Starvation results from the inadequate intake of nutrients or the inability to metabolize or absorb nutrients. It can have a number of causes such as prolonged fasting, anorexia, deprivation, or disease. No matter what the cause, starvation takes about the same course and consists of three phases. The events of the first two phases occur even during relatively short periods of fasting or dieting, but the third phase occurs only in prolonged starvation and can end in death.
During the first phase of starvation, blood glucose levels are maintained through the production of glucose from glycogen, proteins, and fats. At first glycogen is broken down into glucose. However, only enough glycogen is stored in the liver to last a few hours. Thereafter, blood glucose levels are maintained by the breakdown of proteins and fats. Fats are decomposed into fatty acids and glycerol. Fatty acids can be used as a source of energy, especially by skeletal muscle, thus decreasing the use of glucose by tissues other than the brain. Glycerol can be used to make a small amount of glucose, but most of the glucose is formed from the amino acids of proteins. In addition, some amino acids can be used directly for energy.
In the second stage, which can last for several weeks, fats are the primary energy source. The liver metabolizes fatty acids into ketone bodies that can be used as a source of energy. After about a week of fasting, the brain begins to use ketone bodies, as wells as glucose, for energy. This usage decrease the demand for glucose, and the rate of protein breakdown diminishes but does not stop. In addition, the proteins not essential for survival are used first.
The third stage of starvation begins when the fat reserves are depleted and there is a switch to proteins as the major energy source. Muscles, the largest source of protein in the body, are rapidly depleted. At the end of this stage, proteins, essential for cellular functions are broken down, and cell function degenerates.
In addition to weigh loss, symptoms of starvation include apathy, listlessness, withdrawal, and increased susceptibility to infectious disease. Few people die directly from starvation because they usually die of some infectious disease first. Other signs of starvation can include changes in hair color, flaky skin, and massive edema in the abdomen and lower limbs, causing the abdomen to appear bloated.
During the process of starvation, the ability of the body to consume normal volumes of food also decreases.
Foods high in bulk but low in protein content often cannot reverse the process of starvation. Intervention involves feeding the starving person low-bulk food that provides ample proteins and kilo-calories and is fortified with vitamins and minerals. The process of starvation also results in dehydration, and dehydration is an important part of intervention. Even with intervention, a victim may be so affected by disease or weakness that he cannot recover.