What Happens to a Body During Starvation?

November 16, 2025 •

4 min read

Without food and water, the human body is only thought to survive for about one week, though with water alone, survival can be extended to several months. This guide details what happens to a body during starvation, outlining the body's desperate, multi-stage fight for survival as it consumes its own reserves.

Quick Summary

During starvation, the body enters survival mode by consuming its own reserves in a staged process, beginning with glycogen, followed by fat, and finally muscle protein. This progressive breakdown leads to severe metabolic slowdown, systemic organ damage, and immune system collapse.

Key Points

Glycogen Depletion: Within 24 hours of no food, the body burns its limited glycogen stores for energy before moving on to fat reserves.
Ketosis for Survival: The body's shift to burning fat produces ketone bodies, which the brain can use as an alternative fuel source, helping to conserve muscle protein in the short term.
Muscle Wasting: Once fat reserves are gone, the body enters a critical phase of breaking down its own muscle tissue and organ proteins for survival.
Immune System Collapse: Starvation severely weakens the immune system, making infections like pneumonia a major cause of death.
Organ Failure: The degradation of vital organ tissues, particularly the heart, liver, and kidneys, eventually leads to multi-organ failure and death.
Refeeding Syndrome: The process of reintroducing food to a starving individual must be carefully managed medically to avoid the fatal electrolyte shifts of refeeding syndrome.
Psychological Effects: Starvation causes severe cognitive impairment, apathy, irritability, depression, and anxiety due to energy deprivation to the brain.

The human body is remarkably resilient, equipped with several evolved physiological and metabolic defense mechanisms to survive periods of famine or severe caloric restriction. When deprived of food, the body initiates a systematic process of energy conservation and self-cannibalization to sustain vital functions. The progression of starvation can be broken down into distinct metabolic phases, each with its own set of critical physiological consequences.

The Metabolic Stages of Starvation

Phase 1: Glycogen Depletion (First 24 hours)

In the immediate hours after food intake ceases, the body's primary energy source is glucose circulating in the bloodstream. Once this is depleted, the body turns to its stored form of carbohydrates, known as glycogen, which is primarily located in the liver and muscles. The liver breaks down glycogen into glucose, releasing it into the bloodstream to maintain stable blood sugar levels for the brain, which is a significant consumer of glucose. This glycogen reserve is quickly exhausted, typically within 24 hours, triggering the body to shift its metabolic strategy.

Phase 2: Ketosis and Fat Burning (1-3 weeks)

After glycogen stores are depleted, the body's metabolic engine shifts dramatically to conserve protein and begin utilizing fat reserves. The liver starts breaking down fatty acids from adipose tissue into ketone bodies, a process called ketogenesis. Ketone bodies are water-soluble and can cross the blood-brain barrier, allowing the brain to use them as a major fuel source alongside a small amount of glucose. This shift significantly reduces the brain's glucose demand, effectively conserving muscle mass from being broken down prematurely. During this phase, weight loss is rapid initially, largely due to the loss of water associated with glycogen depletion, before slowing down as the body conserves energy.

Phase 3: Protein Breakdown and Organ Failure (3+ weeks)

The most dangerous stage of starvation begins once the body's fat reserves are exhausted. With no other readily available fuel, the body begins breaking down its own muscle tissue and proteins to convert the resulting amino acids into glucose. This process is known as protein catabolism. This leads to severe muscle wasting, weakness, and the deterioration of vital organs, including the heart. As the proteins essential for cellular function are consumed, organ function degenerates. The immune system collapses, making the body highly vulnerable to infections, which are a common cause of death in severe starvation.

The Severe Impact on Major Body Systems

Starvation affects nearly every system in the body in devastating ways, with consequences ranging from neurological deficits to full-blown organ failure.

Cardiovascular System: The heart, being a muscle, atrophies during the late stages of starvation. This can lead to a reduced heart rate, low blood pressure (hypotension), and severe electrolyte imbalances that can trigger fatal cardiac arrhythmias or sudden cardiac arrest.
Immune System: The extreme lack of nutrients compromises the body's ability to fight off infections. This immunosuppression means that a simple illness, such as pneumonia or gastroenteritis, can become fatal.
Digestive System: The digestive tract itself shrinks and its function is impaired. This leads to symptoms like nausea, vomiting, bloating, and severe constipation or diarrhea. In children, a severely protein-deficient state can lead to kwashiorkor, characterized by a bloated belly due to fluid retention and an enlarged fatty liver.
Brain and Mental State: The lack of consistent energy supply and hormonal imbalances have profound psychological effects. Individuals often experience irritability, apathy, depression, cognitive decline, and difficulty concentrating. Children can suffer irreversible brain development impairment.
Other effects: Hair loss, brittle nails, dry and flaky skin, and bone density loss are also common. The body's core temperature regulation fails, leading to a constant feeling of coldness.

Comparison of Metabolic Phases in Starvation


Feature	Phase 1 (First 24 hours)	Phase 2 (1-3 weeks)	Phase 3 (3+ weeks)
Primary Energy Source	Glycogen (stored carbs)	Fat (triglycerides)	Protein (muscle and organ tissue)
Metabolic State	Glycogenolysis	Ketosis, metabolic slowdown	Severe protein catabolism
Brain Fuel	Glucose	Ketones and limited glucose	Ketones and amino acids
Key Changes	Rapid weight loss (water), glucose regulation	Conservation of protein, breakdown of fat, slowed metabolism	Wasting of muscle and organs, immune collapse
Physical Symptoms	Irritability, hunger pangs	Weakness, fatigue, gaunt appearance	Severe weakness, organ failure, edema

The Dangers of Refeeding Syndrome

For those who survive prolonged starvation, the reintroduction of food must be managed carefully by medical professionals to prevent a potentially fatal condition called refeeding syndrome. This occurs when the body's depleted cells are suddenly flooded with carbohydrates, causing a rapid shift in electrolytes (like phosphate, potassium, and magnesium) into the cells. This can overwhelm the body's systems, leading to cardiac arrhythmia, respiratory distress, and heart failure. Specialized therapeutic food and fluids must be introduced gradually to stabilize the patient.

Conclusion

What happens to a body during starvation is a systematic, desperate, and ultimately devastating fight for survival. From the initial use of stored carbohydrates to the eventual consumption of the body's own muscle and organs, each stage brings more severe consequences. The process not only causes profound physical deterioration but also leads to debilitating psychological effects. Ultimately, organ failure, cardiac complications, and a compromised immune system leave the body unable to sustain life. The timeline and severity depend on individual factors like starting weight, but the outcome of unaddressed starvation is inevitably fatal.

For more information on the biochemical processes of starvation, consult the National Library of Medicine publication on Energy Metabolism in Feasting and Fasting.

Frequently Asked Questions

The very first energy source the body uses is the circulating glucose from recently digested food. Once that is gone, it quickly moves to break down stored glycogen in the liver and muscles, which is typically depleted within 24 hours.

Survival time varies significantly depending on factors like starting body fat, age, and health. While maximum survival with water has been cited as up to two or three months, individuals with less fat reserve will enter the most dangerous stages much sooner.

Ketosis is the metabolic state entered during starvation after glycogen is depleted. The liver breaks down fat into ketone bodies, which serve as the primary energy source for the brain and other organs, sparing protein from being used for fuel.

The body breaks down its muscle tissue to access the proteins and amino acids within. The liver converts these amino acids into glucose through gluconeogenesis, providing the brain with the critical energy it still requires after fat stores are exhausted.

Survivors of starvation may experience long-term health issues, including stunted growth in children, weakened bones, chronic fatigue, organ dysfunction, and psychological trauma such as depression or PTSD.

A swollen belly, or edema, can be a symptom of a severe form of protein-energy malnutrition called kwashiorkor. It is caused by fluid retention resulting from low levels of albumin in the blood, which is produced by the liver using protein.

Refeeding syndrome is a dangerous condition that occurs when food is reintroduced too quickly after a period of severe starvation. The rapid metabolic shift and electrolyte imbalances can lead to heart failure, respiratory distress, and death.

The lack of energy and nutrient deficiencies from starvation severely impact brain function, leading to a range of psychological effects. These include irritability, mood swings, depression, anxiety, apathy, poor concentration, and impaired cognitive abilities.