Of the three macronutrients, protein is the one that is most directly involved with building muscle. It is found in all cells in the human body and is especially prevalent in muscles. The main role of protein is to build and repair tissue. The body is constantly breaking down and repairing itself and for your muscles to get bigger you need to build tissue faster than you break it down.
The body breaks down protein into amino acids in order to build muscle. The body uses these amino acids to build muscle in a process called protein synthesis. There are 22 standard amino acids that the body uses to synthesize proteins.
Nine of the amino acids are essential which means the body cannot produce these in high enough amounts and must be obtained through your foods or supplements. There are also 9 conditional amino acids which are usually not essential except in certain cases such as illness.
Protein is available from many different food and supplement sources and each source is absorbed into the body at different rates. Knowing the rates at which the different proteins are digested can help with timing your meals.
A quick absorbing protein is best for after a workout since it starts the muscle recovery process quickly. A slow absorbing protein is good to consume before bed because its slow release provides the body with a steady stream of protein while you are sleeping.
How Quick can the body use the Protein?
Whey and casein both have long held the reputation for being fast and slow proteins but there so many other sources of protein whose absorption rates are less known. A few years ago I saw a chart that broke down how fast proteins were absorbed and all I remembered were those two. I was really interested in researching the other proteins and how quickly they are absorbed.
Luckily for me a 2006 article from Shane Bilsborough and Neil Mann entitled A Review of Issues of Dietary Protein Intake in Humans already compiled data from various studies conducted over the years that measured the absorption rate of different proteins.
Below is a chart summarizing their research.
| Protein Source | Absorption rate (g/h) |
| Egg protein (raw) | 1.3 |
| Egg protein (cooked) | 2.8 |
| Pea Protein | 3.4 |
| Milk Protein | 3.5 |
| Soy protein isolate | 3.9 |
| Free Amino Acids | 4.3 |
| Casein isolate | 6.1 |
| Free Amino Acids (same profile as casein) | 7-7.5 |
| Whey isolate | 8-10 |
So what does all this mean?
Well not surprisingly whey protein is in fact absorbed the quickest. I am however surprised that only 8-10 grams are absorbed every hour. With all the talk of how fast whey is absorbed, I would have thought that more whey would be absorbed per hour.
The other major surprise for me was that casein protein ranked relatively quick compared to the other proteins that were researched. The common belief for a long time has been to use casein before bed because it absorbs very slowly. The data shows that egg, soy and milk absorbs at a rate much slower than casein.
Egg Protein. The data shows raw eggs are absorbed into the body at the slowest rate but, unless you’re like Rocky, you probably won’t be drinking raw eggs. Cooked eggs absorb into the body at a very slow rate as well so they may be a good alternative to casein at night since they will take longer to absorb into the body. The good thing about eggs is that they have a high biological value which mean a larger percentage of the protein is being absorbed into the body. There are protein powders that are made with egg protein but the the research was done on whole eggs. It’s unclear if egg protein powders will absorb at a quicker rate.
Whey Protein: Whey, it is the still regarded as the quickest absorbing protein. This makes it a great choice for a post-workout shake. The good thing about whey is it is a very widely available protein. Not only will you find whey in nutrition stores, but it’s even available in most grocery stores. Whey is a milk protein and is a byproduct of cheese production. Because of this vegetarians may avoid it as well as people with lactose sensitivity. There are 3 major types of whey concentrate, isolate and hydrolysate. Whey concentrate is 29-89% protein by weight and has some lactose, fat and cholesterol. Concentrates are usually the cheapest whey protein. Isolates are 90% and higher in their protein content and are processed to remove more of the fat and lactose. Hydrolysates are usually the most expensive but are predigested so they should be easier for people with a lactose intolerance. Since they are predigested they should absorb even faster than an isolate.
Casein Protein. Casein may not be the slowest absorbing protein as previously thought, but it still absorbs a lot slower than whey. Slow absorbing proteins have their advantages as your body can still get protein absorbed between meals. This is especially important when you sleep. Casein is also a milk protein so vegetarians and those with a lactose sensitivity may want to avoid it. It absorbs at the rate of 6.1 grams per hour still takes the body 7 hours to absorb 42 grams of casein so it is still a good option to take before you go to bed. If you have ever had a casein protein shake you’ll notice it is a lot thicker than a whey shake and just feels like it takes longer to digest.
Soy Protein. Soy is a popular protein choice for vegetarians and those with a lactose sensitivity but I hardly recommend it for my clients. It’s absorption rate is relatively slow absorbing 3.9 grams every hour which can be useful but soy is also associated with higher estrogen levels. While present in both males and females, estrogen is more of a female hormone which is why I do not recommend any males to use soy as their primary protein. Estrogen is also known to increase fat storage so it may be counterproductive to increase your intake of soy for anyone who wants to burn fat. The good thing is that it is a complete protein from a plant source, but there are better sources of vegetable based protein powders like Sun Warrior, Vega, and Plant Fusion powders that don’t contain soy.
Whole foods??? I have long recommended eating whole foods instead of supplements as often as possible. The only time I prefer supplements over food is a whey shake after a workout or when eating is difficult because of time or schedule or some other reason. There is not a lot of data on the absorption rate of protein from foods though. Most of the studies were done with supplements or with supplement that mimic certain foods instead of the foods themselves. I think it’s pretty safe to assume that whole foods will absorb slower than supplements because of the added digestion need to first breakdown the foods.
So hopefully this report can help you make a decision on which protein powder is best for you. If you liked this article or think it might help someone please share it with the button below. Thanks for reading.
