Gold Standard 100% Casein is Optimum Nutrition's slow-digesting protein powder, built on 100% micellar casein rather than whey. It's marketed specifically for nighttime use or extended periods between meals, since casein forms a gel in the stomach that releases amino acids gradually over several hours, unlike whey's fast-absorbing profile. It comes from the same manufacturer as several products in our lab-tested lineup, giving it a comparable manufacturing pedigree even though we haven't independently tested this specific product ourselves.
| Protein Type | 100% Micellar Casein |
| Protein Per Serving | 24g |
| Serving Size | 33g |
| Calories | 115 |
| Sugar | 1-2g |
| Sweetener | Sucralose |
| Digestive Enzymes | Contains Aminogen (a proprietary digestive enzyme blend, per manufacturer) |
| Estimated Price | Approximately $1.15–$1.30 per serving based on typical 2lb tub retail pricing ($28-35 for ~27 servings) |
| Manufacturer Claims | Banned Substance Tested (manufacturer's own claim — not independently verified by us) |
The core difference is digestion speed, not protein quality: casein gels in the stomach and releases amino acids over 6-8 hours, while whey isolate is largely absorbed within 1-2 hours. This makes casein a poor choice immediately post-workout (when fast amino acid delivery is typically preferred) but a reasonable choice before bed or during long gaps between meals. Nutritionally, it's comparable to our lab-tested whey options on protein-per-serving (24g, in the same range as Gold Standard Whey and R1 Protein), but it contains meaningfully more lactose than the isolate-based products in our lab-tested lineup, since casein processing doesn't remove lactose as aggressively as whey isolate filtration does.
Reasonable for anyone specifically wanting a slow-release protein for bedtime or long gaps between meals — a genuinely different use case than a post-workout shake. Likely not the right choice for immediate post-workout use (a fast-absorbing whey isolate is better suited there), and worth avoiding if you have a soy allergy (it lists soy lecithin) or meaningful lactose sensitivity, since casein retains more lactose than the isolates in our lab-tested lineup.
The formula includes micellar casein as the sole protein source, sweetened with sucralose, and includes a gum blend (cellulose gum, xanthan gum, carrageenan) for the thick, pudding-like texture casein powders are known for. Notably, it includes Aminogen, a proprietary digestive enzyme blend the manufacturer states is included to aid absorption — this is a genuine point of difference from every product in our lab-tested lineup, none of which include added digestive enzymes. Some flavors contain Yellow #5 food dye; check the specific flavor's label if artificial dyes are a concern for you.
Optimum Nutrition states this on their own product packaging and site. We have not independently verified this claim ourselves the way we have for our lab-tested picks, so we're presenting it here as a manufacturer claim rather than our own confirmed finding.
Casein makes up a smaller proportion of milk protein than whey (roughly 80:20 casein-to-whey in raw milk, but whey has historically been the cheaper byproduct of cheesemaking to process at scale), and micellar casein specifically requires gentler processing to avoid denaturing it, which adds cost.
Yes — many lifters use both deliberately: a fast whey isolate post-workout, and casein before bed, since the two serve different absorption-speed purposes rather than being redundant with each other.
This is a Research Profile, not one of our independently tested picks. If you want our own lab results and editorial ranking, our #1 independently lab-tested pick is R1 Protein, scoring 9.8/10 in our own testing.
See Our #1 Lab-Tested Pick →