Collagen becomes amino acids after eating, but it will not become collagen needed by the skin, which has little effect on beauty. Generally, protein can only be absorbed by human body after it is decomposed into small molecular compounds. Therefore, if the molecular weight of collagen is large, oral collagen can not achieve the purpose of directly supplementing collagen.

Collagen is a kind of polymer protein, which exists in human bones, tendons, teeth and skin. With the increase of age, the human body's collagen is gradually lost, but the collagen eaten becomes amino acids, which is not the collagen needed by the skin and has little effect on beauty. Generally, protein can only be absorbed by human body after it is decomposed into small molecular compounds. Therefore, if the molecular weight of collagen is large, oral collagen can not achieve the purpose of directly supplementing collagen.

Collagen peptide is an important part of skin. There is no denying the effect of collagen on the skin. Collagen accounts for 70% of the dry weight of the skin and can keep the skin smooth. With the increase of age, the amount in the skin gradually decreases. Collagen powder will be decomposed into free amino acids in digestive tract after entering human body. There are two ways for free amino acids to act in human body, one is to synthesize nitrogen-containing substances such as protein, and the other is the energy needed to decompose the body. However, it is uncertain whether the free amino acids obtained from collagen decomposition can be used for collagen synthesis.

Secondly, protein synthesized in human body will only be synthesized when needed. Even if the human body needs protein, there is no guarantee that it is the gene that guides collagen synthesis. Even if the gene that synthesizes collagen really works in vivo, it will only synthesize the primary structure of the protein. To play its role, protein needs to be a spatial structure to have its specific functions, which requires a series of mechanisms in the human body. Every step from collagen entering digestive tract to collagen synthesis is a small probability event. Therefore, it is almost impossible to supplement collagen by eating collagen.