Reading the label
Amino spiking in protein powder
What amino spiking is, why a protein test can be fooled, and how to check a label yourself for added amino acids and proprietary blends.
The short answer
The protein number should come from protein.
Amino spiking means adding cheap free amino acids to a powder so a nitrogen-based test reports more protein than the powder holds as intact protein. Read the ingredient list for single amino acids named beside the protein sources, and prefer labels that give the amount of every ingredient.
What our catalog shows
From our record of each label, across the 471 powders we have checked.
A powder can be counted in both of the last two. An added amino acid on the label is not proof that a protein number is inflated: a label can list added leucine or BCAAs and still state the protein from the protein sources alone. 1 label is not verified on one or both points, and is not counted as disclosed.
What amino spiking is
Protein is made of amino acids linked together. A free amino acid is a single one, sold as its own ingredient. Glycine and taurine are cheap and both contain nitrogen. Creatine, which the body makes from amino acids, contains even more. None of them gives you the full set of essential amino acids that intact protein from whey, milk, egg or a plant blend does.
Amino spiking is adding these ingredients so the protein figure looks higher than the intact protein in the scoop. A crowd-funded lab study of 34 whey powders sold in India, the Citizens Protein Project 2, reported signs of nitrogen spiking with taurine in most of the powders sold by pharmaceutical companies.
Why nitrogen-based protein tests can be fooled
Labs usually don't measure protein directly. They measure nitrogen and convert it: U.S. labeling rules let the protein figure be calculated as 6.25 times the nitrogen content. The test can't tell whether the nitrogen came from intact protein or from a free amino acid added beside it, so every gram of a nitrogen-rich ingredient adds to the number.
| 1 g of | Nitrogen by weight | Reads as protein (× 6.25) |
|---|---|---|
| Glycine (C₂H₅NO₂) | 18.7% | about 1.2 g |
| Taurine (C₂H₇NO₃S) | 11.2% | about 0.7 g |
| Creatine (C₄H₉N₃O₂) | 32% | about 2.0 g |
Our arithmetic from each compound's formula, rounded. Intact protein averages about 16% nitrogen, which is where the 6.25 factor comes from.
Sources: 21 CFR 101.9(c)(7): protein declaration, quality-corrected protein and the 50 g Daily Value (eCFR)
How to spot it on a label
- 01
Free amino acids listed beside the protein
Read the ingredient list, not just the front of the tub. Look for single amino acids named apart from the protein sources: glycine, taurine, L-glutamine, L-leucine, L-arginine, or added creatine. A protein source is something like whey protein isolate, milk protein or pea protein.
- 02
A “protein blend” with one total
Some labels group the protein sources under a name such as “protein blend” or “protein matrix” with one combined weight. If free amino acids sit inside that blend, you can’t tell how much of the total is intact protein.
- 03
Front-label amino acid claims
Claims such as “added BCAAs” or “with glutamine” tell you something was added. Check whether the label or brand says the protein figure comes from the protein sources alone. A listed amino acid is not proof that the protein number is inflated, but it is worth a closer look.
- 04
Protein that looks high for the scoop
Divide grams of protein by the serving size in grams. Whey isolates typically land at 80% or more, and concentrates and plant blends at 65–80%. A figure that looks high for the protein sources listed is a reason to read the ingredients again.
Protein blend (whey protein concentrate, glycine, taurine, L-glutamine) 30 g, cocoa, natural flavor, sucralose.
Three of the four ingredients in the blend are free amino acids, and the label gives one 30 g total. You can't tell how much of it is whey. Compare a label that lists whey protein isolate on its own with the grams of protein per serving.
What a proprietary blend is
A proprietary blend is a named group of ingredients with one total weight. U.S. rules for dietary supplements allow it: the ingredients inside must be listed in descending order by weight, but the label doesn't say how much of each one you get. A blend isn't a sign of a bad product, but it makes the label harder to check, and it is where free amino acids can sit unseen inside a protein total.
A label with full disclosure names each protein source and gives the grams of protein per serving, plus the exact dose of anything added, such as creatine.
Sources: 21 CFR 101.36: Nutrition labeling of dietary supplements (proprietary blends, paragraph (c)); 21 CFR 101.4: Food; designation of ingredients (descending order of predominance by weight)
How our standard scores both
Label transparency is worth 20 of the 100 points in our score: half for no proprietary blend and half for no added free amino acids. Anything we couldn't verify on the label earns zero, so an unverified label never scores as disclosed.
The protein number is real protein
We look for free amino acids such as glycine, taurine or added creatine listed alongside the protein.
Every ingredient amount is disclosed
We prefer labels that state the amount of each protein source, not a single proprietary blend total.
Top powders that disclose the full formula
See all 329 rankedFilter and sort themRanked by our score. Each one shows no proprietary blend and no added free amino acids on our record of the label. Kids' and pregnancy products are left out here: see our kids' guide and pregnancy guide.
Added ingredients and your health
This page is about reading a label, not medical advice. If you have a health condition, are pregnant, or take medicine, ask your doctor before using a powder with added amino acids, creatine or other extras. Bring the label: the ingredient list is what they will want to see.
Questions people ask
What is amino spiking?
Adding cheap free amino acids (like glycine or taurine) to a powder so that a nitrogen-based protein test reports more protein than the product really contains as intact protein. Check the ingredient list for free amino acids listed separately from the protein sources.
What is a "proprietary blend" on a protein powder label, and should I avoid it?
A proprietary blend is a named group of ingredients for which the label gives only the total weight, not the amount of each one. U.S. rules allow this on dietary supplements: the ingredients in the blend must be listed in descending order by weight, but the label states one combined amount. So a "protein matrix" of 24 g that lists whey isolate, whey concentrate and casein tells you the order, but not how much of each, and a "performance blend" of 5 g tells you nothing about whether a listed ingredient is present at a useful dose. Powders sold as food rather than supplements carry a Nutrition Facts panel instead, but their ingredient list is also in descending order by weight. A blend is not a sign of a bad product, but it makes the label harder to check. Prefer powders that state the grams of protein per serving and, for any added ingredient you care about such as creatine, the exact dose. If a blend matters to you, ask the brand, or choose a product with third-party testing.
Sources: 21 CFR 101.36: Nutrition labeling of dietary supplements (proprietary blends, paragraph (c)); 21 CFR 101.4: Food; designation of ingredients (descending order of predominance by weight); NSF Certified for Sport; Informed Sport
Is a cheap or generic protein powder as good as a name brand?
It can be. Price and brand name are not reliable signs of quality, so check the product itself. In the Citizens Protein Project 2, a crowd-funded lab study of 34 whey powders sold in India, the sports-nutrition powders averaged 75.6 g of protein per 100 g and matched their labels closely, while the powders sold by pharmaceutical companies averaged 29.1 g, 83% were mislabeled by more than 5%, and 89% showed signs of nitrogen spiking with taurine. So a well-known name was no guarantee. Before you buy any powder, cheap or not: work out the protein per 100 g or per serving from the label, compare the cost per gram of protein, check the ingredient list for added free amino acids such as glycine or taurine (a sign of amino spiking), and look for a named third-party certification such as NSF Certified for Sport or Informed Sport that you can check in the certifier's own database.
Sources: The Citizens Protein Project 2: lab analysis of 34 whey protein powders sold in India (2025), Medicine; NSF Certified for Sport; Informed Sport
What ingredients should I avoid in a protein powder?
Most ingredients in protein powder are permitted food ingredients, but a few are worth checking depending on your needs. Free amino acids such as glycine or taurine listed beside the protein can be a sign of amino spiking, which inflates the protein number. Sugar alcohols such as sorbitol, erythritol or xylitol can cause gas or a laxative effect in some people. Gums such as xanthan or guar are safe, but can cause gas in large amounts. Artificial sweeteners such as sucralose, acesulfame potassium and aspartame are FDA-approved, though people with PKU must avoid aspartame. Caffeine is added to some coffee-flavored or "energy" powders. Herbs and botanicals have limited safety evidence, which matters most in pregnancy or breastfeeding. A "proprietary blend" hides how much of each ingredient you get. Heavy metals are not on the label at all, so look for brands that publish contaminant testing or carry a named third-party certification. Each of these has its own answer on this page.
Sources: U.S. Food & Drug Administration: Aspartame and Other Sweeteners in Food; 21 CFR 184.1835: Sorbitol (laxative-effect labeling); EFSA ANS Panel: Re-evaluation of xanthan gum (E 415) as a food additive (EFSA Journal, 2017); FDA: Spilling the Beans: How Much Caffeine Is Too Much?; NIH Office of Dietary Supplements: Dietary Supplements for Pregnancy, Fact Sheet for Health Professionals; Consumer Reports: Protein Powders and Shakes Contain High Levels of Lead (2025); NSF Certified for Sport; Informed Sport
More answers on our protein powder FAQ.