn fat stores to keep us going. In a process called ketosis, the fat is turned into ketones for energy. Due to a higher fat content in our bodies, women will generally survive longer without food then men. The more fat stores a person has, the longer they can survive starvation.
Once the body is out of fat, it will revert to burning the remaining muscles for fuel. Generally speaking, serious medical side effects will start kicking in when a person has lost 18% of their body weight. However, they should be monitored after losing just 10%.
Please do not try this at home.
We are incredibly lucky to live in a country where, in most cases, relief or aid will come after a major emergency. However, emergency responders recommend keeping 1-2 weeks of food on hand to be self-sufficient in a disaster. This helps to keep people from drawing on limited communal supplies without need.
When shopping for emergency food, there are lots of factors to keep in mind: protein, calories, nutrition, shelf life, etc. If you’d like to learn more about these, please check out our other posts on choosing an emergency food source.
How long can you survive without water?
Have you heard the old rule of threes? “Three minutes without air, three days without water, and three weeks without food”? While it is a snappy way to remember a broad guideline of how long we can go without, it’s not entirely accurate. As we’ve already seen, people can survive for months without food in the right conditions. So, what’s the truth about water?
On average, it’s only people on their death beds with very little energy who won’t last more than a few days without water. Average people, in the right conditions, can go from 8-21 days before dehydration will be likely to cause death. Of course, there are many factors that affect this: environment, activity, age, health and food intake (many foods contain moisture.)
People are constantly losing water through sweat, urine and even breathing. As our bodies begin to dehydrate, our cells shrink and our brains will signal our bodies to reduce urination. This can take a toll on our kidneys as they require water to function well.
Eventually, dehydrated kidneys will fail to flush waste from our bodies and other organs may also stop working. Our bodies will stop regulating temperature, our electrolytes will become unbalanced, our joints may ache, blood pressure can increase/decrease and our brains might even swell.
Symptoms of severe dehydration include:
- Heat cramps/stroke
- Hypovolemic shock (what happens when your heart can’t pump enough blood)
- Organ failure
As with food, professionals recommend keeping 1-2 weeks worth of water on hand for emergencies. This can be stored water or a way to treat fresh water from creeks, hot water tanks, rain barrels etc. Generally speaking, you want to budget 2 liters for drinking, 1 for sanitation and 1 for cooking. That’s 4 liters, per person, per day. For example, a family of four would want to store 112 liters for a week’s supply. Click here for our comprehensive post on water supplies.
How long can you survive without sleep?
Yes! You can die if you don’t sleep! But you don’t need to worry the next time you pull an all-nighter to finish an assignment, take care of a sick child or party until the sun comes out – death from a lack of sleep is extremely rare.
The longest time on record for not sleeping is approximately 264 hours (11 days) – though scientists aren’t certain how long it would take to kill you. (For obvious reasons they frown on testing that sort of thing.)
As I mentioned, one all-nighter isn’t going to kill you. That doesn’t mean that there are no consequences for missing your Zzzzz’s. After 24 hours without sleep, you’re considered about as functional as someone with a 0.10 blood alcohol level. Therefore stay out of motor vehicles and away from heavy machinery. You are likely to experience drowsiness, irritability, impaired judgement, memory deficits and even tremors.
Things start getting a little more serious after 36 sleepless hours. Your body uses your sleep cycle to regulate things like hormones. Not getting to rest can start to affect your body at this point, including:
- Stress levels
At this stage we can add risky decisions, inflexible reasoning, decreased attention, speech impairments and decreased motivation to our list of symptoms.
If you miss two nights of sleep in a row, you’ve been awake for 48 hours. At this point, your brain will be forcing you into ‘microsleeps’ – little 30 second periods where the brain is in a sleep-like state. These are involuntary and can end in confusion and disorientation. Your immune system will also become sluggish at this point, becoming worse at responding to immediate threats like bacteria and viruses.
If, for some reason, you find yourself awake after 72 hours then you have my deepest sympathy – it does not sound like fun. Most people can’t stay awake without assistance after 3 days. At this point, the wakeful are having trouble completing simple tasks, multi-tasking, remembering detail and paying attention. They may experience depression, paranoia or anxiety. If that’s not enough, after three days hallucinations and illusions can begin to kick in.
Honestly, there’s not much in supplies that can stave off true sleep deprivation. But there are options that can make you more comfortable in an emergency and more likely to sleep. Things like sleeping bags, tents and blankets are good additions to any kit. If you need medications to help you sleep, talk to your doctor about the possibility of getting extra doses for the emergency kit. Be sure to rotate through it to keep it fresh.
It would feel wrong to do an article on survival times and not touch on the one thing we all need most: air. Drowning and smoke inhalation are the two most common ways to die from a lack of oxygen. Our brains need it constantly, using about 20% of our body’s supply.
While there are certain situations where people have been known to survive for up to half an hour without air (pearl divers, free divers and drowning incidents involving hypothermia), that is far outside the norm. For us average folks, our brains can withstand about 3-6 minutes without oxygen until serious brain damage occurs. After 15 minutes without air, it is very rare for a person to regain any brain function.
In general, we’ll fall unconscious after 1-2 minutes without air.
An ounce of prevention is worth a pound of cure when it comes to suffocation. While there aren’t a lot of supplies to add to a kit for suffocation – short of CPR masks – there are some tips to help you stay safe:
- Wear a lifejacket during water sports or if you are a weak swimmer
- Have a fire plan and understand the best ways to avoid smoke
- Ensure your fire alarms are working and active
- Learn CPR and the Heimlich maneuver
How long can you survive without answering the Call of Nature?
Warning – you might want to skip this one if you’re squeamish.
Yep – you can die without it. Relieving oneself is a critical function for humans, allowing our bodies to get rid of harmful waste. Because we all have different diets and lifestyles, there is no formal timeline for death by constipation. However, if you haven’t answered nature’s call for a week or more, it might be worth looking into over the counter assistance or talking to your doctor.
Depending on your age and health, 5+ weeks is probably in the danger zone for serious health issues/death. Conveniently, there is a handy symptom list to help you decide if it’s been too long since your last visit to the facilities.
- Feeling the need but not having the ability
- Not passing any gas
- Stomach pains
- Vomiting up things better left to the other end (yuck!)
There are a handful of complications that arise when the body does not have a chance to flush waste. Due to an increase in inflammation and stress in the body, the patient may be at an increased risk of cardiovascular events like heart attacks. Not being able to flush waste can also be very difficult on ones kidneys, as they are responsible for processing your waste.
The most direct complication, however, is bowel perforation. Unfortunately, it is exactly what it sounds like. If too much pressure builds up in your intestines they can tear, allowing waste into places it was not meant to go. Human waste is acidic and contains bacteria, so this can cause life-threatening symptoms.
Constipation can be caused by stress, ‘holding it’ too long, diet choices, or dehydration. Besides having adequate food and water in your emergency kit, ensure that you have somewhere to go, toilet paper, and hand sanitizer. This helps people to feel more comfortable and will minimize ‘holding it’ syndrome. Supplies might include a simple shovel and garbage bags or a more familiar portable toilet, and privacy shelter.
How long can I survive without…? Most people can go much longer than they think without life’s basic necessities, but the results of doing so are rarely pleasant. It is prudent to keep emergency kits in strategic places and a shelter-in-place kit at home so you always have what you need to survive comfortably at your fingertips.
Thank you for reading!
This article was written by Zenia Platten – Author and emergency preparedness professional.