Collagen or protein: why they are not interchangeable supplements

The question "why collagen if there is protein" is asked constantly, and usually it is answered in one of two extremes: either collagen is declared a more expensive and worse protein, or it is attributed to properties that ordinary protein does not have. Both answers are wrong for one reason - they skip the step where the goal should be stated. For building muscle mass and for connective tissue, these are different tasks with different data, and that is why a direct comparison of "which is better" does not make sense until it is said "better for what".

Two different goals that are constantly confused

Muscle tissue and connective tissue are made up of different proteins, and the mechanisms that trigger their synthesis are also different. Muscle protein synthesis is triggered primarily by a signal from branched-chain amino acids, primarily leucine, and is enhanced by force loading. Connective tissue — tendons, ligaments, dermis, cartilage matrix — consists mainly of collagen, rich in glycine, proline, and hydroxyproline, and its remodeling is triggered by mechanical loading.

So the question is split in two. Will collagen help build muscle? There is an answer to that, it's unambiguous, and it's below. Does it provide something for connective tissue that regular protein doesn't? That's an open question, and it's much more interesting.

For muscle, the answer is clear.

The most revealing direct comparison was performed by Oikawa et al. (2020). Twenty-two healthy women aged approximately 69 years were given 30 g of either whey or collagen protein twice daily for six days, with single-limb resistance training. Muscle protein synthesis was measured by two independent isotope methods: infusion of labeled phenylalanine for the acute response and deuterated water for the long-term response.

Whey protein gave a greater increase in both measurements. But the most interesting thing about this work is the second-level data that explains why. Total amino acid concentrations in the blood did not differ between the groups. The concentrations of essential amino acids also did not differ significantly. But the concentrations of leucine differed dramatically.

That is, it is not about the amount of protein or even the total amount of essential amino acids. It is about one specific amino acid signal, which is lacking in collagen. A similar picture was described by Aussieker et al. (2023) in young participants: after strength training, whey protein increased the rate of myofibrillar protein synthesis, while collagen did not have such an effect.

Collagen is not a complete protein

This should be said bluntly, without any softening. Collagen has no tryptophan at all—not a single trace—and the remaining essential amino acids are low. By any system of evaluating the quality of dietary protein, collagen is at the very bottom of the scale.

The practical conclusion from this is stark: collagen cannot be the main source of protein in the diet and does not replace it. If a person does not get enough protein and tries to fill the deficit with collagen powder, he gets calories and glycine, but does not get what the body needs protein for in the first place. When calculating the daily protein requirement, it is reasonable to not take collagen into account at all or to take it into account with a large correction.

The skeptic's argument: these amino acids are found in food

The strongest objection to collagen supplements is that glycine and proline are essential amino acids, the body synthesizes them on its own, and they are already supplied with food. The objection is largely valid, and it would be dishonest to pretend that this is not the case.

There are indeed enough sources:

• Connective tissue of meat - sinewy cuts, cartilage, poultry skin.
• Jellied meat and bone broth are concentrated gelatin in a household format.
• Gelatin as a culinary ingredient is the same protein as hydrolysate, only less processed.
• Self-synthesis - glycine is formed in the body mainly from serine.

There is, however, a calculation that complicates this picture. Meléndez-Hevia et al. (2009) brought together all the known flows of glycine formation and consumption in an adult. According to their estimate, the body’s own synthesis provides about 3 g per day, the diet provides another 1.5 to 3 g, and the total metabolic requirement, including collagen synthesis, exceeds this amount by about 10 g in a person weighing 70 kg. From this, the authors conclude that glycine is more correctly considered a semi-essential amino acid.

This should be treated with caution. This is an analysis of the balance of metabolic fluxes, not a direct experimental measurement of deficiency: the authors put together published estimates and showed that the arithmetic does not converge. The work is influential and often cited, but remains a theoretical construct, and presenting it as proven glycine deficiency in the population would be an exaggeration. The correct formulation is: the question of glycine sufficiency is not closed.

What then makes collagen special?

If amino acids are available from food, one thing remains that no other protein source provides: specific peptides.

Hydroxyproline is practically not found in other food proteins, so short fragments containing it can appear in the blood only after collagen raw materials. Neither whey protein, nor meat, nor eggs provide such peptides - simply because they do not have the corresponding sequences in their composition. This is the only undeniable difference between a collagen supplement and any other protein.

The question is whether this difference means anything biologically. In cell cultures, these peptides change the behavior of fibroblasts, and this is what the entire signaling hypothesis is based on—a detailed analysis of it, along with the limits of evidence, is in the material on Pro-Hyp, Hyp-Gly, and Gly-Pro-Hyp. The status of the hypothesis today is as follows: the mechanism is plausible, the data are obtained mainly outside the living organism, and the confirmation at the level of human tissue is partial.

So, the honest answer to the question “is there anything in collagen that is not in protein” is: yes, there is — unique peptides. Whether this provides practical benefits is an open question.

What follows from this?

Comparing these two supplements as competitors is a category error. They solve different problems, and each does not cope well with the other.

If your goal is muscle gain, muscle maintenance with age, recovery from strength training, collagen is not a smart choice, and direct comparisons make that clear. You need a complete protein with sufficient leucine, and whey protein is the best-studied for this.

If the goal is connective tissue, the situation is different, but not because collagen is proven to be better. It's just that ordinary protein has not been studied at all for this purpose as a specific agent, while collagen has been studied, and has given mixed but not empty results. Plus, it is the only one that supplies hydroxyproline-containing peptides. This is a reason for interest, not for confidence.

And separately about the base, which is forgotten in such comparisons: if the total protein intake is insufficient, no specialized supplement will compensate for this. The amino acid form in which you get protein from gelatin or hydrolysate is important only when the basic need is already covered.

A few words about precautions, and here they are different in two categories. Whey protein is obtained from milk, so it is not suitable for allergies to milk protein, and for severe lactose intolerance, the degree of purification is important. Collagen protein comes from fish, pork or cattle - accordingly, the allergens are different, and pork raw materials have religious restrictions. They have one thing in common: the total protein load on the body. That is why, in case of kidney pathology, the appropriateness of any protein powder is determined by a doctor, and it is worth discussing with him the reception during pregnancy, lactation or in parallel with constant drug therapy.

Frequently asked questions

Can protein be replaced with collagen?
No. Collagen has no tryptophan and few other essential amino acids, so it doesn't work as a primary source of protein.

Why doesn't collagen stimulate muscle growth?
In a direct comparison, it turned out that the total amount of amino acids in the blood after both proteins was the same, but there was significantly less leucine after collagen - it is he who triggers muscle protein synthesis.

Can you get the same amino acids from food?
Glycine and proline — yes, they are found in the connective tissue of meat, jellied meat, broth, and gelatin. This is a valid objection to supplements.

Does the body have enough of its own glycine?
The question is not closed. According to one well-known calculation of the balance of flows, the total demand exceeds the inflow, but this is a theoretical estimate, not a measured deficit.

What is there in collagen that no other protein has?
Hydroxyproline-containing peptides. Hydroxyproline is practically not found in other food proteins, so such fragments can appear in the blood only after collagen raw materials.

Is whey protein good for tendons and ligaments?
As a specific agent for connective tissue, it has been little studied. In the available studies, no increase in the synthesis of connective tissue proteins has been recorded after its use.

Does it make sense to take both supplements?
It depends on your goals and whether your basic protein needs are covered. A specialized supplement will not compensate for the overall protein deficiency in your diet.

Sources

• Meléndez-Hevia E. and others. (2009). A weak link in metabolism: the metabolic capacity for glycine biosynthesis does not satisfy the need for collagen synthesis. Journal of Biosciences. https://pubmed.ncbi.nlm.nih.gov/20093739/
• Ohara H. and others. (2010). Collagen-derived dipeptide, proline-hydroxyproline, stimulates cell proliferation and hyaluronic acid synthesis in cultured human dermal fibroblasts. The Journal of Dermatology. https://pubmed.ncbi.nlm.nih.gov/20507402/
• Oikawa SY et al. (2020). Whey protein but not collagen peptides stimulate acute and longer-term muscle protein synthesis with and without resistance exercise in healthy older women: a randomized controlled trial. The American Journal of Clinical Nutrition. https://pubmed.ncbi.nlm.nih.gov/31919527/
• Aussieker T. and others. (2023). Collagen protein ingestion during recovery from exercise does not increase muscle connective protein synthesis rates. Medicine and Science in Sports and Exercise. https://pmc.ncbi.nlm.nih.gov/articles/PMC10487367/
• Virgilio N. and others. (2024). Absorption of bioactive peptides following collagen hydrolysate intake: a randomized, double-blind crossover study in healthy individuals. Frontiers in Nutrition. https://pmc.ncbi.nlm.nih.gov/articles/PMC11325589/

Dietary supplement. Not a medicine. Consult a doctor before use.