Optimum Nutrition Gold Standard 100% Casein Protein Powder review

Our take: good protein, sold on timing

Gold Standard 100% Casein is the slower-digesting sister of Optimum Nutrition’s best-selling whey, and the tub sells it on one idea: “nighttime and between meals muscle recovery”. Take a scoop before bed, the pitch goes, and your muscles are fed while you sleep.

The product behind that pitch is sound. A 33 g scoop gives 24 g of protein, almost all of it from micellar casein, with around 120 kcal and 1 g of sugar. Casein genuinely does digest more slowly than whey, and protein taken before bed genuinely is digested and used overnight.

What the evidence does not show is that the timing is the important part. When studies give people the same total protein across the day, bedtime casein does not build more muscle than the same protein taken earlier. So this is a review about whether you need extra protein at all, and about price — because casein costs more per gram than whey, and this one costs more than most caseins.

This is a desk review. We have read the published label details, UK retailer listings and the research on casein and pre-sleep protein. We have not used this tub, tested its contents or run a trial. We could not open the brand’s own GB product page while writing, so the next section says where each figure came from. Our Gold Standard whey review covers the sister product, which one of our team has used.

What exactly are you buying?

In the UK the powder is sold in a 924 g tub (28 servings) and a 1.8 kg tub. One scoop is 33 g. Per scoop, the brand’s published panel and UK retailer listings give:

• 24 g of protein, including 9 g of essential amino acids
• About 120 kcal
• About 4 g of carbohydrate, of which 1 g is sugar, and 1 g of fat

That is about 73 per cent protein by weight, which is typical for a flavoured casein: the rest is cocoa or flavouring, sweeteners, thickeners and the small amount of fat and lactose that comes with milk protein.

The photo on this page shows the US 1.8 kg tub; the UK packs carry the same product name and protein figure but a UK-format label. Check the one you receive.

Two UK ingredient lists are in circulation

UK retailer listings show two versions of the Chocolate Supreme ingredient list, and one retailer labels its stock “new formula”. The newer version lists micellar casein (88 per cent, from milk, with sunflower lecithin), fat-reduced cocoa powder, flavourings, salt, a stabiliser (sodium carboxymethyl cellulose), magnesium oxide, the sweeteners sucralose and acesulfame K, and zinc oxide. The older version uses soy lecithin, adds cellulose, carrageenan and guar gums, and includes a digestive enzyme blend.

Neither is a problem, and the protein figure is the same. But if you avoid soy, or want to know exactly what you are drinking, read the ingredient list on the tub rather than a retailer’s copy of it. Our guide to what a supplement label hides covers what else to check.

What casein can realistically do

Slow protein is real protein

Casein is the main protein in milk — about 80 per cent of it — and it clots in the stomach, so its amino acids reach the blood more slowly and over a longer period than whey’s. That is a genuine physiological difference, and it is the whole basis of the product.

It cuts both ways. Whey’s faster, sharper rise in amino acids stimulates muscle protein synthesis more strongly in the hours after a workout; a 2009 study by Tang and colleagues found whey outperformed casein at rest and after resistance exercise in young men. Casein’s advantage is duration, not size. Neither is a magic property: both are complete, high-quality milk proteins.

What the bedtime studies show

The case for casein before bed comes largely from a research group at Maastricht University. In a 2012 study, 16 young men who drank 40 g of casein before sleep, after an evening workout, digested and absorbed it overnight and had higher whole-body protein synthesis than those given a placebo. In a 2015 trial, 44 young men training for 12 weeks gained more muscle and strength when they drank 27.5 g of casein before bed each night.

The catch is in the second trial’s design: the casein group was also eating more protein in total, because the placebo group got no protein at bedtime. When Joy and colleagues gave two groups the same 35 g of casein — one in the daytime, one at night — on diets matched at 1.8 g of protein per kilogram a day, both gained muscle and strength equally over 10 weeks. Wider reviews of the evidence reach the same conclusion: the benefit of bedtime protein is mostly the protein.

That is useful to know rather than disappointing. If your daily protein is short, a bedtime casein shake is an easy, well-tolerated way to top it up. If your protein is already where it should be, moving some of it to bedtime is unlikely to make a noticeable difference.

How much protein do you actually need?

For people doing resistance training, a 2018 meta-analysis by Morton and colleagues found that gains in fat-free mass levelled off at around 1.6 g of protein per kilogram of body weight a day. For an 80 kg adult that is about 130 g a day, from food and supplements combined. Our protein calculator works out your figure. Most people who hit it comfortably from meals do not need a shake at all.

The same applies to satiety claims. Casein is filling, and a slow shake between meals can help some people manage hunger, but so do a pot of Greek yoghurt or a glass of milk, which are largely casein too.

Third-party testing: what the brand does and does not claim

This matters mainly if you compete under anti-doping rules. As we set out in our Micronised Creatine review, Optimum Nutrition’s customer-service page on Informed Sport says its Middlesbrough manufacturing site is Informed-Sport registered, and names only three specific products as registered: Gold Standard 100% Whey England Rugby, Gold Standard 100% Plant and the Optimum Bar. Gold Standard Casein is not among them.

A registered site is a genuine quality signal for an ordinary buyer. It is not a certificate for the tub in your hand. If you are drug-tested, buy a batch-tested product you can look up in the certifier’s database.

Price: work it out per 100 g of protein

Because every serving is 24 g of protein, the fair comparison is the price per 100 g of protein, not per tub. Search listings for UK retailers on 28 September 2026 showed:

• 924 g tub: £36.95 to £38.95 at one sports-nutrition retailer, depending on flavour — about £5.50 to £5.80 per 100 g of protein, or roughly £1.32 to £1.39 a serving.
• 1.8 kg tub: £55.79 on sale and £64.99 at full price at another retailer — about £4.26 to £4.96 per 100 g of protein.

The 924 g tub costs roughly the same per gram of protein as Gold Standard whey, which our whey review put at £5.55 to £6.94 per 100 g of protein. The 1.8 kg tub is noticeably cheaper per gram.

Against an own-brand casein the gap is clearer. Myprotein’s Slow-Release Casein, at 23 g of protein per 30 g scoop, was listed at £29.99 for 1 kg on offer and £41.99 at full price — about £3.91 to £5.48 per 100 g of protein. As with most sports nutrition, the difference between brands is largely the difference between buying on offer and not. We have not reviewed Myprotein’s casein in full, so treat this as a price comparison rather than a recommendation.

We read all these prices from search listings rather than taking an order through checkout, so confirm the delivered price before you pay.

Who should skip it, and what to watch for

Casein is milk protein, so it is not suitable for anyone with a milk allergy, and it is not vegan. UK listings also carry a may-contain warning for gluten, egg, soy, nuts and peanuts, because of the factory it is made in. The older formula uses soy lecithin as an ingredient.

Most people with lactose intolerance tolerate a small serving of casein powder, since the lactose content is low, but a large shake can still cause bloating in sensitive people. Casein can also feel heavy: some people find a thick shake right before bed uncomfortable, and mixing it thinner or taking it an hour earlier helps.

Protein powders are safe for healthy adults at normal intakes. Anyone with kidney disease should ask their GP or dietitian before increasing protein, because the right intake for damaged kidneys is different. Food supplements sold in Great Britain are not approved by a regulator for safety or effectiveness before sale, so the label is the manufacturer’s responsibility rather than a regulator’s endorsement.

Casein, whey, or neither?

If you are short of protein and want a shake after training or during the day, whey is usually cheaper per gram and mixes more easily. Our Gold Standard whey and Myprotein Impact Whey reviews cover the two most common choices.

If you want a shake before bed or a filling snack between meals, casein’s slower digestion and thicker texture are a reasonable reason to choose it. Gold Standard Casein is a well-made example; the question is only whether you pay the brand price or find the same protein cheaper.

And if you already reach your daily protein from food, neither is necessary. A bowl of Greek yoghurt or cottage cheese before bed gives you casein for less, with no scoop required. If you want one supplement with strong evidence for strength training, creatine has a much clearer case than protein timing.

Best alternatives

The ones we have fully reviewed are linked, and appear in the comparison cards below this article. The others we name for comparison only: we have not reviewed them in full, so do not read their inclusion as a recommendation.

• Greek yoghurt, skyr or cottage cheese — the best alternative for most people. They are mostly casein, filling, and a 200 g pot gives roughly 15 to 25 g of protein before bed without a scoop.
• Myprotein Slow-Release Casein (reviewed) — the own-brand casein we priced against: 23 g of protein per 30 g scoop, about £3.91 per 100 g of protein on offer and £5.48 at full price.
• Optimum Nutrition Gold Standard 100% Whey (reviewed) — if timing does not matter to you, whey does the same job for daily protein, mixes more easily and is usually cheaper per gram.
• Myprotein Impact Whey (reviewed) — the value whey, and the cheapest way to add protein of the products we have reviewed.
• Kinetica Whey Protein (reviewed) — the most completely labelled whey we have reviewed, and the better choice for drug-tested athletes because of its banned-substance testing claim.

Sources and shopping: our UK buying checklist

Before you order, confirm the flavour, the pack size, the delivered price and the seller. On marketplaces, check that the seller is the brand or an authorised retailer — counterfeit sports nutrition is a documented problem, and a verifiable seller is the simplest protection. Then work out the cost per 100 g of protein: price ÷ (servings × 24) × 100.

When the tub arrives, check that the seal is intact, that the label is in English with a GB or EU address for the responsible business, and that the batch code and best-before date are legible. Read the ingredient list to see which formula you have, especially if you avoid soy.

Our commercial link for Optimum Nutrition in the UK is our UK Optimum Nutrition link. It earns us a commission at no extra cost to you, and it has no influence on the score above — which is a 6.6, held back by a timing claim that mostly reduces to “eat enough protein” and a price that is only competitive in the larger tub, not by any doubt about the protein itself.

The fair summary is this. Gold Standard 100% Casein is a clean, well-labelled milk protein that does what protein does. Take it before bed if that is when protein is easiest for you to fit in — but do not pay extra expecting the clock to do the work.