What is casein, and why do so many bodybuilders underestimate this protein? In brief, casein is a slowly absorbed protein derived from milk that works better in combination with whey than either does alone. Below are the study results and a practical guide to when to drink each.
What is casein, and why does it matter?
Not all dietary proteins are equal. Protein quality depends on its source — milk, eggs, soy — and how it has been processed.
Today, bodybuilders often favor whey protein, which comes from milk. It is a good protein: rich in essential amino acids, particularly branched-chain amino acids (L-leucine, isoleucine and valine), readily soluble and mild in flavor. Whey protein’s biological value may not be 157, as some manufacturers claim, but laboratory findings and decades of practical experience have justified this preference.
Whey is not the only milk protein, however. The other is casein — underestimated and often disparaged, yet backed by strong science. People who dismiss casein often either lack the relevant knowledge or sell a competing product.
One fact has been known for years. When you take whey on an empty stomach, a large proportion of its amino acids are used for energy rather than going to your muscles. Whey is absorbed extremely quickly, and in a fasted state, your body simply burns its amino acids as fuel. It does stimulate protein synthesis, but the benefit is small when you are in an energy deficit.
Casein is absorbed slowly, which spares its amino acids. It does not stimulate protein synthesis as strongly as whey, but it has a powerful anti-catabolic effect — something whey lacks.
Combining casein and whey slows whey absorption and protects its valuable amino acids. This is why the two are used together in meal replacement powders (MRPs).
The exception is the period around your workout. Use whey before, during and after your workout, and combine it with carbohydrates. Choose simple carbohydrates during training; before and after training, you can also include complex carbohydrates.
Study: whey vs. casein over 12 weeks
R.H. Demling and L. DeSanti compared whey and casein in a study published in Annals of Nutrition and Metabolism (44[1]:21–29, 2000). Its title translates as: the effects of a hypocaloric diet, increased protein intake and strength training on lean body mass in overweight police officers.
The study lasted 12 weeks and involved 38 police officers, with an average age of 34 years, a body weight of 98 kg and a body fat percentage of 27%. They were on active patrol duty rather than doing desk work.
The participants were divided into three groups:
- Control group (10 officers): a diet with a 15–25% calorie deficit and 0.8 g of protein per kg of body weight. No training was added.
- Whey group (14 officers): the same calorie intake, plus strength training, with 1.5 g of protein per kg. Two whey shakes supplied 75 g of their daily protein.
- Casein group (14 officers): the same training and the same 1.5 g/kg protein diet, but with 75 g of casein powder per day instead of whey.
Both protein powders were ordinary retail products, not special experimental formulas. All participants also received a multivitamin and minerals every day.
Diet structure: fat supplied up to 25% of total calories, and 70–75% of calories were consumed during active hours. The final meal and food eaten before bed accounted for around 25%. Two-thirds of carbohydrates were complex carbohydrates.
Their starting habits were poor. Before the study, 70% of participants consumed 50% of their daily energy intake immediately before bed, while breakfast supplied less than 10% of calories. Carbohydrates accounted for approximately 60% of total calories, half of which came from simple carbohydrates, and more than half of all carbohydrates were eaten either in the evening or before bed. Protein intake was below the recommended level (under 0.8 g/kg) in 75% of participants, and only 10% took vitamins.
Strength training: 4 days a week, with each session devoted to one of four major muscle groups for 30–35 minutes. Aerobic exercise was optional and could be done on days off from the gym or immediately after strength training.
Results after 12 weeks
Fat loss:
- Control group: body fat percentage 27% → 25%, loss of 2.5 kg
- Whey group: 27% → 23%, loss of 4.2 kg
- Casein group: 26% → 18%, loss of 7 kg
Muscle mass:
- Control group: no loss of quality muscle mass (surprising on a diet)
- Whey group: +2 kg
- Casein group: +4 kg
Strength gains (measured over 8–10 repetitions for the chest, shoulders and legs):
- Whey group: +29%
- Casein group: +59%
Four kilograms of muscle in 12 weeks works out to about 300 g a week. For people whose bodies had previously failed to respond to training, that is a significant result. The casein group stands out in particular — despite the fact that they were complete beginners.
It should be said that the study was small (38 people), but the casein used was high-quality and undenatured. One trial does not settle the debate, but a 59% gain in strength is hard to ignore. The study makes one thing clear: casein should not be underestimated.
Casein in practice: when to drink each protein
The simple answer: use both. The only question is when to use each.
Whey can be compared to simple carbohydrates. It reaches the bloodstream in 15–20 minutes and peaks within 40–45 minutes. Whatever is not used during that window goes to waste.
If your stomach is empty and you are in a large energy deficit, have carbohydrates before your whey (simple carbohydrates, 5–10 min beforehand); otherwise, your body will simply burn the amino acids for energy. Around training — before, during and after — whey is only worthwhile when combined with carbohydrates. That way, the whole serving is put to good use.
Whey arrives quickly and disappears quickly. Absorption peaks within an hour, and after 2–3 hours there is nothing left for your body to use. If you have done a leg workout and had your first serving of protein as whey, but no more protein follows, your body starts looking for it elsewhere — for example, in your chest muscles, to repair the structures of your thigh muscles. The whole system suffers: enzymes, hormones — all are partly made of protein.
Casein does the opposite. Its slow absorption provides a steady supply of amino acids. Its anti-catabolic effect means your body does not break down its own muscles in search of protein — casein supplies enough to the bloodstream.
A steady intake of protein every 2.5–4 hours throughout the entire 24-hour period is vital for muscle building. A substantial serving of fast-absorbing whey after a workout will not help if you neglect protein quantity and quality for the rest of the day — your body returns to a catabolic state, and your progress stalls.
And let us not forget ordinary food. Meat, fish, cottage cheese, eggs — with thoughtful food choices, you can get most of the protein you need, in terms of both quality and quantity, from your meals. Powders fill the gaps; they do not replace cooking.
FAQ
Are casein and whey equally good?
They have different roles. Whey: fast absorption, around training. Casein: slow absorption, at bedtime and during long gaps between meals. Both are worth using — it is a question of timing, not which is the better protein.
When should you drink casein?
Before bed is the classic choice — 7–9 hours of sleep without food is your longest daily fasting period, and casein’s slow absorption covers that window. It is also useful between meals when your next meal is more than 3 hours away.
Can I get all my protein from food?
With thoughtful, well-informed food choices, yes — cottage cheese, egg whites and meat provide slow-absorbing protein. Powders are a convenience, not a necessity. A quick serving of whey after training, however, is one situation where powder is usually more practical than food.
Author: Janar Rückenberg
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