Protein at night: is it needed

The advice to "drink casein before bed so your muscles don't break down overnight" has echoed through gyms for decades. Yet it was only in the 2010s that researchers at Maastricht University tested it in controlled studies. The editorial team examined what happens to muscle protein during sleep, whether an evening portion of protein gives a real advantage and who needs it most.

What happens to muscles at night

Muscle protein is constantly renewed: the synthesis of new proteins and the breakdown of old ones proceed at the same time. The balance between them determines whether a muscle grows, stays stable or loses mass. After a meal, when the level of amino acids in the blood rises, synthesis prevails. Between meals, on the contrary, breakdown prevails, and the body uses amino acids from its tissues.

Sleep is the longest period without food during the day. If the last supper was at 7–8 p.m. and breakfast at 7–8 a.m., a person spends 10–12 hours in a state of overnight fasting. Studies using labelled amino acids show that during this time the muscle protein balance is usually negative, though small in absolute terms.

For a person who does not train, this nighttime "dip" is normally compensated by daytime eating. For an athlete the situation is different: an evening workout triggers increased muscle sensitivity to amino acids that lasts at least 24 hours. If amino acids are lacking during this period, part of the training's adaptive potential goes unused.

It is on exactly this logic that the idea of evening protein rests: to deliver amino acids into the blood during the period when muscles are most sensitive to them, while ordinary food is not being supplied. The question was whether the body is even able to digest and absorb protein during sleep, since digestion slows down at night.

What the research showed

The first important step was the work of Groen and colleagues (2012), who administered protein to elderly men through a tube at night. It turned out that protein is digested and absorbed during sleep, amino acids enter the blood, and the rate of muscle protein synthesis increases. In other words, there are no physiological obstacles to nighttime absorption.

The same year, Res and colleagues published a study with young men who performed an evening strength workout. Before sleep, participants drank 40 g of casein or a placebo. In the protein group, the rate of muscle protein synthesis over the night was roughly a quarter higher, and the whole-body protein balance was positive.

The most interesting question is whether the acute effect translates into real muscle gain. Snijders and colleagues (2015) conducted a 12-week study: young men trained three times a week and every evening received a drink with 27.5 g of casein and 15 g of carbohydrates, or a calorie-free placebo. The protein group achieved greater gains in strength and in the cross-sectional area of muscle fibres.

An important caveat: in this study the total amount of protein per day in the supplement group was also higher. It is therefore impossible to cleanly separate the effect of "the evening timing itself" from the effect of "simply more protein". Later work, in which daily protein was equalised, gave less clear-cut results.

Which protein to choose at night

Most studies used casein — the main milk protein. It curdles in the acidic environment of the stomach, forming a clot that is digested slowly. Thanks to this, amino acids enter the blood gradually over several hours, which theoretically matches the duration of sleep well.

Whey protein is absorbed faster and gives a higher but shorter peak of amino acids in the blood. For nighttime intake it also works, though the effect may be less prolonged. There are few comparative studies specifically in the nighttime context, so it is impossible to claim with full confidence that one protein is superior to another.

The good news is that you do not have to use a sports supplement. Ordinary products high in casein — quark, Greek yogurt, skyr — provide a similar amino acid profile. A 200–250 g serving of quark contains roughly 30–40 g of protein depending on fat content and manufacturer.

For vegans and people with dairy intolerance, plant protein blends can be used, for example pea with rice. Because of the lower leucine content, it makes sense to take a slightly larger serving than for animal protein.

How much and when: practical guidelines

The position stand of the International Society of Sports Nutrition (ISSN, 2017) notes that taking 30–40 g of casein before sleep can increase nighttime muscle protein synthesis and improve adaptation to training. Smaller servings, around 20 g, proved insufficient for a noticeable nighttime effect in some studies.

The intake timing in the studies is usually 30–60 minutes before sleep. The supplement should not replace supper: it complements a complete diet. If supper was late and rich in protein, a separate intake before sleep makes much less sense.

• The main priority— the daily amount of protein: for people who train, usually 1.4–2.0 g per kilogram of body weight.
• The second priority— an even distribution of protein across 3–5 intakes throughout the day.
• The third priority— an evening portion as one of these intakes, especially after an evening workout.

Those who benefit most from evening protein are people who train in the evening, those who find it hard to reach their daily protein target, and older people. In older age muscles respond worse to protein ("anabolic resistance"), and an additional intake helps partly compensate for this problem, as confirmed by the studies of Kouw and colleagues (2017).

By contrast, for a person who already eats enough protein evenly throughout the day and trains in the morning, an additional shake before sleep is unlikely to make a noticeable difference. In such a case it is a matter of convenience and calories, not a mandatory element of the programme.

Myths and limitations

Myth 1: "Protein at night is stored as fat".There are no studies showing that a moderate portion of protein before sleep worsens body composition, provided total calorie intake is maintained. Fat accumulates because of a surplus of calories over the day, not because of the timing of food. In addition, protein has a high thermic effect and is very satiating.

Myth 2: "Without nighttime casein your muscles 'burn up'".The nighttime negative balance really does exist, but it is small and fully compensated by daytime eating. People built muscle long before casein shakes appeared, and the main factors of success remain training and the total amount of protein.

Myth 3: "Evening protein worsens sleep".For most people a portion of 30–40 g does not affect sleep quality. However, a large volume of liquid or heavy food immediately before sleep can cause discomfort, heartburn or nighttime awakenings. In such cases it is better to move the intake 1–1.5 hours earlier.

The limitations of the evidence base should be stated honestly: the studies are small, conducted mostly on young men and elderly people, and there is little long-term work with women. People with chronic kidney disease or other conditions that require limiting protein should discuss any dietary changes with a doctor.

Editorial conclusions

Protein is absorbed during sleep, and a portion of 30–40 g of casein before bed increases nighttime muscle protein synthesis. This has been proven in controlled studies, so the idea has a scientific basis.

At the same time, evening protein is "fine-tuning", not the foundation. The daily amount of protein, regular training and sufficient sleep have a far greater impact on results than the timing of the last intake.

Evening intake is most justified for those who train in the evening, fall short on protein during the day or are in older age. Quark or skyr can be a full-fledged alternative to a supplement.

The editorial team also recommends reading our materials about casein and whey protein, about the daily protein requirement for athletes and about the role of sleep in recovery after training.

References

1. Res PT, Groen B, Pennings B, et al. Protein ingestion before sleep improves postexercise overnight recovery. Med Sci Sports Exerc. 2012;44(8):1560–1569.
2. Groen BBL, Res PT, Pennings B, et al. Intragastric protein administration stimulates overnight muscle protein synthesis in elderly men. Am J Physiol Endocrinol Metab. 2012;302(1):E52–E60.
3. Snijders T, Res PT, Smeets JSJ, et al. Protein ingestion before sleep increases muscle mass and strength gains during prolonged resistance-type exercise training in healthy young men. J Nutr. 2015;145(6):1178–1184.
4. Trommelen J, van Loon LJC. Pre-sleep protein ingestion to improve the skeletal muscle adaptive response to exercise training. Nutrients. 2016;8(12):763.
5. Kouw IWK, Holwerda AM, Trommelen J, et al. Protein ingestion before sleep increases overnight muscle protein synthesis rates in healthy older men. J Nutr. 2017;147(12):2252–2261.
6. Jäger R, Kerksick CM, Campbell BI, et al. International Society of Sports Nutrition position stand: protein and exercise. J Int Soc Sports Nutr. 2017;14:20.