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What are slow digesting proteins?

If you’ve spent any time researching health and fitness online, you probably hear often about the importance of protein. There’s a good reason for this: protein is essential for building and retaining muscle, as well as for healthy skin, bones and hair.


in many cases, discussions of the importance of protein leave out the differences between the various kinds available. Not only can protein be derived from many different sources including peas, whey and rice, it can be broadly categorized into two types: fast digesting and slow digesting.   


In this article, we’ll go over the difference between fast and slow digesting proteins, provide a few common examples of each, and talk about how to incorporate each of these different proteins into your current health and fitness plan.

What are slow digesting proteins?

As the name implies, slow-digesting proteins are those that take longer to travel through the body’s digestive system than other kinds. All types of proteins are formed from long chains of molecules called amino acids. Slow digesting proteins have a different molecular structure than fast digesting proteins.


One of the most common examples of slow digesting proteins is micellar casein.  Casein is one of the two types of milk protein that are derived from dairy (cow's milk). About four-fifths of the protein content of dairy milk is derived from casein - the rest is whey. The biological purpose of casein is to form “clots” in the stomach that aid in the body’s digestive process, part of the reason for its slow digestion rate.


Pea protein and rice protein are also sometimes considered forms of slow digesting protein, but they don't travel through the body as slowly as casein. Soy is a type of protein that is more slowly digested than whey, but faster than casein.

What are fast digesting proteins?

A fast digesting protein is one that moves through the body and is absorbed more quickly than other kinds. Whey protein is generally considered a fast digesting protein, because it has a faster absorption rate when compared to casein. A study published in the Journal of the 

American College of Nutrition found that consumption of whey protein reduced short-term food intake more than other types of proteins, carbohydrates and placebos. That’s likely because of the speed at which whey moves through the body allows for the “full” signal to reach your brain more quickly.


Whey protein is also considered valuable because it is one of the complete protein sources, meaning it contains all the essential amino acids the body requires. These are amino acids that must be consumed through protein intake of food and/or supplements, since they are not produced naturally in our bodies.

As you might imagine, the downside of fast-digesting proteins is that they won’t keep you full as long as slower-digesting ones that stay in the body longer. Typically, faster-digesting proteins like whey are used when it’s important for the body to receive a supplement of proteins sooner rather than later - such as after an intense workout. However, as you’ll see below, while there are certain situations where fast or slow-digesting proteins are recommended, there is also some flexibility.  

When to use fast digesting proteins vs slow digesting proteins

Now that you have a better understanding of the digestion rate of different types of proteins, you may be wondering when it’s appropriate to use each type.


Here are a few general recommendations for when it’s often best to use fast vs. slow-digesting proteins:

  • Elderly people generally see the best results with fast-digesting proteins. A 2014 study published in the Clinical Nutrition medical journal indicated that milk protein was retained better by a group of elderly subjects, when compared to the same amount and ingestion timing of casein protein. Other studies show that fast-digesting protein is more effective at preventing muscle loss in the elderly.

  • In the morning it’s often best to consume slow-digesting proteins for satiety, since these will stay in your system longer and curb your appetite for more of the day. Nothing’s worse than feeling pangs of hunger around mid-morning when you are still several hours away from lunchtime!

  • After a workout it’s typically best to consume fast-digesting proteins. A research study found that 10 weeks of supplementation with whey protein led to greater muscle mass gains than 10 weeks of supplementation with casein protein.

  • Before bedtime slow-digesting proteins are usually best. This is because your protein absorption rate is already slowed down while your body is at rest. A 2012 study found that casein protein helped healthy young males add more muscle during recovery than only consuming post-workout protein shakes.


As mentioned, remember that these are only broad suggestions. You are free to experiment with the specific types of protein you consume to determine which is best for your own unique needs. Some research indicates that the best choice for improving muscle synthesis is actually a "protein blend" of different types of proteins that may include casein protein powder as well as whey. 


Your overall protein consumption level matters much more than the specific kind of protein you ingest - hitting a consistent daily target for grams of protein is significantly more important for muscle growth than whether you reach that target with casein protein, whey protein, or any other variety of protein powder.

How to use slow digesting proteins

The first consideration to make when planning how to incorporate slow digesting proteins into your diet is the type of supplementation you’d like to incorporate. Most people associate protein supplements with the various powders available on the market. Protein powders derived from whey, casein and other blends are the most popular category of protein supplement available, but you can also find bars, gels and other forms of high quality protein depending on your preferences. 


It’s also fine to increase your consumption of slow-digesting proteins through whole foods such as certain types of yogurts and dairy products that are good sources of casein. However, people who are lactose intolerant or sensitive to dairy may prefer to use casein supplements. 


Others simply like the convenience that protein supplements provide for their busy schedule that doesn’t allow much time for cooking.


The next step is scheduling times for when you want to consume your proteins. If you look at the schedules of professional bodybuilders and other athletes, they've likely created an exact time each day when they consume a specific amount of protein, carbs, and other nutrients required for them to build and maintain muscle mass. While you don't have to be as rigid in your schedule as someone competing for "Mr. Universe," a more consistent dietary routine will help your body adjust to desired changes, whether your goal is weight management or muscle building.

Final thoughts on the best protein sources

Whether you're consuming protein to support muscle building and repair or as a tool to help you lose weight, it's important to consider all the various kinds of proteins available to create a personalized nutrition plan that works best for you. When choosing between protein with slow absorption rates or faster-digesting proteins, planning and timing are key. Dairy proteins like whey that are absorbed in a faster period of time are typically ideal for after a hard workout, while slow release options like casein are better for morning and night. 


By continuing to do your own research and looking for the best quality protein options available on the market – with transparent ingredients and as many natural sources as possible – you can craft a high protein diet that tastes great, fits your life and allows you to achieve your most important fitness goals.