Protein before bed may help your muscles by raising your daily total

Protein before bed means quark, a glass of milk, a bowl of yogurt or a shake, eaten in the half hour before you switch the light off. The idea behind it is that your body keeps repairing muscle while you sleep, so amino acids at bedtime give your body the raw material while that repair happens. One study from Maastricht University is quoted almost every time the subject comes up, usually as a single number, and that number is worth reading properly before you change anything about your evening.

The claim you meet on social media is that forty grams of protein before bed increases muscle protein synthesis by twenty two percent. Muscle protein synthesis is the rate at which your body builds new muscle protein, measured in a laboratory by feeding people amino acids labelled with a heavy isotope and then taking a small muscle sample. The figure is real, it comes from a published trial, and almost everything implied around it is weaker than the number makes it sound.

What your body does with protein while you sleep

Your muscle is rebuilt and broken down continuously, every hour of every day, and the balance between those two rates decides whether you gain muscle or lose it. When you have not eaten for several hours, breakdown is faster than rebuilding, so the balance is negative. Phillips and colleagues measured this directly in fasted volunteers and reported a net muscle protein balance of minus 0.057 percent per hour at rest, which was different from zero at every time point they sampled ¹.

A night of sleep is the longest stretch most people spend without eating. If you finish dinner at eight in the evening and eat again at seven in the morning, your body has eleven hours with no amino acids arriving from food. That is the reason researchers became interested in bedtime protein in the first place, because it is the one long stretch in an ordinary day when nobody had tried feeding people.

One honest caveat belongs here before you read any further. Nobody has measured the hour at which a normal dinner stops supplying amino acids during real overnight sleep, so the popular description of the whole night as a long fast is an assumption rather than a measurement.

Why casein is the protein in almost every study

Casein is the slow protein in milk, and it is what almost every bedtime study uses. Boirie and colleagues compared casein with whey in the same volunteers. Casein raised blood amino acids to a plateau lasting six to seven hours, while whey produced a higher peak that was over within four to five hours ². Casein forms a soft clot in the stomach, which slows how fast it empties into the intestine, so the amino acids arrive over most of a night instead of all at once.

That same study contains a detail that most articles leave out. Casein produced the better overall protein balance mainly because it suppressed protein breakdown by thirty four percent, while whey stimulated protein synthesis roughly twice as hard as casein did ². The common claim that casein is the better protein for building muscle is the opposite of what that experiment found.

The question that matters for a bedtime snack is whether any of it is absorbed while you are asleep, because digestion could plausibly slow down overnight. Digestion does not slow enough overnight to make a difference, because researchers labelled the casein itself so that they could trace it through the night. About half of the ingested protein appeared in the bloodstream as amino acids over the following seven and a half hours, in both the original trial and its larger successor ³⁴.

What the most quoted study actually measured

Res and colleagues gave healthy young men forty grams of labelled casein thirty minutes before sleep, or a drink with nothing in it, and measured what happened across the next seven and a half hours ³. The men were split into two separate groups rather than doing both conditions, and one trial was lost to a blocked catheter, so the muscle result compares eight men with seven. Whole body protein balance, meaning everything built across the body minus everything broken down, was clearly better after the protein, at plus 61 against minus 11 micromoles per kilogram at a p value below 0.01. That part of the result is clear and nobody disputes it.

The synthesis number is far less certain than its popularity suggests. The paper reports that mixed muscle protein synthesis rates were about twenty two percent higher after protein, and then says in the same sentence that this reached borderline significance at a p value of 0.05 ³. The p value is the chance of seeing a difference that large if the protein had done nothing, and 0.05 is exactly the line most researchers treat as the threshold for believing a result. Four further details of the design limit what that number can be used for.

• The men had done a resistance training session that same evening, so the result describes a trained state rather than an ordinary night.
• They had already eaten 1.2 grams of protein per kilogram of body weight that day, plus twenty grams of whey after training.
• The comparison drink contained nothing at all, so the trial compares protein against fasting rather than bedtime protein against protein eaten earlier.
• The measurement was mixed muscle protein, which includes proteins that have nothing to do with contraction, rather than the myofibrillar protein that makes up the working part of a muscle.

The same laboratory could not repeat it at a lower dose

Six years later the same group ran the study again with thirty six men, using thirty grams of casein and measuring myofibrillar protein directly ⁴. The amino acids from the drink were demonstrably built into muscle protein, and whole body balance improved again, yet the synthesis rate itself did not change at all. The three groups came out at 0.057, 0.055 and 0.055 percent per hour, with a p value of 0.850.

The authors read this as a dose effect, because thirty grams is less than forty. That reading is reasonable, though a second reading is equally available, which is that a borderline result in fifteen men did not survive a much better powered repeat. A trial in older men supports the dose explanation, since forty grams raised overnight synthesis while twenty grams did not ⁵.

Either way, one conclusion is firm. Thirty grams of casein before sleep did not raise muscle protein synthesis in the best powered experiment anybody has run.

The training study that everybody cites had a flaw

A single overnight measurement is interesting, though what people want to know is whether the habit builds muscle over months. Snijders and colleagues trained forty four young men for twelve weeks and gave half of them 27.5 grams of protein with fifteen grams of carbohydrate every night before sleep ⁶. That group gained more: 3.6 square centimetres more quadriceps cross sectional area, and 34 kilograms more combined one repetition maximum, meaning the heaviest weight they could lift once, added up across the exercises.

The problem is the comparison group, which received a drink with no calories in it. The protein group therefore ate about 1.9 grams of protein per kilogram per day while the comparison group ate about 1.3 ⁷. That trial compares more protein with less protein, so it cannot tell you anything about the time of day at which the protein was eaten.

The researchers who ran it say the same thing themselves. In their later review they write that the benefit is hypothesised to work mainly as a function of increased total protein intake rather than by its specific timing. Any surplus benefit from the timing itself, they add, remains to be established ⁸.

What happened when researchers changed only the clock

Four trials have done the obvious experiment, which is to give the same protein at two different times of day. All four of them found no difference at all, and two of them held the total daily protein steady across every group.

• Trained men and women took 54 grams of casein either in the morning or before sleep for eight weeks, with no difference between the groups on any measure ⁹.
• Men on matched diets at 1.8 grams per kilogram took 35 grams of casein by day or at night for ten weeks, with no difference in lean tissue, muscle size or strength ¹⁰. The authors call that study preliminary, because it included only thirteen men.
• Professional cyclists during a training camp took 40 grams of casein before sleep, the same casein in the afternoon, or carbohydrate before sleep, with no difference on any outcome ¹¹.
• Untrained older men trained for twelve weeks with 40 grams of protein after exercise, the same protein before sleep, or no supplement, and all three groups improved by the same amount ¹².

A meta-analysis of protein timing in general came to the same conclusion. When Schoenfeld and colleagues controlled for the other variables, the timing effect disappeared entirely, while total daily protein intake was the strongest predictor of how much muscle people gained ¹³.

So the honest summary is that a bedtime snack is an extra meal. It works because it adds protein to your day, and there is no good evidence that the same protein does more at eleven at night than it would have done at three in the afternoon.

Your sleep, your appetite and your morning are unaffected

The worries people have about eating before bed do not appear in the data either.

• Sleep onset and sleep quality were unchanged by bedtime protein in both young and older volunteers ⁸.
• Next morning appetite and next day food intake were unchanged in older adults given 40 grams of protein ¹⁴.
• Resting energy expenditure was unchanged when 30 grams of protein came from cottage cheese or from a shake ¹⁵.

One trial did measure more energy used during sleep after bedtime protein, though the difference was about 33 calories across a whole night, which is too small to matter for anyone ¹⁶. A systematic review of eleven studies concluded that 24 to 48 grams of casein before sleep has limited to no effect on metabolism or appetite ¹⁷.

One finding is unfavourable and deserves saying plainly. In sedentary women with overweight or obesity, a bedtime snack raised fasting insulin the next morning and raised the HOMA-IR score, a calculated measure of insulin resistance, whether the snack was whey, casein or carbohydrate ¹⁸. Every group in that trial had a snack, so the comparison is between kinds of snack rather than against eating nothing.

How much protein before bed, and which foods reach it

The dose that worked in a laboratory is 40 grams, and 30 grams did not raise muscle protein synthesis in the one properly powered test ³⁴. If you are eating before bed for the muscle effect specifically, aim at the higher figure, though remember that the daily total is what the evidence actually supports.

Here is what each food gives, per 100 grams and then per normal serving.

• Magerquark, meaning low fat quark, has 10.6 grams per 100, so a 250 gram tub gives about 27 grams ¹⁹.
• Hüttenkäse, meaning cottage cheese, has 12.4 grams per 100, so a 200 gram tub gives about 25 grams ¹⁹.
• Whole milk has 3.2 grams per 100, so half a litre gives about 16 grams ¹⁹.
• A raw egg has 12.6 grams per 100, so three medium eggs give about 19 grams ¹⁹.
• Plain fat free Greek yogurt has 10.3 grams per 100, so a 170 gram pot gives about 18 grams ²⁰.
• Whey and casein powders are around 78 grams per 100, so a 40 gram scoop gives about 31 grams ²⁰.

To reach 40 grams from food alone you therefore need about 375 grams of Magerquark, 320 grams of cottage cheese or 390 grams of fat free Greek yogurt. That is a large bowl, which is the practical reason most of the research used a powder.

Who protein before bed actually helps

The answer depends entirely on what you already eat, and it splits into two clear groups.

If you already eat more than about 1.6 grams of protein per kilogram of body weight per day, and you spread it across your meals, a bedtime snack has nothing left to add. Every trial that tested exactly this situation reported no difference. The cyclists in the camp study were already eating over 2.5 grams per kilogram, and adding 40 grams before sleep changed no measurement ¹¹.

If your daily protein is low, which is common in people who eat little at breakfast and lunch, then a bedtime snack is one of the easiest ways to add 25 to 40 grams without changing any other meal. That is a real benefit, though the reason is the total rather than the hour.

Older adults are the group most often told to do this, so the evidence there is worth stating plainly. Forty grams before sleep does raise overnight muscle protein synthesis in older men ⁵. No trial has yet turned that into more muscle or more strength over a training programme. Two have tried in older men, and neither found any advantage for the bedtime timing over protein given at another hour or none at all ¹²²¹.

What to do tonight

A percentage change in a synthesis rate is also a smaller thing than it sounds. Trommelen and colleagues traced where the amino acids in new muscle protein had come from. A 25 gram drink accounted for nine percent of what was built, and a 100 gram drink accounted for twenty seven percent ²². The rest was recycled from protein your own body had broken down.

There is a wider lesson in this than a bedtime snack, which is that a single laboratory measurement is not a promise about your body over a year. Mitchell and colleagues measured a 235 percent rise in muscle protein synthesis after a first training session, then followed the same men through sixteen weeks of training. The size of that early rise predicted nothing about how much muscle each man gained, at a correlation of 0.10 ²³.

So the practical answer is short. Work out your daily protein first, aim for roughly 1.6 grams per kilogram if you train, and use the evening if that is the easiest place in your day to put it. Quark, yogurt, cottage cheese and milk all do the same job as a powder, without any measurable effect on how you sleep.

Protein is one of the few things in nutrition where the amount you need depends on numbers you can actually measure in yourself, including your muscle mass, your kidney markers and your activity. A blood panel is how you find out whether protein is the limit on your results, or whether your iron or your vitamin D is.

Notes and sources

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2. Boirie Y, Dangin M, Gachon P, Vasson MP, Maubois JL, Beaufrère B. Slow and fast dietary proteins differently modulate postprandial protein accretion. PNAS 1997;94(26):14930-14935. doi.org/10.1073/pnas.94.26.14930
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