Casein protein vs whey protein compares two parts of the same food. The International Society of Sports Nutrition (ISSN) describes milk protein as dividing into these two classes, casein and whey.1 Casein is by far the larger share, making up nearly 70 to 80% of the protein in cow's milk.2 Both are complete proteins, carrying all the essential amino acids the body cannot make for itself.2 Where they differ most is in how quickly the body digests them.
Fast vs slow protein
The ISSN position stand on protein and exercise describes whey as water-soluble, easy to mix and rapidly digested.1 Casein does not dissolve in water. It clots in the gut and is digested more slowly than whey.1
That difference is what people mean by fast vs slow protein. Amino acids from whey rise in the blood soon after a drink and fall again within a few hours, while those from casein rise slowly and stay up for longer.1 Neither speed is better in itself, and each suits a different part of the day.
You already eat both in Indian food. When milk is split to make paneer, the whey drains away, and ICMR-NIN's Dietary Guidelines for Indians, 2024, describe that whey as a by-product of paneer making.3 The protein left behind in paneer is therefore mostly casein, while a glass of milk keeps the two together. Curd, which is made by setting milk rather than splitting it, also holds on to both.
Which is better for muscle recovery
For the hours around a workout, either can play a part. The ISSN stand says protein brings benefits whether it is taken before or after training, and that the best window is likely a matter of individual tolerance.1 It also suggests spreading protein doses evenly across the day, every 3 to 4 hours.1
As a rough size for each of those servings, the stand gives 0.25 g of high-quality protein per kg of body weight, or 20 to 40 g.1 For a 65 kg adult, the per-kg figure comes to about 16 g a serving.
For the night, the same position stand singles out casein. It says 30 to 40 g of casein before sleep increases overnight muscle protein synthesis, the process of building muscle protein.1 So the fair answer to casein vs whey for recovery is that neither is better all day long. Casein has a clear place at night, while either protein can serve around training.
None of this replaces the exercise itself. ICMR-NIN's guidelines are clear that protein only goes into muscle building alongside physical activity and resistance exercise.3
A whey and casein blend
A glass of milk is already a whey and casein blend, since it carries both kinds of protein in their natural proportions.1 Some protein powders mix the two on purpose, and ICMR-NIN notes that some powders combine protein from more than one source.3 A tub that does this will name both in its ingredients list. Hoffman and Falvo's review suggested that, because casein works over a longer stretch and whey acts sooner, a combination of the two could be useful.2
USDA lists whole milk at 3.27 g of protein in 100 g.4 A 200 ml glass weighs a little over 200 g, so it carries roughly 6.5 to 7 g of protein, most of it casein. Paneer, curd and milk at different meals already give you both kinds through an ordinary Indian day.
Casein, whey and Horlicks Protein
On the Horlicks Protein Unflavoured pack, whey protein concentrate sits alongside fermented yeast protein, and each 36 g sachet holds 24 g of protein. The pack suggests stirring it into 200 ml of cold water or milk. The milkshake uses milk protein as well, ultra-filtered, at 20 g in each 240 ml bottle.
If you mix a sachet into 200 ml of whole milk, the milk adds its own casein and whey on top of the sachet's 24 g. The glass then holds just over 30 g of protein. Against the 54 g a day that ICMR-NIN gives a 65 kg adult, that one glass covers a little over half.3
Conclusion
Casein and whey both come from milk and are both complete proteins, but whey dissolves easily and is digested quickly, while casein clots in the gut and is digested slowly. On recovery, the ISSN position stand says protein helps whether it is taken before or after training. It also singles out 30 to 40 g of casein before sleep for overnight muscle protein synthesis. Neither replaces the exercise, which ICMR-NIN sees as the condition for protein to be used for muscle. Milk already blends the two, and a Horlicks Protein sachet made up with 200 ml of whole milk gives just over 30 g of protein in one glass.
Sources
1. Jäger R, et al. International Society of Sports Nutrition position stand: protein and exercise, 2017. PubMed 28642676. https://pmc.ncbi.nlm.nih.gov/articles/PMC5477153/
2. Hoffman JR, Falvo MJ. Protein, which is best? Journal of Sports Science and Medicine, 2004. PubMed 24482589. https://pmc.ncbi.nlm.nih.gov/articles/PMC3905294/
3. ICMR-National Institute of Nutrition. Dietary Guidelines for Indians, 2024. https://nin.res.in/dietaryguidelines/pdfjs/locale/DGI_2024.pdf
4. USDA FoodData Central. Milk, whole, 3.25% milkfat, with added vitamin D. FDC 746782. https://fdc.nal.usda.gov/food-search/?query=746782&type=Foundation