What Happens When You Stop Eating?

Survival without food depends on body fat, hydration and overall health, so there is no fixed timeframe. With adequate water, people may survive for weeks or even months, but serious health complications can occur much sooner. During starvation, the body first uses stored carbohydrates, then fat and eventually breaks down muscle for energy. As starvation progresses, metabolism slows and serious complications, such as low heart rate, slowed digestion and fatigue can develop.

How long can you survive without food?

Overall, fats are the most important fuel in the body, and the length of time that a person can survive without any food depends mainly on the amount of fat stored.¹

However, because starvation affects each person differently, there is no single timeframe that applies to everyone. Survival is influenced by multiple other factors as well, including overall body composition, hydration, underlying medical conditions and access to medical support. For this reason, researchers generally describe broad ranges rather than a specific number of days that a person can live without food.

What does the research say about starvation?

There are no studies indicating how long it would take for an individual to die of starvation. The longest fast ever recorded lasted about 382 days, but included medical monitoring and IV fluids.²

Some studies have looked at the experiences of people on hunger strikes and discuss how long they have historically been endured, including³:

• Partial fasting: No solid food is consumed, but fluids and dietary supplements are taken; an indefinite survival estimate, but severely impacts health
• Total fasting: Only fluids are consumed; a survival estimate of up to three months
• Dry fasting: No fluids or solids are consumed; a survival estimate of up to one week

Studies of hunger strikes have shown that people can survive much longer without food than without water. Historical accounts of starvation and hunger strikes suggest that when adequate water intake is maintained, survival may be measured in weeks or even months, but serious health complications can still develop well before death occurs.

Although hunger strikes provide some insight into the effects of prolonged food deprivation, they do not establish a definitive timeline for starvation-related death.

Once the body is starved for long enough, there are a number of physiological changes across all organ systems that are difficult to reverse.

What happens during starvation?

When you stop eating, eventually your body will look for non-carbohydrate sources of glucose, through a process known as gluconeogenesis. Glucose is the body’s primary source of energy and fuels all functions of the body.

When you’re eating balanced and regularly, you’re getting glucose via different carbohydrate sources throughout the day, like grains, fruit, starchy vegetables, beans and legumes. When you’re not eating, your body finds different ways to synthesize glucose for fuel.

Starvation phase 1: Gluconeogenesis

Once you stop eating and no longer get glucose from your diet, your blood sugar will begin to fall, which will trigger the start of gluconeogenesis.⁴

When your body doesn’t have an immediate need for glucose for energy, it stores glucose in the muscles and liver in the form of glycogen, where it waits to be used later. These glycogen reserves are the first thing your body uses as a source of energy. Glycogen stores only last about a day or two before the body starts using other sources of fuel.

Starvation phase 2: Lipolysis

The body will deplete its glycogen reserves quickly before shifting to the breakdown of fat tissue or lipids, known as lipolysis, which will act as its primary source of energy during starvation.¹

When the body is starved, insulin levels fall and counter-regulatory hormones (like glucagon, epinephrine, cortisol and growth hormone) rise. This hormonal shift activates hormone-sensitive lipase and triggers fat breakdown in fat (adipose) tissue, primarily triglycerides, including:

• Free fatty acids (FFAs)
• Glycerol

Once these triglycerides are released, they are used directly by muscles and other tissues as fuel. They’re also broken down further in the liver into high-energy molecules. A byproduct of this is the creation of ketone bodies, which are also used to fuel the brain, muscle, heart and kidneys.

Ketones are particularly important for the brain because at this stage of starvation they are the brain's only source of fuel, as they can pass easily through the blood-brain barrier.

Starvation phase 3: Proteolysis

In addition to using fat reserves, the body also breaks down structural proteins and muscle tissues in a process called protein catabolism.

To do this, it begins breaking down proteins in skeletal muscle into amino acids. One important amino acid, alanine, is released into the bloodstream and transported to the liver to be converted into pyruvate, which is then used to produce new glucose through a process called gluconeogenesis.⁴

The newly made glucose is released back into the bloodstream and can be used by muscles and other tissues for energy. This recycling process, known as the glucose-alanine (Cahill) cycle, helps maintain blood sugar levels during prolonged fasting, but it comes at the cost of gradual muscle loss.⁴

Other energy sources

Certain tissues, including red blood cells and parts of the eye, cannot use fat or ketones for energy and rely almost entirely on glucose. When these tissues break down glucose, they produce lactate as a byproduct.

The body transports lactate through the bloodstream to the liver, where it is converted back to glucose and released into circulation. This process, called the Cori cycle, allows the body to recycle metabolic byproducts and stretch limited energy resources during periods of starvation.⁴

Metabolic changes during starvation

Basal metabolic rate (BMR) represents the energy required to perform essential functions at rest, such as maintaining body temperature, circulating blood, supporting brain function and keeping organs working. When calorie intake falls, the body responds by reducing the amount of energy it spends on these processes, allowing it to survive longer with limited energy.

There is an incomplete understanding of the cause of the hypometabolic state associated with starvation, which is greater than expected if it were only from a reduction of body mass.⁵ Tissue breakdown is one cause — direct atrophy of the organs results in lower metabolism. Hormonal changes, such as the changes to the thyroid hormone axis, also probably contribute to a reduced BMR, but this has not been directly studied in those with eating disorders.

Medical complications of starvation

Slow gut motility and gastroparesis

Malnutrition is frequently followed by gastroparesis, also known as delayed gastric emptying.⁶ As the body adapts to prolonged energy deficiency, it slows gastrointestinal function to conserve energy, including delayed gastric emptying and slow-transit constipation.

Low heart rate and blood pressure

Bradycardia (low heart rate) and hypotension are very common adaptations to malnutrition and starvation, in part due to increased activity of the parasympathetic nervous system.⁷

Low body temperature

Since heat is a byproduct of metabolism, a slower metabolic rate means less heat is generated. For example, digestion of consumed protein requires the body to use about 20-30% of the calories consumed to digest the proteins, which further contributes to the reduced metabolic rate. Also, as body fat and muscle mass are lost, the body loses both insulation and metabolically active tissue that helps produce heat.

Brain and mood changes during starvation

Brain fog

One common effect of starvation is difficulty concentrating and slower cognitive processing. People may experience "brain fog," trouble focusing, impaired memory or slower decision-making. This occurs because the brain has less readily available energy and because starvation alters neurotransmitter production and signaling.

Mood changes

Malnutrition can also have profound effects on mood and emotions, including⁸:

• Tension
• Depression
• Anger
• Fatigue
• Confusion
• Food behaviors

We know from the Minnesota starvation experiment that starvation itself results in many of the food behaviors that we see in individuals with eating disorders. It was observed that food became somewhat of an obsession, and individuals would toy with their food, often making fantastic concoctions and combinations. Many individuals would also dawdle over meals for hours.

Some of these changes are thought to result from alterations in neurotransmitters such as serotonin and dopamine, while others may reflect the psychological and physical stress of prolonged energy deprivation.

Sleep disruption

Sleep can also be affected.⁹ Some people have trouble falling asleep or staying asleep, while others report fatigue despite sleeping more. Hormonal changes associated with starvation, including alterations in cortisol and other regulatory hormones, may contribute to these disruptions.

Types of malnutrition

Malnutrition

Malnutrition is a broad term that includes both undernutrition and overnutrition, but in clinical contexts it often refers to deficiencies in energy, protein or micronutrients. It can occur even in individuals who appear to eat enough food if their diet lacks nutritional quality or if illness affects nutrient utilization.

Undernutrition

Undernutrition occurs when the body does not receive enough energy, protein or essential nutrients to maintain normal physiological function.¹⁰ It can result from inadequate food intake, poor nutrient absorption, increased metabolic needs or a combination of these factors.¹⁰

Protein-energy malnutrition

Protein-energy malnutrition (PEM) is a severe form of undernutrition characterized by insufficient intake of both protein and calories.¹⁰ PEM is classified as:

• Primary: occurring from inadequate nutrient intake
• Secondary: resulting from disorders or medications that disrupt nutrient absorption or use

Starvation

Starvation is the most extreme form of PEM that occurs when the body is deprived of total nutrition for a prolonged period, which can become life-threatening if not reversed.

Get Help for Malnutrition

If you or a loved one is struggling with malnutrition or an eating disorder, you’re not alone. Specialized medical care can address nutrient deficiencies, support healing and improve long-term outcomes. Don’t wait to get the support you need.

Start with a free assessment.

References

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2. Stewart, W. K., & Fleming, L. W. (1973). Features of a successful therapeutic fast of 382 days’ duration. Postgraduate Medical Journal, 49(569), 203-209. https://doi.org/10.1136/pgmj.49.569.203.
3. Haselwarter, D., Wild, V., & Kuehlmeyer, K. (2021). Providing health care in politically charged contexts: A qualitative study about experiences during a public collective hunger strike of asylum seekers in Germany. International Journal of Qualitative Studies on Health and Well-Being, 17(1), Article 2018770. https://doi.org/10.1080/17482631.2021.2018770.
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7. Yahalom, M., Spitz, M., Sandler, L., Heno, N., Roguin, N., & Turgeman, Y. (2013). The significance of bradycardia in anorexia nervosa. International Journal of Angiology, 22(2), 83-94. https://doi.org/10.1055/s-0033-1334138.
8. Stanga, Z., Field, J., Iff, S., Stucki, A., Lobo, D. N., & Allison, S. P. (2007). The effect of nutritional management on the mood of malnourished patients. Clinical Nutrition, 26(3), 379-382. https://doi.org/10.1016/j.clnu.2007.01.010.
9. Mutti, C., Malagutti, G., Maraglino, V., Misirocchi, F., Zilioli, A., Rausa, F., Pizzarotti, S., Spallazzi, M., Rosenzweig, I., & Parrino, L. (2023). Sleep pathologies and eating disorders: A crossroad for neurology, psychiatry and nutrition. Nutrients, 15(20), Article 4488. https://doi.org/10.3390/nu15204488.
10. Bhupathiraju, S. N., Hu, F., & Braunstein, G. (2025, December). Protein-energy undernutrition (PEU). Merck Manual Professional Version. https://www.merckmanuals.com/professional/nutritional-disorders/undernutrition/protein-energy-undernutrition-peu.