Also known as: Micellar casein, Milk protein, Calcium caseinate, Slow protein
Muscle & RecoveryStrong evidence
The slow-digesting protein fraction of milk, making up around 80 per cent of it. Forms a gel in the stomach and releases amino acids over several hours, which is why it dominates the before-bed category.
Typical dose
30.0–40.0 g per day
30 minutes before bed; works fine at other times with no particular advantage
What it is
Casein is the other protein fraction of milk, accounting for roughly 80 per cent of milk protein against whey's 20. It is what curdles and forms the solid curds in cheesemaking, while whey drains away as liquid.
In milk, casein exists as micelles, spherical clusters held together by calcium phosphate. Micellar casein preserves that native structure, which is what gives it the slow digestion. Calcium caseinate is processed more aggressively, disrupting the micelles, and digests faster as a result — which rather defeats the purpose of buying casein.
When casein hits stomach acid it forms a gel. That physical clot is the entire mechanism: it slows gastric emptying and meters out amino acids over hours rather than delivering them in a spike. It also explains why casein shakes are thick and why they sit heavily.
How it works
Casein's gelling in the stomach produces a sustained, low-amplitude release of amino acids over roughly five to seven hours, against whey's sharp peak within ninety minutes.
That sustained release is better suited to suppressing muscle protein breakdown than to maximally stimulating synthesis. Whey spikes leucine higher and drives a stronger synthesis response; casein keeps amino acids available for longer and limits the breakdown side of the equation.
This is the coherent argument for taking it before bed. Overnight is the longest daily period without protein, and a slow-release source keeps amino acids available across it. Casein is a complete protein with all nine essentials, though its leucine content is somewhat lower than whey's.
What the evidence shows
Pre-sleep casein has a genuine evidence base. Controlled trials have shown that 30-40 g taken before bed is digested and absorbed overnight, raises overnight muscle protein synthesis, and over longer training studies supports greater gains in muscle mass and strength.
This is one of the more convincing timing findings in sports nutrition, and it is unusual for that reason — most protein timing claims do not survive scrutiny.
The honest caveat is that these trials generally compare casein against nothing rather than against an equivalent amount of any other protein. Some of the benefit may simply be the extra protein and the extra feeding rather than casein specifically. Over 24 hours, total protein intake still dominates.
Dosing
For pre-sleep use, 30-40 g taken 30 minutes before bed is what the research protocols used, and the higher end appears more reliable than smaller servings.
Buy micellar casein rather than calcium caseinate if slow release is the point. Caseinate digests faster and gives up the one property you are paying for.
Casein is thick and can be unpleasant in low liquid volumes — use more water than you would for whey. It can also be made into a pudding-like consistency, which many people find easier at night than another drink. As a daytime protein it works perfectly well, it simply has no particular advantage there.
At a glance
Common forms
Micellar casein, Calcium caseinate, Milk protein concentrate (whey + casein), Within blended protein powders
Half-life / duration
Amino acid release sustained over 5-7 hours
Timing
30 minutes before bed; works fine at other times with no particular advantage
Competition status
Permitted — not on the WADA Prohibited List
Category
Muscle & Recovery
Safety and side effects
Casein is a food and is well tolerated. The most common complaints are heaviness, bloating and a feeling of fullness, which are direct consequences of the gel it forms rather than signs of a problem.
Milk allergen declaration is mandatory. Casein is in fact the milk protein most commonly responsible for milk allergy, so anyone with a milk allergy must avoid it entirely.
It contains lactose, though less than concentrate in micellar form. Some people find casein sits too heavily before bed and sleep worse for it, which is worth testing before committing to it as a nightly habit.
Who should avoid it
Milk allergen declaration applies; avoid entirely with a milk allergy — casein is the milk protein most often responsible. Not suitable for vegans. Speak to your doctor about protein intake if you have been told your kidneys are not working normally. May sit heavily before bed for some people.
This entry is provided for information only. Food supplements should not be used as a substitute for a varied and balanced diet and a healthy lifestyle. Consult a qualified healthcare professional before use if you are pregnant, breastfeeding, taking medication or under medical supervision.
