Keratin is a structural protein frequently discussed in relation to hair and nail health, leading many to wonder if it is found in food. This tough, fibrous protein is a fundamental part of the integumentary system in many animals. While the body uses amino acids obtained through the diet to synthesize keratin, the protein itself is not a direct dietary nutrient. Confusion often arises because the body requires the building blocks for keratin, not the final product, and because other similar structural proteins are consumable.
The Role and Location of Keratin in the Body
Keratin is best described as a fibrous structural protein, meaning it forms strong, thread-like structures that provide mechanical strength and protection to cells and tissues. This protein is naturally synthesized within the body by specialized cells called keratinocytes. These cells push upward and eventually die, leaving behind a highly resilient protective layer that forms the outer layer of the skin, the epidermis.
The protein is most famously concentrated in structures like human hair and fingernails. In the animal kingdom, it forms harder, more rigid structures such as horns, hooves, claws, beaks, and feathers. Scientists distinguish between two main forms: alpha-keratins, the more flexible type found in mammalian hair, skin, and nails, and beta-keratins, the harder forms found in the claws and feathers of birds and reptiles. Keratin imparts strength and durability, making the structures it forms resistant to damage and degradation.
Why Keratin is Not a Dietary Nutrient
Keratin is not considered a viable dietary nutrient because its unique molecular structure makes it virtually indigestible by the human body. The protein is characterized by a high content of the amino acid cysteine, which forms strong covalent links known as disulfide bonds. These bonds cross-link the protein chains into a rigid, highly stable matrix that is insoluble in water, acids, and organic solvents.
This high degree of cross-linking means that the proteolytic enzymes in the human digestive system, such as pepsin and trypsin, cannot effectively break down the protein structure. Consequently, if keratin were consumed, it would pass through the digestive tract largely intact. The body would be unable to access the amino acids locked within the protein.
Confusion with Related Structural Proteins
The search for keratin in food often stems from a confusion with other, more digestible structural proteins, primarily collagen and gelatin. Collagen is the most abundant protein in the human body, providing structure to connective tissues, bones, and skin. Unlike keratin, collagen is readily digestible and is routinely consumed for its perceived benefits to joint, skin, and hair health.
Gelatin is a derivative of collagen, created when animal connective tissues are boiled, which partially degrades the collagen structure. Both collagen and gelatin are found in food sources like bone broth and are commonly sold as dietary supplements. The perceived health and beauty benefits of these consumable proteins are similar to those incorrectly attributed to dietary keratin, leading to the common mix-up.
The Use of Keratin in Topical Products
The public most frequently encounters keratin through its use in cosmetic and hair care products, which reinforces its association with hair strength and appearance. In these applications, the keratin protein is not used in its native, insoluble form. Instead, it is subjected to hydrolysis, a chemical process that breaks the large protein molecules down into smaller fragments called hydrolyzed keratin or keratin peptides.
These smaller fragments possess a lower molecular weight, allowing them to temporarily penetrate the hair shaft’s outermost layer, the cuticle, or deposit on the surface. This topical application helps fill in minor gaps in the hair structure, which can reduce frizz and impart a smoother, shinier appearance. However, this effect is localized and temporary, functioning as a conditioning treatment rather than a permanent structural change.