Only a part of carbohydrates contained in our food is degradable to glucose. Fiber and other carbohydrates that are not degradable to glucose are excreted from the body. Thus, carbohydrates contained in food products may be divided into degradable and undegradable carbohydrates. Food products differ therefore not only in the total carbohydrate content, but also in the content of degradable carbohydrates. The latter is the only and most important glucose indicator of food quality for diabetics.
Glucose that appears in the stomach as a result of carbohydrate degradation, is next absorbed into the bloodstream. Its concentration in the blood may be determined with a glucometer.
The glucometer and the stomach may be, therefore, treated as components of the same measuring tool. The stomach converts the carbohydrates in ingested food to glucose, and the glucometer measures the glucose concentration in blood.
After intake of pure glucose that is used as a reference substance, it passes without any changes directly to the the bloodstream. Both the reference glucose and glucose produced from carbohydrates in the stomach, when in blood are subject to the same regulating action of insulin.
After meal the concentration of glucose in blood changes with time. These changes are revealed in a glucose response regardless of whether glucose was produced in the stomach by decomposition of carbohydrates, or whether it was consumed as a pure substance.
AG = kG*mG ……….. (1)
AG – the area of glucose response after glucose intake;
mG – the amount of glucose intake;
kG – the coefficient of proportionality.
ApG = kG*mpG ………. (2)
ApG – the area of the glucose response recorded after ingestion by the same person of a sample of the food product;
mpG – the amount of carbohydrates degradable into glucose contained in the sample of the food product
Glucose response of the tested sample and of the reference sample should be performed under the same conditions after overnight fasting on two adjacent days, in any order.
mpG = (mG/AG)* ApG ……….. (3)
(mpG*100)/mp = 100*(mG/AG)* (ApG/mp) ………… (4)
PpG = (mpG*100)/p = 100*(mG/AG)* (ApG/mp) ………… (5)
mp – the amount of the sample of the tested food product in g;
PpG – the percentage of degradable carbohydrates contained in the sample of the food product.
The percentage of carbohydrates degradable into glucose PpG determines the glucose value of the food product for the diabetics. Therefore, references to such ambiguous terms as „low carbohydrate” or „high carbohydrate”, as well as to inaccurately determined glycemic indices and glycemic loads, can be discarded.
In the relationships (3) – (5) the ratio (mG/AG) is a calibration factor. The calibration factor is equal to the inverse of the area of the related glucose response of pure glucose (POWW).
As the absorption of glucose by the body cells increases, the glucose response AG decreases. Therefore, the greater is the calibration coefficient, the more efficient is absorption of glucose by the body cells. Glucose response area after ingestion of a certain amount of glucose by a healthy human is much smaller than that after ingestion of the same amount of glucose by a diabetic.
The percentage of the total carbohydrate content in tested foods , on which the system of glycemic indexes (GI) and glycemic loads (GL) is based, does not appear in the equations (1) – (5).
To some extent one may say, that the carbohydrate contents in food products are not known. Carbohydrate contents, that are printed on the packages of food products are in fact that what remains after deducting from 100 g sample the contents of proteins, fats, water and ash:
Carbohydrates g = 100 g – g ash – water g – g protein – fat g
Without such calculated contents of carbohydrates in food products neither glycemic indices (GI), nor glycemic loads (GL) can be determined.
According to the definition of glycemic index (GI), and the methodology imposed by it, the glycemic indices can be determined only by healthy people since after ingestion of 50 g of pure glucose by diabetics the glucose response significantly exceeds the renal threshold.
Equation (5) does not specify arbitrary neither the mass of reference sample (50 g of glucose), nor the weight of the tested food product. On the contrary, the masses of glucose reference samples should be adjusted to the contents of degradable carbohydrates in the tested foods. The maximum accuracy of measurement can only be achieved when the glucose reference response is equal to the glucose response of the sample of tested food. This means that the masses of the reference glucose should be adjusted to the weight of degradable carbohydrates in the tested sample and not vice versa.
Glucose responses of the tested food product and of the reference glucose should be as large as possible in order to minimize the errors associated with the determination of baseline and the area of glucose responses. However, they should not exceed the renal threshold.
Thus, it enables diabetics and diet managers to control effectively diabetes and weight loss programmes on the basis of reliable data concerning particular food products of their interest. They can also verify these data themselves.