From Gelatin, Stress, Longevity by Ray Peat, Ph.D.
http://raypeat.com/articles/articles/gelatin.shtml
“People have asked me why I recommend gelatin since I recommend eating only whole foods. That is right, but we rarely eat whole foods, including whole animal foods. We throw away the bones and skin and are told not to eat the skin because it has fat in it. However this is precisely here where the gelatin is found. Gelatin contains thyroid-protective amino acids which can help balance the anti-thyroid (thyroid-suppressing) amino acids prevalent in muscle meats (beef, lamb, poultry and fish), mainly cysteine and tryptophan. In addition, the anti-thyroid amino acids are released in large quantities during stress and hypothyroidism itself increases the catabolism (tearing down) of protein even though general metabolism is slowed down.
Both tryptophan and cysteine inhibit thyroid function and mitochondrial energy production, and have other effects that decrease the ability to withstand stress. Tryptophan is the precursor to serotonin, which causes inflammation, immunodepression, and generally the same changes seen in aging. Histidine is another amino acid precursor to a mediator of inflammation, histamine.
Gelatin contains no tryptophan, and only small amounts of cysteine, methionine, and histidine. The main amino acids in gelatin are glycine and proline; alanine is also present in significant quantity. 35% of the amino acids are glycine, 11% alanine and 21% proline and hydroxyproline. These amino acids have cyto (cell) protective actions. Increasing consumption of gelatin and gelatin-rich foods will support normal function and structure in people who have a tendency towards the degenerative and inflammatory diseases of aging.” – Ray Peat PhD