Prof Jennie Brand-Miller answers your questions.
I don’t understand how you can bake sweet foods like cakes or desserts that don’t have sugar in them (I'm not talking about artificial sweeteners here). What makes them sweet? Can you explain?
I can see why it is a confused and confusing area. We have to go back to carbohydrate 101 for this. Sugar is a carbohydrate. So is starch. They are nature’s reserves created by energy from the sun, carbon dioxide and water. The simplest form of carbohydrate is a single-sugar molecule called a monosaccharide (mono meaning one, saccharide meaning sweet).
- Glucose is a monosaccharide that occurs in food as glucose itself and also as the building block of starch. Fructose and galactose are also monosaccharides.
- Sucrose, or table sugar (refined sucrose from sugar cane), is a disaccharide. Every molecule of sucrose yields one molecule of fructose and one molecule of glucose. Thus 10 grams of sucrose (or 2 teaspoons) yields 5 grams of fructose and 5 grams of glucose. Lactose (glucose + galactose), the sugar in milk, and maltose (glucose + glucose) are also disaccharides.
What about GI? Table sugar which as I have said is refined sucrose has a GI of between 60 and 65. Remember, sucrose is a disaccharide (double sugar) composed of one glucose molecule coupled to one fructose molecule. So, when we consume sucrose, only half of what we’ve eaten is actually glucose; the other half is fructose. While the blood glucose response to glucose is high (GI 100), it is very modest to fructose (GI 19), because fructose is absorbed and taken directly to the liver where it is immediately used as the source of energy. This explains why the blood glucose response to 50 grams of sucrose is approximately half that of 50 grams of corn syrup or maltodextrins – where the molecules are all glucose.
GI testing by an accredited laboratory
Dr Alexandra Jenkins
Glycemic Index Laboratories
20 Victoria Street, Suite 300
Toronto, Ontario M5C 298 Canada
Phone +1 416 861 0506
Research Manager, Sydney University Glycemic Index Research Service (SUGiRS)
Human Nutrition Unit, School of Molecular and Microbial Biosciences
NSW 2006 Australia
Phone + 61 2 9351 6018
Fax: + 61 2 9351 6022