Sunday, July 5, 2009
Carbohydrates, or sugars, are made primarily of carbon, hydrogen and oxy- gen atoms that cyclize into a ring. Carbohydrates can be “simple” or “complex” depending on the number of rings you hook together and the way in which they hook together. Though the rings can be slightly di erent, their common theme is the ring struc- ture as their nal shape. Similar to amino acids and fats, when you link the simple units (the sug- ars) together you get carbohydrates with di erent properties. You can link glucose units together to get a glucose polymer. In fact, when the body stores units of glucose linked together in the liver and muscle, it is called “ glycogen,” a term with which most people are familiar.
You can also link di erent kinds of sugars to get di erent products. For in-
stance, if you combine glucose with fructose you get sucrose (table sugar).
If you combine glucose with galactose you get lactose (milk sugar), and so
Link a bunch of sugars together and you get polysaccharides. Combine
two sugars together like the previously mentioned lactose and you get a
disaccharide. Of course, by themselves they are called monosaccharides.
Are you starting to see a repeating theme here?
Link a simple unit together with other units and you get a product the body
can do all sorts of things with. Linking units together gives you a product
(fats, carbs, and proteins), and breaking down the products into units (ulti-
mately) gives you energy.
You will notice I have not mentioned the “essential carbohydrates” because
there is no such thing! Though the body runs best on an intake of some
carbs in the diet, the body can make its own carbohydrates from protein
and other non-carbohydrate substrates, as mentioned in the protein sec-
Digestion reverses the process: the body breaks down complex carbohy-
drates into simple carbohydrates and ultimately blood sugar (glucose)
which can then be used for many di erent functions, such as the produc-
tion of ATP (the body’s universal energy molecule). Depending on the car-
bohydrate and other factors, di erent carbohydrates will have di erent ef-
fects on blood sugar; in particular, how fast blood sugar rises and falls.
The ability of a carbohydrate food to raise blood sugar quickly or slowly is
called the glycemic index ( GI). The GI was developed to track how di erent
foods a ect blood sugar.
Interestingly, many carbohydrates that are considered“complex” have been
found to raise blood sugar rapidly while a few “simple” carbohydrates don’t
have a dramatic e ect on blood sugar. The GI rating of a food is based on
how much blood glucose rises after consuming a carbohydrate food over a
2 hour period. This is compared to a reference, glucose, a simple sugar.
Some GI scales now use white bread as the reference, but we will use the
glucose scale in this chapter. For instance, if you consume 50 grams of
glucose (yuk), you will get dramatic elevation in blood sugar. If you eat, say
50 grams of carbs found in the form of oranges, your blood glucose would
probably rise approximately 44 percent when compared to glucose. So,
the GI rating for oranges would be 44 on the glucose scale. Using white
bread as the reference carbohydrate, it would be a di erent number. Capi-