Myprotein Slow-Release Casein review

Our take: good casein at a fair price

Myprotein’s Slow-Release Casein is the own-brand answer to the big-name caseins, and on the basics it does everything right. A 30 g scoop gives about 23 g of protein, almost all of it micellar casein, with around 110 kcal and very little carbohydrate or fat. The ingredient list is short, and at typical offer prices it costs well under two-thirds as much per gram of protein as Optimum Nutrition’s Gold Standard Casein.

What it shares with every casein is the marketing. “Slow release” is true: casein does digest more slowly than whey. But when studies give people the same total protein across the day, taking casein at bedtime does not build more muscle than taking the same protein earlier. So this is a good way to add protein, not a way to make protein work harder.

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 product, tested its contents or run a trial. We could not open Myprotein’s own product page while writing, so the next section says where each figure came from.

What exactly are you buying?

Slow-Release Casein is sold in 1 kg and 2.5 kg pouches, unflavoured and in flavours including chocolate, vanilla and strawberry. A serving is one 30 g scoop, so a 1 kg pouch holds about 33.

Per 30 g serving, listings give about:

• 23 to 24 g of protein, depending on flavour
• About 110 kcal
• About 2 g of carbohydrate and 1 g of fat

Micellar casein makes up about 91 to 95 per cent of the powder depending on flavour, with flavouring and sucralose making up most of the rest in the flavoured versions. That is a higher casein share than Optimum Nutrition’s 88 per cent, and a shorter ingredient list with no gums or enzyme blend. The unflavoured version is simply casein.

Listings note that it is made in a facility that also handles egg and gluten, which matters for anyone with a severe allergy.

What casein can realistically do

Slow protein is real protein

Casein is about 80 per cent of the protein in milk. It clots in the stomach, so its amino acids reach the blood more slowly and over a longer period than whey’s. Whey’s faster rise stimulates muscle protein synthesis more strongly after a workout — a 2009 study by Tang and colleagues found whey outperformed casein at rest and after resistance exercise — while casein’s advantage is duration. Both are complete, high-quality proteins.

What the bedtime studies show

In a 2012 Maastricht study, 40 g of casein taken before sleep after an evening workout was digested and absorbed overnight. In a 2015 trial, young men who drank 27.5 g of casein before bed during 12 weeks of training gained more muscle and strength — but they were also eating more protein in total than the placebo group.

When Joy and colleagues gave two groups the same 35 g of casein, one in the daytime and one at night, on diets matched for total protein, both gained muscle and strength equally over 10 weeks. The benefit of bedtime protein is mostly the protein.

How much protein do you need?

For people doing resistance training, a 2018 meta-analysis by Morton and colleagues found gains in fat-free mass levelled off at around 1.6 g of protein per kilogram of body weight a day — about 130 g for an 80 kg adult. Our protein calculator works out your figure. If you already reach it from food, a casein shake adds little.

Price: work it out per 100 g of protein

At about 23 g of protein per 30 g scoop, a 1 kg pouch holds about 767 g of protein and a 2.5 kg pouch about 1.9 kg. In listings read on 28 September 2026:

• 1 kg: £23.95 at one sports-nutrition retailer and £29.99 on offer elsewhere, with a price comparison site listing it at £41.99 — about £3.12, £3.91 and £5.48 per 100 g of protein respectively.
• 2.5 kg: £48.99 at the same sports-nutrition retailer — about £2.56 per 100 g of protein.

Against Optimum Nutrition Gold Standard Casein, which we priced at about £5.50 to £5.80 per 100 g of protein in its 924 g tub and £4.26 to £4.96 in the 1.8 kg, Myprotein is clearly cheaper except at full price. Myprotein runs frequent site-wide offers, and at full price it is rarely worth buying. We read these prices from listings rather than taking an order through checkout.

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.
• Optimum Nutrition Gold Standard 100% Casein (reviewed) — the big-brand casein, with slightly more protein per scoop but a longer ingredient list, two UK formulas in circulation and a higher price per gram.
• Myprotein Impact Whey (reviewed) — if timing does not matter to you, whey does the same job for daily protein, and mixes more easily; compare the price per 100 g of protein on the day.
• Kinetica Whey Protein (reviewed) — the better choice for drug-tested athletes, because of its batch-tested banned-substance claim.
• Milk — a pint of semi-skimmed milk gives about 20 g of protein, roughly 80 per cent of it casein, for well under a pound.

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. The facility also handles egg and gluten, so anyone with a severe allergy to either should take the cross-contact warning seriously.

Most people with lactose intolerance tolerate a scoop of casein powder, since the lactose content is low, but a large shake can still cause bloating in sensitive people. Casein mixes thick; if a shake before bed feels heavy, mix it thinner or take it an hour earlier.

If you are drug-tested, note that the listings we read made no batch-tested banned-substance claim for this product; choose one whose batch you can look up. Anyone with kidney disease should ask their GP or dietitian before increasing protein. 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.

Sources and shopping: our UK buying checklist

Before you order, check the flavour, the pack size, the delivered price and the seller. Work out the cost per 100 g of protein — price ÷ (servings × protein per serving) × 100 — and compare it with a whey and with Greek yoghurt. The 2.5 kg pack is the cheapest per gram if you will finish it before its best-before date.

When the pack arrives, check the seal, the batch code and the best-before date, and read the nutrition panel for your flavour.

Our commercial link for this product is our Myprotein Slow-Release Casein link. It earns us a commission at no extra cost to you, and it has no influence on the score above — which is a 7.6, the higher of the two caseins we have reviewed, held back by a timing claim that mostly reduces to “eat enough protein” and no batch-tested claim.

The fair summary is this. Myprotein Slow-Release Casein is a clean, cheaper-than-brand casein that does what protein does. Take it before bed if that is when protein fits your day — and buy it on offer.