For years, we’ve been told a simple story about protein: eat it, digest it, break it down into amino acids, and rebuild. Clean, logical… and, as it turns out, incomplete.
What researchers are now uncovering feels less like a small update and more like a quiet revolution. Hidden within protein digestion are tiny fragments—di- and tri-peptides—that don’t just nourish the body, but communicate with it. And among the most fascinating of these are peptides built from glycine, proline, and leucine, amino acids long associated with collagen, muscle, and recovery.
The deeper you go into the science, the clearer it becomes: these molecules may be doing far more than we ever imagined.
A Shift in Understanding: Protein as a Messenger
One of the most pivotal human studies on collagen metabolism set out with a fairly straightforward question: what actually enters the bloodstream after we consume collagen?
Researchers conducted a controlled crossover trial in healthy participants, expecting to mostly find free amino acids circulating after digestion. Instead, they discovered something unexpected—significant levels of intact di- and tri-peptides, particularly those containing hydroxyproline (a derivative of proline), were present in the blood within hours. This landmark study confirmed that peptides such as Pro-Hyp and Hyp-Gly survive digestion and are absorbed intact into circulation (Iwai et al., 2005).
This was a turning point. It showed that these small peptides reach concentrations high enough to plausibly influence cellular behaviour. In other words, the body isn’t just receiving raw materials—it’s receiving instructions.
The Muscle Connection No One Saw Coming
If peptides can act as signals, the next logical question is: what are they telling the body to do?
A fascinating cellular study explored how collagen-derived peptides influence muscle development. Researchers exposed developing muscle cells (myoblasts) to peptides such as Pro-Hyp and observed a marked increase in their differentiation and fusion into mature muscle fibers (Shiro Jimi et al., 2021).
This wasn’t just a minor effect. The peptides appeared to enhance the very process of muscle formation itself.
Traditionally, muscle growth has been associated almost entirely with amino acids like leucine, known for activating the mTOR pathway—the body’s primary “on switch” for muscle protein synthesis. But here was something different: a collagen-derived peptide, rich in glycine and proline, influencing muscle development from another angle.
It suggests that building muscle isn’t just about flipping the growth switch—it’s also about creating the structural and cellular environment that allows muscle to form properly.
Ageing, Reconsidered at the Molecular Level
Perhaps the most striking insights come from newer translational research examining what might be the minimal effective unit of collagen activity: a simple tri-peptide composed of glycine, proline, and hydroxyproline.
Research led by Shigemura and colleagues demonstrated that these small peptide structures improved lifespan and mobility in animal models while enhancing collagen homeostasis in human cells. Early human findings also showed improvements in skin health and measurable reductions in biological ageing markers over several months of supplementation (Nicolina Virgilio et al., 2024).
That’s a profound concept. Not just feeling better or looking better—but measurable changes in the biological processes associated with ageing.
And again, the common thread wasn’t whole protein. It was specific peptide sequences.
Why These Three Amino Acids Matter So Much
At this point, a pattern begins to emerge. Glycine and proline form the backbone of collagen, the most abundant protein in the human body, accounting for a significant proportion of its amino acid composition. They give structure to skin, tendons, ligaments, and even the scaffolding that supports muscle itself. Glycine, in particular, also plays a broader physiological role, supporting anti-inflammatory processes and recovery.
Leucine, on the other hand, operates differently. It’s less about structure and more about activation. Research has shown that leucine directly regulates the initiation of muscle protein synthesis by activating the mTOR signalling pathway. This pathway becomes less responsive with age, contributing to anabolic resistance.
Seen together, they form a kind of partnership: glycine and proline help rebuild and stabilise tissue, while leucine signals the body to grow and adapt.
Translating Research Into Real Life
Most human studies on collagen peptides use doses in the range of 10–15 grams per day, providing several grams of glycine along with meaningful amounts of proline—levels associated with improvements in connective tissue health and recovery (Australian Institute of Sport, Collagen Supplement Framework).
For leucine, the effective threshold for stimulating muscle protein synthesis is typically around 3 grams per serving (Norton & Layman, 2006).
Here’s where things become interesting from a practical standpoint.
Traditional diets can provide these nutrients, but not always efficiently. Bone broth and slow-cooked meats contain collagen-derived peptides, while dairy and whey proteins are rich in leucine. However, achieving consistent, therapeutic levels—especially in the peptide forms shown to be biologically active—is difficult through food alone.
And consistency, as the research suggests, is everything.
A More Complete Approach to Strength and Ageing
When you step back and look at the full picture, a more nuanced model of health begins to take shape.
It’s no longer just about “getting enough protein.” It’s about delivering the right signals to the body—signals that support structural repair, stimulate muscle growth, and improve resilience against ageing.
This is where combining collagen peptides (rich in glycine and proline) with leucine aligns closely with the science. Rather than acting in isolation, these nutrients complement each other—one supporting the body’s physical framework, the other activating the processes that build and maintain muscle.
Formulations like 40up reflect this emerging understanding by bringing these elements together in a way that mirrors the pathways highlighted in research. Not as a replacement for whole foods, but as a more targeted way to consistently deliver the signals the body needs.
The Takeaway: A New Lens on Nutrition
What makes this area of research so compelling isn’t just the individual findings—it’s the shift in perspective they demand.
We’re moving from a view of nutrition as passive fuel to one where it acts as active biological communication. Small peptides, once overlooked, are now being understood as messengers capable of influencing how our bodies repair, grow, and age.
And perhaps the most exciting part is this: this isn’t abstract science. It’s something you can act on.
By paying attention not just to how much protein you consume—but to the forms it takes, the peptides it contains, and the signals it delivers—you begin to engage with your health on an entirely different level.
Not just feeding your body…
…but guiding it.
Author: Matt Hough – Director & Co-Founder of CollagenX
Matt Hough is a renowned researcher and innovator in the field of collagen science, serving as the Chief Researcher at CollagenX, one of Australia’s leading collagen brands. With over a decade of experience in scientific research and a passion for wellness, Matt has become a key figure in advancing the understanding and application of collagen in both skincare and overall health.
With a firm belief in the potential of collagen to improve quality of life, Matt’s work at CollagenX is driven by a commitment to producing scientifically-backed solutions that empower individuals to look and feel their best at any age.