Saturday, February 09, 2008

It's All About the Sugars, Baby

Glycemic Index

The Glycemic Index (or GI) of a food is defined as the area under a two-hour blood glucose response curve. In other words, the GI of a food is a measure of how much glucose (sugar) is dumped into our blood stream over a two hour period. But why do we care about blood glucose? Because of the hormone insulin. Insulin is secreted in response to high blood glucose levels. If there is more glucose in our blood than we can use as fuel, insulin scrubs the glucose out of the body by storing it as fat. A side-effect of this mechanism is then blood sugar levels get low, the body is signaled to increase hunger and get more glucose because we are obiously low on energy, thus creating a vicious cycle of eating, storing fat and crashing.

Unfortunately, even though it sounds good in theory to look at blood glucose of a food, how often do we make a meal out of only kidney beans? Most people eat meals with multiple ingredients, each one of which will affect the blood glucose curve. For example, fats and protiens have little effect on blood glucose or insulin and when eaten with a high GI food, will slow down the absorption of the sugar and decrease the GI.

Foods are broken in high, medium and low GI values thus:

  • High - 70 or greater
  • Med - 55 - 70
  • Low - 55 or less.
An excellent resource for Glycemic Index is the Home of the Glycemic Index managed by the University of Sydney.

Glycemic Load

The Glycemic Index is based off of a 50 gram portion of food and the height of the blood glucose curve. It stands to reason, then, that a 25 gram portion of the same food would only produce a curve half of the height. Therefore portion size tends to mitigate GI also. Glycemic Load is a calculation used to take this fact into account.

The calculation goes like this:

The quantity (in grams) of a food's carbohydrate content, multiplied by its GI, and divided by 100.

For example, a 100g slice of watermelon has a GI of 72 but only 5g of carbohydrates. This gives us
(5g carbs * 72 GI)/100 = 3.6 GL

In comparison, a banana has a GI of 52 (avg) and carbohydrate count of 20g. This gives us (20g * 52 GI)/100 = 10.4 GL and white rice with a GI of 64 and 24g carbs/serving has a Glycemic Load of (64 * 24g)/100 = 15.4 GL.

Watermelon is a high GI food, banana is low GI and rice is medium, and yet as you can see, the Glycemic Load of each food is not predicted solely by Glycemic Index.


So insulin looks like the bad guy in all of this. It causes fat storage. It causes energy crashes. Insulin resistance (Metabolic Syndrome) has been linked to all kinds of health problems, including Type II Diabetes. Why then would we want insulin? I'll tell you:

For up to two hours after exercise, the body is very receptive to insulin's effects of delivering glucose to muscles. As a matter of fact, muscles are two to three times more receptive than at other times. This is the mechanism behind all of those fancy "recovery" drinks that are on the market now. The drinks are really just fancy forms of sugar water pushed into the muscles by insulin. The body is just as well served by chocolate milk, Smarties, or glucose tablets as long as they are consumed quickly post-exertion.

Studies also show that a bit of protein helps the body store glycogen as well. Most articles say the ratio should be 4 parts carbohydrate to 1 part protein and as little fat as possible (since fat delays absorption of the sugars) and the sugars themselves should be as high Glycemic Index as possible.

This means probably the best post-exercise snack one could have is 6 packages of Smarties (150g glucose) and 2 eggs (13g protein). I think I'll stick to the chocolate milk :D.

1 comment:

BlueEyedBikinBabe said...

Impressive. Thank you for sharing.