Science has not arrived at any exact formula, but experience has taught a good deal regarding the length of time a person can last without food. That length of time is dependent on a number of variables, as follows:
We know that human beings can survive for many weeks without food, so technically food is not vital in a survival situation. Food deprivation is similar to dehydration in the effects it has on the body long before it finally causes death, such as irritability, weakness, low morale, disorientation, loss of mental clarity and/or judgment. Other notable physical effects include inability to control fluctuations in body temperature and a weakened immune system.
Water of course is the most essential element we need for survival but food is still high up on the list of critical needs. Going without food for even a short time, even as long as a week, while not long enough to produce starvation, can have many undesirable effects, both physically and mentally. Commonly noted conditions resulting from a lack of food is weakness (both weakness, experienced as a lack of strength and weakness of the immune system), irritability, general lowered morale, disorientation and inability to make good judgment calls, and an inability to control one’s own body temperature so as to increase the persons chances of hypothermia, heat exhaustion or heat stroke. Therefore, it is clear that the only way to achieve success as a survivor is to face all the adverse conditions that you may be forced to contend with on a full stomach.
The Will to Live and Hunger
It is generally accepted that the will to live plays a significant role in survival, regardless of the availability of food. A person’s will to survive can get him through an extended period of food deprivation while another individual who has given up will succumb to starvation much more quickly.
Your general health at the outset
If you’ve been safeguarding your health by sticking to a nutritious diet, you’ll be able to count on those nutrients you’ve consumed to carry you through the initial phase of the survival crisis and you will be able to last longer without food than someone whose diet has not been nutritionally adequate prior to the survival situation.
What your muscle mass provides
When you are starving, your body breaks down your muscle mass to provide both nutrients and calories. However, lean muscle burns calories even when the body is resting.
Your body fat and calories
In a survival situation, a little extra body fat is desirable, because when there isn’t any food, your body fat will step in as a substitute. There are 3600 calories in a pound of human body fat, and depending on the rate the body burns those calories, it will provide energy for about a day and a half.
Metabolism
It varies with each individual. As food deprivation continues, your metabolism will slow down; however, if you’re a person who already had a slow metabolism at the outset, you will be in a more favorable position than others because you will be burning less calories right from the start, and thus will be able to live longer.
The work done under food deprivation
The more work you have to do, the more calories and nutrients your body will burn. So, when under food deprivation, efficiency of motion becomes essential, since the less activity you have to perform, the better your chance of living longer.
Temperature
This plays an important role in the determination of how long you can live under food deprivation, since in both uncomfortably cold and uncomfortably hot environments, the body burns more calories than it typically does. If the temperature is heading to extremes of cold, the body spends the calories trying to keep you warm. If it’s heading to extremes of heat, the body will be releasing valuable electrolytes in the sweat it produces in its effort to keep you cool. You are more prone to heat exhaustion and heat stroke during food deprivation, but since water is always the primary factor in any survival situation, it is even more crucial when enduring food deprivation, because adequate hydration in the absence of food will keep you going longer than if you were facing a simultaneous lack of food and water.