Consuming food and water is essential for human life. Your body needs energy from food sources and hydration from water to function properly. The many systems in your body work optimally with a varied diet and adequate daily water intake.
But our bodies can survive for days without water. We can go days or sometimes weeks without food because we adjust our metabolism and energy use.
Why the period varies
Eliminating food intake and water intake for a significant period of time is also called starvation. Your body may starve after a day or two without food or water. At this point, the body begins to function differently to reduce the amount of energy it burns. Eventually, starvation leads to death.
There is no hard and fast “rule of thumb” for how long you can live without food. There is a lack of scientific research on hunger because it is now considered unethical to study hunger in human subjects.
There are some studies that examine old research on hunger and examine more recent occurrences of hunger in the real world. These cases include hunger strikes, religious fasting, and other situations.
These studies have uncovered several observations about hunger:
An article in Archiv Fur Kriminologie states that the body can survive 8 to 21 days without food and water and up to two months if there is access to adequate water intake.
Modern hunger strikes have provided insight into hunger. A study in the British Medical Journal cited several hunger strikes that ended after 21 to 40 days. These hunger strikes ended because of the severe, life-threatening symptoms experienced by the participants.
There appears to be a specific “minimum” number on the body mass index (BMI) scale for survival. According to the journal Nutrition, men with a BMI of less than 13 and women with a BMI of less than 11 cannot sustain life.
An article in the British Medical Journal concludes that those who are normal weight lose a higher percentage of their body weight and muscle tissue faster than those who are obese if they starve to death during the first three days.
According to Nutrition magazine, the body composition of women makes them endure hunger longer.
How is this possible?
Being able to live for days without food or water seems unimaginable to many of us. After all, fasting for days or even going for hours without food and water can leave many of us irritable and low on energy.
Your body actually adapts when you fast for short periods of time or are unable to access food and water for very long periods of time. This allows people to religiously fast and even try “fasting” diets like the Eat-Stop-Eat approach without irreparably damaging their bodies.
It takes about eight hours without eating for your body to change the way it functions. Before that, it functions as if you were eating regularly.
Under normal circumstances, your body breaks down food into glucose. The glucose provides energy for the body.
Once your body has not had access to food for 8 to 12 hours, your glucose stores are depleted. Your body begins to convert glycogen from your liver and muscles into glucose.
After your glucose and glycogen are depleted, your body begins to use amino acids to provide energy. This process affects your muscles and can starve your body for about three days before your metabolism makes a major shift to maintain lean body tissue.
To prevent excessive muscle loss, the body begins to rely on fat stores to create ketones for energy, a process known as ketosis. You will experience significant weight loss during this time. One of the reasons women can go hungry longer than men is because their bodies have a higher fat composition. Women are also able to hold protein and lean muscle tissue better than men during starvation.
The more fat stores available, the longer a person can usually survive during starvation. Once fat stores are fully metabolized, the body returns to muscle breakdown for energy, as it is the only remaining fuel source in the body.
You will experience severe adverse symptoms during starvation when your body is using its muscle reserves for energy. A study in the British Medical Journal states that those who undergo starvation should be closely monitored for severe side effects of starvation after they have lost 10 percent of their body weight. It also says that very serious conditions occur when a person loses 18 percent of their body weight.
Why does water intake affect this?
You are much more likely to starve yourself for weeks – and possibly months – if you can consume a healthy amount of water. Your body has many more reserves to replace food than liquid. Your kidney function will decline within a few days without adequate hydration.
According to one article, those on their deathbeds can survive between 10 and 14 days without food and water. Some longer survival times have been noted, but are less common. Remember that people who are bedridden do not use much energy. A person who is healthy and mobile would likely perish much sooner.
One study that looked at hunger strikes suggested that a person needs to drink at least 1, 5 liters of water per day to survive hunger for an extended period of time. The study also suggested adding half a teaspoon of salt per day to the water to support kidney function.
Side effects and risks of restricted eating
Living without access to food and water can have a detrimental effect on your body. Your body’s many systems begin to deteriorate, even though your body can go on for days and weeks without food and water.
Some of the side effects of starvation include:
- drop in blood pressure
- slowing of the heart rate
- thyroid dysfunction
- abdominal pain
- low potassium
- fluctuation of body temperature
- post-traumatic stress or depression
- heart attack
- organ failure
Those who experience prolonged starvation cannot immediately begin to eat normal amounts of food. The body must be eased back into eating very slowly to avoid side effects known as refeeding syndrome, including:
- heart disease
- neurological conditions
- swelling of the body tissues
Resuming eating after starvation requires the supervision of a physician and may include cooked vegetables, lactose-free foods, and a low-protein, low-sugar diet.
The human body is quite resilient and can function for days and weeks without proper food and water. This is not to say that going without food for an extended period of time is healthy or should be practiced.
Your body can sustain itself for a week or two without access to food and water and possibly even longer if you consume water. Those who suffer from hunger need to be monitored by a doctor to recover after the period without food to avoid this syndrome.