The glycemic index brings us to a new paradigm in food. Instead of deciding on what foods to eat based on calories or fat content, the road to success in weight control lies in evaluating food according to their glycemic properties.
Glyco is a Greek word for sweet or sugar, thus "glycemic" is a word derivation that describes numerically the effect that any given food has on our blood sugar levels.
So what we have is a number scale that rates the glycemic effect of a food from 0 to 100.
Low glycemic foods fall into the bottom range from 0 to 54, medium is 55 to 70, and high is over 70.
The higher the index number, the greater is the rise in blood sugar from that particular food.
A fast rise in blood sugar will produce an insulin spike from the pancreas to deal with the sudden influx of blood sugar.
As we will see, the end result is obesity, a worn out pancreas and diabetes.
Take the white baked potato, please! It is one of the highest foods on the glycemic chart, having an index of 93 or higher. A sweet potato or yam, on the other hand, has index numbers of 54 and 51 respectively.
They're all potatoes, so why the difference?
In a word, fiber. Fiber is hard, and often impossible, to digest. The significance is that it takes longer to digest, if at all, and the longer a food takes to digest, the longer it takes to convert to blood sugar.
This minimizes the insulin reaction, maximizes conversion of food to energy over time, and minimizes the amount that gets stored as fat.
The measurement standard of all glycemic index numbers is Glucose and with a glycemic index of 100, it would sit at the very top of the chart.
Well, maybe so; maybe not, and this is the main criticism of the glycemic index. The index only considers the resulting glucose in the blood chemistry from eating a particular food or beverage. It doesn't take other sugars into account, such as fructose, that may be in the food and also cause a blood sugar spike.
There are other criticisms such as quantity of food. A low glycemic food can produce a high glycemic response if the portions consumed are too large.
For example, a slice of 100% whole grain bread is low glycemic but if we eat four slices at a sitting, the glycemic load becomes excessive and we get the blood sugar spike and insulin response. Portion control is important and the index alone does not take the glycemic load into account (see below).
One last criticism worthy of mention is that the condition of the food can change its index rating.
By "condition" we mean the ripeness of a fruit or vegetable, how long it has been stored, how it was cooked and even its variety. Some foods can exhibit a range of glycemic responses among their varieties, potatoes are a good example.
Any cooking of vegetables that breaks down its fiber will raise the glycemic response. Raw carrots are low but cooked carrots are moderate.
Now we know what the glycemic rating of a particular food is and the glycemic load (GL) takes it a step further. The glycemic load brings "portion size" into the equation.
It takes the carbohydrate content in a particular food portion
based on its GI then looks at the amount of that food consumed and gives it a ranking.
The idea of the glycemic load is that a high glycemic index food eaten in small quantities would give the same effect as a larger quantity of a low GI food on blood sugar.
The theory goes something like this: white mashed potatoes are very high on the glycemic index. Thus eating two big scoops of mashed potatoes, say 100 grams, would result in a very high glucose (blood sugar) curve in the blood; while eating 50g would give the same shaped curve but half the height.
Photo: Various Potato Dishes, Pass me the Insulin Spike, Please.
Since the height of the blood sugar curve is the most important parameter, multiplying the amount of carbohydrates in a food serving by the glycemic index gives an idea of how much effect an actual portion of food has on blood sugar level and thus the severity of the insulin response that follows.
One study, reported in the American Journal of Clinical Nutrition, Vol. 85, No.4, 2007, of weight loss comparing low GL to high GL diets has found no significant differences between the two.
The conclusion drawn was that excessive attention to the glycemic load within weightloss programs of little value and that a range of foods with widely varying GL values can be part of a healthy diet.
The conclusion is faulty in that one of the key measurement criteria was the resting Metabolic rate which determines how many calories a person needs to sustain life; ie, organ function. The abstract of the study did not state whether or not a person’s genetic propensity to burn calories or store them as fat was taken into account.
The glycemic load is calculated for a serving of food by taking the quantity in grams of its carbohydrate content and multiplying it by its GI number then dividing by 100. The grams of carbohydrate can be found on the label of packaged foods. The glycemic index number is found by referring to GI tables, the rest is math.
For example, one slice of the whole grain bread I eat has 17 grams of carbs. Its glycemic index is 50 so the glycemic load is (17 x 50)/100 = 8.5. The GL of my hamburger bun is (36 x 61)/100 = 22.
When it comes to how we metabolize food, it's definitely "different strokes for different folks". With respect to food, metabolism is just a word that refers to how our bodies convert food intake to energy, OR NOT.
The "or not" is thrown in because not all of us metabolize food the same. Some of us burn calories faster and release lots of energy. Others of us have bodies that choose to store those calories as fat instead of burning them.
This divergence of pathways to either burning calories or storing fat is controlled by something called the Glucagon Mechanism. Glucagon is a hormone produced by the pancreas and this hormone decides what gets stored as fat or burned for energy.
An insulin spike caused by a rapid rise in blood sugar (hyperinsulin) causes the glucagon mechanism to store fat instead of burn it. A hyperinsulin response has been shown to be directly linked to obesity and this is where a knowledge of the glycemic index becomes critical.
Photos: above right - Glucagon hormone depiction;<br>above - Glucagon image stain
The following is a rough guide of what food classes fall into which index range.
The low GI range of 55 or less contains:
And the highest of the high with a glycemic index of 100 is our standard, straight glucose.
There is an excellent website for further and much more detailed information on the glycemic index and glycemic load.
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