Medically speaking, humans can go about four to eight weeks without food as long as they have water [source: professorshouse]. Hunger strikes have lasted longer, and people have starved to death in less time -- it all depends on the individual and several other factors.
The body stores energy in the form of fat, carbohydrates and proteins. Carbs are the first to go if you aren't eating. Fat goes next, which explains why people with more of it can survive longer. Then it's protein's turn. If you reach the point where your body is using up proteins -- basically itself -- you're in bad shape.
Your metabolism, converting food to energy, plays a role as well. If your metabolism is slow, you'll burn food slower and go longer without replacing it. If you go without food for a length of time, your metabolism adjusts itself on its own, pitching in for survival's sake.
Climate plays a part as well -- both cold and hot weather are no good if you have no food. In terms of living without food, heat means faster dehydration; cold means more energy is burned to keep the body's temperature at a cozy 98.6 degrees Fahrenheit (37 degrees Celsius). If you're lucky enough to be in a comfy 68 to 78 degrees Fahrenheit (20 to 25 degrees Celsius) environment, you'll be able to live a little longer without food.
Some symptoms you may see if you go more than a couple of days without food are:
- chronic diarrhea
- bad decision making
- immune deficiency
Advanced starvation will cause your organs to shut down one at a time. If you're in the throes of severe starvation, you might experience the following:
- muscle spasms
- irregular heart beat
If you're suffering from starvation, look to plants and insects for some protein and food energy. A rule of thumb for both is to avoid eating any insect or plant that's brightly colored, spiny or gives off a strong, pungent odor.