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The Amino Acid Index: A Corollary to the Glycemic Index

Recently the question was raised as to whether or not adding milk to a post-workout concoction, such as Surge, would be detrimental or inhibitory to the proven benefits. The question was immediately greeted with what we’ve all accepted as true: that adding a milk-based protein (i.e. casein) to whey will slow the digestion and absorption of whey.

This is a belief that I have, in the past, prescribed to as well, and, to this day, I still recommend only mixing the rapid digesting and absorbing ingredients contained in a post-workout concoction with agua.

However, I have been rethinking this somewhat. For example, when we have a beautfiul protein blend like Low-Carb GROW!, which contains whey isolate, milk isolate and calcium caseinate, don’t we get a large, acute hyperaminoacidemia from the whey and a moderate, longer-lasting hyperaminoacidemia from the casein?

This is my line of thinking and seems to be what I gather from JB’s Bedtime Story, as well as from the highly overpriced Night-Time proteins.

Now, I’m not at all disagreeing with the recommendation that one should not screw with Surge and just add some high-quality H20, no, not at all. I’m just bringing forth an issue that I think needs some clarification.

Timbo: A man as good as his word.

Is this a friggin’ BUMP or what? Since 1222 BC.

Char, my man, you cannot doubt a true T-Bro.

I would love some fish to bite at this one though.

Just wanted to add another nightcrawler to the line.

Just wanted to say whats up bud, I crossed over to the dark side, it was getting pretty boring over at the other site, so I decided I sould give this one a shot, and see if I can pick up anything new.

Jay: This is an extremely pleasant surprise. I was going to recommend you step on over the next time I contacted you, but you beat me to the punch, brutha! Good call. This is far from the dark side, though:-)

You’re going to be exposed to awesome people and information here. Get ready to soak it up like sponge, Jay.

Now, will someone bite on the dayum question?

Alright, Timmy, I’ll bite.

I’ve been wondering about a similar question for quite some time now. Hoping to get it all cleared up when JMB gets his shot at the guest forum.

Anyway, here’s what I think.

Whey is “fast absorbing” and casein is “slow absorbing.” Milk protein is some whey, some casien. But absorbtion doesn’t happen until the small intestine. The milk will hit the stomach first. The stomach’s job is mechanical digestion in the form of mixing waves (not really needed for an all liquid meal) and HCl; and chemical digestion in the form of breaking down of proteins to polypeptides. These polypeptides are broken down to amino acids once they reach the small intestine. Chemical breakdown of carbs and fat doesn’t start until the small intestine.

Perhaps the stomach will not empty until the casien is broken into polypeptides, which may take an hour or so. Whey is partially pre-digested, right? Maybe this means it is already in the form of polypeptides and doesn’t need to be broken down in the stomach. But if casien is present, the whey has to wait for it. Once the stomach empties, and the chyme hits the small intestine, the whey is free to be absorbed right away, while the casien is slowly broken down even further, and gets absorbed when it’s ready.

Whey taken by itself would leave the stomach after a few minutes, enter the small intestine, and be absorbed in a few more minutes.

Actually, I have no idea, but I think this is a pretty good guess. If I’m way off base, someone let me know.

Thanks for the bite, Patman. I appreciate the conversation.

I see what you’re saying, but I can’t say that I believe it.

I don’t think the rate of gastric emptying would be affected by the type of protein ingested.

Perhaps, with a combo of the two proteins, rather than whey alone, the amount of whey that enters the small intenstine would be relatively less in the former situation. That is, if whey alone was ingested, then it alone would be emptied into the small intestine. Thus the rate of hyperaminoacidemia would remain rapid.

In the case when both proteins are ingested, you would get emptying into the small intestine of both whey and casein. In this case, you’d not get the same hyperaminoacidemia that you did in the case with whey alone.

This is pure speculation.

What I don’t think changes at all is the rate of absorption of the proteins. That is, I don’t see how ingesting both proteins would slow down the breakdown of whey such that the appearance of amino acids is slower.

It may be useful to know whether casein will lower the GI of a meal. I like the idea of an “amino acid index.” Has anyone measured the length and size of an insulin spike after ingestion of an insulinogenic amino acid? For example, 5 grams of leucine free-form vs. 5 grams of leucine in a whole protein source: which insulin spike is bigger, which has the larger duration?

When you ingest something that slows gastric emptying like casein or fiber, everything that is ingested with it will also be slowed in its absorption.
This is one of the reasons that whole grains are better than processed grains in regards to the GI and II. Most of the carbohydrates aren’t structurally different between whole grain and processed grain, but the fiber helps to blunt the insulin response.
Of course, it depends on the amount of casein (or fiber, etc.) that is ingested. Five or six grams of casein probably won’t be enough to slow the absorption of a drink like Surge down to any significant degree.

Brian: It’s not plausible to measure the insulin response to any meal. This requires blood sampling and the like and would be restricted to a laboratory environment. Obviously not something that can be done for “fun.”

Tony: I guess my question becomes, on a more basic level, does casein slow the rate of gastric emptying? I did not necessarily make this assumption.

I agree that fiber will blunt the blood glucose and insulin responses, probably due to the fact that the fiber makes it more difficult for the enzymes to “attack” the carbohydrate and due to the lower rates of gastric emptying.

Thanks, guys, for your input. Perhaps I should visit those physiology websites posted in an earlier thread.

I’m not advocating that one make any changes to Surge or the current post-workout format just yet, though.

But I’m still not certain that you’ll get a reduced burst of hyperaminocidemia from the whey even when it’s simultaneously ingested with casein.

Timbo, of course, I meant in the lab. Let me rephrase: Does anyone know any studies that measure the insulin spike and duration from amino acids, both free form and in whole proteins?

I would assume that the casien would slow the gastric empting of the combined proteins. But this is all guess work really. How would you design a study to prove/disprove this? use tracers?
As far as the real world solution, why not go for surge post workout then a slow release protein (grow/steak/tuna etc about an hour later, problem solved. isn’t it?

Brian, well I posted a reference yesterday, but it didn’t seem to go up. Let me try again.

From our favorite Insulin Index study, the authors say in the introduction:

Several insulinotropic factors are known to potentiate the stimulatory effect of glucose and mediate postprandial insulin secretion. These include fructose, certain amino and fatty acids, and gastrointestinal hormones…

They cite the following:

Nuttall FQ, Gannon MC. Plasma glucose and insulin response to macronutrients in nondiabetic and NIDDM subjects. Diabetes Care 1991. 14: 824-38

Morgan L. Insulin secretion and the entero-insular axis. In: Flatf PR. ed. Nutrient regulation of insulin secretion. London: Portland Press Ltd. 1992: 1-22.

Hmmm, this didn’t go through last night. Lets see if I can remember it all…

Whetu: That’s the best option I can see as well. I drink my whey + maltodextrin right after a workout, and an hour later I have a hamburger or two.

Timbo: That’s right, the question that really needs answering is does casien slow gastric emptying? Another question is how long does whey protein (with fast carbs in a post-w drink) stay in the stomach? My belief is that it’s a pretty short amount of time. Anyway, everything I’ve read indicates that after the whey/casien combo is consumed, there is a spike in amino acid levels (whey absorbtion), followed by a long-term, smaller elevation of amino acid levels (casien absorbtion). Therefore, if the casien is slowing anything, it can’t be actual absorbtion, since the whey and casien appear to be absorbed independently of each other; so must be gastric emptying.

If casien does slow gastric emptying, I wonder if other proteins, like eggs or meat, have a similar effect, and to what degree? Well, I guess that they would stay in the stomach longer due to increased mechanical digestion, but I wonder if there is any data on the absorbtion rates?

Good question! I have been wondering about this topic for a long time myself but in a broader sense (encompassing all three macronutrients).

That’s why I started a thread titled “Digestion Physiology” but got no bites.

Basically, my question was if you eat different fast and slow digeting foods in the same meal, would the faster digesting foods get digested and absorbed first or is it “averaged out” with the slower digesting foods in the stomach? Or as Patman put it, “wait” for the slower digesting foods to breakdown before gastric emptying?

There are contradicting theories on this.

Many gurus say that a mixture of a fast-digeting protein like whey and a slow-digesting protein like casein is best as the whey will provide fast acting anabolism and the casein will provide long lasting anti-catabolism suggesting that they will be absorbed independantly.

On the other hand, it is suggested that fat slows down the digestion a meal suggeting that the meal will be “averaged out”.

I also remember reading a response to a reader mail (I can’t remember which issue) by an alarmed reader about having a high GI carb like maltodextrin in Classic Grow. The response was to look at the meal as a whole and not the maltodextrin individually and the meal as a whole will have a smooth insulin curve.

On the other hand, JMB’s recommends not eating P+C+F in the same meal as the C will raise insulin which will promote storage of the F.

Wouldn’t the P and F slow down the digestion of the C rendering it harmless?

Additionally, doesn’t P (and to a lesser extent F) also raise insulin?

I’ve read that a dose of whey protein raises almost as much insulin as an equivalent dose of dextrose. If I’m not mistaken, according to Christian Thibaudeau, 50g of whey raises about the same amount of insulin of about 30g of glucose.

Ah, the confusion!

Though certain food combinations will slow digestion or gastric emptying (ie fat & fiber), gastric emptying does not occur all at once or simultaneously. As your stomach breaks food down, the valve between the stomach and intestine periodically opens enough to let the “liquid contents” pass through to the intestine as breakdown occurs, while limiting undigested chunks from passing. Thicker semi liquid contents (such as casein, which “jells”) are released more slowly than the liquid contents (as the viscosity controls the extent of passing through the valve opening…and the stomach controls how much the valve opens also controlling what gets to pass). This is why liquid meals are digested so much quicker than solid meals…and why fiber slows digestion, as fiber is hard to break down. But with a liquid meal consisting of whey and casein, the casein may jell in the stomach, but the casein will not cause the whey to jell and the whey will stay liquid and pass fairly quickly through the stomach while the casein is held back…of course the casein will slow the whey down slightly, but not near as much as the casein itself. In brief, the more liquid contents and higher processed contents (ie flour, etc) of a meal will need less digestion before beinng released into the intestine while the more solid components of the meal will digest and pass more slowly and gradually as the breakdown of different foods is not at the same rate. And this is why when eating bread with a meal, you should eat whole grain rather than refined as the refined white bread will digest much quicker even in a mixed meal.

Hebber: You know you’ve got quite a name and reputation for yourself down here in Texas. You’ve got a whole chain of grocery stores named after you (i.e. H.E.B.)! Just messing with ya, but a great response.

A7: I am of the belief that you will get the transient increase in hyperaminoacidemia from whey and a subsequent, sustained hyperaminoacidemia from casein, when the two are combined. I do not feel that whey’s absorption–and subsequent rapid breakdown and appearnce of amino acids (i.e. anabolic nature)–will be attenuated by the anti-catabolic properties of casien.

Although nutrients like fat and fiber will slow down the gastric emptying of nutrients, I don’t see how they’ll slow down the rate of absorption.

Now, as far as your questions about combining carbs and fats, this is still a no-no. Even if these nutrients are released slower, you’re still bound to have high levels of carbs (i.e. blood glucose=insulin) and plasma fats. Bad combo.

And, yes, certain amino acids are insulinogenic in nature.

Thank you Heb. That is very helpful.

Timbo: how did you post the active link “Bedtime Story” ?

So in terms of post workout drinks, it is a better choice to go with a whey/ casein blend, as opposed to solely a whey blend? I have been pondering on this one for quite a while, and still am a little mixed up.

J-Dog, I’m thinking that if you’re going to be eating a whole-food meal within about an hour or so after your post-training liquid meal, then having pre-digested whey (or whey isolate) and dextrose/maltodextrin is still probably your best bet.

If you’re opting for whole-food post-workout or won’t be eating for another two or three hours, then I’d opt for the blend.

Patman, it’s all about HTML code, bro. I can try to explain later if you want. But I gotta run!