Without food, a person can survive between three to four days.
Bodies are not designed to go without adequate nutrition for very long periods of time. The body’s requirements for food are so stringent that the decision has been compared to deciding when to cut off your arm because it needs surgery. One way in which starvation causes problems is by depriving the brain of glucose (energy from the blood). This causes problems with thinking and other mental functions as well as some physical ones like decreased sexual ability and muscle loss. Ultimately, after approximately 12-16 hours into a fast, most people will experience headaches and dizziness, followed by lethargy or extreme weakness soon afterwards.