1Private research, Kraków, Poland.
*Corresponding author. e-mail: email@example.com
Background and aims: Glycemic indices (GI) are believed to be the best indicators of glycemic properties of foods. For that reason, a lot of work has been done for their determination. The aim of this study is to propose a new method for determination of the percentage contents of glucose in digested foods.
Results: Contrary to the widespread belief GI are not the reliable indicators of glycemic properties of foods. Glycemic loads (GL) are in fact equal to the percentage contents of glucose in digested foods. They are, however, biased by errors in determinations of GI and in the determination of total contains of carbohydrates.
Conclusions: The methods that are used for quantitative determination of glucose ought to be compared in different laboratories using the same selected foods such as raw and cooked carrot, sucrose, rice and other comestibles. Both healthy subjects and type 2 diabetics may participate in that research.
Key words: Glycemic index; Glycemic load. Glycemic carbohydrates; Glucose; Glucose response function; Diabetics
There are no “good” or “bad” carbohydrates. Taking into account the needs of diabetics all carbohydrates may be divided into two types: glycemic carbohydrate (GC) and nonglycemic carbohydrates (NGC). Only active glucose (AG) produced by decomposition of glycemic passes through the stomach walls into the bloodstream and increases its concentration in blood. Nonglucemic carbohydrates are resistant to digestive juices and therefore they are not broken down to glucose but they are excreted from the body.
GI had been introduced to characterize glycemic properties of food products and to enable diabetics to control their glucose blood levels. A lot of research has been donein order to determineGI of all kinds of foods. The obtained data have been compiled in the International Tables of GI and GL … .
Glycemic index and Glycemic load of a food
The GI of any food is defined as the percentage ratio of the glucose response functions (GRF) obtained after ingestion of a food containing 50 g of carbohydrates to the GRF that is obtained after ingestion by the same person of 50 g of reference glucose:
GI = 100*Ap* / AG* (1)
Ap* is the area of GRF obtained after ingestion the portion of a food containing 50 g of carbohydrates,
AG* is the area of GRF obtained after ingestion by the same person of 50 g of reference glucose.
According to that definition of GI the mass of tested food may be calculated using the relation:
(mp* / mpC*) = (100 / PC ) (2)
mp* is the mass of the ingested food,
mpC* is the mass of all carbohydrates contained in that food,
PC is the percentage content of carbohydrates.
An asterisk * indicates that the mass of a food product, the mass of the reference glucose and the respective GRF are mutually dependent.
GC is the only component of a food that is hydrolyzed and broken down to glucose during digestion. The mass of glucose that appears in the stomach due to hydrolysis of GC is grater than the mass of GC from which it was obtained. Therefore, the relation:
mG = 1,11*mGC (3)
may be used when it is necessary.
The glucose, which is formed in the stomach, is the only variable that determines the area of GRF of the tested food:
Ap* = ApG* (4)
ApG* is the area of GRF of glucose that is formed during digestion of a tested food.
GI = 100 * (mpG*/mG* ) (5)
mpG* is the mass of glucose obtained by decomposition of GC contained in the sample of a food that has been used for determination of GI,
mG* is the mass of 50 g of pure glucose that is consumed by the same person for determination of GI..
Thus GI is equal to the percentage ratio of the mass of glucose obtained by digestion of a tested food mpG* to the mass of reference glucose mG* that is equal to 50 g.
mG* = mpC* = (mp* * PC)/100 (6)
then using (4) and (5) the following relation is obtained:
GL = PG (7)
PG is the percentage content of glucose that is formed by digestion of GC contained in the food sample of mass mp* .
That means that GL is equal to the percentage content of glucose which is formed from GC during digestion of a tested food PG*. Therefore, only GL has clear physical and chemical meaning.
Determination of glycemic carbohydrates in foods in an indirect way
The percentage content of GC (PGC) may be calculated the most simply by subtracting PNGC (fiber) from the PC.
PGC = PC – PFIB (8)
PFIB is the the percentage content of fiber in a tested food (PNGC = PFIB).
Carbohydrates in foods are calculated from the rest to one hundred percent after subtracting the contents of fats, proteins ash and water :
PC = 100 – PFAT – PPRO – PASH – PWAT (9)
THence, the content of glycemic carbohydrates may be calculated according to the equation:
PGC = 100 – PFAT – PPRO – PASH – PWAT – PFIB (10)
PFAT, PPRO , PASH , PWAT and PFIB are percentages of fats, proteins, ash, water and fiber in a food, respectively.
The variables on the left hand side of Equation (9, 10) are biased by errors in determination of the variables indicated on the right hand side of those equations.
Determination of glucose transferred to the blood stream after ingestion of the food product
Determination of glucose produced in the stomach after ingestion of the food product
The area of GRF obtained after ingestion of reference glucose is proportional to its mass:
AG = kG*mG (11)
AG is the area of GRF after ingestion of the reference glucose,
mG is the mass of the ingested reference glucose,
kG is the proportionality factor.
The area of GRF after ingestion of the sample of a tested food by the same person is proportional to the mass of glucose that is formed from it:
ApG = kG*mpG (12)
ApG is the area of GRF after ingestion the sample of a tested food,
mpG is the mass of glucose that is produced in the stomach after ingestion of the sample of a tested food.
Therefore,the mass of glucose contained in the portion of the tested food may be calculated using the relation:
mpG = (mG/AG)* ApG (13)
The percentage content of glucose in a tested food may be calculated by one of the following relations:
PG = 100*(mG/AG)*(ApG /mp ) (14)
PG = 100*(mG/AG)/ (mp/ApG) (15)
PG is the percentage of glucose that is formed after ingestion of a tested food.
mp js the mass of a tested food.
In the last expression only ratios of mass over A (m/A) are used. The area of GRF is a linear function of the mass ofglucose(11, 12), provided that the maximum of GRF does not exceed the renal threshold. When the concentration of blood glucose is higher than the renal threshold then thekidneys begin to participate in removing glucose from the blood. In such case an nonlinear model should be applied instead the linear one. To avoid those complications the masses of the reference glucose and of the tested food should be small enough so that the respective GRF to be smaller than the renal threshold.
The percentage contents of glucose in meals composed of a few raw foods may be determined in the same way as for any food product (14, 15). However, they may be also calculated using previously obtained data for the ingredients used to prepare those meals:
PmG = (m1 * PG1 + … mi * PGi … + mN * PGN ) / (m1 + … mi … + mN ) (16)
PG\mG is the percentage contents of glucose in an ingested meal calculated with (16),
PG1 , PGi ,PGN are the percentage contents of glucose in ingredients 1, i and N, respectively,
m1 , mi ,and mN are the masses of ingredients 1, i and N, retrospectively.
The sample sizes of foods that are ingested by volunteers, in order to determine their glycemic indexes have been calculated according to the formula (2) and presented in Table 1. The sizes of the test samples of different food products are not the same, they depend on the total carbohydrate content in a food product and they vary considerably.
In order to determine the glycemic indexes of fruits or vegetables which contain small quantities of carbohydrates (approximately 5 to 10%) healthy volunteers should consume these products in so large quantities such as 500 grams, or even 1,000 g. These amounts are many times greater than those normally consumed.
Table 1. The masses of food products mp* that ought to be consumed in order to determine their GI depending on the contents of carbohydrates PC.
The errors in determination of GI are relatively great, for example: 101.0 ± 30.78 ; 70.3 ± 37.98 (SD) , and 54.0 ± 6.1 (SEM) . This is due to the fact that GI and GL are biased by errors in determination of the areas of respective GRS and by errors in determination of the total contents of carbohydrates in foods (9).
Determination of glucose in digested foods is based on relations (11) and (12), which do not impose any restrictions on the masses of ingested glucose and of the tested food (2). However, in order to achieve the highest accuracy, the masses of ingested glucose and of the tested food should be so chosen that the respective GRF to be of similar sizes and they to not exceed the renal threshold. Those requirements can be fulfilled both by healthy subjects and by type 2 diabetics. Diabetics may, therefore, determine the contents of glucose in their foods and meals using only a glucometer and a kitchen scale.
The area of GRF is the main but not the only parameter that can provide information on the performance of the regulation system of insulin, but also about the efficiency of the stomach. The GRF of raw carrots is distinctly different from DRF of cooked carrot. Raw carrot – even in the form of grated – is much less digestible than cooked carrot . GRF of food products which contain 50 grams of carbohydrates are very similar [3, 4]. By contrast, GRF which are observed after ingestion smaller quantity of glucose may show the very interesting anomalies 
The ratio of the mass of reference glucose to the area of GRF mG/AG is the calibration factor. in relations (14, 15). However, the values of those ratios are specific for each individual and therefore they may be also used for diagnostic purposes. The highest values of those ratios ought to be observed for healthy individuals and the smallest for type 2 diabetics with advanced diabetes.
Determination of the contents of the active glucose in food products can be carried out by various methods, using the equation (7), the equation (10) and the equation (14) or equation (15).
These methods differ from each other not only in their performance, but also in their accuracy.
It would be useful if the accuracy of those methods were compared in different laboratories using the same selected foods such as raw and cooked carrot, table sugar, rice and other foods.
Acknowledgment: I would like to thank my children and especially my son for their help.
Funding: The research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
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