A person's body can go without oxygen for approximately five to ten minutes and around three to eight days without water. Yet remarkably, people have been known to live for more than seventy days without food. The question that arises is, 'How can this be?'
The answer to this question lies in a series of evolved physiological and metabolic defenses that work to keep a person alive for as long as possible in the event they do not have access to food. Just because a person is starving does not mean they have become helpless. What follows is an explanation of how a person's body fights to keep them alive and active.
Starvation is defined as a severe deficiency in caloric energy intake needed to maintain human life. It is the most extreme form of malnutrition. In humans, prolonged starvation can cause permanent organ damage and eventually, death. The basic cause of starvation is an imbalance between energy intake and energy expenditure. The term inanition refers to the symptoms and effects of starvation. Starvation can be caused by factors, other than illness, outside of the control of the individual.
By its very definition, starvation is a process. Our bodies are not like vehicles which promptly shut down when they are out of gasoline. When we experience prolonged low-energy intake and as long as water is available, our bodies enter into a series of metabolic modes. It is the body's way of recognizing that food is scarce and that it needs to re-allocate resources in preparation for what might be an extended period of time. Basically, a person's body is buying them some time to give them a chance to find some food.
Starvation results from the inadequate intake of nutrients or the inability to metabolize or absorb nutrients. It may have several causes such as:
Despite the cause, starvation takes about the same course and consists of three phases. The events of the first two phases happen even during fairly short periods of dieting or fasting. The third phase happens only in prolonged starvation and may end in the person's death.
During the first stage of starvation, blood glucose levels are maintained through the production of glucose from proteins, glycogen and fats.
At first, glycogen is broken down into glucose. Only enough glycogen; however, is stored in the person's liver to last a few hours. After that period of time, blood glucose levels are maintained by the breakdown of fats and proteins.
Fats are decomposed into glycerol and fatty acids. Fatty acids can be used as a source of energy, particularly by skeletal muscle, thereby decreasing the use of glucose by tissues other than the brain.
Glycerol may be used to make a small amount of glucose, yet most of the glucose is formed from the amino acids of proteins. Some amino acids might be used directly for energy.
In the second phase, which might last for several weeks, fats are the main energy source.
A person's liver metabolizes fatty acids into ketone bodies that can be used as a source of energy.
After approximately a week of fasting, a person's brain starts to use ketone bodies, as well as glucose, for sources of energy. Proteins not essential for survival are used first.
The third phase of starvation starts when a person's fat reserves are depleted and there is a switch to proteins as the major source of the person's energy. Muscles, the largest source of protein in the body, are quickly depleted. At the end of this phase, proteins - essential for cellular functions, are broken down and cell function degenerates. Along with loss of weight, symptoms of starvation include:
Few people die directly from starvation because they usually die of an infectious disease first.
Additional signs of starvation may include flaky skin, changes in hair color and massive edema in the lower limbs and abdomen, causing the person's abdomen to seem bloated. During the process of starvation, the ability of the human body to consume volumes of food also decreases.
Foods low in protein yet high in bulk often times cannot reverse the process of starvation.
Intervention involves feeding the affected person low-bulk food that provides lots of proteins and kilo-calories and is fortified with minerals and vitamins.
The process of starvation also results in dehydration and dehydration is an important part of intervention. Even with intervention, a person might be so affected by weakness or disease they do not have the ability to make a recovery.
Starvation wreaks havoc on a person's immune system, largely on account of an extreme deficiency of minerals and vitamins.
Some people will become weak and perish of immune-related diseases during starvation. Eventually, the person's body will run out of options. Fats, glucose, muscle mass and tissue are finite resources that will eventually be spent and the person will die. The end-stage of starvation usually brings with it one of two different diseases - kwashiorkor and marasmus.
Marasmus happens due to extreme energy deficiency, often from inadequate amounts of calories and protein. The person's body weight reaches dangerously low levels and infections are common. Kwashiorkor is a related disease that affects children who are protein-energy deficient and might result in edema and an enlarged and fatty liver, resulting in the distending of the children's bellies, providing the illusion that children who are starving are well-fed.
When the person's death finally arrives, its most immediate cause is by cardiac arrhythmia or a heart attack brought on by either extreme tissue degradation brought about by autophagy, or severe electrolyte imbalances. People can die of starvation in as little as three-weeks, or as long as seventy days.