Bone Broth: Since bone broth is made of bones and connective tissue, it contains calcium, magnesium, phosphorus, collagen, glucosamine, chondroitin, amino acids, and many other nutrients.

Chicken: There’s a lot connective tissue contained in chicken, these tissues make chicken a rich source of dietary collagen.

Fish and shellfish: The “meat” of fish contains less collagen than other, less desirable parts. In fact, researchers have used fish skin as a source for collagen peptides, which Crushed Tonic is using marine collagen that is extracted from fish skin.

Egg whites: Egg whites have large amounts of proline which is one of the amino acids necessary for collagen production.

Citrus fruits: Vitamin C plays a major role in the production of pro-collagen, the body’s precursor to collagen. Therefore, getting enough vitamin C is critical.

Source: Healthline.com