Dominic Stone
Starvation is an unhealthy state for the body, and it can have detrimental effects on both physical and mental health. During starvation, the body breaks down protein, releasing amino acids into the bloodstream, which are converted into glucose by the liver. As a large portion of muscle mass is made up of protein, this process leads to muscle mass loss. The body's primary energy source during starvation is fat reserves, but when these are exhausted, the body begins to break down muscle tissue as a secondary energy source. This results in a decline in stamina, strength, and overall physical effectiveness.
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What You'll Learn
Muscles are broken down for energy
Starvation puts the body in an unhealthy state, and it will work hard to get out of this state. While at first, an individual may lose weight quickly, the body needs a certain number of calories to function properly. It will work hard to restore weight and health as quickly as possible. During long-term calorie deprivation, the body begins to use its fat stores as a primary energy source and muscle and skeletal tissue as secondary energy sources.
The body's energetic requirements are composed of the basal metabolic rate (BMR) and the physical activity level (ERAT, exercise-related activity thermogenesis). This caloric requirement can be met with protein, fat, carbohydrates, or a mixture of those. Glucose is the general metabolic fuel and can be metabolized by any cell. After several days of fasting, all cells in the body begin to break down protein. This releases amino acids into the bloodstream, which can be converted into glucose by the liver. Since a large part of the human body's muscle mass is protein, this process is responsible for the wasting away of muscle mass seen in starvation.
However, the body can selectively decide which cells break down protein and which do not. About 2–3 g of protein must be broken down to synthesize 1 g of glucose; about 20–30 g of protein is broken down each day to make 10 g of glucose to keep the brain alive. But to conserve protein, this number may decrease the longer the fasting period. Starvation ensues when the fat reserves are completely exhausted and protein becomes the only fuel source available to the body. Thus, after periods of starvation, the loss of body protein affects the function of important organs, and death results, even if there are still fat reserves left unused.
During starvation, less than half of the energy used by the brain comes from metabolized glucose. Because the human brain can use ketone bodies as major fuel sources, the body is not forced to break down skeletal muscles at a high rate, thereby maintaining both cognitive function and mobility for up to several weeks. This response is extremely important in human evolution and allowed humans to continue to find food effectively even in the face of prolonged starvation.
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The body selectively breaks down cells
The human body is incredibly complex and, during starvation, it will selectively break down cells. While it may be tempting to try, starvation puts your body in an unhealthy state. After several days of fasting, all cells in the body begin to break down protein. This releases amino acids into the bloodstream, which can be converted into glucose by the liver.
Since a large proportion of the human body's muscle mass is protein, this process is responsible for the wasting away of muscle mass seen in starvation. However, the body can selectively decide which cells break down protein and which do not. The body will first exhaust the contents of the digestive tract, along with glycogen reserves present in both muscle and liver cells. After prolonged periods of starvation, this store of glycogen runs out, and the body then starts burning fat reserves and consuming muscle and other tissues. The body uses the proteins within muscle tissue as a fuel source, which results in muscle mass loss.
The body's glycogen stores are consumed in about 24 hours. In a normal 70 kg adult, only about 8,000 kilojoules of glycogen are stored in the body (mostly in the striated muscles). The main source of energy during prolonged starvation is derived from triglycerides. Triglycerides are much richer in energy content than glycogen, and a 70 kg adult stores over 400,000 kilojoules of triglycerides (mostly in adipose tissue).
During starvation, less than half of the energy used by the brain comes from metabolized glucose. Because the human brain can use ketone bodies as major fuel sources, the body is not forced to break down skeletal muscles at a high rate, thereby maintaining both cognitive function and mobility for up to several weeks. This response is extremely important in human evolution and allowed humans to continue to find food effectively even in the face of prolonged starvation.
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Loss of muscle mass and strength
Starvation puts your body in an unhealthy state. While you may lose weight quickly at first, your body needs a certain number of calories to function properly. It will work hard to restore your weight and health as soon as possible. During long-term calorie deprivation, your body begins to use its fat stores as a primary energy source and muscle and skeletal tissue as secondary energy sources. This results in muscle mass loss.
The body's glycogen stores are consumed in about 24 hours. In a normal 70 kg adult, there are about 8,000 kilojoules of glycogen stored in the body (mostly in the striated muscles). After several days of fasting, all cells in the body begin to break down protein. This releases amino acids into the bloodstream, which can be converted into glucose by the liver. Since much of the human body's muscle mass is protein, this is responsible for the wasting away of muscle mass seen in starvation. However, the body can selectively decide which cells break down protein and which do not. About 2–3 g of protein must be broken down to synthesize 1 g of glucose; about 20–30 g of protein is broken down each day to make 10 g of glucose to keep the brain alive.
The rate of protein synthesis, required for growing and repairing muscle tissue, decreases during starvation. This results in a loss of muscle mass and strength. Studies have shown that a decline in the body's ability to burn fat also occurs during starvation, increasing the likelihood of fat storage. This loss of muscle mass and strength makes it hard to maintain an active lifestyle.
Research by the National Institute of Health found that the muscles of the legs and arms atrophy during starvation. This can lead to a decline in stamina, strength, and overall physical effectiveness. The same study also reported an increased risk of osteoporosis and fractures, indicating malnutrition as a risk factor for low bone density.
In summary, starvation causes a loss of muscle mass and strength as the body breaks down muscle for energy. This can lead to a decline in physical effectiveness and overall health.
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Hormonal imbalances and reduced metabolism
Starvation in humans is a set of adaptive biochemical and physiological changes triggered by a lack of food or extreme weight loss. During starvation, the body seeks to conserve energy by reducing its metabolic rate and non-resting energy expenditure. This results in a slower basal metabolic rate (BMR), which is the number of calories the body uses to maintain vital functions such as breathing, heart rate, and brain function.
Studies have shown that during starvation, the body's glycogen stores are consumed in about 24 hours. In a normal 70 kg adult, there are only about 8,000 kilojoules of glycogen stored in the body, mostly in the striated muscles. After this store of glycogen runs out, the body starts burning fat reserves and consuming muscle tissue, resulting in muscle mass loss.
The process of muscle loss during starvation is due to the breakdown of protein in all cells of the body, releasing amino acids into the bloodstream. These amino acids can be converted into glucose by the liver, and since muscle mass is made up of protein, this breakdown results in the wasting away of muscles.
Hormonal and metabolic changes during starvation are profound and occur within the first few hours of food deprivation. One of the earliest changes is a decrease in insulin levels, which leads to an increase in glucagon, epinephrine, and norepinephrine. These hormonal changes trigger a cascade of events, including up-regulation of glycogenolysis, gluconeogenesis, lipolysis, and ketogenesis.
While the exact mechanisms of these hormonal and metabolic changes are complex, they ultimately result in a reduction in the body's energy expenditure and an increase in the efficiency of energy utilization. This metabolic slowdown is a protective response that has likely contributed to the survival of the human species over thousands of years. However, in modern times, when overfeeding is a more significant health threat than starvation, this protective response can sometimes do more harm than good.
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Bone density and strength are affected
Starvation puts your body in an unhealthy state, and while you may lose weight initially, your body will work hard to restore your weight and health as quickly as possible. During starvation, the body starts burning fat reserves and consuming muscle and other tissues, which results in muscle mass loss. The body can selectively decide which cells break down protein and which do not.
Malnutrition and starvation's possible adverse impacts on bone health and bone quality first came into the spotlight after the horrors of the Holocaust and the ghettos of World War II. During this time, severely diminished food intake and frequently concomitant calcium and vitamin D deficiencies were observed. This resulted in severely increased risks of fracture, poor bone mineral density, and decreased cortical strength.
Similar studies have been performed on moose in Norway, which had a high incidence of fractures and osteoporosis. The moose that had osteoporosis also had decreased bone mass, bone mineral density, and cortical strength. They also had the lowest carcass weights of their population, which was associated with starvation caused by overcrowding and increased competition for food.
Prospective animal studies have also been performed on rats to understand the effect of energy restriction and starvation on fetal bone development.
Starvation-induced catabolism of fat and muscle makes sense, as fat is an energy source, and muscle is energetically expensive to maintain. However, bone resorption does not provide energy for maintaining the brain or body, and it costs energy to carry out. If conditions improve, the lost bone must be replaced, imposing further metabolic costs.
One possible reason for bone resorption is to liberate minerals, primarily calcium, from the skeleton. Calcium is critical for cell physiology, and insufficient calcium intake quickly stimulates bone resorption to liberate calcium bound to bone hydroxyapatite.
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Frequently asked questions
Yes, starvation leads to muscle loss as the body breaks down muscle for energy. This is because the body can selectively decide which cells break down protein and which do not.
Starvation can lead to a decline in stamina, strength, and overall physical effectiveness. It can also cause hormonal imbalances, reduced fat stores, and a slower metabolism. Starvation can also negatively impact mental health and lead to disordered eating behaviors.
Instead of starvation diets, it is better to adopt healthy and sustainable habits such as exercising regularly, eating a nutritious diet, and allowing yourself time to lose weight slowly and safely.
