When you go shopping for protein supplements, you’ll probably encounter a lot of sales copy that discusses the “speed” of different proteins. “Fast” proteins are digested and absorbed quickly, leading to a rapid rise and a high peak in plasma amino acid levels, followed by a (relatively) quick decline in plasma amino acid levels. “Slow” proteins are digested and absorbed more slowly, leading to a more gradual rise and lower peak in plasma amino acid levels, followed by a slower decline.
All of the marketing material will tell you that “fast” proteins, such as whey, are ideal most of the time: the rapid digestion and high peak in blood amino acid levels will stimulate greater muscle protein synthesis. Conversely, the marketing material will tell you that “slow” proteins, such as casein, are ideal to consume before sleep. Since blood amino acid concentrations will stay elevated for a longer period of time, slow-digesting proteins consumed before bed will keep stimulating muscle growth all night, ensuring you never spend a single moment in a net catabolic state.
However, the research suggests that the first claim is mostly incorrect: whey does cause a higher peak in blood amino acid concentration than casein, but despite that, whey and casein are similarly effective at stimulating muscle protein synthesis (one, two, three). In other words, whey is a faster-digesting protein than casein, but that advantage in digestion speed doesn’t actually result in greater muscle protein synthesis.
I’m sure you can already tell where I’m going with this: a recent study suggests that the claimed advantages of consuming a slower-digesting before sleep are also overblown. Casein does elevate plasma amino acid levels for a longer duration than whey, but it doesn’t do a better job of stimulating muscle protein synthesis overnight.
In a recent randomized, placebo-controlled, double-blind study by Trommelen and colleagues, a sample of healthy, untrained men were recruited to test the effects of pre-sleep protein supplementation. You can see more details about the subjects below.
Subjects were randomly assigned to three groups. Subjects in all three groups underwent some pre-assessment testing, including a cycling test to assess subjects’ maximal workload capacity (wattage at the point of exhaustion during a progressive cycling test). During their experimental session, subjects reported to the lab at 5pm. At 5:30, they consumed a standardized dinner. Between 7:45 and 8:45, they completed a 60-minute cycling protocol at 60% of their maximal workload, and then consumed a standardized carbohydrate beverage immediately after completing the cycling protocol. Finally, subjects consumed experimental beverages around 11:30, containing either a) 45g of whey protein (whey protein group), b) 45g of casein protein (casein group), or c) a non-caloric placebo (placebo group). After consuming their beverages, subjects went to bed (in the lab) around midnight, and were woken at 7am.
Blood amino acid levels were assessed via blood samples obtained from catheters that were inserted into the subjects’ antecubital veins. Muscle protein synthesis was assessed using tracer amino acids, with muscle samples obtained via biopsies taken a) before the subjects consumed the experimental beverages, and b) when the subjects were woken the next morning. You can see a visual representation of the study design below.
Overnight blood amino acid concentrations followed the pattern you’d expect: there was a higher peak in the group consuming whey protein, but blood amino acid levels stayed elevated for longer in the group consuming casein (leading to similar areas under the curve for overnight elevations in blood amino acid levels).
However, the longer-lasting elevations in plasma amino acid levels didn’t result in greater muscle protein synthesis in the casein group. Myofibrillar and mitochondrial protein synthesis rates were non-significantly greater in the casein group than the placebo group, and non-significantly greater in the whey group than the casein group (the difference between the whey group and the placebo group was statistically significant).
I wanted to write about this study for a very simple reason: I think people tend to make protein-related messaging way too complicated. We’re told we need to worry about digestion speed, how many times per day we consume protein, protein quality, and how close to our workouts we consume protein, and so on and so forth.
As time has gone on, it’s appearing that most of those considerations only matter at the extremes. This article discusses digestion speed (slower- and faster-digesting proteins end up having similar effects), but the same generally applies to the frequency of protein consumption, protein quality (one, two), and protein timing. For most people, most of the time, total protein intake is the only thing you really need to worry about.
To be clear, you can concoct scenarios where some of these other considerations would become relevant. For instance, protein quality could become a concern if you got all of your protein in the form of collagen, which has very low levels of most essential amino acids (and completely lacks tryptophan). But, if you consume a more-or-less normal diet, you probably don’t need to worry about it. Similarly, if you took protein intake frequency to the extreme, you could make an extremely persuasive case that eating all of your weekly protein in a single meal wouldn’t be ideal. But, if you consume a more-or-less normal diet with at least 2-3 protein feedings per day, you probably don’t need to worry about it.
Circling back to the topic of this article, pre-sleep protein feeding has gotten a fair amount of research attention, but I suspect it’s another detail that ultimately doesn’t matter too much. The research on pre-sleep protein intake has findings that mirror the results of the present study: pre-sleep protein intake does increase overnight protein synthesis. So, over time, consuming a bolus of protein before bed should result in more total protein synthesis over time, and thus, greater muscle growth … or so the thinking goes. However, all of the other protein-related details are supported by this same sort of logic. Consuming protein immediately after a workout leads to greater muscle protein synthesis post-workout, so it should result in more muscle growth over time…but it doesn’t. You can stimulate a new spike in muscle protein synthesis every 3-4 hours, so eating more frequently (with 3-4 hours between meals) should result in greater total muscle protein synthesis, and thus greater muscle growth over time, than sticking with a typical meal pattern (with 5-7 hours between meals)…but it doesn’t.
Basically, I think there’s a tendency to draw a straight line between muscle protein synthesis and muscle growth. But, as we’ve previously discussed on the podcast, there are quite a few assumptions baked into that chain of logic that aren’t always correct.
So, just to wrap up this research spotlight, if you do want to take a better-safe-than-sorry approach to protein intake, and so you do want to consume a protein bolus right before bed, you probably don’t need to worry about selecting a slow-digesting protein source. However, I also suspect that you don’t really need to worry about consuming protein immediately before bed in the first place – as long as your total protein intake is sufficient, and you have at least 2-3 sizable protein feedings per day, you should be in good shape.