The Three Phases of Starvation: What Happens to the Body
Author: Thomas C. Weiss
Published: 1 Feb 2016 - Updated: 8 Nov 2026
Publication Type: Informative
Table of Contents:
Synopsis - Definition - Overview - FAQs - Insights, Updates - Related Content
Synopsis
This information explains how the human body responds when it gets far less energy than it needs, and why people can survive for weeks without food while lasting only days without water. Written by Thomas C. Weiss, it describes starvation as the most extreme form of malnutrition and walks through its three phases: the early use of stored glycogen and newly made glucose, a second phase in which fat and ketone bodies become the main fuel, and a final phase in which the body breaks down muscle and the proteins its cells need to function. It also covers the signs of advanced starvation, why treatment needs protein-rich, fortified food rather than bulk, and how marasmus and kwashiorkor differ. The material is useful for caregivers, nurses and families supporting people with eating disorders, malabsorption, swallowing problems or serious illness, where poor nutrition can creep up unnoticed.*
At a Glance
- 1 - Fatty acids fuel skeletal muscle, saving glucose for the brain.
- 2 - Advanced starvation can cause flaky skin, hair color changes and swelling in the legs and abdomen.
- 3 - Kwashiorkor can make a starving child look well fed, because fluid and a fatty liver swell the belly.
- 4 - Few people die directly from starvation, because a weakened immune system usually lets an infection take hold first.
Topic Definition
- Starvation
Starvation is the most severe form of malnutrition, in which the body takes in far less energy than it needs to survive, whether because food is unavailable or because illness stops it from being eaten, absorbed or used. The body adapts in stages, burning stored glycogen first, then fat, and finally its own muscle and essential proteins, which weakens the immune system and damages organs. Without treatment, prolonged starvation leads to infection, heart failure and death.
Overview
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.
Defining the Word "Starvation"
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:
- Disease
- Anorexia
- Deprivation
- Prolonged fasting
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.
The First Phase of Starvation
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 about a day. 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.
The Second Phase of Starvation
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
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:
- Apathy
- Withdrawal
- Listlessness
- Increased susceptibility to disease
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 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. Refeeding must be done slowly and under medical supervision, because restoring food too quickly can cause refeeding syndrome, a dangerous shift in fluids and electrolytes.
The process of starvation also results in dehydration, and treating 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 and Death
Few people die directly from starvation because they usually die of an infectious disease first.
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 usually 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.
More on this topic: Nutrition Publications - Metabolism Publications - Eating Disorders Publications
Frequently Asked Questions
NOTE: Researched FAQs by Disabled World (DW)
What is refeeding syndrome?
Refeeding syndrome is a dangerous shift in fluids and electrolytes such as phosphate, potassium and magnesium that can occur when a severely malnourished person starts eating again too quickly. It can cause heart and breathing problems.
How is malnutrition diagnosed?
Doctors look at weight loss, body mass index, muscle loss, eating history and sometimes blood tests. Screening tools such as MUST or the Mini Nutritional Assessment are often used in hospitals and care homes.
Can the body recover fully after starvation?
Many people recover with careful treatment, but long periods of starvation can cause lasting effects on the heart, bones, growth in children and mental health.
What is the difference between fasting and starvation?
Fasting is a short, usually voluntary break from eating that the body handles with stored energy. Starvation is a prolonged lack of energy that begins breaking down essential tissue.
Does starvation slow down metabolism?
Yes. The body lowers its resting energy use, body temperature and heart rate to save fuel, which is one reason weight loss slows during long periods of very low intake.
Who is most at risk of malnutrition in developed countries?
Older adults, people in hospital or long-term care, people with eating disorders, cancer, dementia or swallowing problems, and those living in poverty or isolation are at higher risk.
What are early signs that someone is not eating enough?
Unplanned weight loss, loose clothing, tiredness, weakness, feeling cold, dizziness, poor concentration and frequent infections can all be early signs.
How do eating disorders cause starvation?
In anorexia nervosa and some other eating disorders, a person severely restricts food, so the body goes through the same phases of starvation, which can damage the heart and other organs.
Insights, Analysis, and Developments
Editorial Note: Starvation is not only a problem of famine and war. In wealthy countries it shows up quietly in older adults living alone, in hospital and nursing home patients, in people with anorexia nervosa, and in people whose disabilities make eating, swallowing or absorbing food difficult. Weight loss, weakness, slow wound healing and frequent infections are early warning signs that deserve attention long before the final phase is reached. Recovery also carries risk: feeding a severely malnourished person too quickly can trigger refeeding syndrome, so nutrition should be restored gradually with medical monitoring of fluids and electrolytes. Anyone worried about a family member's weight or eating should involve a doctor or dietitian early.*
Author Credentials: Thomas C. Weiss is a researcher and editor for Disabled World. Thomas attended college and university courses earning a Masters, Bachelors and two Associate degrees, as well as pursuing Disability Studies. As a CNA Thomas has provided care for people with all forms of disabilities. Explore Thomas' complete biography for comprehensive insights into his background, expertise, and accomplishments.
* Editorial additions by Ian C. Langtree.