What's it called when your body eats muscle?

December 19, 2025 •

4 min read

Over 200 million people are projected to be affected by sarcopenia, a form of muscle loss, in the next 40 years. When your body eats muscle, it's called catabolism, a metabolic process that breaks down complex molecules, including muscle tissue, for energy. This natural process can be exacerbated by conditions like starvation, chronic illness, and lack of exercise, leading to serious health consequences.

Quick Summary

The medical term for when the body breaks down its own muscle tissue is catabolism. This process is triggered when the body's primary energy sources, like glucose and fat, are depleted, forcing it to metabolize protein from muscles. Catabolism is a feature of serious conditions such as starvation, cachexia, and sarcopenia, and is often linked with chronic diseases, inactivity, or malnutrition. Understanding the causes and consequences is crucial for preventing muscle loss and maintaining overall health.

Key Points

Catabolism: The primary metabolic process where the body breaks down muscle tissue for energy, triggered when other fuel sources like fat and carbohydrates are depleted.
Sarcopenia: A specific type of age-related muscle atrophy, where muscle mass and strength progressively decline with age, often exacerbated by inactivity and malnutrition.
Cachexia: A severe muscle-wasting syndrome associated with chronic, advanced diseases such as cancer and heart failure, involving systemic inflammation that drives muscle and fat loss.
Prevention: Counteracting muscle breakdown involves a diet with adequate protein and calories, alongside regular resistance training to stimulate muscle repair and growth.
Symptoms: Signs of muscle loss include visible muscle thinning, unexplained weight loss, fatigue, and decreased strength or endurance.

When your body eats muscle, it's undergoing a metabolic process called catabolism. While this can happen normally, excessive or prolonged catabolism can lead to significant muscle wasting and health problems. The body preferentially uses carbohydrates and fats for fuel, but when these stores are depleted, it turns to protein, breaking down muscle tissue to provide amino acids for energy.

The Mechanisms of Muscle Breakdown

The breakdown of muscle tissue is a complex physiological process regulated by hormones and cellular signaling. The balance between two opposing metabolic states—anabolism (building up) and catabolism (breaking down)—determines whether you gain or lose muscle mass.

Hormonal Regulation: Hormones like cortisol, often released during periods of stress, fasting, or intense exercise, promote catabolism by stimulating the breakdown of protein for fuel. Conversely, hormones like insulin and testosterone promote anabolism, or muscle growth.
Nutrient Deprivation: When the body is deprived of calories, it enters a state where it must break down stored energy. After glycogen and fat stores are used, muscle protein becomes a primary fuel source. This is a survival mechanism, but prolonged use of muscle for energy can be dangerous.
Inflammatory Responses: Conditions associated with chronic inflammation, such as cancer or heart failure, can trigger a heightened catabolic state. Pro-inflammatory cytokines can disrupt the normal balance of protein synthesis and degradation, leading to muscle wasting.

Conditions Associated with Muscle Wasting

Several medical conditions and lifestyle factors can cause or accelerate muscle catabolism, resulting in a loss of muscle mass known as muscle atrophy.

Sarcopenia: This is age-related muscle loss and a common cause of muscle atrophy in older adults. It involves a gradual decrease in both muscle fiber size and number. While a natural part of aging, physical inactivity and poor nutrition can worsen the condition.
Cachexia: A severe muscle-wasting syndrome linked to underlying chronic illnesses like advanced cancer, HIV, and heart failure. Unlike simple starvation, cachexia is driven by systemic inflammation and increased metabolism, making it unresponsive to simple nutritional support.
Disuse Atrophy: This occurs when muscles are not used enough due to a sedentary lifestyle, bed rest from illness or injury, or immobilization in a cast. It can happen rapidly, but is often reversible with exercise and proper nutrition.
Neurological Disorders: Conditions that damage the nerves connecting to muscles, such as multiple sclerosis, amyotrophic lateral sclerosis (ALS), and stroke, can lead to neurogenic muscle atrophy. The lack of nerve signals prevents muscle contraction, causing the muscle to waste away.

Signs and Symptoms

Recognizing the signs of muscle breakdown is important for early intervention. These symptoms can vary depending on the underlying cause but often include:

Visible muscle loss: A noticeable reduction in muscle mass, with affected limbs or areas appearing smaller or thinner.
Muscle weakness: A significant decrease in strength or endurance, making everyday activities difficult.
Fatigue: A persistent feeling of tiredness or low energy.
Decreased physical performance: Finding it challenging to perform exercises or physical tasks that were previously manageable.
Unexplained weight loss: Losing weight without intentionally changing diet or exercise habits.

Preventing and Reversing Muscle Loss

Preventing muscle loss involves a multi-pronged approach combining diet, exercise, and addressing any underlying medical conditions. While some muscle breakdown is a natural part of metabolism, you can tip the balance back towards anabolism.

Adequate Protein Intake: Providing your body with sufficient high-quality protein (lean meat, eggs, fish, dairy) supplies the amino acids needed for muscle repair and growth. Experts suggest 25–30 grams per meal can be beneficial.
Resistance Training: This is the most effective way to stimulate muscle growth and prevent loss. Activities like weightlifting, resistance bands, and bodyweight exercises create tension on muscle fibers, triggering growth signals.
Sufficient Calories and Carbohydrates: Ensuring enough carbohydrates for energy prevents the body from breaking down muscle for fuel. A balanced diet prevents a significant caloric deficit that would force catabolism.
Rest and Recovery: Muscle synthesis and repair happen during rest and sleep. Adequate sleep is critical for maintaining an anabolic state and allowing muscles to recover after intense training.

Catabolism vs. Anabolism: A Comparison


Feature	Catabolism	Anabolism
Primary Function	Breaks down larger molecules into smaller ones.	Builds up smaller molecules into larger ones.
Energy State	Releases energy (exergonic).	Requires energy (endergonic).
Muscle Impact	Breaks down muscle tissue for energy (muscle wasting).	Builds and repairs muscle tissue (muscle growth).
Associated State	Starvation, chronic disease, overtraining, stress.	Proper nutrition, resistance training, rest.
Key Hormone	Cortisol, Glucagon.	Insulin, Testosterone, Growth Hormone.

Conclusion

When your body eats muscle, it is undergoing catabolism, a process that can be a normal metabolic function or a sign of an underlying issue. From age-related sarcopenia to disease-induced cachexia, understanding the mechanisms behind muscle wasting is essential for prevention. A balanced diet rich in protein and carbohydrates, paired with regular resistance and aerobic exercise, is the most effective strategy for promoting muscle maintenance and growth. For unexplained or severe muscle loss, a medical evaluation is crucial to identify and manage the root cause and ensure overall health and well-being.

Frequently Asked Questions

The primary medical term for the metabolic process of the body breaking down muscle for energy is catabolism. This is the counterpart to anabolism, which is the process of building muscle.

Under normal circumstances, your body burns available carbohydrates first, then stored fat. It only turns to muscle tissue for energy when these primary fuel sources are severely depleted, such as during starvation or prolonged, intense exercise without proper fueling.

The body is forced to break down its own muscle when it is in a prolonged caloric deficit and has exhausted its glycogen and fat stores. This can happen due to starvation, malnutrition, or chronic diseases that increase metabolism and inflammation.

To prevent muscle catabolism, you should ensure you consume enough calories and protein to meet your body's energy and repair needs. Engaging in regular resistance training is also key, as it signals your body to preserve and build muscle mass.

Sarcopenia is a medical condition characterized by the age-related, progressive loss of skeletal muscle mass, strength, and function. It is a natural part of aging but can be slowed with exercise and a healthy diet.

Some muscle loss can occur during weight loss, especially with a significant calorie deficit. However, strategies like a high-protein diet and resistance training can help preserve muscle mass while primarily burning fat.

Cachexia is a muscle-wasting syndrome driven by underlying disease and systemic inflammation, making it difficult to reverse with nutrition alone. In contrast, simple starvation is a lack of nutrient intake and can typically be reversed with proper nourishment.