Glitches in the Glycemic Index
GI Diets Show Promise but Need More Research
-- By Becky Hand, Licensed & Registered Dietitian
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Imagine a categorizing system in which numbers are assigned to foods, allowing you to choose the foods that curb appetite, help shed excess pounds, lower your risk for diabetes, and improve heart health. These in fact are the claims of popular diets that use the Glycemic Index—GI diet, for short.
The Glycemic Index ranks carbohydrate-containing foods (on a scale from 0 to 100) based on their effects on blood sugar levels in the body. Eating highly processed foods, such as bread made from refined white flour, raises blood sugar higher and faster than does eating whole foods, such as whole-wheat bread or an apple. Foods—like white bread—that cause the most rapid rise in blood sugar are given a higher number, while whole-wheat breads and apples have lower ratings. A rating of 55 or below is considered low, and 70 or above is considered high.
Additional information and values for the GI diet can be found at: www.GlycemicIndex.com, and www.Mendosa.com. The Glycemic Indexes of a few foods are listed here:
|
Food Item
|
GI
|
|
Peanuts
|
14
|
|
Grapefruit
|
25
|
|
Pizza
|
30
|
|
Oranges
|
48
|
|
Potato Chips
|
54
|
|
Snickers Bar
|
55
|
|
White Rice
|
64
|
|
White Bread
|
70
|
|
Popcorn
|
72
|
|
Baked Potato
|
85
|
The Premise
Proponents of the GI diet believe that the lower the GI number of a carbohydrate food, the better. High GI foods are digested and metabolized more quickly, causing a rapid rise in blood glucose levels. This creates a dramatic spike in levels of the hormone insulin, which works to remove sugar from the blood. These responses can lead to an overproduction of insulin, contributing to weight gain. Therefore, carbohydrate foods with low Glycemic Indexes cause less insulin secretion and slow the clearing of glucose from the blood stream—resulting in greater satiety, and fewer calories consumed throughout the day.
The Spark Response
Using the Glycemic Index for meal planning is a very complicated process. Here are some of the limitations:
- Only about 5% foods in the national food database have been tested.
- There is usually a wide variation in the GI measurement. A potato can be as low as 56 or as high as 100. In fact, a food’s GI score can change based on the food’s ripeness level.
- A food’s GI score can also change based on preparation techniques. Grinding and cooking can elevate the GI score of some foods, because they become quicker and easier to digest.
- GI testing is done on individual foods, but we consume most foods in combinations. Fiber, protein, and fat will usually reduce the Glycemic Index of a meal.
- The rate at which different people digest carbohydrates varies. And each person’s glycemic response may vary throughout the day.
- When certain high glycemic foods are eliminated from the diet, so are vital vitamins, minerals, fiber, and phytochemicals. Watermelon has a GI of 72 but it is high in potassium, vitamin A, and lycopene, for example.
- Relying on the Glycemic Index can still lead to overeating and weight gain. Peanuts look like the perfect choice with a GI of 14, but with about 400 calories in ½ cup, they won’t help shed pounds when eaten in excess.
The Glycemic Index is a marvelous tool for ranking carbohydrates. However, it is currently only in its infancy regarding health benefits. More research is necessary to make it a truly valid, reliable, and applicable teaching tool. The simple facts still remain:
- 20% of Americans’ calories come from high carbohydrate foods, such as cakes, cookies, pies, pastries, ice cream, sugar, candy, soda pop, and chips.
- Fresh fruits and vegetables, and whole grain products (whole-wheat breads and pastas, brown rice, and wheat germ) are nutritionally superior to highly processed, refined products.
- Simply limiting the total number of carbohydrates you consume at a meal can more easily control your blood sugar levels.
- You probably don’t need a complicated rating system to confuse you about which carbohydrates to include in your diet.
