Casein Hydrolysate – The Perfect Post Workout Protein?

Having the optimal post workout nutrition is imperative if your goal is to build muscle and improve your performance, and post workout protein is crucial to maintain a positive nitrogen balance at this critical time.

Man taking protein after his workout

The different grades of whey protein have been well documented and there is detailed information available, see the article The Complete Guide to Whey Protein Supplements in Health & Fitness. In that article you can see that whey protein hydrolysate (WPH) is the most rapidly absorbed and efficient form of protein to be consumed post workout. However, more recently, casein hydrolysate has come onto the scene with an interesting background.

What are protein hydrolysates?

Literally the word hydrolysate means ‘the product of hydrolysis’. Hydrolysis is the chemical process where a substance, in this case protein, is broken down into smaller units. Thus, a protein hydrolysate by definition is ‘a mixture of amino acids prepared by splitting a protein with acid, alkali or enzyme’. Hydrolysed proteins are equivalent in nutritional terms to the original protein they were derived from in respect of their amino acid composition, but their structure is broken down making them more readily digested and absorbed. Even the primary structure is damaged resulting in short chain peptides, known as oligopeptides, including di- or tripeptides which are two or three amino acids in length, respectively.

The importance of protein post workout

We need to be in a positive nitrogen (protein) balance in order to grow muscle. However, it has been indicated that this on its own is not enough. Bohé et al (2001) demonstrated that a constantly high plasma amino acid level is, in itself, not sufficient to promote protein synthesis and there needs to be sufficient amino acids available during times of highest demand when metabolic processes limit the accretion of muscle protein. This time is post workout when it is advantageous to have both plasma insulin and amino acids level high. Therefore, in theory, a protein which is absorbed faster would be the most efficient.

Why casein hydrolysate?

Koopman et al (2009) showed that ingestion of a protein hydrolysate, as opposed to its intact protein, accelerates protein digestion and absorption from the gut, augments postprandial amino acid availability, and tends to increase the incorporation rate of dietary amino acids into skeletal muscle protein. And the type of hydrolysate used in this study was casein hydrolysate. The research demonstrated also that the protein increased insulin levels. Insulin is a very anabolic hormone which increases the rate of protein synthesis as well as putting carbohydrate into the muscle.

So, not only with casein hydrolysate do we have a protein which is easier to digest and absorb, hence is more bioavailable, but we have a protein which increases insulin, thus increasing the rate of protein synthesis.

Furthermore, compared to other protein types, hydrolysates are also easier to digest, and they don’t sit on the stomach for so long leaving you feeling bloated. Clinically protein hydrolysates are used in some special semi-elemental diets for people with digestive issues.

Why casein hydrolysate over whey protein hydrolysate?

So, now we’ve established that hydrolysed proteins are the cream (please excuse my dairy-related pun!) of post workout proteins, no doubt you’ll be wondering why we can’t stick to the long tried and tested hydrolysed whey protein. Furthermore, aren’t casein proteins supposed to be slow digesting? We’re always told that casein is an ideal pre-bed protein as it takes ages to digest and is far more slowly digested than whey, which is known for its rapid digestion.

Certain amino acids are glucogenic, which means that they can be converted to glucose through metabolic processes, i.e. gluconeogenesis. In the case of protein hydrolysates which are digested and absorbed so quickly, some of the glucogenic amino acids may be converted to glucose and this is related to an insulin response. Whey protein is comparatively lower in the amino acids arginine, phenylalanine and glutamine, which are three glucogenic amino acids. Casein is high in threonine, arginine and glutamine and in the total number of glucogenic aminos. This indicates that casein hydrolysate is more advantageous than whey.

This isn’t backed up by any studies, but you can see there is a valid theory. Also absent form the literature is a comparison of the digestion rates between WPH and casein hydrolysate. Therefore, it does seem that casein hydrolysate is slightly more advantageous than WPH. It is important to note though that the quality of products vary for both whey and casein hydrolysates as the degree of hydrolysis may be different between different brands.

Casein protein in its unaltered form, i.e. as a regular protein supplement or in its milk protein form, is very slowly digested and absorbed making it an ideal choice for a night-time shake. This is because its quaternary structure has loads of complex bonds which are less available to digestive enzyme degradation. Also, the molecules themselves clump together and sit in the stomach for a long period slowing the rate of gastric emptying. In casein hydrolysate these bonds have all been broken down, leaving the peptide chains short and rapidly digested.

How are casein hydrolysates produced?

Casein hydrolysates are derived from the casein protein fraction of cow’s milk. Typically a good casein hydrolysate should consist of around 85% protein and the protein is rich in oligopeptides with 50-60% being smaller than 500 Daltons.

Usually casein undergoes enzymatic hydrolysis, after which the solution is heat treated such that all enzymes are irreversibly inactivated. The solution is then concentrated and spray dried.

Is it worth using casein hydrolysate post workout?

The above is the science and all of it seems really convincing. But in the real world, will changing your post workout protein to casein hydrolysate actually give you better results? On the great scale of things probably nothing that you will be able to measure, especially in comparison to WPH. Indeed, for optimal post workout nutrition you’ll be adding carbohydrates post workout, possibly high molecular weight carbs like Vitargo® and waxy maize starch (information on carbohydrate powders); these will directly and considerably increase blood insulin levels, negating any small effect from the post workout choice of protein.

However, casein hydrolysate does appear to be the cream of post workout proteins, and, let’s be honest, many of us waste our money on worthless supplements with little or no evidence to back them up. So, maybe spend that money on some casein hydrolysate where there is some evidence to its usefulness and include 25g as part of your post workout nutrition.


  • Bohé et al (2001). Latency and duration of stimulation of human muscle protein synthesis during continuous infusion of amino acids. J Physiol 15;532: 575-9.
  • Koopman et al (2009). Ingestion of a protein hydrolysate is accompanied by an accelerated in vivo digestion and absorption rate when compared with its intact protein. Am J Clin Nutr 90: 106-115.
Photo of author

James Collier

James first started bodybuilding as a teenager back in the 1980s and obtained his degree in Nutrition and Dietetics from the University of Surrey back in 1995. After qualifying he worked as a clinical Dietitian for the NHS in various UK hospitals.

Having competed several times during the 1990s, his passion now lies in helping other bodybuilders, strength and fitness trainees reach their goals.

He is a Registered Nutritionist and a full member of The Nutrition Society in the UK. James is also co-founder and developer of Huel, nutritionally complete food.

As an Amazon Associate we earn from qualifying purchases.