What will happen to your body if you don't eat anything?

October 29, 2025 •

4 min read

Within the first 24 hours of not eating, your body depletes its primary glucose reserves, triggering a cascade of metabolic adaptations. Understanding what will happen to your body if you don't eat anything is crucial, as it involves a complex survival response with serious health consequences.

Quick Summary

The body initiates survival mode by burning stored carbohydrates, then fat, and eventually muscle tissue for fuel. This metabolic process leads to significant physical and cognitive impairments, organ damage, and can become fatal if prolonged.

Key Points

Metabolic Shift: In the absence of food, the body switches from burning glucose to utilizing fat stores (ketosis), and eventually breaking down muscle and organ tissue.
Initial Symptoms: Early effects of not eating include irritability, fatigue, and difficulty concentrating due to rapidly dropping blood sugar levels.
Organ Damage: Prolonged starvation leads to muscle wasting, a dangerously slow heart rate, low blood pressure, and potential damage to the heart, liver, and kidneys.
Cognitive and Psychological Impact: The brain, deprived of its primary fuel, can experience brain fog, anxiety, depression, and obsessive thoughts about food.
Hormonal Disruption: Fertility issues, irregular periods, low testosterone, and decreased thyroid function are common consequences of prolonged caloric restriction.
Refeeding Risk: Reintroducing food after extended starvation can trigger refeeding syndrome, a potentially fatal electrolyte imbalance that requires medical supervision.

The Body's Survival Mechanism: A Timeline of Starvation

When faced with a complete lack of food, the human body is remarkably adapted to survive by rationing its internal energy stores. This process is not a linear decline but rather a multi-stage metabolic shift designed to prolong life for as long as possible. However, this is a state of emergency, not a sustainable lifestyle, and comes with progressively severe health consequences.

Stage 1: The First 24 Hours

In the initial hours after your last meal, your body functions normally, using readily available glucose for energy. However, as blood sugar levels drop, the pancreas releases glucagon, a hormone that signals the liver to break down its stored glycogen (a reserve form of glucose) into usable energy. This liver glycogen is typically depleted within 18 to 24 hours, causing initial symptoms like fatigue, irritability, and difficulty concentrating.

Stage 2: 1 to 3 Days

With glycogen stores gone, the body enters a metabolic state called gluconeogenesis, creating its own glucose from non-carbohydrate sources, primarily amino acids derived from breaking down proteins. Simultaneously, the liver ramps up the production of ketone bodies from stored fat through a process called ketogenesis. These ketones become a primary fuel source for the brain and other tissues, significantly reducing the body's need to burn protein for glucose.

Stage 3: Weeks to Months

As starvation continues, the body becomes more efficient at utilizing fat stores and ketones to protect its muscle mass. This stage is often associated with significant weight loss, as fat reserves are systematically depleted. Symptoms like fatigue, dizziness, and low blood pressure become more pronounced. However, once fat reserves are exhausted, the body is left with no option but to accelerate the breakdown of muscle and other structural proteins for energy, a process known as protein wasting.

The Devastating Health Consequences

While the body's metabolic shifts are a testament to its resilience, prolonged starvation leads to widespread systemic damage. Nearly every organ system is negatively impacted, often with long-term or irreversible effects.

System-Specific Damage from Starvation

Cardiovascular System: The heart, being a muscle, is broken down for energy. This leads to a dangerously slow heart rate (bradycardia) and low blood pressure, increasing the risk of cardiac arrest and heart failure. Electrolyte imbalances can also cause irregular heart rhythms.
Endocrine System: Hormone production plummets. This can cause a cessation of menstruation in women (amenorrhea), low testosterone in men, and thyroid dysfunction. These hormonal disruptions impact fertility, growth, and metabolic rate.
Gastrointestinal System: Digestion slows dramatically, leading to severe constipation, bloating, and stomach pain. This is often due to the weakening of intestinal muscles and the lack of material to process.
Musculoskeletal System: Muscle mass wastes away as the body sacrifices it for protein. Bone density decreases over time, raising the risk of osteoporosis and fractures.
Immune System: A lack of essential nutrients, vitamins, and minerals severely compromises immune function. This makes the body highly susceptible to infections.
Neurological System: The brain, dependent on a stable energy supply, experiences significant impairment. Chronic under-eating can cause brain fog, difficulty concentrating, irritability, depression, anxiety, and obsessive thoughts about food. In severe, long-term cases, a loss of grey matter can occur and may be irreversible.

Starvation vs. Fasting: A Critical Comparison

It's important to distinguish between prolonged, involuntary starvation and controlled, supervised fasting, although both involve periods without food.


Feature	Prolonged Starvation	Controlled Fasting (e.g., Intermittent Fasting)
Intent	Involuntary, due to lack of food access or an eating disorder.	Voluntary, for potential health benefits or religious purposes.
Duration	Extended periods (weeks to months) without adequate nutrition.	Shorter, specific windows (e.g., 16-24 hours) with refeeding periods.
Metabolism	Body enters a severe hypometabolic state, reducing energy expenditure to a minimum.	Metabolic rate may adapt slightly but is not as severely suppressed as in starvation.
Risks	Life-threatening due to organ damage, electrolyte imbalance, immune failure, and muscle wasting.	Generally safer, but still carries risks like dehydration, dizziness, and electrolyte imbalance, especially if not done correctly.
Refeeding	Dangerous due to the risk of refeeding syndrome, which must be medically supervised.	Gradual reintroduction of food to avoid digestive distress is recommended, but a significant risk of refeeding syndrome is rare.

The Extreme Danger of Refeeding Syndrome

Paradoxically, the act of reintroducing food after a prolonged period of starvation can be deadly if not handled carefully. This is known as refeeding syndrome, a potentially fatal shift in fluids and electrolytes. During starvation, the body's mineral reserves are depleted. When food is reintroduced, the sudden metabolic demand to process it requires phosphorus, potassium, and magnesium, which are drawn from the bloodstream. This rapid depletion can lead to heart failure, respiratory failure, neurological issues, and seizures. Medical supervision is essential for those recovering from severe malnutrition.

Conclusion: Starvation is a Critical Health Emergency

Attempting to survive without eating is not a viable health strategy; it is a critical emergency that forces the body into a damaging survival state. While the body can endure short periods of fasting by utilizing its energy reserves, prolonged deprivation leads to malnutrition, muscle wasting, organ damage, and profound psychological distress. The risks are severe and can cause irreversible harm or death. For individuals struggling with restrictive eating patterns or an eating disorder, seeking professional medical and psychological help is vital. The human body is designed for sustenance, not deprivation, and its health depends on consistent, balanced nutrition. To ensure your long-term health, prioritizing regular, nourishing meals is the only safe and sustainable path.

For more information on the dangers of malnutrition and its treatment, consult resources like the Cleveland Clinic's detailed page on Malnutrition.

Frequently Asked Questions

In the first 24 hours, your body uses up its primary energy source, which is glucose stored in the liver as glycogen. This can lead to initial feelings of hunger, irritability, and low energy as blood sugar levels drop.

With adequate water intake, a person can potentially survive for a couple of months, depending on body fat reserves and overall health. However, without both food and water, survival is typically limited to about one week.

While starvation does cause rapid initial weight loss, it is extremely dangerous and unsustainable. The body eventually breaks down muscle tissue, and the long-term health consequences far outweigh any short-term weight loss.

Ketosis is a metabolic process where the body breaks down stored fat into molecules called ketones to use as an alternative energy source. It is a natural survival response that kicks in after the body's glycogen stores are depleted from not eating.

Not eating enough has significant negative effects on mental health, including anxiety, depression, heightened irritability, and obsessive thinking about food. The undernourished brain struggles to function properly, impacting mood and cognitive abilities.

Refeeding syndrome is a dangerous condition that occurs when a severely malnourished person is fed too quickly. The rapid shift in fluids and electrolytes can cause serious complications, including heart failure and respiratory distress.

No, intermittent fasting is a controlled eating pattern that cycles between periods of eating and fasting, typically lasting for shorter durations. Unlike prolonged starvation, it does not lead to the severe nutrient deprivation and metabolic shutdown that characterize true starvation.