Yes, ATP Can Be Made From Proteins: The Metabolic Pathway Explained

December 19, 2025 •

2 min read

While carbohydrates are the body's primary energy source, accounting for most of its metabolic fuel, proteins can also be catabolized to produce ATP. This process serves as a crucial backup energy pathway, particularly during periods of starvation or prolonged fasting, when carbohydrate and fat stores are depleted.

Quick Summary

This article details the process by which the body breaks down proteins into amino acids to produce ATP. It explains protein catabolism, the role of deamination, and how the resulting carbon skeletons enter cellular respiration pathways, including glycolysis and the Krebs cycle.

Key Points

Metabolic Flexibility: The body can use proteins for energy, although carbohydrates and fats are the preferred fuel sources.
Breakdown into Amino Acids: Proteins are first broken into amino acids.
Deamination is Key: Amino acids must undergo deamination to remove their nitrogen-containing group.
Cellular Respiration Entry: The resulting carbon skeletons enter cellular respiration pathways at various points.
Last-Resort Energy: Protein is primarily used for ATP production during prolonged starvation or low energy states.
Lower Efficiency: Generating ATP from protein is less efficient than from carbohydrates.

The Basics of ATP Production

Adenosine triphosphate (ATP) is the universal energy currency for all living cells. The primary method of generating ATP is through cellular respiration, which is most efficient when using glucose from carbohydrates. The three main stages of cellular respiration are glycolysis, the Krebs cycle (citric acid cycle), and oxidative phosphorylation. While glucose is the most common substrate, the body is capable of converting other macronutrients, including fats and proteins, into usable energy. This metabolic flexibility is a critical survival mechanism.

The Journey from Protein to ATP

When the body needs energy and its preferred fuel sources (carbohydrates and fats) are scarce, it turns to protein. The metabolic pathway to generate ATP from proteins involves a few key steps:

Step 1: Protein Catabolism into Amino Acids

Proteins consumed in the diet are broken down by enzymes in the digestive system into their monomer components: individual amino acids. Intracellular proteins are also broken down and recycled in a process known as proteolysis, which is essential for normal cell turnover.

Step 2: Amino Acid Deamination

Before an amino acid can be used for energy, its amino group ($–NH_2$) must be removed. This process, called deamination, primarily occurs in the liver. This step removes the amino group, generating a carbon skeleton and toxic ammonia, which is processed for excretion.

Step 3: Entry into Cellular Respiration

After deamination, the carbon skeletons (keto acids) can enter cellular respiration pathways at various points depending on the amino acid. Some enter as pyruvate, others as acetyl-CoA, and some directly enter the Krebs cycle. These are then oxidized to produce ATP.

Comparison of ATP Yields: Proteins vs. Carbohydrates

The efficiency and ATP yield vary significantly between different energy sources, as shown in the table below.


Feature	Carbohydrates	Proteins
Primary Function	Immediate energy source, stored as glycogen	Structural, enzymatic, hormonal roles
Energy Yield (per molecule)	High (e.g., ~36-38 ATP per glucose)	Variable, lower than carbs, depends on amino acid
Metabolic Pathway	Glycolysis, Krebs cycle, oxidative phosphorylation	Deamination, then entry into glycolysis or Krebs cycle
Metabolic Byproducts	Carbon dioxide, water	Urea (requires energy to excr ete), carbon dioxide, water
Efficiency	High, preferred fuel source	Lower, used when other stores are low

When is Protein Used for Energy?

Protein is typically used for energy during specific conditions: when glycogen and fat are depleted, in low-carbohydrate diets where glucogenic amino acids can be converted to glucose, or when protein intake exceeds synthesis needs.

Conclusion

ATP can be produced from proteins, although this process is less efficient than using carbohydrates and is a secondary energy source. This pathway involves breaking proteins into amino acids, deamination, and integrating the carbon skeletons into cellular respiration. This metabolic adaptability is crucial during energy scarcity, but protein's primary roles are structural and functional. {Link: NCBI https://www.ncbi.nlm.nih.gov/books/NBK556047/}.

Frequently Asked Questions

The body's primary and most efficient way to get ATP is by breaking down glucose from carbohydrates through cellular respiration.

Amino acids enter the Krebs cycle after being deaminated (losing their amino group). The resulting carbon skeletons are converted into various intermediates of the cycle, such as alpha-ketoglutarate, succinyl-CoA, or oxaloacetate.

The removed amino group forms toxic ammonia ($NH_3$), which the liver converts into less toxic urea. The urea is then transported to the kidneys and excreted in the urine.

No, the pathway an amino acid takes to produce energy depends on its specific structure. Some are converted to pyruvate (glucogenic), others to acetyl-CoA (ketogenic), and some can do both.

While it is a vital survival mechanism, using protein for energy is less efficient and typically not ideal. Protein serves more important roles like tissue repair and enzyme creation, and relying on it for fuel can lead to muscle wasting.

Eating more protein doesn't directly increase your ATP levels. The body will first use protein for its primary functions. Only excess protein or protein consumed during energy deprivation will be broken down for fuel.

Fat provides significantly more ATP per gram than protein due to the higher energy content in its fatty acid chains. The process of breaking down fats (beta-oxidation) is a more concentrated source of energy than protein catabolism.