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Strong evidencePhysical performance

Casein Protein

Casein is a complete, slowly digested milk protein that builds muscle about as well as any other high-quality protein when it fills a gap in daily intake. Its one genuinely distinctive use is the pre-sleep dose, where 30-40 g sustains amino acid delivery overnight.

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What the science says

  • Adds muscle and strength when it raises total protein intake Strong evidence

    A meta-analysis of 49 RCTs in 1,863 adults found protein supplementation during resistance training added 0.30 kg fat-free mass and 2.49 kg to 1RM strength versus control. The benefit plateaued once total protein intake reached about 1.6 g/kg/day, so casein helps mainly if you are below that.

  • Pre-sleep casein increases overnight muscle protein synthesis Moderate evidence

    In 16 young men given 40 g casein immediately before sleep after evening resistance exercise, whole-body protein synthesis rose (311 vs 246 umol/kg per 7.5 h) and net protein balance turned positive (+61 vs -11 umol/kg per 7.5 h). Mixed-muscle protein synthesis was about 22% higher, though this was only borderline significant (p = 0.05).

  • Pre-sleep protein improved 12-week training gains Moderate evidence

    In 44 young men doing 12 weeks of resistance training, 27.5 g casein plus 15 g carbohydrate before sleep beat placebo for 1RM strength (+164 vs +130 kg) and quadriceps cross-sectional area (+8.4 vs +4.8 cm2). Important caveat: the placebo was energy-free, so the result may reflect more total daily protein rather than the timing itself.

  • Superior to whey for muscle growth Limited evidence

    Acute studies show whey stimulates muscle protein synthesis more strongly than casein because of faster digestion and higher leucine content. But long-term head-to-head training trials show no reliable difference in lean mass or strength, and the "anti-catabolic overnight shield" marketing is well ahead of the data.

Dosage & safety

Studied dose20-40 g per serving. Pre-sleep trials used 27.5-40 g (roughly 0.5 g/kg) taken about 30 minutes before bed. What actually drives gains is total daily protein of ~1.4-2.0 g/kg; supplementing beyond ~1.6 g/kg/day adds little.
SafetyA dairy protein, so it is off-limits with cow's milk allergy. Micellar casein is very low in lactose but not lactose-free; bloating and gas are the usual complaints, and it thickens heavily in water. High intakes are safe for healthy kidneys, but people with chronic kidney disease should have protein set by a clinician. Protein powders are not pre-market tested by regulators, so drug-tested athletes should choose third-party certified products (Informed Sport, NSF Certified for Sport).

How to take it

TimingAny time of day; the one evidence-based slot is 30-40 g about 30 minutes before bed.
With food?With or without food — it is food.
Worth knowingCasein thickens dramatically in water, so use more liquid than you would for whey unless you want a pudding.

Interactions

With medications

  • levothyroxine

    Milk protein and its calcium reduce levothyroxine absorption, as any meal does. take levothyroxine on an empty stomach at least 30-60 minutes before a shake

Well-established interactions only — this is not a complete list. Always tell your doctor and pharmacist what you take.

Frequently asked questions

Does casein protein build muscle?

Yes, when it raises your total protein intake — the evidence is strong. Casein builds muscle about as well as any high-quality protein, with the benefit of protein supplementation plateauing once total intake reaches about 1.6 g/kg/day.

Should I take casein before bed?

Pre-sleep casein is the one distinctive use with moderate evidence: 30-40 g about 30 minutes before bed sustains amino acid delivery overnight and raised overnight protein synthesis in trials. Whether the timing itself matters, rather than the extra daily protein, is not settled.

Is casein better than whey protein?

No. Whey stimulates muscle protein synthesis more strongly in short-term studies, but long-term training trials show no reliable difference between casein and whey in lean mass or strength.

How much casein protein per serving?

Take 20-40 g of casein per serving; pre-sleep trials used 27.5-40 g. What actually drives muscle gains is total daily protein of about 1.4-2.0 g/kg.

Scientific references

Where to buy

NOW Foods, Sports, Micellar Casein Protein Powder, Unflavored, 1.8 lbs (816 g)

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