What Are Good Sources of Protein? – Speed of Digestion Part 3

Ok, somehow this mini-topic got a little bit out of control (I have a lot to say) so I want to wrap up the discussion on speed of digestion and move into the other topics that go into answering the question What are good sources of protein?


Whole Foods vs. Protein Powders

I finished up What are Good Sources of Protein? Speed of Digestion Part 2 with a short chart showing the estimated digestion speeds of various proteins, including some whole foods.  As someone brought up in the comments, it’s unfortunate that there isn’t more data for whole foods because of the fact that, outside of athletes, most people are eating whole food protein sources, not protein powders, to obtain the majority of their daily protein.

And, in that chart, with the exception of an estimated value for tenderloin that seems impossibly high, most whole food proteins were on the slow end of the digestion scale.  This actually makes perfect sense.  Whole food proteins are generally contained within a matrix of connective tissue and such (e.g. think of the chewing that you have to put into eating meats such as beef, tuna, or chicken) and that alone will slow the process of digestion down.  Basically, even without direct data, I’d expect most whole food proteins to be slowly digesting proteins.

Research using whole food meals find that amino acids are still be released into the bloodstream up to 5 hours after eating them; this certainly supports the idea that whole food proteins take a long time to digest.  Other researchers have suggested that a given meal will maintain the body in an anabolic state for 5-6 hours so clearly whole food proteins aren’t digesting particularly quickly.

Basically, the majority of proteins that people who aren’t obsessed athletes will be eating are going to be slowly digesting proteins.

The primary exception that I’ve examined, of course, is whey protein which digests quickly; soy isolate is also a fast protein (another that I’ll mention briefly in a second is pea protein hydrolysate).  Now, whey has some nice characteristics in terms of its amino acid profile (discussed in a later segment of this article), it may improve immune system function, and have other functional health benefits.  Outside of athletes, life extension folks and the obsessed health types, I’m not sure that whey protein powder is going to make up a major source of protein for the majority of people.

However, this brings me in a very roundabout way to a related topic having to do with protein powders and the different forms that they come in.


Types of Protein Powder: Concentrates, Isolates and Hydrolysates

On this note, before moving on, I want to make a couple of quick comments about protein powders since, as usual, there is a lot of confusion, hype and outright lies being made about them.  Quoting directly from The Protein Book:

Protein powders come in three primary forms which are isolates, concentrates and hydrolysates.  Protein concentrates typically contain roughly 80% protein with 5-6% carbohydrate and fat while isolates may contain up to 90% protein.  Hydrolysates are simply isolates or concentrates which have been pre-digested (digestion of protein is called hydrolysis) by subjecting them to specific enzymes.  Practically speaking, you will typically pay the least for a protein concentrate, more for an isolate and the most for a protein hydrolysate.  Because of the presence of free form amino acids in protein hydrolysates, they often have a more bitter taste than either concentrates or isolates.

In the last couple of years, there has been a real push by supplement companies for expensive (and often bitter tasting) hydrolysates based on the claim that they digest much more quickly than either isolates or concentrates and thus super-speed amino acids to just worked muscles.

Ignoring the question of whether faster is actually better (see below), there is the question of whether hydrolysates actually do digest significantly faster than protein isolates.  Limited research is available and while one study showed that pea protein hydrolysate digested more quickly than other concentrates, this data can’t be applied to any protein except pea protein.

One study compared the digestion speed of whey and casein to their respective hydrolysates and the simple fact is that there was no significant difference in digestion speed.  Quoting from the results:

The rate of gastric emptying for all solutions was found to fit an exponential pattern (r=0.92–1).Solutions were emptied at similar rates, with half-times of (mean ± S.E.M.) 21.4±1.3, 19.3±2.2, 18.0±2.5 and 19.4±2.8 min,for the whey hydrolysate, casein hydrolysate, casein and whey protein,respectively.

Basically, there was no real difference (maybe a couple of minutes faster for the hydrolysates) between whey isolate and its hydrolysate and casein and its hydrolysate.

Translation: there is no advantage to whey or casein hydrolysates in terms of digestion speed.  None.  Well, unless you think paying three times the price and accepting an often bitter taste is an advantage.

Which brings me in a roundabout way to the final topic of this series within the series:


Is Faster Digestion Better?

Although this question would pretty much never come up with regards to general health and nutrition, it is one that is relevant to sports nutrition (and as noted in part 2, older individuals may obtain beneifts from fast proteins).  Is it better for protein to be quickly digesting or slowly digesting?

Of course the answer is context dependent and depends on what the goal is.  For the majority of applications, I hope that readers get the basic idea that I think slower digesting proteins, or a mix of slow and fast are generally superior to fast proteins by themselves.

This is especially true for non-athletic applications where I think most should simply stick with whole food proteins most of the time anyhow; in the context of a mixed meal, that will mean that the proteins being consumed will digest slowly.

As I noted in What are Good Sources of Protein? Speed of Digestion Part 2, there is emerging data that older folks may benefit from spikes of amino acids in terms of offsetting age-related muscle protein breakdown.  So that is clearly one exception to my general belief that slower or slow/fast mixes are best under most conditions.

Now, a recent trend in sports nutrition is to consume nutrients (carbs, protein) around the entire training bout, this often means before, during and after training.  I actually spend about 35 pages discussing this issue in The Protein Book examining the most recent research and giving specific recommendations for both strength/power and endurance athletes in terms of when, how much and what to consume around training for different types of workouts.  I’m not going to repeat that here, clearly.

As discussed thoroughly in that chapter, there is emerging data that a slow or mixed fast/slow protein following training is superior to a fast protein alone (I realize that this goes against what all of the supplement companies are saying but, as usual, they are taking research out of context to sell product).

Readers might simply refer back to my article on Milk: The New Sports Drink – A Review as research clearly showed that milk (a combination of whey and casein, that is a combined slow/fast protein) was superior to soy protein (a fast protein) for supporting muscle mass gains.  Post-training, slow or a combination of fast and slow is simply superior to a rapidly digesting protein.

But that’s after training and folks are currently consuming protein before and during workouts these days.  Under those situations, clearly a slowly digesting protein is inappropriate if for no other reason than having protein sitting in the gut digesting while you try to train is a good way to throw up.

For pre- and during-workout protein intake, I recommend a quickly digesting protein such as whey or a good soy isolate.  That is one condition where, clearly, a fast digestion speed will be superior.  Under most others, I feel that a slower digesting protein or at the very least a combination of slow and fast will give the best results.

There are other possible exceptions to the above, which I’ll come back to later in this series.  As a primary example, some research suggests that hormonal impact of a fast protien like whey may blunt hunger better than slowly digesting proteins such as casein.

However, empirically, I can’t say I’ve seen this be the case: most report that casein (a slow protein) or milk protein isolate (a protein powder containing both whey and casein) keeps people fuller on a diet by sitting in the stomach longer.  Again, I’ll come back to this in more detail when I talk about dieting.

And that’s that for speed of digestion.  On Wednesday, I’ll look quickly at protein quality before moving onto the rest of the topics I outlined in the Introduction to this series.

Go to What Are Good Sources of Protein – Protein Quality

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