Protein supplements: Is protein absorption the problem? | Precision Nutrition

Protein supplements:
Is protein absorption the problem?

By Helen Kollias


For ages the great debate over protein has been how much protein do I need? There have been many knock-down, drag-out fights over how much is enough and how much is too much.

In the red corner: the RDAs who recommend 0.36-0.8 grams of protein per pound of bodyweight (0.8 g/kg to 1.2-1.8 g/kg) in daily protein intake!

In the blue corner: the fitness experts who recommend 1-2g/lb (2.2 to 4.4 g/kg)!

Ding! Ding!

Now I’m going to be the one who leaps into the ring unexpectedly with the folding chair.

Forget how much you’re eating. How much are you absorbing?

What if you aren’t absorbing all – or even half – of the protein you’re eating?

Whoa, now that’s a knockout idea!

Eating versus absorbing

You may be smugly thinking, “Helen, this isn’t news. Everybody know that most people have low stomach acid and can’t absorb all the protein from a steak.” But what about whey protein? You should be able to absorb that pretty easily, right? Figure you could absorb pretty close to 100% of a whey protein shake, right?  You feeling lucky, protein punk?

Well, you’re wrong. We only digest a small amount of whey protein in liquid form. Are you surprised? If not, I’m not ashamed to admit that I was.

Surprise aside, the research is pretty clear.  Indeed, a recent study examined how much whey protein we can absorb in one sitting.  And let me just say that it looks like a lot of whey is literally going down the toilet.

Forget the spider – Little Miss Muffet has other problems

Turns out that it takes 1.5 hours for viscous liquids (e.g. a whey protein shake) to pass through the section of the gut that can actually absorb it.  But that’s not the breaking news.  Here’s the big story.  The maximum rate that whey protein can be absorbed is about 8-10 grams per hour.

WARNING! Math ahead!

Little Miss Muffet drank a 50 gram whey protein shake.  Since Miss Muffet can absorb only 10 grams every hour. How long does it take for Miss Muffet to absorb all the protein?

50 grams / 10 grams per hour = 5 hours

So, it would take 5 hours to digest all that protein.  But remember, we have only 1.5 hours to get ‘er done.  Therefore Miss Muffet has no chance of absorbing all of it.  She’ll absorb – at most  – 15 grams.  And the other 35 grams?  Well, they’re wasted. Unless…

Research question

As mentioned above, a recent article looked at one possible way of boosting whey protein absorption – and, by extension, amino acid delivery and muscle growth.  Here’s the reference:

Oben J, Kothari SC & Anderson; ML. An open label study to determine the effects of an oral proteolytic enzyme on whey protein concentrate metabolism in healthy males JISSN 2008 5(10).

In this study the researchers asked the question: what can people do to increase whey absorption?

(Well, actually, they asked whether “digestive proteases would increase the absorption rate of [whey protein concentrate] WPC.”  But the question above just sounds better…that’s why we translated the academese for you.)


In this study, forty-one participants volunteered to have their blood and urine analysed. They were healthy men that were lean (with BMI between 20 and 24), and relatively younger – between 19-35 years old.

These participants were given a plain vanilla flavoured whey protein concentrate powder that was 85% protein, 6% fat, 3% ash, and 6% lactose – no solublizers, emulsifiers or “fillers”. (By the way, it turns out that 50 grams of whey protein powder is actually 42.5 grams protein.)

What next?

Well, first, the researchers looked at what happens when these guys drank a 50g serving of whey protein alone (known as the control sample).  And after the supplement, they tested two things: serum amino acid levels (the amount of amino acids circulating in the bloodstream) and total nitrogen excreted.

They measured serum amino acid levels before drinking the whey and at various points afterwards (30 minutes, 1 hour, 2 hours, 3 hours, 3.5 hours and 4 hours after drinking the whey protein).

To measure total nitrogen excreted, researchers also collected participants’ urine for 24 hours after drinking the whey. Knowing how much protein in ingested (the whey) and how much nitrogen is excreted (urine) you get a sense of the overall nitrogen balance. It’s important to note that there are are more sensitive methods for determining overall nitrogen balance using blood analysis.

Geek alert!
More in-depth scientific explanation!

Nitrogen balance is when nitrogen intake (food with protein) = nitrogen excretion.

If nitrogen intake is more than nitrogen excretion then you have an anabolic state in the body that allows for growth (good if you want to gain or maintain muscle).

If nitrogen is less than nitrogen excretion then you have a catabolic state in the body that allows for tissue breakdown (not good if you want to gain or maintain muscle).

Since the amount of whey ingested is the same in all cases a decrease in nitrogen excretion means a more positive nitrogen balance. So, in this case less nitrogen excretion means a situation for more muscle growth!


It turns out that when participants drank whey alone, it took 4 hours to reach maximum total serum amino acids levels, which increased about 30% from baseline (from 1.71mg/L to 2.22mg/L).  So, with straight unadulterated whey you get a 30% increase in total amino acid levels after 4 hours. Now what?

Maybe Little Miss Muffet should get off her tuffet and try digestive enzymes.

While the findings about whey alone are interesting, the real purpose of this study was to test whether proteolytic enzymes helped increase protein absorption. Proteolytic enzymes (in this case, Aspergillus niger and Aspergillus oryzae) are simply digestive enzymes that help digest protein.

After the entire group took whey without any enzymes, researchers split the group up. One group drank whey along with 2.5 grams of enzymes; the second group drank the same amount of whey, but with 5 grams of enzymes.

As with drinking whey on its own, both groups had peak serum amino acid levels 4 hours afterwards. Nothing exciting there. We’ve already learned that it takes time for whey to be absorbed.

But whey and enzymes together had much higher amino acid levels after 4 hours. Remember that without any enzymes there was only a paltry 30% increase in amino acid levels. With 2.5 grams of enzymes, amino acid levels were 110% higher after 4 hours. With 5 grams of enzymes, even better: 127% higher.

Holy curds! 127% versus 30% in the same time frame – that’s impressive!

As it happens, the researchers also looked at individual amino acids. You know, alanine, valine and a bunch of other ‘ines. The group taking in 5 grams of enzymes also had higher individual amino acid levels than when drinking whey alone, with the exception of serine and methionine. So all branched chain amino acids (BCAAs) were higher with 5 grams of enzymes.

Another interesting finding was that less nitrogen was excreted when the whey also had enzymes. Again, remember: less nitrogen excreted means a more positive nitrogen balance, which means a more anabolic environment in the body.


First, it’s pretty clear that you probably aren’t absorbing all the protein in your whey if you’re drinking it plain and in viscous (liquid) form.  From this study (and others), it seems that under normal conditions, liquids rush through the GI tract too quickly and that only a small amount of protein can be absorbed during normal transit time.

From this study it’s also evident that higher doses of whey protein are better absorbed if you take digestive enzymes at the same time.  When you do this, you get higher amino acid levels in your blood, so that you have more available to your muscles and other tissues, which is pretty much the whole point of drinking whey – to make amino acids available to your body.

Second, it got me thinking: what other things help us absorb whey protein? My questions:

  1. If I sip my whey protein drink, or drink small amounts every 15 minutes or so, therefore spreading the whey drink out over an hour or two, is the absorption better?
  2. If I find some way to slow down transit time, by making a Super Shake, by adding the protein to oatmeal, or by using a milk blend containing casein, would that slow transit time enough to make a difference in absorption?

My suspicions are yes – both would help increase absorption.  Although not as much as seen with enzyme supplementation.  So the best of both worlds, if you’re looking for increased absorption, would probably be to slow down transit time AND supplement with proteolytic enzymes.

Now, on a side not, I do have to mention that this study was sponsored by the company that makes whey protein powder with these enzymes.  Of course, I’m not saying the study isn’t accurate.  However, I always, always look at where the money comes from for studies. Why? Because to some degree, funding will influence the interpretation, design, or outcome of the research.

But back to the physiology.  It appears that in the end, we should all be more concerned about how much of whatever we are eating is actually being absorbed. What you eat doesn’t necessarily mean what you absorb and have available to you.

In the case of whey protein supplementation, thanks to the science, the days of slamming a 50g protein shake are gone.  If you don’t find ways to slow transit time and/or increase the rate of whey absorption, you’ll be spending your hard earned cash on boosting fecal and urinary nitrogen vs. increasing muscle protein.

Eat, move, and live…better.




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