Protein supplement labels are legally required to disclose certain information, but the industry has developed several well-documented ways to make a product look better than it performs. Here's what to actually check.
Amino acid spiking
Because total protein content on U.S. labels is typically calculated from total nitrogen content (multiplied by a standard conversion factor), and because cheap free-form amino acids like glycine and taurine contain nitrogen without offering the same muscle-building value as intact whey or casein protein, some lower-quality products have historically added these cheap aminos specifically to inflate the label's protein number — a practice known as amino acid spiking. It's less common today after lawsuits and reputation damage to several major brands, but checking the ingredient list for glycine, taurine, or glutamine listed unusually high (rather than the primary protein source) is still worth doing.
Serving size tricks
"25g of protein per serving!" printed prominently, next to a scoop size that's actually 35-40g of powder, isn't dishonest, but it does mean you're paying for meaningful non-protein filler, flavoring, and thickener weight alongside the protein. Compare protein grams to total scoop weight, not just the headline protein number, to judge actual protein density.
"Proprietary blend" listings
When a label lists a "proprietary blend" of multiple protein sources with only a combined total weight, not individual amounts, there's no way to know the actual ratio — a blend could be 90% cheap filler protein and 10% the premium source featured on the front label, and you'd have no way to tell from the panel alone. Single-source products, or blends that disclose individual gram amounts per ingredient, are more transparent by design.
What actually matters, ranked
In order of practical importance: total protein per serving relative to total calories and scoop weight; a recognized third-party certification (see our safety and testing guide); individually disclosed ingredient amounts rather than a proprietary blend; and finally, added sugar and artificial sweetener content, which is a personal-preference and health factor separate from protein quality itself.