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Collagen Supplements: What They Are, Types, Sources and Evidence

VITAMINS & SUPPLEMENTS · GUIDE

Collagen Powders as a Protein Source: Incomplete Protein and What That Means

Collagen is called an incomplete protein because it lacks tryptophan. What that means, what a few small trials compared with whey, and what the sources do not show.

Content last updated . This page has not been medically reviewed.

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Quick answer
Collagen is classed as an incomplete protein. A 2019 paper says that by the PDCAAS protein-quality method (a score that combines amino acid make-up and digestibility), collagen protein lacks one essential amino acid, tryptophan. [1] Essential amino acids cannot be made by the body and must come from food; tryptophan is one of the nine. [2] "Incomplete" describes protein quality. It does not say collagen is unsafe or useless. This page looks only at collagen as a protein source. For skin, joints and bone see Collagen for skin, joints and bone, and for the head-to-head comparison see Collagen vs protein powder.

What "incomplete" means

A complete protein supplies all nine essential amino acids; an incomplete one is missing or low in at least one. The nine are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. [2] The same authors who classified collagen as incomplete also describe it as a source of physiologically active peptides and conditionally essential amino acids. [1] MedlinePlus lists glycine and proline among the conditionally essential amino acids, needed mainly in illness and stress. [2] The authors' modeling suggested up to 36% of the protein in a typical Western-style diet could come from collagen peptides while still meeting essential amino acid needs. [1] Treat that as a calculation, not advice: one author reports research services for a maker of collagen-containing supplements. [1]

On a US label, protein grams may be calculated as 6.25 times the nitrogen content. [3] When a Percent Daily Value for protein is shown, the grams are first multiplied by a protein-quality score (the PDCAAS), so the percentage can be lower than the grams suggest for a lower-quality protein. [3]

What small trials compared

4 findings · 2 supported · 1 mixed · 1 limited or unclearThe colour follows the evidence label on each card.

  1. Oikawa 2020

    Promising but limited (very small)

    The rise in muscle protein synthesis (myofibrillar) was 13% greater with alpha-lactalbumin; its tryptophan and leucine in blood were higher [4]

    Design and amounts (study amounts, not advice): 11 endurance-trained adults, double-blind crossover; collagen peptides vs alpha-lactalbumin (a milk protein), 20 g after exercise and 40 g before sleep, after short intense cycling [4]

  2. Jacinto 2022

    Promising but limited

    Whey gave a larger increase in muscle thickness; strength and power gains were similar [5]

    Design and amounts (study amounts, not advice): 22 untrained young adults, 10 weeks of resistance training; 35 g whey vs 35 g collagen peptides matched for leucine [5]

  3. Impey 2018

    Biomarker only

    Whey raised blood leucine and a muscle signaling marker more than collagen [6]

    Design and amounts (study amounts, not advice): 8 men, one cycling session; 22 g servings of whey vs a hydrolyzed collagen blend [6]

  4. Zdzieblik 2015

    Mixed: placebo comparison, not whey

    Collagen group gained more fat-free mass and strength than placebo; an erratum was later published and one author is affiliated with a collagen research institute [7]

    Design and amounts (study amounts, not advice): 53 older men with sarcopenia (age-related muscle loss), 12 weeks of resistance training; 15 g a day collagen peptides vs placebo [7]

None of these trials proves collagen can replace complete proteins, and none tested long-term health outcomes. Proper evidence not found in what we read for collagen as the main or only protein source over months; we searched PubMed and Europe PMC for collagen protein quality, tryptophan and muscle trials. For older adults see Strength training and protein for older adults.

Frequently asked questions

Is collagen a complete protein?

No. A 2019 paper using the PDCAAS method says collagen lacks the essential amino acid tryptophan, so it is classed as incomplete. [1]

Is collagen as good as whey for muscle?

In the small trials we read that compared them, whey did better on muscle thickness or signaling markers, though strength gains were similar in one. [5][6] A trial in older men compared collagen only with placebo. [7]

Can I get all my protein from collagen?

We did not find a source that supports this. Essential amino acids must come from food, and collagen lacks tryptophan. [2][1] A dietitian can review your overall diet.

Does collagen count as protein on a label?

Label grams can be calculated from nitrogen, while a Percent Daily Value uses a quality-corrected amount. [3] Check which figure you are reading.

Does adding tryptophan fix collagen's amino acid gap?

Proper evidence not found. We did not read any source testing collagen with added tryptophan. Ask a clinician before adding amino acid supplements.

More details: evidence, limits and cautions

The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.

How to read the evidence labels

Labels used on this page: evidence in adequately nourished people, promising but limited, mixed, proper evidence not found.

Limits and uncertainty
  • Sample sizes are small and the studies short.
  • Comparators differ (placebo, alpha-lactalbumin, whey), so results do not transfer between them.
  • Muscle signaling and blood levels are not the same as lasting muscle or health outcomes.
  • Collagen products differ in source and processing; see Collagen types and sources.
Safety and who should ask a clinician
The NCCIH says many supplements have not been tested in pregnant women, nursing mothers or children, and that supplements can interact with medicines or pose risks before surgery. [8] People with kidney disease may need to limit protein; the NIDDK says to work out the amount with a dietitian or health care professional. [9] Ask a pharmacist or clinician about medicines. See Medication interactions and Quality testing and certifications.
References
  1. Paul C, Leser S, Oesser S. Significant amounts of functional collagen peptides can be incorporated in the diet while maintaining indispensable amino acid balance. Nutrients 2019;11(5):1079. One author declares research services for a maker of collagen-containing supplements. Read 2026-10-23.
  2. MedlinePlus (US National Library of Medicine). Essential amino acids. Review date 21 January 2025. Read 2026-10-23.
  3. U.S. Electronic Code of Federal Regulations. 21 CFR 101.9, Nutrition labeling of food. Text as published in the version dated 2025-10-01. Read 2026-10-23.
  4. Oikawa SY, et al. Lactalbumin, not collagen, augments muscle protein synthesis with aerobic exercise. Med Sci Sports Exerc 2020;52(6):1394-1403. Read 2026-10-23.
  5. Jacinto JL, et al. Whey protein supplementation is superior to leucine-matched collagen peptides to increase muscle thickness during a 10-week resistance training program in untrained young adults. Int J Sport Nutr Exerc Metab 2022;32(3):133-143. Read 2026-10-23.
  6. Impey SG, et al. Whey protein augments leucinemia and postexercise p70S6K1 activity compared with a hydrolyzed collagen blend. Int J Sport Nutr Exerc Metab 2018;28(6):651-659. Read 2026-10-23.
  7. Zdzieblik D, et al. Collagen peptide supplementation in combination with resistance training improves body composition and increases muscle strength in elderly sarcopenic men. Br J Nutr 2015;114(8):1237-1245 (erratum Br J Nutr 2025;134(5):440). Read 2026-10-23.
  8. NCCIH (US National Institutes of Health). Using dietary supplements wisely. Last updated January 2019. Read 2026-10-23.
  9. NIDDK (US). Eating and nutrition for chronic kidney disease. Last reviewed January 2025. Read 2026-10-23.
Education, not medical advice. This page is for general information. It does not diagnose or treat any condition and is not a substitute for care from a qualified health professional. Natural does not automatically mean safe. Ask a clinician or pharmacist before changing your care, especially if you take medication, are pregnant or breastfeeding, or have a health condition.