CuratedFit
Optimum Nutrition
Gold Standard 100% Casein
A slow-release micellar casein protein designed for overnight recovery and between-meal support.
Protein & Nutrition
924g / 1.82kg
24g Protein per serving
WHAT IT IS
Gold Standard 100% Casein is a slow-release micellar casein protein designed for overnight recovery and between-meal protein support. Each serving delivers 24g of premium micellar protein. Micellar casein is derived from mild and digest slower than whey protein, allowing the body to absorb protein and amino acids over longer periods when eating is not possible or practical. Such as during sleep or between meals. Optimum Nutrition was the first brand to bring powdered casein to the market and uses only micellar casein as its protein source. The only genuinely slow-digesting form of casein. Other forms such as calcium caseinate digest at a similar rate to whey.
WHO IT IS FOR
Anyone who trains regularly and wants a reliable overnight protein source. If whey is your post-training protein, casein is the overnight insurance policy. Taken before bed it delivers a sustained release of amino acids while you sleep. It works equally well on busy days when a proper meal is not going to happen for several hours and you need something that actually holds.
INGREDIENT BREAKDOWN
Micellar Casein
24g per serving
Primary protein source. Slow-digesting, acid-sensitive, thickens in the stomach to create a sustained release of amino acids over several hours.
Inulin
Not declared individually
Naturally occurring prebiotic fibre. Supports gut health and adds mild texture. A positive addition to the formulation.
Gum Blend
Trace amount
Cellulose gum, xanthan gum, and carrageenan used as thickeners and stabilisers. See transparency note for carrageenan.
Soy Lecithin
Trace amount
Emulsifier for mixability. Present in very small amounts. Relevant for those with soy sensitivity.
Aminogen
Proprietary enzyme blend
Patented digestive enzyme blend designed to improve protein absorption and reduce bloating. Third-party tested.
Sucralose
Flavored variants only
Artificial sweeteners. Not present in unflavored version. See transparency note.
Certifications
Informed Sport
Certified
Banned substance tested
Via Informed Sport
GMP Certified
Certified
Heavy metals tested
Not confirmed
BRCGS
Not confirmed
FSSC 22000
Not confirmed
CURATEDFIT STANDARD CHECK
No synthetic enhancers or undisclosed additives
No synthetic performance enhancers present. All ingredients serve a declared functional purpose.
No proprietary blends hiding in ingredient doses
Aminogen is a proprietary enzyme blend but its function and third-party testing status are publicly declared. All individual ingredients are listed on the label.
Label accuracy
Protein content is consistent with third-party testing data. 24g micellar casein per serving is accurate.
No insect-derived ingredients
All protein sources are dairy-derived. No insect proteins, chitin, or insect-based additives present.
Allergen declaration
Contains milk and soy lecithin. Clearly declared on the label. Relevant for those with dairy or soy sensitivity.
Sugar content
Less than 1g sugar per serving. No significant added sugar present.
Country of manufacture
Manufactured in EU-compliant facilities, meeting European food safety standards.
Banned substance risk
Informed Sport certified. Safe for tested athletes. Tested against over 250 substances banned in professional sport.
Artificial sweeteners present in flavored variants
Flavored versions contains sucralose. Flagged for transparency.
Heavy metals, not independently confirmed
No published independent heavy metal test data available at time of review. Informed Sport certification provides partial coverage. CuratedFit recommends choosing Informed Sport certified batches.
Sustainability and sourcing
Whey sourced from conventional dairy. Grass-fed or sustainability certified sourcing not confirmed by the brand. No palm oil present.
TRANSPARENCY NOTE
The EU version of Gold Standard Casein is currently only available in flavored variants, which contains sucralose. This is an artificial sweetener with an established safety record. CuratedFit flags it here because you should know what is in what you are buying, not because we consider it a disqualifying factor. If you prefer to avoid artificial sweeteners entirely, consider an unflavored casein alternative. CuratedFit will list options as they are reviewed and approved.
FREQUENTLY ASKED QUESTIONS
When is the best time to take Gold Standard Casein?
Before be is the most well-researched timing. The slow-release nature of micellar casein means amino acids are delivered gradually over several hours while you sleep. It can also be used between meals on days when extended periods without food is unavoidable.
What is the difference between casein and whey protein?
Whey is fast-absorbing, ideal immediately after training. Casein is slow-absorbing, ideal for overnight or between meals. They serve different purposes and work well together as part of a complete daily protein strategy.
Can it replace a meal on a busy day?
It can fill a protein gap on a busy day but is not a complete meal replacement. It provides protein and very little else. For extended period without food it is best combined with other nutrition sources where possible.
Is this product safe for drug-tested athletes?
Yes. Gold Standard Casein holds Informed Sports certification which tests for over 250 substances banned in professional sport.
Does it contain insect-derived ingredients?
No. The only protein source is micellar casein derived from dairy milk. No insect proteins, chitin, or insect-based additives are present.
Last reviewed: May 2026 by
CuratedFit
Sources: ON label declaration, Informed Sport database, third-party testing records.
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