The human body can survive weeks without food, but most people can only survive 2 to 4 days without water. There are no controlled scientific studies on how long people can survive without food or water since that would be unethical.
That’s why most research in this area involves case studies of people in emergency survival situations. For example, an imprisoned Austrian man went 18 days without food or water — the longest in recorded history — after being forgotten in his cell.
However, if you’re deliberately severely restricting food and water either to try andor for a hunger strike, it’s important to know about the serious damage this can wreak on your body.
How long can you go without food?
People can generally go weeks without food, says Mir Ali, MD, a bariatric surgeon and the medical director of MemorialCare Surgical Weight Loss Center at Orange Coast Medical Center.
How long you can survive without food depends on a variety of factors including your sex, body composition, the last thing you ate and drank, and your environment, says Andrea Paul, MD, co-founder of Health Media Experts, a consulting service for.
For example, people with more fat reserves may survive longer since the body can burn stored fat for fuel in times of extreme hunger, says Ali. Moreover, if a person has access to water, but no food, they may be able to survive for up to two months.
In fact, research on hunger strikes and voluntary fasting examined cases where people had water, but no food. In three cases, people went for 28, 36, and 38 days without food, before becoming too sick to continue their strikes. In other cases, those on hunger strikes died after 45 to 61 days without food.
In general, healthy, lean individuals experience severe effects of starvation when they lose 18% of their body weight or reach a body mass index of less than 16.5, which is considered severely underweight.
In general, women can withstand starvation longer than men and survive at a lower BMI. This may be due to the fact women naturally have a higher body fat percentage, but also that their bodies tend to use fat rather than lean muscle for energy during periods of starvation.
How starvation affects the body
When you are deprived of food, your body goes through stages of starvation because you’re no longer consuming the calories you need to fuel organ function. So, without calories, your body finds that fuel from other sources.
“The body will try to break down tissue and use stored nutrients to preserve life as long as possible,” Paul says. “Our bodies are incredibly resilient when pushed to the brink.”
First, your body taps into whatever glucose you have left. Within the first few hours, it’ll target the glucose in your blood, aka blood sugar. After that, it goes after glycogen — the glucose in your liver — which will take around 24 hours to deplete.
Beyond that, your body has to make a significant transition from burning glucose to burning stored fat, through a process called ketosis. This is when you’ll start to experience significant weight loss and preliminary starvation symptoms like dizziness, brain fog, and fatigue.
Your body can take anywhere from days to weeks to deplete fat stores, depending on how much there is. But once those are gone, the only thing left for your body to burn is the protein inside of your muscle, says Ali. This can include your heart muscle, increasing the risk of cardiac arrest.
Once your body starts burning protein, your health goes downhill very quickly causing:
- Osteoporosis or reduced bone density
- Cardiovascular disease
- Organ failure
If you are not treated soon, inevitable organ failure can prove fatal.
How long can you go without water?
It is estimated people can only survive 2 to 4 days without water. For example, in 1944, two scientists abstained from drinking water while still eating a dry diet that had all the necessary nutrients. One lasted 3 days and the other went for 4 before they had to stop the experiment.
While the body can break down tissue to replace the fuel from food, there is no internal process to make up for lack of hydration, Paul says. Within hours of not drinking, you can start to experience symptoms of dehydration including:
- Dry skin
With time, these progress to:
- Racing heart
- Organ failure
Dehydration can become fatal quickly, especially in hot climates, says Ali.
If you don’t have access to food, your body can still survive for weeks by breaking down tissue and stored fat. The fuel released by this process lets your organs continue to function. However, there is no way for your body to replace fluids, so most people can only survive 2 to 4 days without water.
You should never severely limit food or water as a way to lose weight. Not only can it be unsafe, but it can also be counteractive, Ali says. If you’re taking in less than 800 to 1,000 calories per day, your metabolism may slow, meaning you burn fewer calories thereby making weight loss harder, not easier.
Moreover, “you’ll feel more tired and run down,” Ali says. Therefore, stick to a diverse diet of primarily healthy foods like fruits, vegetables, and lean proteins if weight loss is your goal.