Digestive health

Thailand caves: How long can you survive without food or water?

How long can you last without food or water? Probably longer than you think.
How long can you last without food or water? Probably longer than you think.

On 23 June 2018, 12 boys and their football coach went missing in Tham Luang cave, one of Thailand’s longest caves. News24 reported that it’s one of the hardest to navigate as the corridors are winding and narrow.

They were exploring the cave when heavy rains hit the area, flooding the entrance and trapping them deep underground.

Nine days later, two British Navy Seal divers reached them. They are alive and mostly well, but now the real challenge begins as they try to get them out safely.

But this begs the question – how long can a person survive without any food or water? Hint: It’s probably longer than you think, but definitely not something you should try.

Living without food

Michael Peel, a senior medical examiner at the Medical Foundation for the Care of Victims of Torture, reviewed available literature regarding human starvation in a 1997 article in the British Medical Journal. According to this information, people can survive without food for between 30 and 40 days, but they need to remain hydrated. 

Severe symptoms of starvation (apathy, withdrawal, listlessness and extreme weight loss, for example) will display around day 35 to 40, while death can occur at between 45 to 61 days, according to literature describing the hunger strikers of the Belfast Maze Prison in the ‘80s.

There are, however, a number of factors that can influence how long a person can survive without food – these include age, weight, general health and how the body’s metabolism slows to help conserve energy.

Dr Mike Stroud, a senior lecturer of Medicine and Nutrition at Southampton University, told the BBC he believes it is possible to survive for 60 days without food. "That is about the time hunger strikers in prisons tend to die," said Dr Stroud. "But they are normally in warmer conditions."  

He continued, "The average resting human body, doing absolutely nothing, produces about 100 watts of body heat, which could function a light bulb. The body needs more than just [kilojoules] – it will start to shut down its organs one by one. But it could still take up to 60 days for that to happen."  

Dr Claude Piantadosi at Duke University in North Carolina says going without food for six weeks is about the limit for an average person. He told NBC News, "If somebody's really huge, really fat, they could live longer than six weeks."

What happens to your body?

If you stop eating for six hours, your body breaks down glycogen (stores energy in your body) into glucose. About 25% of this energy is used by your brain.

Your body goes into ketosis after six to 72 hours without food, where it is forced to use an alternative source of energy when the glucose is depleted. Your brain breaks down the body’s protein, which releases amino acids that can convert into glucose. Your body is using its muscle mass to produce energy and survive.   

After one to two weeks your body becomes depleted of minerals and vitamins, which can lead to a weakened immune system. Death can be a result of illness or a heart attack due to the severe degradation of the muscles in the heart, diaphragm and body.

Dehydration is deadly

Without drinking water your survival time is lot shorter. Experts estimate you can live for about one week without water depending on the weather conditions. However, if it's hot and dry, the estimation drops to just a few days. 

“I have sort of a 100-hour rule," said Dr Piantadosi. "Depending on the temperature you are exposed to, you can go 100 hours [4.2 days] without drinking at an average temperature outdoors. If it’s cooler, you can go a little longer. If you are exposed to direct sunlight, it’s less," he said.

According to Randall Packer, an expert on the body’s water balance at George Washington University, “The more energy you expend the more likely you are to lose water. You lose a little bit of water every time you exhale. You lose water when you sweat. You do make a little water when you metabolise food … but the balance is such that you always need some sort of water intake.”

How dehydration can kill you

“Under extreme conditions an adult can lose 1 to 1.5l of sweat per hour. If that loss is not replaced by drinking, the total volume of body fluid can fall quickly and, most dangerously, blood volume drops,” said Packer.

When you lose more than 7% of your body weight, your body struggles to maintain blood pressure. As this happens, blood flow to non-vital organs, such as your kidneys and gut, begins to slow. If your kidneys are unable to filter blood, cellular waste begins to build up, which can cause kidney failure and death.

Image credit: iStock 

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