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The "Paleo" cult has repopularized eating and preparing your own (Chicken) bone broth, but will this also help with bone and cartilage health?

Although youre probably thinking of collagen as the stuff thats important for joint health, its implications in human health are more far-reaching than most of us believe.

In fact, collagens are the most abundant group of organic macro-molecules in human and animal body. Because of their tensile strength, they perform numerous structural functions within the body - specifically in connective tissues which include among other tissue also organs as your heart, your intestines, your lungs and the parenchymal organs like the liver and the kidneys and even the fibrous matrix of skin and blood vessels.

As I already said, collagens are yet by far best known as structural components of the protein matrix of the skeleton and its related structures, like bones, teeth, tendons, cartilage and ligament, which bring us back to the original question that bothered me after assuring Chris who emailed me asking about the necessity of taking glycine and proline supplements in the absence of any other protein (my answer was "thats bullocks"): Do glycine and problem supplements even help with collagen synthesis and joint health? Or is the supplement vendor next door the only person who benefits?
We do have evidence (from rodent studies) that the ingestion of low molecular weight (=small peptides) collagen hydrolysates with intact glycyl-prolyl-hydroxyproline tripeptides that actually make it through the gut into the bloodstream and will increasee the organic substance content and decreased the water content of the left femur (Watanabe-Kamiyama. 2009). Previous studies had already shown hat the content of an orally administered gelatin hydrolysate will be incorporated into the cartilage tissue of rats (Oesser. 1999). Similar observations have been made by Iwai et al. for human volunteers and porcine gelatine hydrolysate, as well.

"After the oral ingestion, the peptide form of Hyp significantly increased and reached a maximum level (20-60 nmol/mL of plasma) after 1-2 h and then decreased to half of the maximum level at 4 h after the ingestion. Major constituents of food-derived collagen peptides in human serum and plasma were identified as Pro-Hyp. In addition, small but significant amounts of Ala-Hyp, Ala-Hyp-Gly, ProHyp-Gly, Leu-Hyp, Ile-Hyp, and Phe-Hyp were contained." (Iawai. 2005)

If we assume a similar physiological effect as it was observed by Watanabe-Kamiyama in rodents, the ingestion of (large) quantities of gelatine could thus very well, after its hydrolysation in the gut, have similar effects on human cartilage tissue as the collagen hydrolysate that was used in the Watanabe-Kamiyama study.

Table 1: Summary of Structure and Recovery of Food-Derived Collagen Peptide in Human Serum or Plasma after Oral Ingestion of Gelatin Hydrolysates (Iawai. 2005).

With respect to the occurence of glycyl-polyl-hydroxproline tripeptides, of which the Watanabe-Kamiyama study suggests that they may be responsible for the beneficial effects on cartilage synthesis it should yet be said that it occurred in human plasma only after the ingestion of chicken, but not in porcine collagen in the Iawai study (see Table 1). If thats no coincidence, HARIBO, which is usually made with porcine gelatine is no "collagen builder", a real chicken soup, cooked with bone, on the other hand, could be.

Given that your stomach is working properly a nice paleo bone broth (preferably from chicken bone) could thus produce similar results as a collagen hydrolysate of which a recent review in Current Medical Research and Opinion says that its ingestion stimulates a statistically significant increase in synthesis of extracellular matrix macromolecules by chondrocytes.

Figure 1: Physician rated (top) and subject-rated (bottom) improvement in joint pain walking (left) and standing (right) in the Clark study (Clark. 2008).

The authors, researchers from the University of Illinois College of Medicine at Chicago and the University of Kiel in Germany add:

"These findings suggest mechanisms that might help patients affected by joint disorders such as OA. Four open-label and three double-blind studies were identified and reviewed; although many of these studies did not provide key information – such as the statistical significance of the findings – they showed collagen hydrolysate to be safe and to provide improvement in some measures of pain and function in some men and women with OA or other arthritic conditions." (Bello. 2006)

Subsequent studies such as Benito-Ruiz et al. (2009) or Clark et al. who evaluated data from 97 athletes from a varsity team or a club sport in Pennsylvania support Bellos conclusion (see Figure 1).

Similar beneficial effects were also observed by  et al. in a more recent study with "normal" subjects with articular pain in response to 1,200mg/day of collagen hydrolysate (Bruyère. 2012). When were looking into the effects of single amino acids, however, things look different. If theyre ingested separately, glycine and proline are not going to form a tripeptide in the course of the digestive process. And while they may still serve as a raw material for the endogenous synthesis of such peptides the chance that they actively promote the synthesis of new collagen is slim.
References:

• Bello, Alfonso E., and Steffen Oesser. "Collagen hydrolysate for the treatment of osteoarthritis and other joint disorders: a review of the literature." Current Medical Research and Opinion® 22.11 (2006): 2221-2232.
• Benito-Ruiz, P., et al. "A randomized controlled trial on the efficacy and safety of a food ingredient, collagen hydrolysate, for improving joint comfort." International journal of food sciences and nutrition 60.S2 (2009): 99-113. 
• Bruyère, Olivier, et al. "Effect of collagen hydrolysate in articular pain: a 6-month randomized, double-blind, placebo controlled study." Complementary therapies in medicine 20.3 (2012): 124-130.
• Iwai, Koji, et al. "Identification of food-derived collagen peptides in human blood after oral ingestion of gelatin hydrolysates." Journal of agricultural and food chemistry 53.16 (2005): 6531-6536.
• Oesser, Steffen, et al. "Oral administration of 14C labeled gelatin hydrolysate leads to an accumulation of radioactivity in cartilage of mice (C57/BL)." The Journal of nutrition 129.10 (1999): 1891-1895. 
• Ross, B. D., R. Hems, and H. A. Krebs. "The rate of gluconeogenesis from various precursors in the perfused rat liver." Biochem. J 102 (1967): 942-951.
• Saito, Masataka, et al. "Effect of collagen hydrolysates from salmon and trout skins on the lipid profile in rats." Journal of agricultural and food chemistry 57.21 (2009): 10477-10482.
• Watanabe-Kamiyama, Mari, et al. "Absorption and effectiveness of orally administered low molecular weight collagen hydrolysate in rats." Journal of agricultural and food chemistry 58.2 (2009): 835-841.