1.2 Glycaemic Index & Glycaemic Load Flashcards
What is glyaemic index used for?
To tell us how much glucose a food contains, and how quickly the glucose is released
Low glycaemic index = slow release, feel fuller for longer
How do you find glycaemic index?
- Scientists feed 10 volunteers enough of one specific food to give 50g of carbohydrates (excl. dietary fibre)
- Take blood samples afterwards to see how much the food has raised the glucose levels in the blood
- Concentration measured several times over 2 hours
- Average value found, converted to the GI (a figure out of 100, 50g of glucose = 100, other foods compared to glucose)
Release of insulin causes…
Liver & muscle cells to store the glucose as glycogen
However, if the blood glucose level stays too high for too long, excess glucose is stored as fat
The release of insulting causes the blood glucose levels to fall - a lot of insulin released may cause blood glucose level to fall more sharply
Dip in glucose levels - making you feel hungry
A GI of 70 or over is…
High
A GI of 56-69 is…
Medium
A GI of 55 or less is…
Low
Factors that affect GI of foods are…
- starch molecules can be different in different plants - exact shape of starch molecule and the amount of branching it has can vary, will affect how quickly it is hydrolysed by enzymes and absorbed into the blood
- whether starch is combined with dietary fibre (slows down the absorption of sugars into the blood)
- presence of other components in food, e.g. Presence of fat affects carbohydrate digestion rate, adding vinegar to food (lowers pH) also slows down digestion & absorption of carbohydrates
What is glycaemic load?
A measure of the effect of a portion of food on blood glucose level
How is GL calculated?
Glycaemic load=
carbohydrate content of food X (GI of food)/100
A GL of 20 or more is…
High
A GL of 11-19 is…
Medium
A GL of 10 or less is…
Low
