How long does it take the body's organs to go into failure after not eating?

October 10, 2025 •

4 min read

While the human body is remarkably resilient, capable of surviving for weeks without food if water is available, the process of starvation begins almost immediately and puts immense strain on the body's organs. Understanding the timeline of how long does it take the body's organs to go into failure after not eating is crucial, revealing the critical physiological adaptations that occur when facing severe nutrient deprivation.

Quick Summary

This article details the physiological process of starvation, from initial glycogen and fat consumption to the breakdown of muscle tissue. It outlines the progressive impact on vital organ function, explaining how severe nutrient deprivation ultimately leads to irreversible organ failure and death. The timeline varies depending on individual factors like starting weight and health.

Key Points

Initial Stages: The body first burns stored glycogen in the liver (Phase 1) within the first 24 hours of not eating.
Mid-Stage Starvation: After about a day, the body enters ketosis, burning stored fat for energy (Phase 2), which can last for weeks depending on fat reserves.
Terminal Phase: When fat reserves are depleted, the body begins consuming its own muscle tissue, including vital organs like the heart, for energy (Phase 3).
Organ Failure Timeline: Significant organ decline, particularly in the heart, kidneys, and liver, typically begins after prolonged periods of fat and muscle consumption, potentially within a few weeks of severe starvation.
Cause of Death: The final cause of death in starvation is most often due to cardiac arrest, heart failure from muscle degradation, or fatal infections from a compromised immune system.
Water is Critical: The timeline for survival is far shorter without water; dehydration significantly accelerates organ failure, potentially causing death within a week.
Individual Factors: The exact timeline is not fixed and varies based on an individual's starting weight, body fat, age, and general health.

The body's intricate and efficient systems are designed to keep us alive, even in the absence of food. When calorie intake ceases, a series of metabolic changes are triggered to conserve energy and find alternative fuel sources. However, this emergency response can only last for so long before vital functions begin to fail, a process known as starvation. The timeline for this severe physiological decline is not a fixed number but is heavily influenced by factors such as initial body composition, age, and health status.

The Body's Emergency Fuel System

Within the first 24 hours of not eating, the body's primary energy reserves are depleted. In a well-fed state, the body primarily runs on glucose, which is derived from carbohydrates and stored as glycogen in the liver and muscles. Once this readily available glycogen is used up, the body must find a new source of fuel to maintain crucial brain function and energy levels.

Phase 1: Glycogen Depletion (First 24 hours)

The initial phase of starvation begins after about 8 to 24 hours without food. At this point, the liver converts its stored glycogen back into glucose to be used for energy. This phase is short-lived, as the liver's glycogen reserves are small. Individuals may experience initial symptoms like hunger, fatigue, and headaches as their blood sugar levels start to drop.

Phase 2: Ketosis and Fat Consumption (Days to weeks)

After the first day, with glycogen stores exhausted, the body enters a state of ketosis. The liver begins converting stored fat into ketone bodies, which are released into the bloodstream and can be used by most tissues, including the brain, for energy. This metabolic shift is the body's way of conserving muscle mass, which it views as a more critical asset for survival. The duration of this phase depends heavily on the individual's body fat percentage. People with higher fat reserves can sustain themselves on this fuel for weeks. Symptoms during this period include further fatigue, dizziness, and cognitive changes.

Phase 3: Protein Catabolism and Organ Failure (Weeks to months)

Once fat reserves are nearly or completely depleted, the body has no choice but to break down muscle tissue for energy, a process known as protein catabolism. This is the most dangerous stage of starvation and directly leads to organ failure. As muscle tissue from the body, and eventually the vital organs themselves, is consumed for fuel, the heart begins to shrink and weaken, leading to low blood pressure and a slow, irregular heartbeat. The kidneys, deprived of energy and proper fluid balance, begin to fail, resulting in electrolyte imbalances and a build-up of toxins. The immune system also becomes severely compromised, making the individual highly susceptible to infection. At this point, death is not far off, and can often be caused by cardiac arrest or pneumonia.

The Critical Role of Water in Survival

While food deprivation is the root cause of starvation, dehydration is a rapid and critical accelerant of organ failure. Without water, a person can only survive for about a week, as kidney function diminishes within a few days. The presence of adequate water allows the body to continue its metabolic processes longer, prolonging the timeline of starvation but not preventing its ultimate conclusion.

Organ Degradation in Starvation vs. Short-Term Fasting

It is important to distinguish between short-term fasting, which can have health benefits, and prolonged, involuntary starvation, which is destructive.


Feature	Short-Term Fasting (e.g., 1-3 days)	Prolonged Starvation (e.g., 3+ weeks)
Energy Source	Primarily glycogen, then fat via ketosis.	Primarily muscle protein after fat reserves are depleted.
Metabolic State	Shift to fat-burning (ketosis), often reversible.	Extreme catabolism; irreversible damage.
Organ Impact	Minimal, typically no long-term harm.	Severe decline in function, muscle wasting of heart and other organs.
Immune System	May see a temporary boost in cellular repair (autophagy).	Severely weakened, high risk of life-threatening infections.
Psychological Effects	Temporary hunger, mood changes.	Apathy, irritability, severe anxiety, cognitive decline.
Risk of Death	Extremely low for healthy individuals.	High; usually from heart failure or infection.

Conclusion: A Devastating Process

The question of how long does it take the body's organs to go into failure after not eating reveals the body's desperate final attempts to survive. After weeks of consuming fat stores, the process of breaking down vital muscle tissue, including that of the heart, marks the terminal phase of starvation. The ultimate cause of death is often cardiac arrest or overwhelming infection, a culmination of the body's systems failing under prolonged nutrient deficiency. Starvation is not a simple linear process; it is a gradual, devastating decline that ultimately leads to irreversible organ damage. It is a severe medical emergency requiring urgent intervention and careful refeeding to avoid refeeding syndrome, a potentially fatal complication that can occur when nutrients are reintroduced too quickly.

For more information on malnutrition and its effects, you can visit the World Health Organization website.

Frequently Asked Questions

The body first utilizes glucose derived from glycogen, a storage form of sugar located in the liver and muscles. These reserves are typically depleted within the first 24 hours of fasting.

With access to water, a person can survive for an extended period, possibly weeks or even a few months, depending on their initial body fat and health. With no food and no water, survival time is drastically reduced to about one week.

Initially, the body's central nervous system and liver are heavily involved in the metabolic changes. As starvation progresses, the heart and kidneys are significantly impacted as the body catabolizes their muscle tissue for fuel.

Yes. Short-term, voluntary fasting differs significantly from prolonged starvation. Fasting often involves controlled periods of calorie restriction, while starvation is a severe, involuntary deficiency that leads to long-term organ damage and is life-threatening.

Yes, prolonged starvation causes irreversible damage to organs. As the body breaks down muscle and tissue, critical organs like the heart and kidneys sustain damage that may not be fully recoverable, even with subsequent medical care.

The ultimate cause of death is generally cardiac arrest or cardiac arrhythmia, brought on by the severe degradation of heart muscle and critical electrolyte imbalances. Infections can also be a fatal complication due to a weakened immune system.

Refeeding syndrome is a potentially fatal shift in fluids and electrolytes that can happen when a severely malnourished person begins to eat again. It requires careful medical supervision to manage.