Ask A Scientist
How long can the average human live without food or water?
Asked by: Deanna Braun
School: Maine- Endwell Middle School
Teacher: Kevin Wagstaff
Hobbies/Interests: Soccer, softball, swimming, playing the drums
Career Interest: Something in the medical field
Answer from Michael A. Little
Distinguished professor of anthropology, Binghamton University
Research area: Human adaptation to the environment
Ph.D. school: Pennsylvania State University
Family: Wife, Adrienne, and two grown children
Interests/hobbies: Swimming, choral singing, antique toys and books
Web page address: http://anthro.binghamton.edu/littlem.html
This is an important question suggesting there must be a number of weeks or days that any individual can live without food or water. But there is no simple answer because people are so different and will survive for varying periods without food or water.
Another reason for different survival periods is that the environment plays an important role, particularly in the case of our water needs. For example, we need drinkable (potable) water every day for maintaining the body and because we lose water all the time. In hot environments, we lose a lot of water by sweating and also we sweat when we are active. So, if we engage in vigorous activity in a hot environment and cannot find water, then our survival time is very limited. Pregnant or nursing women also need more water than other women. Babies and young children will survive for less time than adults without water because they have a small body size. What is especially dangerous in babies is if they are ill (fever and/or diarrhea), cannot be given clean water, and then become dehydrated. It is quite clear that water is the most essential element that we must have and the survival time without water is likely to be just a few days to a bit more than ten days, depending on a person’s age, gender, physical state, and the environmental conditions.
When we eat food, it provides fuel to operate the body (its metabolism). Even when the body is resting or sleeping it must have food and water. Otherwise it must draw energy and nutrients stored inside the body. A person who is lean or thin will survive less time than a person who is overweight. People who are overweight and have abundant body fat can survive longer with less food because their body fat can be converted to energy (calories) needed to maintain the body’s metabolism. But a starvation diet is still dangerous in very overweight (obese) people because there are other harmful changes that starvation produces in the body. When people involuntarily or voluntarily stop eating (fast) for a long period, they use up their body fat, muscle and other tissues. Some of the other tissues used to maintain the body may be heart tissue, so starvation can cause serious heart and other problems. Again, depending on all of the same factors listed for surviving without drinking water, survival without food may be as little as six or seven days or as much as several months. All of us would hope never to have to experience any of these conditions.