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Page 16 of 24 Reilly et al. Plast Aesthet Res 2021;8:2 I http://dx.doi.org/10.20517/2347-9264.2020.153

Figure 12. Collagen protein, whether intact or partially hydrolysed, is enzymatically hydrolysed in the gut to amino acids, dipeptides
and tripeptides, which allows for transport across the intestinal wall and into the bloodstream (A,B,C). Perfusion of peptides and amino
acids and bioavailability in the ECM allows for stimulation of fibroblasts and collagen synthesis (D). (By permission of MINERVA
Research Labs Ltd - London)

All proteins and peptides need to be hydrolysed in the gut to allow absorption into the bloodstream and
transport throughout the body [Figure 12]. Following ingestion, partially hydrolysed collagen peptides
[91]
in supplements are further digested and hydrolysed in the gut . This is carried out by the action of the
acidic environment in the stomach, as well as by the action of specific enzymes in the intestines (trypsin,
chymotrypsin, elastase, carboxypeptidase) which break up the collagen peptides into smaller molecular
weight fragments. The peptides are progressively broken down as they pass into and through the intestines
to yield small peptides (typically di- and tri-peptides) and free amino acids. It has been estimated that 90%
of absorbed proteins is represented in the circulatory system as amino acids, where only 10% is present
as di- or tri-peptides [92,93] . This enzymatic processing facilitates cellular uptake typically via transporter
proteins (such as amino acid cotransporter systems or the low-affinity, high-capacity peptide transporter,
PEPT1) to deliver the nutrients from the lumen into the enterocyte cells, and across the basolateral
membrane of the enterocyte into the bloodstream.

From a liquid format, the ingredients are readily absorbed into the bloodstream (typically in about 20 min
after ingestion). By comparison, absorption from solid foods can take several hours. Similar to the process
for digestion and absorption of proteins, the majority of minerals, vitamins and other nutrients (e.g., sugars,
[94]
lipids) are absorbed as simple compounds into the bloodstream . From the bloodstream, these ingredients
are then distributed throughout the whole body. Perfusion of micronutrients out of capillary loops and into
the skin, creates a microenvironment enriched with nutrients which bathes the dermis.