A protein label says 25 grams. That number came from a lab test — and the test didn’t measure protein.
It measured nitrogen, then multiplied. Everything in this post follows from that one substitution.
The measurement, and why it’s a proxy
The two standard assays are the Kjeldahl method and the Dumas method. Both measure total nitrogen in a sample and multiply by a conversion factor to estimate protein[1].
The factor is usually 6.25, though it varies by food group — Codex Alimentarius ranges run 5.18 to 6.38, with 6.38 used for dairy[5].
This works reasonably well in ordinary food, where protein is the main source of nitrogen[6].
The gap is stated plainly in the literature: these methods measure total nitrogen and cannot distinguish nitrogen coming from protein or from freely added nitrogen-rich compounds[5].
So the test answers “how much nitrogen is here” and the label reports “how much protein.” Those are the same question only if all the nitrogen came from protein.
How the gap gets exploited
Adding cheap nitrogen-rich compounds raises the reading without adding usable protein.
The compounds named repeatedly across sources: glycine, taurine, creatine, glutamine, arginine, lysine[1][2][5].
Two properties make them useful for this. They’re cheaper than whey, and some are higher in nitrogen per gram than protein itself[4]. Glycine is described as particularly favoured because it’s among the cheapest available[2].
The result is a label showing 25 grams where a meaningful portion of the nitrogen came from compounds that don’t contribute to the essential amino acid pool[7].
There’s a precedent worth knowing, because it shows how far the logic extends. The melamine scandal involved adding an extremely nitrogen-rich industrial compound to pet food and infant formula to boost protein analytics[4].
Same exploit, different substance.
It has been litigated
This isn’t hypothetical.
A class action against Iovate Health Sciences — manufacturer of brands including MuscleTech, Six Star and Epiq — resulted in a California federal court approving a $2.5 million settlement[4].
The settlement terms are the informative part. It required the company to change its testing practices and eliminate amino acids, creatine, and other nitrogen-producing non-protein compounds from its protein claims going forward[4].
That tells you what the disputed practice was, in the company’s own settlement language.
Why labs can’t easily fix it
You might expect a better test to close this. It’s harder than it sounds.
An industry analysis describes the sequence. To get an accurate figure, a lab must first correct for non-protein nitrogen by subtracting it from the Kjeldahl result[3].
A free amino acid test finds nitrogen from added amino acids like lysine and glycine. Subtracting that gives a better measure — but it doesn’t account for other non-protein nitrogen like creatine and taurine[3].
The analyst’s own question captures the problem: at what point does the lab stop searching for non-protein nitrogen in a product?[3]
Each correction requires knowing what to look for. A compound nobody tested for stays counted.
Alternative approaches are being explored — mid-infrared spectroscopy has been identified as potentially complementing Kjeldahl by characterising protein structure rather than counting nitrogen[8]. That’s a research direction, not current standard practice.
What you can check
You can’t confirm spiking without a lab test[4]. But the panel gives signals.
| Signal | What it suggests |
| Individual amino acids listed separately — glycine, taurine, creatine, glutamine | Nitrogen sources outside the protein blend |
| Proprietary blend with no individual amounts | Quantities not disclosed |
| No amino acid profile published | Composition unverifiable |
| Price notably below comparable products | Cheaper nitrogen substituted |
[Table 1] Signals on a protein label · Source: Compilation of related materials[1][2][4]
The first row needs a qualifier. Seeing these amino acids as part of the declared protein blend is normal — they occur in protein. The signal is when they appear as separate line items in the ingredient list of a protein powder[2].
A bit more detail — on reading an amino acid profile if you obtain one. A reference point for a plant blend is roughly leucine 7–8 g, isoleucine 4–5 g, valine 4–5 g per 100 g protein[7]. One caveat: during the hydrolysis step of amino acid analysis, some amino acids such as tryptophan are partially destroyed, so a discrepancy of 5–15% between methods is not in itself evidence of a problem[7].
Where this sits in the wider picture
Two connections worth drawing.
This is the same shape as problems covered earlier in this series. Cranberry PAC content varied 3.6-fold depending on the reference standard. Collagen molecular weight depends on which averaging method was used. In each case, a number on a label is the output of a measurement procedure — and knowing the procedure changes how much the number means.
And it doesn’t change the underlying advice. As covered in the protein requirement post, middle-aged Korean women on average already exceed the recommended intake, and the more useful variable was distribution across meals rather than total. A label problem matters most for people relying heavily on powder.
If you’re in Korea
Two practical notes.
Protein products sold as health functional foods carry the mark and an approved functional claim, with the associated review. Protein powders sold as ordinary processed food do not — as covered in the mark post, that distinction determines what oversight applied.
Third-party certification is one available check. Certification programmes verify content against label claims, though the specific scope varies by programme, so it’s worth reading what a given certification actually tested.
Closing
What struck me was that the loophole isn’t a regulatory oversight so much as a consequence of using a proxy.
Nitrogen stands in for protein because measuring nitrogen is cheap and, in ordinary food, close enough. The substitution is reasonable until someone has a reason to exploit it — and then correcting for it turns into an open-ended search, as the lab analyst’s question makes clear.
The melamine precedent is the uncomfortable version of the same point. Once a number becomes the target, the number and the thing it stood for can come apart.
Practically, the checks are modest: read the ingredient list for separately declared amino acids, ask for an amino acid profile, and treat an unusually low price on a high-protein claim as a question rather than a bargain.
Key Terms
- Kjeldahl method — the standard laboratory assay that measures total nitrogen and converts it to an estimated protein figure.
- Dumas method — an alternative nitrogen-measurement assay with the same underlying limitation.
- Conversion factor — the multiplier applied to nitrogen to estimate protein, usually 6.25.
- Non-protein nitrogen (NPN) — nitrogen from sources other than intact protein, such as free amino acids or creatine.
- Free amino acids — individual amino acids not bound into a protein chain.
- Amino acid profile — a breakdown of which amino acids a product contains and in what amounts.
At a Glance
- Standard assays measure total nitrogen, then multiply by a conversion factor (usually 25, ranging 5.18–6.38 by food group)
- They cannot distinguish protein nitrogen from added nitrogen-rich compounds
- Commonly cited spiking agents: glycine, taurine, creatine, glutamine, arginine, lysine
- Some are higher in nitrogen per gram than protein itself, and cheaper than whey
- The melamine scandal exploited the same measurement gap
- A class action against Iovate settled for $2.5 million, requiring removal of non-protein nitrogen compounds from protein claims
- Correcting for non-protein nitrogen is open-ended — each correction requires knowing what to look for
- Panel signals: separately listed amino acids, proprietary blends, no published profile, unusually low price
※ This article explains how protein content is measured and labelled, for general information only. It does not evaluate or accuse any specific product or brand, and does not replace medical or nutritional advice. If you have kidney disease or have been advised to manage protein intake, consult a clinician before using protein supplements.
References
- “How to Spot Amino Spiking on a Nutrition Label”, ALLMAX Nutrition (Kjeldahl and Dumas methods, conversion factor, panel signals), https://www.allmaxnutrition.com/blogs/nutrition/how-to-spot-amino-spiking
- “Amino Acid Spiking — The Supplement Industry’s Protein Fraud Problem”, Optimal Amino (compounds used and ingredient-panel interpretation), https://optimalamino.com/blogs/the-science/amino-acid-spiking
- “Protein Products Vulnerable to Amino Acid Spiking”, Nutritional Outlook (laboratory correction sequence and the limits of NPN subtraction), https://www.nutritionaloutlook.com/view/protein-products-vulnerable-amino-acid-spiking
- “What Is Protein Spiking and How Do You Spot It?”, ScienceInsights (Iovate settlement terms, nitrogen density of glycine and lysine), https://scienceinsights.org/what-is-protein-spiking-and-how-do-you-spot-it/
- “How Different Is EAA Fortification Versus Amino Spiking?”, GPNI (Codex conversion factor ranges and measurement limitation), https://www.thegpni.com/articles/show/169/How-Different-Is-EAA-Fortification-Versus-Amino-Spiking
- “What Is Amino Spiking in Protein Supplements?”, Biology Insights (why nitrogen works as a proxy in ordinary food), https://biologyinsights.com/what-is-amino-spiking-in-protein-supplements/
- “Amino Spiking: What It Is and How to Spot Protein Quality”, Bunaroba (reference amino acid profile and hydrolysis caveat), https://bunaroba.ch/en/knowledge/aminospiking/
- “Whey Protein Powder Analysis by Mid-Infrared Spectroscopy”, PMC (alternative analytical approaches to Kjeldahl), https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8151012/