Talk:Glycemic index/Archive 1

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Archive 1

Variability of Quoted GI Values

A recent report summarizes some of the difficulties involved in estimating Glycemic Index

Some factors affecting the digestion of glycaemic carbohydrates and the blood glucose response 
Dr MC Vosloo

Department of Consumer Science University of Stellenbosch http://www.up.ac.za/saafecs/vol33/vosloo.pdf

"The blood glucose response to food is reflected by the glycaemic index of the particular food. Glycaemic index (GI) has been accepted as “an index that indicates the relative extent to which post prandial blood sugar increases” (Nishimune et al, 1991:414) and is defined as the incremental area under the blood glucose response curve elicited over a two-hour period by a 50-g carbohydrate portion of a food, expressed as a percentage of the response to the same amount of carbohydrate from a standard food taken by the same subject (Anderson, 1997, Wolever, 1999). The South African Department of Health (2002:10) gives the same definition, though stipulating glucose as standard and not referring to the time period (e.g. two or three hours). In an unofficial copy of the draft (Department of Health, 2003:11) they refer to the particular carbohydrates affecting blood glucose response as “glycaemic (available) carbohydrate”. This available carbohydrate – glycaemic carbohydrate – is available for metabolism and is the summation of the analytical values of mono, di- and oligosaccharides, starch and glycogen but excludes fructo- oligosaccharides and other non-digestible oligosaccharides and resistant starch (Department of Health, 2002:10)

CONCLUSIONS This overview has made it clear that the glycaemic response to food is a complex phenomenon determined by many factors including the following: the botanical source of the carbohydrate, the main classes and subclasses of the carbohydrate, the chemical and physical structure of the carbohydrate, calcium, cooking, acids and additions to formulated foods. To be able to consider one factor successfully in reliable and valid research the researcher should be fully aware of extraneous variables (Bless & Higson-Smith, 2000:154). Procedures should be accurately described and assumptions carefully investigated. Fields that can benefit from this review include the researcher in the field of blood glucose response testing and the GI of foods; the internist physician concerned with the diabetic patient; the dietician concerned with the diabetic patient or other dietary applications of the GI of foods; and the food scientist/technologist involved in food formulation aimed at making glycaemic index claims."

In addition, poor analytical techniques are used in determining Glycemic Index. The basic assumption that a "50-g carbohydrate portion of a food" , i.e. a portion of food containing 50 g of digestible carbohydrate, can be compared with 50g of glucose is erroneous. As both of these food portions have differing chemical units, the calculation of GI by comparing "areas under curves" does not give a dimensionless GI number. The resultant "GI number" has units "g glucose released from a portion of food containing 50 g of digestible carbohydrate per g glucose". Only food containing pure glucose and/or starch can have a true Glycemic Index. Other carbohydrate foods such as the simple sugars fructose and galactose and the di-saccharides lactose and sucrose need considerable processing by the body before they become glycemic. For example, fructose is partially converted to glucose by the liver. However, the amount converted is dependent on both blood glucose and liver glycogen storage levels. As any excess fructose cannot be stored in the liver, it is converted to fatty acids for subsequent storage as body fat. In this case. not all fructose is converted to blood glucose within the prescribed reference time of say 2 hours.This means that the total grams of digestible fructose overestimates the amount of fructose converted to blood glucose over the reference time. This results in giving false low Glycemic Index values for fructose. —Preceding unsigned comment added by 202.172.116.105 (talk) 23:20, 4 January 2008 (UTC)

I don't see how the values are "false": If Fructose doesn't sharply raise blood sugar levels after consumption, it doesn't have a strong glycemic effect, so it really shouldn't have a high GI. What's the problem? --Slashme (talk) 06:05, 17 January 2008 (UTC)

Sorry, ALL digestible carbohydrates raise blood glucose levels some 30 to 60 minutes after eating. The level of elevation is the only difference observed- see Hughes at ajcn.org/cgi/reprint/49/4/658. The major problem is that excessive consumption of carbohydrates, especially by pre-diabetic and diabetic patients, can lead to an increase risk in cardiovascular disease- see The New England Journal of Medicine, January 17, 2008. The role of glycated hemoglobin in CVD is at last being recognized, see Wikipedia Glycosylated_hemoglobin ." Persistent elevations in blood sugar (and therefore HbA1c) increase the risk for the long-term vascular complications of diabetes such as coronary disease, heart attack, stroke, heart failure, kidney failure, blindness, erectile dysfunction, neuropathy (loss of sensation, especially in the feet), gangrene, and gastroparesis (slowed emptying of the stomach)."

To summarize, consistently high levels of blood glucose levels can be dangerous and can lead to increase risk of CardioVascular Diseases. Over consumption of carbohydrates, irrespective of the foods apparent GI, needs to be avoided. In particular, consumption of "low GI" foods needs to be restricted as these foods tend to keep blood glucose levels high for longer periods after consumption. —Preceding unsigned comment added by 202.172.116.105 (talk) 21:57, 18 January 2008 (UTC)

OK, let's ask a different question: What is worse for a person with poor insulin control, a food which causes a sharp spike in blood glucose shortly after consumption, like bread does, or a food which causes a more gradual release of the same amount of glucose, like a baked potato? --Slashme (talk) 05:37, 21 January 2008 (UTC)

Both foods will give a sharp rise in blood glucose levels some 30 to 60 minutes after consumption. If insulin is naturally produced or dosed , blood glucose levels should decrease sharply with high GI food but less rapidly with moderate or low GI foods. The result is unfortunately very difficult to predict as each indvidual responds differently. This is where the validity of GI has been seriously questioned.

The main point is in the dangers of overeating high carbohydrate foods irrespective of their apparent Glycemic Index. The value or otherwise of GI has been questioned since its inception in the 1980's. Maybe now is a good time to finally dismiss its value in assessing food quality. —Preceding unsigned comment added by 202.172.116.105 (talk) 06:32, 21 January 2008 (UTC)

Contradictory Unclear Statements

"Unrefined breads with higher amounts of fibre generally have a lower GI value than white breads, but, while adding butter or oil will lower the GI of bread, the GI ranking does not change. That is, with or without additions, there is still a higher blood glucose curve after white bread than after a low GI bread such as pumpernickel."

Does anyone understand what bread GI or GI ranking is (with or without butter) at any point in time after reading this?Ace Frahm 08:47, 26 February 2007 (UTC)

It says, basically, more fiber lowers GI; buttered bread has lower GI; Low GI bread always has a lower GI than high GI bread regardless of added butter. —The preceding unsigned comment was added by 66.153.117.118 (talk) 21:56, 4 April 2007 (UTC).

A related ambiguity is this - 'While adding butter or oil will lower the GI of a meal, the GI ranking does not change. That is, with or without additions, there is still a higher blood glucose curve after white bread than after a low GI bread such as pumpernickel.'

The first sentence of this seems to be a straightforward self-contradiction which is not ameliorated by the following 'that is..' -

'While adding butter or oil will lower the GI of a meal, the GI ranking does not change'.

A possible resolution of these points is that butter or oil acts on the digestive system so as to delay the absorption of carbohydrates. The GI of all foods would then be reduced when foods are eaten with added butter or oil, but their order of ranking might remain unchanged. Andrew Smith Jan 2009.

Inherent Dangers

This page is especially for common folks, yet chocolate is listed. This could lead to the naive assumption that any refined chocolate product (which usually contains massive amounts of processed sugars) are okay to eat. This should be clarified. Go ahead and lemme know what you think about this.193.170.48.34 16:17, 7 June 2006 (UTC)

To say these are "inherent dangers" is nonsense. The use of the glycemic index or any other dietary lifestyle requires some common sense. The GI is simply a tool that covers one aspect of eating - mainly choosing "smart" carbohydrates. Of course a person's diet should not be high in chocolate or potato chips or lard - that's a no-brainer. Just because they are low GI doesn't make them a healthy food choice.

== Both of you have made very good points == (by siung99)

it's true that some findings can create controversy or be misleading if communicated/ worded badly. this is why researchers always have to be careful to make sure people wont misunderstand their findings.
Very true - "Just because they are low GI doesn't make them a healthy food choice." - GI is not meant to be used in isolation. that's what the GI experts say. GI helps when we are comparing different brands or varieties within one group, e.g. multigrain bread, brown bread, and white bread; and deciding which one is best (without added butter of course. :))

i'm listening to GI podcast by Prof Jennie Brand Miller who is a world-leading GI expert and she says, although watermelon has a high GI, she wouldn't discourage people from eating watermelon because it contains only a small amount of carbohydrate. what's more, it has antioxidants (that anti-aging thing) and is fat free too! :)

for more info on GI check this website out: http://ginews.blogspot.com/ siung99 20 May 2007

Definitions

Okay ... but what is the Glycemic Index ? Where do these numbers come from? Are they arbitrarily assigned or do they represent the end product of some calculation? I think an encyclopedia entry would have to relate this! Zuytdorp Survivor 22:47, 8 Feb 2004 (UTC)

I believe they're measured by having a group of people eat 100 grams of <carbohydrate>, then taking blood samples every few minutes to measure the blood sugar level. The index value is either the height or the time of the average peak relative to glucose. -- wwoods 08:32, 18 Mar 2004 (UTC)

wwoods is on the right track. I'm not sure about the "every few minutes". I have read that the index value is based on the area under the graph, but that doesn't quite square in my mind with the information that the index is supposed to provide, so I want to research this more before (if nobody else does it sooner) editing the page with the info rightly requested by Zuytdorp Survivor.

Right now I'm doing a major edit, which includes some deletions, so I want to explain the main features. For context, I've just been diagnosed with diabetes and so I'm doing a lot of research to understand GI and other issues so that I can repair what is repairable and learn to manage and live with what is not.

Key changes:

Deleted erroneous information about sugars and starches/complex carbohydrates. Dietary advice used to favour complex carbohydrates over sugars because the notion made sense that the body takes longer to process complex carbohydrates than sugars. After all, the processing involves breaking them down into sugars. However, research proved conclusively that the notion was incorrect. The starch in many foods is converted to blood glucose faster than table sugar! These findings were what prompted the development of the GI as an indicator of carbohydrate quality.

Deleted the examples of GI values - too few to be useful. I'll be working on something useful.

Deleted the links. One was less informative than any of the many pages I've found in my research. The other, with a GI list, was (like nearly all the GI lists I've found) an ad for a book. There are a great many such lists on the web, and I can't see grounds for selecting a particular one to promote. Moreover, short GI lists, designed to be of practical help to individuals, are culturally restrictive. They list foods thought to be most likely to be used by their target audience.

I question the practice of linking to pages that provide info that should be in Wikipedia, but maybe it's valid as a stopgap, an aid to readers while content is in preparation. So I've linked to what I understand to be the most comprehensive and authoritative list of GI values, in three ways. One is a searchable database, presumably up to date. Then there's the research group's data published in the American Journal of Clinical Nutrition in 2002. Finally, there's a simplified version of that list published by Rick Mendosa.

My intention is to try to condense the information from these sources into a list that is still comprehensive and culturally unbiased, but of practical use to individuals who want to control their carbohydrate diet. --Richard Jones 11:37, 20 Mar 2004 (UTC)

I think the last paragraph is wrong. GI is the measurement of how the blood sugars raise: foods with fat do lower the rate of which they raise. So how is it a 'false' rating? Fineform, if that was the source at which you got the information, was trying to say that foods aren't healthy just because of a low GI; not that they don't have a false GI. That, in any cae, is biased in favor of a low fat diet. Juan Ponderas

The comment suggesting that a short fall of the GI is that it only measures glucose should be removed. While this is true that it measures only glucose, it is not a shortfall as it is *glucose* we are concerned about and high glucose levels (spikes) which have been implicated in disease aetiology. It actually does measure the glycemic response from fructose (after conversion to glucose) as low GI and is therfore extremely valid. This explains why honey has a low GI and table sugar a moderate one. The glycemic response correlates very strongly with insulin response. The statement written in the article is incorrect. I will add to this article soon hopefully when I have more time.--sd 03:58, 2 Feb 2005 (UTC)

Just wrote a major revision and tightened it up in many places. I have a good image to load but need to get clearance from the University of Sydney first.

Booze

The sentence "Alcoholic beverages are also low GI" seems like, at the very best, a gross oversimplification. Beer contains maltodextrin, which has a relatively high GI, right? Let's at least use a qualifying word like 'some,' or get specific and talk about red wine, which as a lower GI than beer.

Beer contains, on average, 10 g of carbohydrate per serve. The amount is negligible for raising blood glucose levels when drunk at a reasonable rate. If, on the other hand, someone were to drink 6 beers in an hour than it may become significant. It is therefore incorrect to say that red wine has a lower GI than beer - it is irrelevant.

Check the link to the GI database. They say that foods with very low carbohydrate content do not have well defined GI values. --Slashme 11:14, 26 October 2005 (UTC)

There's a lotta stuff defined as "booze" that would seem to be at least medium, if not high on the GI, like chocolate liqueurs, cordials, creme liqueurs. It wouldn't be the booze part of the booze that would raise its GI, but the unfermented sugary flavorings added to the booze. Booze is a broad, complicated category. Much karma to the person who tries to index the sugary cordials for GI. --basilwhite 12:39, 08 February 2007 (EST)

Vegetables

Carrots do NOT have a high GI. This was inaccurate and incorrectly reported data back in the 1980s. Unfortuantely the myth prevails. Most fruit and veg have a low GI by virtue of their very low carb content per serve. The rate of absorption in such foods is irrelevant.

From the GI database:
Food	GI	Serving	Carbs/serving	GL
Carrots, raw (Romania)	16	80	4.2	0.7
Carrots, peeled, boiled(Australia)	41	80	4.6	1.9
Carrots (Canada)	92	80	4.2	3.9

You're thinking of glycemic load. Carrots (and many other healthy vegetables) can indeed have realatively high GI values in spite of their low carb content, because GI is defined in terms of an amount of glucose equal to the amount of carbs in the food tested. However, this does not make them unhealthy foods, as their glycemic load is low. --Slashme 11:14, 26 October 2005 (UTC)

Notice the large difference between the values. This occurs because you're measuring such a small effect that small variations can completely throw the result.

No, I am not talking about glycemic load. Carrots and most fruit and veg (not potato) have a negligible GI. The glycemic load is low as you state above simply because the GI is low. The high value of carrots given at 92 is not accurate data.

Well, I don't think fruits should be compared with most vegetables. The problem with measuring GI with vegs is that they normally contain very little carbs compared to fruits, and most other foods measured with GI in general. GL is probably a more fair measurement in the case with vegs. Still, fruit GI is not very high compared to, for example, pasta and bread, but seems to rise as the fruit ripens. - Wintran ^(talk) 01:36, 6 August 2006 (UTC)

Glycemic load

The external link [1] lists Glycemic Load aside the Glycemic Index, which sounds very helpful. But why does it depend on the "serve size"?
For example watermelon. "Its glycemic index is pretty high, about 72. According to the calculations by the people at the University of Sydney's Human Nutrition Unit, in a serving of 120 grams it has 6 grams of available carbohydrate per serving, so its glycemic load is pretty low, 72/100*6=4.32."
Why not take the percentage of carbohydrates in it, 5% (6/120) in this case, and multiply the glycemic index by that? 0.05*72=3.6. To not use a percentage sounds pretty strange, why would anyone not do that? - Jerryseinfeld 18:04, 16 Oct 2004 (UTC)

Actually, the GL does not depend on the serving size. That 120 grams they quote makes absolutely no difference to the calculated GL. Dunno why they chose to express it that way. Wikipedia (obviously a superior site) doesn't. --Slashme 11:23, 26 October 2005 (UTC)

i'd say it does make a difference on the GL, because GL has something to do with how much a certain food can increase blood sugar levels. so it has something to do with the amount of carbohydrate, and the bigger the serving size, the greater the increase. if they used 150 g serving size for example, the available carbohydrate per serving would be 7.5 g, and the calculated GL would be 72/100*7.5 = 5.4. this is what the GI experts said: "...If you eat more (or less) of that food you will need to calculate another GL value." (quoted from http://ginews.blogspot.com/2005/12/whats-new.html). siung99 20 may 2007

I have a puzzle for you

The effective ranking of foods into three distinct categories is important for functional use of GI. High=x range Med=y range Low=z range

If I change the reference food, why do these ranges stay the same?

You have to change the ranges if you change the reference food. For example, white bread is a popular reference food these days, but if you look at lists of GI these days, you'll sometimes find two lists, one for bread=100%, one for Glucose=100%, and different ranges. The range is not so important anyway, as "high" and "low" are relative concepts with grey areas. --Slashme 11:06, 26 October 2005 (UTC)

Why is the link i add being removed constantly(and anonymously)?

And , on the somewhat strange grounds that calculating gi for and entire meal is not meaningful??
1. The site doesn't do that.
2. It is meaningful and correct if you do it right: "Using this type of calculation, there is a good correlation between meal GI and the observed glycemic responses of meals of equal nutrient composition."

Also, i noticed an error in the article, the list of food that most use contains only 700-800 actual foods. Not 1500 as the "Searchable database of glycemic load values for over 1500 food items." claim. Most rows in the table are headings and groupings.

The link

Bfs007 14:38, 24 April 2006 (UTC)

GI Values

It is stupid for the article to be devoid of actual GI Values. I added a few examples.

And it seems wrong to only list low-GI foods in detail. It would be better if someone added the GI values, and added more examples of medium and hi-GI foods and their scores. 69.87.202.5 01:24, 9 June 2006 (UTC)

I'm not sure I agree that the article would be improved with such a list. It would just make an already long article even longer and you could end up with a few thousand values on there. There are loads of good lists out there on other sites (e.g. Sydney University,GI Diet Guide, Mendosa GI & GL list). Surely it is just better to link to them, as this is an encyclopedia, not a complete reference to everything about everything.

I agree. If you want to find a pile of GI values use the referenced databse at the official site. This article is not a database of GI values. I think the values listed so far should be removed to clean this article up.

EDIT: I removed the low GI foods list. It is unnecessary in this article and looked bad on the page. The original table showing a handful of example foods is enough.

I am re-adding it as a separate article. This is the kind of reference material people seek from Wikipedia. jengod 20:37, 14 August 2006 (UTC)

Shell Fruits

pardon my ignorance, but what are shell fruits?

Apparently, nuts. Why do you ask? Has it got anything to do with this article? Beanluc 03:53, 25 July 2006 (UTC)

If this Wikipedia user doesn't find it clear how many others will find it transparent. It's a good question. One can't assume that everyone knows what a shell fruit is. I certainly didn't know!. If a term is likely to be ambiguous or specific to a limited geographical region it ought to be linked to it's own topic page. If that page doesn't exist then I'd suggest that by this fact it should not be used at all. If you mean nuts say nuts. 86.3.101.212 (talk) 23:48, 10 October 2008 (UTC)

"Ranking system for carbohydrates"

I think some of the statements are phrased in a somewhat misleading way. For example, the introduction says

Glycemic index (also glycaemic index, GI) is a ranking system for carbohydrates based on their immediate effect on blood glucose levels. It compares carbohydrates gram for gram in individual foods, providing a numerical, evidence-based index of postprandial (post-meal) glycemia. The concept was invented by Dr. David J. Jenkins and colleagues in 1981 at the University of Toronto.

The reality is that it is an index for the food, not simply the carbohydrate in the food. The way this is phrased it loosely implies that, for example, if two carbohydrate-free foods have one gram of glucose added to each then they should both have the same GI value because the GI is related only to the carbohydrates. Although there is a correlation this implication would still be false in the most general case. The statements need to be rephrased to say that the GI is a ranking of foods not simply carbohydrates. --Mcorazao 20:22, 28 November 2006 (UTC)

probably the proponents of GI are just trying not to mislead people by implying that they can tell whether a food is good for you simply by looking at their GI values. e.g. potato chips has a lower GI than jacket potatoes but they are not a better alternative. (siung99 20 May 2007

Why is Dr Atkins not given any credit?

Dr Robert Atkins published his book in 1972 and clearly described the relationship betwwen the glycemic impact of foods and their correlation to weight loss and insulin levels. Why is his contribution not noted here. It was his and other leaders in the field that even prompted the work of Dr Jenkins. Please correct me if I am wrong. 198.143.193.186 17:15, 13 April 2007 (UTC)Jesse Sewell198.143.193.186 17:15, 13 April 2007 (UTC)

Atkins promotes a low carb, high protein diet. This is poles apart from the GI which involves a carb intake of between 45 and 60%. Furthermore Atkins advocates the consumption of saturated fat - a well-known and strong correlate with cardiovascular disease.—Preceding unsigned comment added by Studio34 (talk • contribs) 11:33, 21 May 2007

Atkins doesn't deserve any credit. He never published a paper in a peer-reviewed journal, and his books and popular articles are so riddled with contraditions and misinformation that he is simply not taken seriously in the scientific community.—Preceding unsigned comment added by 38.117.172.158 (talk) 16:25, 1 June 2007

Dr Bernstein appears to follow a more logical approach to blood sugar control. He recommends a very low carbohydrate diet, particuarly for diabetics. Best read his site- http://www.diabetes-book.com/ Ernie Lee —Preceding unsigned comment added by 202.172.116.105 (talk) 11:03, 5 June 2008 (UTC)

GI & Carrots

Not sure if this is the right place for this, but...

I note that in the Spanish version of the GI page: http://es.wikipedia.org/wiki/%C3%8Dndice_gluc%C3%A9mico that a GI table is included which gives only one value for carrots (92 . . . . . . Zanahorias cocidas)- being "cooked carrots".

Given the English page suggests this is an error "This also applies to carrots, which were originally and incorrectly reported as having a high GI.[2]" it would seem some updating is needed.

As a new user I have no idea how to do this so I leave it in the hands of those more knowledgeable.

I have put a similar comment on the Spanish page.

MarcTurner 08:56, 25 April 2007 (UTC)

the English page is right - the new value (world's average) is 47. source: http://ginews.blogspot.com/2005/08/gi-values-update.html. Siung99 12:05, 20 May 2007 (UTC)

Pasta

Why is pasta listed as high GI when it's not? 212.161.95.66 (talk) 15:11, 23 January 2008 (UTC)

The Science RD is good at handling these kinds of questions.

Zain Ebrahim (talk) 14:06, 26 February 2008 (UTC)

Criticism of GI

I was just reading through this section and found this

// A study from the University of Sydney in Australia suggests that having a breakfast of white bread and sugar-rich cereals may make a person susceptible to diabetes, heart disease, and even cancer.[2] //

I don't understand how this could be seen as a criticism of GI. This is a point that would support GI.

Or am I understanding this incorrectly? Let me know what you think.

Madman91 (talk) 18:22, 23 March 2008 (UTC)

I would agree. Although the issues presumably involves the use of GI as a metric it isn't relevant within the context of a discussion of GI unless it can be made thoroughly and transparently clear how this is so. This does't seem to be the case 86.3.101.212 (talk) 23:46, 10 October 2008 (UTC)

Table Sugar

The line in the table 'straight glucose (i.e. table sugar)' - does that imply to anyone other than myself that table sugar is straight glucose? Which it isn't, right, its sucrose which is a combination of glucose and fructose, right? Does table sugar have the GI of straight glucose? And can anyone find a better way to state the info? --Neil (talk) 11:43, 12 June 2008 (UTC)

Table sugar is now in the right row, where it belongs. --Aspro (talk) 12:49, 12 June 2008 (UTC)

This is where determining Glycemic Index goes terribly wrong. If we accept the work carried out by Hughes, the real GI of fructose is very near that of glucose see http://www.ajcn.org/cgi/reprint/49/4/658. figure 1. He reports that the blood glucose response for pure fructose is some 75% of that observed with a similar amount of glucose. So why do other investigators report low values of GI (approx. 20) for fructose come from ? Only Hughes uses non insulin dosed diabetic 1 subjects. See my explanation at top of page. Ernie Lee. BSc Chemistry. —Preceding unsigned comment added by 202.172.116.105 (talk) 11:04, 21 June 2008 (UTC)