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What is the most abundant protein in the human body?
Collagen is considered the most abundant protein in the human body, but its exact share of total protein has never been measured in a whole human.
Matic Broz Computational chemist
Collagen is generally considered the most abundant protein in the human body. More precisely, type I collagen is the dominant member of a large collagen family. Together, collagens are often said to make up about 30% of the body's protein mass.
No study has directly measured every protein in an entire human body. A 2023 whole-mouse study traced the 30% claim through more than 50 papers and found no original measurement behind it. Published human research still identifies type I collagen as the most abundant protein, while its exact share remains unknown.
What is the most abundant protein in the human body?
Collagen is the conventional answer, and type I collagen is the form usually meant by the claim.[1][2]
Collagen is a family of 28 proteins found mainly in the extracellular matrix, the material around cells that gives tissues structure. Its members form much of the framework of skin, bone, tendons, ligaments, cartilage, blood vessels, and many organs.[1]
That ranking applies to the human body. Across the biosphere, Rubisco is the best-supported candidate for the most abundant protein on Earth.
“Most abundant” refers to estimated total mass across the body. It does not mean the number of distinct protein sequences, the number of protein-coding genes, or the number of molecules in one cell. Those are separate questions, as explained in our guide to how many proteins humans have.
At sequence level, collagen is not one entry. The alpha chains that assemble into collagen are distinct proteins, which alignment tools such as Clustal Omega compare separately. Whole-body estimates usually group these chains and collagen types under the single name “collagen.”
How much collagen is in the human body?
The often-repeated estimate is that collagen accounts for about 30% of total body protein. Applied to the 10.5 kilograms of protein in a 70-kilogram reference man, that would be roughly 3.2 kilograms (7 pounds) of collagen.[1][6]
The 3.2-kilogram figure comes from a calculation, not a whole-body measurement: 10.5 kilograms of protein multiplied by 30% equals 3.15 kilograms. It should not be read as 30% of total body weight. The reference-man model describes a standardized male body, not an average for every adult.[6]
Even the 30% share is uncertain. No direct whole-human measurement establishes it.[1][3]
In 2023, researchers searched more than 50 papers that repeated the 30% figure. None pointed to an original measurement. The likely trail led to older mouse work that put collagen closer to one-fifth of total body protein.[3]
The researchers then measured whole mice using hydroxyproline, an amino acid enriched in collagen. Collagen made up about 12% of total protein in female mice and 17% in male mice. The same study found large differences by tissue, from about 0.1% in brain and liver to 40% to 50% in tendon.[3]
Mouse values cannot be substituted for human values. They show why “about 30%” should be treated as a common estimate rather than a measured human constant.
Collagen is also hard to quantify. Its cross-linked fibers are difficult to dissolve and digest, so mass spectrometry can undercount it. In the mouse study, proteomics detected only about 5% to 6% collagen, while hydroxyproline measurements on the same animals gave 12% to 17%.[3]
What is the most abundant type of collagen?
Type I is the most abundant collagen in the human body.[1][2]
It forms strong fibrils in skin, bone, tendons, ligaments, cornea, and other connective tissues. This wide distribution is why “type I collagen” and “collagen” are often used interchangeably when sources name the body's most abundant protein.
Other collagen types have more specialized distributions. Type II predominates in cartilage, type III occurs alongside type I in skin and blood vessels, and type IV forms sheet-like networks in basement membranes. These are different proteins with different genes and structures, even though all belong to the collagen family.[1]
How much protein is in human blood?
A 70-kilogram reference-man model assigns about 0.99 kilograms of protein to blood, or 9.3% of total body protein. That estimate covers whole blood, including proteins inside blood cells, rather than the result of a clinical total-protein test.[6]
Clinical total-protein tests measure the fluid portion of blood. A common reference interval is 60 to 80 grams per liter in serum or plasma.[7] An average adult has nearly 5 liters of blood, of which about 60% is plasma.[8] Combining those reference values gives roughly 180 to 240 grams of dissolved plasma protein. This is a derived estimate, and the actual amount varies with blood volume, hydration, and the laboratory's reference range.
Whole blood contains much more protein because red blood cells are packed with hemoglobin. Adult reference ranges for hemoglobin are about 130 to 170 grams per liter for men and 120 to 150 grams per liter for women.[9] Across 5 liters of blood, those concentrations correspond to roughly 600 to 850 grams of hemoglobin. This calculation uses reference values rather than a measurement from one person.
Albumin is the most abundant protein in plasma and makes up more than half of serum protein. Hemoglobin is the dominant protein inside red blood cells, accounting for about 90% of their dry weight.[4][5]
Albumin and hemoglobin lead within their compartments, while collagen refers to estimated protein mass across the whole body.
| Scope | Most abundant protein | Basis |
|---|---|---|
| Whole body, by estimated protein mass | Collagen family, especially type I | Common estimate; exact human share is unmeasured |
| Blood plasma or serum | Albumin | 60 to 80 g/L total protein; albumin makes up more than half |
| Whole blood | Hemoglobin | 120 to 170 g/L hemoglobin in common adult reference ranges |
| Red blood cells | Hemoglobin | About 90% of red-cell dry weight |
| Collagen family | Type I collagen | Dominant collagen across connective tissues |
The comparison draws on collagen-family reviews, clinical reference intervals, and red-cell proteomics.[1][2][4][5][7][9] When a source names albumin or hemoglobin as the most abundant protein, check whether it means plasma, whole blood, or red blood cells rather than the whole body.
Sources▼
- The Collagen Family Cold Spring Harbor Perspectives in Biology · 2011. https://pmc.ncbi.nlm.nih.gov/articles/PMC3003457/
- RNA protein interactions governing expression of the most abundant protein in human body, type I collagen Wiley Interdisciplinary Reviews: RNA · 2013. https://pubmed.ncbi.nlm.nih.gov/23907854/
- Collagen constitutes about 12% in females and 17% in males of the total protein in mice Scientific Reports · 2023. https://www.nature.com/articles/s41598-023-31566-z
- Serum Albumin and Globulin Clinical Methods, NCBI Bookshelf · 1990. https://www.ncbi.nlm.nih.gov/books/NBK204/
- Red blood cell proteomics update: is there more to discover? Blood Transfusion · 2017. https://pmc.ncbi.nlm.nih.gov/articles/PMC5336341/
- Skeletal Muscle Markers National Academies Press · 1999. https://www.ncbi.nlm.nih.gov/books/NBK224632/
- Total Protein Oxford University Hospitals NHS Foundation Trust · July 22, 2026. https://www.ouh.nhs.uk/biochemistry/tests/tests-catalogue/total-protein/
- Physiology, Blood Volume StatPearls, NCBI Bookshelf · 2023. https://www.ncbi.nlm.nih.gov/books/NBK526077/
- Test Repertoire and Reference Ranges University Hospitals Dorset NHS Foundation Trust · July 22, 2026. https://www.uhd.nhs.uk/services/pathology/haematology/test-repertoire-and-reference-ranges
Founder and computational chemist, ProteinIQ
Dr. Matic Broz is the founder of ProteinIQ and a computational chemist. He completed a PhD focused on protein structure, molecular dynamics, and neural networks, and writes about structural biology and scientific software.