Fast vs. Slow Protein... Is Casein Bogus?
by Will Brink
Enter stage right, the “fast vs. slow” protein . The study that got this craze rolling was called “Slow and fast dietary proteins differently modulate postprandial protein accretion” and was responsible for causing a resurgence of interest in casein. The basic premise of this much-touted study was that the speed of absorption of dietary amino acids (from ingested proteins) varies according to the type of dietary protein a person eats.
The researchers wanted to see if the type of protein eaten would affect postprandial (e.g., after a meal) protein synthesis, breakdown, and deposition. To test the hypothesis, they fed casein (CAS) and whey protein (WP) to a group of healthy adults, a single meal of casein (CAS) or whey WP following an overnight fast (10 h). Using this specific study design, they found:
•WP induced a dramatic but short increase of plasma amino acids.
•CAS induced a prolonged plateau of a moderate increase in amino acids (hyperaminoacidemia)
•Whole body protein breakdown was inhibited by 34% after CAS ingestion but not after WP ingestion.
•Postprandial protein synthesis was stimulated by 68% with the WP meal and to a lesser extent (+31%) with the CAS meal.
The basic non-science summary is: the study found that CAS was good at preventing protein breakdown (proteolysis), but was not so good for increasing protein synthesis. WP had basically the opposite effects: it increased protein synthesis but didn’t prevent protein breakdown. The problem is that they were using fasted subjects for a single meal. ***
Keep that in mind as we move along here…
So far so good right? So what can we conclude from this study and how useful are the results? Like so many studies, the results were interesting—and of little use to people in the real world. Do these results hold up under more “real world” conditions where people are eating every few hours and/or mixing the proteins with other macronutrients (i.e., carbs and fats)?
The answer is probably not, which is exactly what the researchers found when they attempted to mimic a more realistic eating pattern of multiple meals and or the addition of other macronutrients. The follow up study was called “The digestion rate of protein is an independent regulating factor of postprandial protein retention.” Four groups of five to six healthy young men received:
• a single meal of slowly digested casein (CAS).
• a single meal of free amino acids mimicking the composition of casein (AA).
• a single meal of rapidly digested whey proteins (WP).
• repeated meals of whey proteins (RPT-WP) mimicking slow digestion rate of casein (i.e., reflecting how people really eat).
So what did they find? In a nut shell, giving people multiple doses of whey—which more closely mimics how people really eat-—had basically the same effects as a single dose of casein, and mixing either with fats and proteins pretty much nullified any big differences between the two proteins.
*Edit: I'm not saying that I "buy" what this guy is saying regarding whey/casein or his other points. Although, I personally never have spent 1 extra cent on casein. I'm just throwing this out there to get feedback.