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Glycemic What?
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When
it comes to low carb dieting, one of the most hotly debated subjects
has to do with, well, carbs. Simple carbs vs. complex carbs. High
glycemic carbs vs. low glycemic carbs. Glycemic index vs. glycemic
load. There’s been a lot of talk about the glycemic index or GI. A lot
of my friends are eating foods based on the GI. They’re hung up on it.
Like dieters who get fixated on scale weight, they think all the
answers they need are in numbers. They forget that the glycemic index
is just a tool, not a be all, end all. To decide what foods to eat and
what foods to avoid based solely on GI is a mistake.
In
the real world, what’s more important for individuals is something
called the “glycemic load”. According to recent research, the glycemic
load can be more important than the glycemic index of individual foods.
The glycemic index measures how fast carbs enter the blood after a
meal, how fast ingested carbs become sugar. Traditionally, experts
thought that the higher the GI, the larger the insulin spike. Using
this logic, we were told us to stick to low GI foods only. Recently
though, researchers have discovered that certain low GI foods can
actually raise insulin levels to a greater degree than high GI foods
(and vice versa). How can this be? The concept of “glycemic load” can
explain this.
The glycemic load gives a fuller picture of the impact of foods on
blood sugar and insulin levels. It was developed by scientists to
describe both the quality (glycemic index) as well as the quantity of a
carb in a meal. The glycemic index, after all, is a fixed number. It
measures how fast 50g of carbs or a food enter the blood. That’s it.
The glycemic load, on the other hand, is calculated by multiplying the
glycemic index by the amount of carb (in grams) and then dividing the
total by 100.
What the glycemic load takes into account is that different foods have
different carb levels. You can’t neatly categorize foods based on 50g,
as the glycemic index requires. This is why some low GI carbs can
actually raise insulin levels higher than high GI carbs. For example,
watermelon has a high GI score of 72. Yet watermelon has a low GL score
of 4. Look at pineapple. The GI score is 66, but the GL is only 6. The
main reason is that watermelon and pineapple aren’t necessarily high in
carbs. You’d have to eat a lot of watermelon and pineapple to get to
the 50g of carbs needed for its high GI score.
Here’s another example. Based on a glucose standard, jelly beans have a
GI score of 78. White bread is 73. Both are considered high GI.
However, if you ate 30g of jellybeans vs. 30g of white bread, the
glycemic load varies significantly. Jellybeans score 22 (a “high” GL
score), while white bread scores 10 (a “low” GL score). A large part if
this is due to the fact that jellybeans have 28g of carbs to only 14g
in white bread per each 30g. NOTE: For the glycemic index, 1-55 (Low);
56-69 (Medium); and 70+ (High). For the glycemic load, 1-10 (Low);
11-19 (Medium); and 20+ (High).
As Dr. Monro puts it, “The glycemic index (GI) is a
component-referenced index, defined as the effect on blood glucose of
glycemic carbohydrate in a food as a percentage of the effect of an
equal amount of glucose. GI is not suitable for dietary management of
postprandial glycemia because it refers to glycemic carbohydrate, not
to food, it is static, i.e., unresponsive to intake, and it is relative
in that it can be used appropriately only for equicarbohydrate
comparisons. Food values for dietary management, in contrast, must be
food-based, intake responsive and sensitive to variations in
composition typical of diets.”
Bottom line, people should stop focusing on a single meal or food, but
rather look at a set of meals over the course of a day or week. They
should also stop being fixated on GI, but instead, look at GL which
offers a much more practical way of judging what foods to eat and when.
GL offers a more useful way of controlling insulin response as a way to
maximize bodybuilding gains. It provides real world applications, not
just theoretical numbers. |
Selected Sources
Brand JC, et al. Physiological validation of the concept of glycemic laod in lean young adults. J Nutr 2003;133(9):2728-32.
Ebbeling CB, et al. A reduced glycemic load diet in the treatment of
adolescent obesity. Arch Pediatr Adolesc Med 2003;157(8):773-79.
Ludwig DS. Glycemic load comes of age. J Nutr 2003;133(9):2695-96.
Monro J. Redefining the glycemic index for dietary management of postprandial glycemia. J Nutr 2003 Dec;133(12):4256-8.
Salmeron J, et al. Dietary fiber, glycemic load, and risk of
non-insulin-dependent diabetes mellitus in women. JAMA 1997; 277:
472-77.
Scaglioni S, et al. Dietary glycemic load, overall glycemic index, and
serum insulin concentrations in healthy schoolchildren. Am J Clin Nutr
2004;79(2):339-40. |
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