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Author Topic: validity of glycemic index  (Read 11608 times)

Offline Ylide

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validity of glycemic index
« on: 18/01/2004 03:28:40 »
A question for you nutrition freaks out there:

What is the validity of the glycemic index value of foods?  I've heard conflicting stories from credible sources about wether or not the glycemic index is an accurate measure of how healthy a food is for a diabetic.

For instance... comparing a pasta made with semolina vs one made with whole wheat, after subtracting grams of fiber, the semoline pasta only has maybe 5g more carbohydrate per serving.  (38g vs 33g)  But the whole wheat pasta has a lower glycemic index, which leads me to believe it has a less pronounced spike of insulin levels as it's digested.  (presumably because the complex carbohydrates have additional digestive steps to undergo before conversion to blood glucose)

Is this accurate?  Is it recommended for diabetics to eat lower glycemic index foods?

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Offline bezoar

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Re: validity of glycemic index
« Reply #1 on: 18/01/2004 12:44:52 »
Also, the fiber slows the absorbtion of carbohydrates.  There ahve been studies with diabetics placed on a high fiber diet and they get better control of their diabetes and even need less insulin.  Then too, I guess, slowing the absorbtion of carbs means less spikes in insulin levels and less cravings.  Weight loss results in less insulin resistance.  Seems to me it all fits together.

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Offline Ylide

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Re: validity of glycemic index
« Reply #2 on: 18/01/2004 23:33:26 »
But what is the correlation?  Is it because they're eating more fiber or is it because the foods that contain more fiber tend to have a lower glycemic index because of the more complex carbohydrates they contain?  (e.g. monosaccharides cause a sharper spike than di or polysaccharides, and high fiber foods tend to have more polysaccharides)





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Offline tweener

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Re: validity of glycemic index
« Reply #3 on: 20/01/2004 04:13:57 »
The glycemic index is definitely for real, but I often wonder how some people arrive at theirs for certain foods.  From what I know, whole wheat versus white flour makes very little (but definitely some) difference in how fast the starches are digested and absorbed.  Any sort of grain is relatively high on the glycemic list, and if they are finely ground, they are right up there with refined sugar.

I've found that consistently eating low glycemic carbohydrates (i.e. vegatables) with lots of fiber and protein makes a huge difference in my cravings.  It also makes a huge difference in how I feel after a meal, which I attribute to the lower spiking of blood sugar level.  It also allows me to go several hours and not get shaky and weak from my blood sugar plummeting for lack of food.

I will recommend Dr. Barry Sears' "Enter the Zone" as a source on the biochemistry of what different types of foods do once they enter the body.  The whole focus of the book is about feeling good and losing weight by controlling insulin levels throughout the day.  It is not written for scientists, but for people like me that know nothing about chemistry.  All I can say is that it works for me and it is the first "diet" book I've seen that actually has some science behind the claims.  

One specific point is "what is a complex carbohydrate?".  There really is no such thing.  The higher fiber content makes it more difficult for the body to digest the carbohydrates that are there.  Protein also slows down the process because it takes longer to break down.  Fats do the same.

BTW, I'm not diabetic, so I can't really help with the specifics, but this definitely applies.  Dr. Sears talks about diabetic symptoms, their causes and the relationship of food to insulin levels.




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Offline Ylide

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Re: validity of glycemic index
« Reply #4 on: 20/01/2004 04:37:46 »
by complex carbohydrate, I mean polysaccharides.  They cause a slower rise in blood sugar because of the time your body needs to convert them to nice simple glucose.  

I'll be sure to check that book out though, I've been starting to get really interested in nutrition chemistry lately.



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Offline tweener

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Re: validity of glycemic index
« Reply #5 on: 22/01/2004 04:41:11 »
You just lost me.  Anything green is good, anything white is bad.  Fruit is good in moderation.


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Offline Ylide

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Re: validity of glycemic index
« Reply #6 on: 22/01/2004 07:59:44 »
Glucose, a monosaccharide, consists of one 5-membered ring with the appropriate function groups.  (OH groups)  Other monosaccharides include fructose and galactose.  (they are stereoisomers of each other)

Disaccharides are the product of a dehydration reaction taht joins two monosaccharades.  Maltose is 2 joined glucose molecules, lactose is glucose + galactose.

A polysaccharide is a polymer chain of various sugars.  Starch, chitin, and cellulose are examples of polysaccharides.  

Presumably, starchy foods have less of an impact on your blood sugar than sugary foods because of the time it takes your body to break down the polymer into glucose.  Ultimately, any sugar (and protein or fat!) you ingest becomes glucose, as that's the initial molecule that provides energy to your cells.  This is the basis of the glycemic index...how complex the carbohydrate content is in terms of needed enzyme action to convert the sugar to glucose.  

Ultimately, I was just wondering if the debunkers of glycemic index have a case or it's valid.

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Offline chris

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Re: validity of glycemic index
« Reply #7 on: 22/01/2004 11:20:58 »
quote:
Originally posted by cannabinoid

Glucose, a monosaccharide, consists of one 5-membered ring with the appropriate function groups.


If you include the oxygen then then ring is 6 membered isn't it ?

Carbon 6 hangs off the top and the other 5 participate in the ring. The Oxygen links 1 and 5.

Chris

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Offline Ylide

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Re: validity of glycemic index
« Reply #8 on: 22/01/2004 15:36:27 »
oops, thanks for catching that chris.  You'd think I'd know better right about now.  It is indeed a 5 membered ring.  I saw the pentagonal shape in my head but wrote 6 anyway.  :P



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Offline tweener

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Re: validity of glycemic index
« Reply #9 on: 23/01/2004 05:53:05 »
Thanks for the chemistry lesson.  I still don't understand very much, but every little bit helps.  

I know from experience that eating sugar or potato or bread all have about the same effect on me.  I'm basing it only on my body's response to the food and the way it makes me feel over the course of a few hours.  All of these "white" foods hit me like a hammer - I'm up for about an hour and then I crash after about two.  Then I'm hungry by three hours.  The same amount of carbohydrates in vegatables (not counting fiber) does not have the same effect.  It is much slower and gentler.  Fats with a meal that includes protein and veggies make me feel satiated for about four hours, even when the caloric intake is relatively low.


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Offline Ylide

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Re: validity of glycemic index
« Reply #10 on: 23/01/2004 07:12:01 »
That's because fats and proteins take yet even longer to be broken down to usable form.  Even the most complex digestible sugars (i say digestible because polysaccharides like chitin and cellulose are undigestible except to some microorganisms) will hit your blood stream pretty fast comparatively.  It takes your system a while to digest proteins and fats, hence they sit in your stomach longer and you feel full longer.

I'm sure there's more to it than that, but that's my layman's take on the digestive system.  

Anyway, Chris never answered my question as to wether the glycemic index is a useful tool in managing sugar intake for diabetics.  :P



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Offline MachineGhost

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Re: validity of glycemic index
« Reply #11 on: 11/02/2004 06:48:17 »
quote:
Originally posted by cannabinoid

A question for you nutrition freaks out there:
What is the validity of the glycemic index value of foods?  I've heard conflicting stories from credible sources about wether or not the glycemic index is an accurate measure of how healthy a food is for a diabetic.



I have seen less the optimal validity with the Glycemic Index because it is the body's insulinic response to foods that matter the most, not the absorption rate of carbohydrates.  Unfortunately, there is not an extensive Insulin Index available yet so the current obvious differences between the very large Glycemic Index and the very small Insulin Index lie with oatmeal (low insulinic), semolina (low insulinic), unflavored yoghurt (high insulinic) and all milled wholemeal grains (high insulinic) and most fruit (high insulinic).  I'd guess the oatmeal tested was not the instant type, but old fashioned or steel cut.  Semolina (the ground-up fibrous endosperm of durum wheat, NOT the same thing as durum flour) has a certain enzyme that makes it low insulinic.  I view fiber still being up in the air for any effect on mitigating insulin response, and needs to be controlled for soluble or insoluble.  A Paleolithic Diet avoiding high insulinic fruit/fructose and sticking to oatmeal and semolina for grains (if you're not a purist or are a vegetarian) seems to me to be the healthiest approach to eating.  Insulin is the single biggest factor in promoting physical aging, so there are pragmatic reasons besides being concerned about managing diabetes to avoid ingesting high insulinic foods.

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Offline Ylide

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Re: validity of glycemic index
« Reply #12 on: 11/02/2004 08:59:23 »
Can you clarify what you mean by insulinic response?  Do you mean the ability of insulin to act on foods of that type or the amount of insulin the body is stimulated to secrete in reponse to those foods being digested?

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Offline MachineGhost

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Re: validity of glycemic index
« Reply #13 on: 12/02/2004 08:23:19 »
quote:
Originally posted by cannabinoid

Can you clarify what you mean by insulinic response?  Do you mean the ability of insulin to act on foods of that type or the amount of insulin the body is stimulated to secrete in reponse to those foods being digested?

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I meant the latter (stimulation).

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Offline Ylide

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Re: validity of glycemic index
« Reply #14 on: 13/02/2004 01:28:13 »
I was under the impression that blood sugar levels were the only stimulus for insulin secretion.  Can you explain more about the mechanism?



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Offline MachineGhost

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Re: validity of glycemic index
« Reply #15 on: 16/02/2004 02:00:56 »
quote:
Originally posted by cannabinoid

I was under the impression that blood sugar levels were the only stimulus for insulin secretion.  Can you explain more about the mechanism?



I don't believe anyone has the exact answer yet as to why insulin response seems to be somewhat independent of serum glucose.  But I surmise it lies with "signature identification" of various glucose pre-cursors that trigger the insulin release before the glucose is in the blood, and/or fiber quantity or form.  Compare whole-grain bread to the cereal All Bran (which is certainly junk food considering it has sugar and high fructose corn syrup).  The former is high insulinic, the latter is low insulinic, yet both have fiber.

The only time you want an insulin spike is immediately after working out to replenish depleted glyocgen stores in the muscles and to halt catabolism.  Any other time and you start to join the 60% of Americans who are overweight

Machine Ghost
« Last Edit: 16/02/2004 02:15:17 by MachineGhost »
 

Offline Ylide

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Re: validity of glycemic index
« Reply #16 on: 16/02/2004 07:48:56 »
I joined that group a few years ago.  I'm trying to leave them now.  :P  

By glucose precoursers, do you mean di and polysaccharides that are eventually broken down into glucose?  

Also, above, you mention that sticking to low-insulinic foods is healthier.  I assume that is not true for diabetics as you would WANT them to to have a higher insulin response?  (I mean insulin-dependent diabetics, not insulin-resistant type II)  It seems to me you're saying that the junk food cereal you mention is in fact better for you.  Maybe I'm misinterpreting?





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Offline tweener

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Re: validity of glycemic index
« Reply #17 on: 16/02/2004 17:31:13 »
My understanding is that digestion of carbohydrates causes insulin production, while digestion of protein causes production of glucagon.  Digestion of fats doesn't affect either, but does have other effects.  Thus eating a high-protein snack will not cause an insulin spike.  Eating a snack with both protein and carbohydrates will produce some insulin and some glucagon, but not a spike of either one.


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Offline MachineGhost

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Re: validity of glycemic index
« Reply #18 on: 18/02/2004 06:25:09 »
quote:
Originally posted by cannabinoid

I joined that group a few years ago.  I'm trying to leave them now.  :P  

By glucose precoursers, do you mean di and polysaccharides that are eventually broken down into glucose?  

Also, above, you mention that sticking to low-insulinic foods is healthier.  I assume that is not true for diabetics as you would WANT them to to have a higher insulin response?  (I mean insulin-dependent diabetics, not insulin-resistant type II)  It seems to me you're saying that the junk food cereal you mention is in fact better for you.  Maybe I'm misinterpreting?



I meant all the forms other than the monosaccharide form necessary for absorption into the blood.  However, now that I think about it some more, this absorpotion of monosaccharides occurs first before the liver can convert galactase or fructose into glucose, so the pancreas must clearly be responding to the absorportion of the monosaccharides, not serum glucose.

Type I diabetics cannot produce enough or sufficient insulin so it's sort of academic about "efficiency".  Forcing a higher insulin response would just speed up the wear-and-tear of the pancreas, plus increase systemic insulin resistance, again sort of academic, as external insulin injections and diabetic drugs chronically destroy the pancreas anyway.  

Neither All Bran nor wholemeal bread is particularly nutritious food but from an low-insulin standpoint, the All Bran is preferable.  It would depend on whats in the bread and what your priority is.  If the bread is "clean" with no added sugars, trans-fat, etc., then it would be a good post-workout food to take along with protein.  The All Bran may have a low insulinic response, but the sucrose and high fructose corn syrup each have their own health negatives.

I guess the best thing we can learn from all this is that at least moderate amounts of soluble fiber taken with high insulinic carbs may be the key to keeping the insulin response chronically low.  I fear it may not be that simple, however.  e.g. There isn't a real noticeable difference in the fiber content of a slice of mixed grain bread (low insulinic) compared to a slice of wholemeal bread (high insulinic).

Machine Ghost
« Last Edit: 18/02/2004 12:13:41 by MachineGhost »
 

Offline MachineGhost

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Re: validity of glycemic index
« Reply #19 on: 18/02/2004 06:40:19 »
quote:
Originally posted by tweener

My understanding is that digestion of carbohydrates causes insulin production, while digestion of protein causes production of glucagon.  Digestion of fats doesn't affect either, but does have other effects.  Thus eating a high-protein snack will not cause an insulin spike.  Eating a snack with both protein and carbohydrates will produce some insulin and some glucagon, but not a spike of either one.



Protein does cause an insulin spike, just not as severe relative to carbs alone, or in conjunction with carbs which actually produces a higher insulin response than carbs alone!  This is why more modern post-workout drinks have glucose and protein, rather than just glucose alone.

Dr. Barry Sear's Zone Diet theory seems plausible at face value, but there is no hard science to specifically back up his claims.  Just look at the guy himself -- hes overweight!  So what good is having steady insulin at a chronically high insulin level?  It is insulin itself that is the enemy, not the crash below serum glucose homeostasis (20grams) that is the result of poor food choices.

Machine Ghost
« Last Edit: 18/02/2004 12:14:56 by MachineGhost »
 

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Re: validity of glycemic index
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