Glycaemic Index of Bread, UK

Objectives: 

1.    Practise a method to measure Glycaemic Index of foods.
2.    Practise the GI calculation of food
3.    Compare the GI of different foods 

Definition:

Glycaemic Index of Foods:  The glycaemic index (GI) is a classification of carbohydrate foods based on their acute blood glucose responses. The GI is defined as the incremental area under the blood glucose response curve (iAUC) after consumption of a 50 g available-carbohydrate portion of a food expressed as a percentage of that after 50 g oral glucose.

Incremental area under the blood glucose response curve (iAUC): Mathematical Principles and Formulas 
The IAUC (Figure 1) was determined using calculus (integration, as the sum of all 24 trapezoid areas) according to the formula: IAUC = ΣSi i = 1,…,
Si=1/2 ×[(Gi−G0)+(Gi-1−G0)]וΔt,
where Gi is glucose concentration at a particular time, G0 is starting glucose concentration. For Gi≤G0, Si = 0. 

Calculation of the incremental area under the curve. IAUC is calculated as the sum of areas of 24 individual trapezoids. G0, glucose concentration before meal intake; Gi, glucose concentration at a particular time; Δt, time interval between estimations (in CGMS, always 5 minutes); Si, area of the respective trapezoid.
https://pmc.ncbi.nlm.nih.gov/articles/PMC2769714/

Methods

Food: 80 g of white bread or 80 g Bread enriched with Dietary fibre for each participant
Materials
•    Gloves
•    Handheld glucose monitor
•    Blood glucose test strip (DO NOT open the blood glucose test strip until you are ready to use it)
•    Alcohol swabs
•    Sterile lancets
•    Plasters

Carefully read the instructions below before starting

Instruction 

1.    8 hours fasting time (no food, but allow to drink the water)
2.    Wash your hands using warm soapy water and dry them completely
3.    Wear gloves 
4.    Remove the test strip from its packet
5.    Insert the test strip into the machine. Push the test strip in until it stops

Baseline blood sugar testing 

6.    Obtain a blood drop, hold your arm down BEFORE pricking you finger to help blood flow. 
7.    Wipe the end of the finger being used with an alcohol wipe
8.    Allow this to dry before pricking the end of finger (it is best to do this slightly off centre)
9.    Wipe away the first blood drop with gauze (have a think about why this is important)
10.  Gently squeeze the finger to form a new blood drop
11.  Touch the blood drop to the end of the test strip
12.  Continue to touch the blood drop to the end of the test strip until the sensor begins the test
13.  Recorder: Note the reading on the glucometer. This is T0.
14.  Remove the test strip and place this, the gauze and the wipe in the biohazard bins. Place the used lancet in the sharps bin. 
15.  Cover the pricked finger immediately with gauze and apply pressure to avoid any blood spills. 
16.  Consume food (80 g of bread) with 250 ml of water within 10 min. 
17.  Timekeeper: Note the time
18.  After you have consumed this be sure to wash your hands thoroughly. This is important to avoid contamination of your blood sample from food substances on your skin
19.  Repeat steps 6 - 15 at 20 min, 40 min, 60 min, 90 min and 120 min as shown on the recording sheet. 
20.  Record your results and the group average in the table in your handbook.