"Because of advances in nutritional biochemistry, many physiologists (along with individuals seeking leaner physiques) have learned that various types of carbohydrates affect the body differently."

Understanding the Glycemic Index and Glycemic Load:

What Are They? How Are They Related? And How Can They Help You Build a Leaner, Healthier Body?

By Bill Campbell, Ph.D., Exercise and Performance Nutrition Laboratory, University of South Florida

Introduction

In terms of weight loss and physique enhancement, the scientific community focused on counting calories for many years. It then focused on fat, and the low-fat movement was born. For the past several years, however, the focus has moved on to carbohydrate ingestion/restriction. Because of advances in nutritional biochemistry, many physiologists (along with individuals seeking leaner physiques) have learned that various types of carbohydrates affect the body differently.

Amazingly, some types of carbohydrates are preferentially converted to fat, raise blood glucose levels to stratospheric levels, and are linked to many health problems (diabetes, obesity, cancer, etc.)^1-4. Other types of carbohydrates are not converted to fat easily and are not considered to be a deterrent to good health.

To understand the differences between the various types of carbohydrates, it's best to possess a working knowledge of the glycemic index, the glycemic load, and how they are related.

What is the glycemic index?

The glycemic index was developed by Dr. David Jenkins in 1981 and was primarily used as a tool for diabetics looking to control their blood glucose (blood sugar) levels. Today, many other non-diabetic individuals are also using this index as a way to choose foods to eat for health, weight loss, and performance.

"...carbohydrates that are low on the glycemic index (~55 and below) are more slowly absorbed and subsequently cause a relatively small increase in blood sugar and insulin."

Quite simply, the glycemic index is a numerical ranking of carbohydrate-containing foods based on their potential to raise blood sugar levels. Carbohydrates that are high on the glycemic index (>70) are quickly digested and absorbed. These carbohydrates tend to cause a rapid rise in blood glucose and, in most cases, a quick rise in insulin.

Conversely, carbohydrates that are low on the glycemic index (~55 and below) are more slowly absorbed and subsequently cause a relatively small increase in blood sugar and insulin. Hence, the glycemic index allows an individual to indirectly estimate both blood glucose and insulin levels. This is not only important for diabetics but, it may also be good for anyone looking to help control their weight or determine what type of carbohydrates to consume around exercise workouts for improved performance.

Which Foods Have a High Glycemic Index?

Generally speaking, foods that rank high on the glycemic index include products made from finely ground flours like bread and baked goods; processed breakfast cereals; snack foods like chips and pretzels; baked, mashed, and French fried potatoes; and short-grain (sticky) rice⁵. Foods that rank lower on the glycemic index include most vegetables and fruits; sweet potatoes; legumes; minimally processed whole grains such as thick-cut oatmeal, oat bran, long-grain brown rice, barley, and bulgur wheat; pasta; and dairy products⁵. The following table lists some common foods and their glycemic index.

Table 1. Common foods and their glycemic index scores.

High Glycemic Index (>70)	Moderate Glycemic Index (70-56)	Low Glycemic Index (<55)
Boiled Potato - 101	Croissant - 67	Wheat Bread - 53
Baked Potato - 85	Brown Rice - 66	Potato Chips - 51
Pretzels - 83	Whole Meal Bread - 65	Peas - 51
Corn Flakes - 80	Oreo Cookies - 64	White Pasta - 50
Gatorade - 78	Raisins - 64	Apple Juice - 40
Shredded Wheat - 75	Ice Cream - 61	Oranges - 40
Cheerios - 74	Raisin Bran - 61	Skim Milk - 32
Bagel - 72	Sucrose - 59	Whole Milk - 27
Watermelon - 72	Coca-Cola - 58	Fructose - 20
White Rice - 72	Fruit Cocktail - 55	Peanuts - 13

"Foods that rank lower on the glycemic index include most vegetables and fruits..."

How Do Nutrition Research Scientists Determine the Glycemic Index of a Food?

Researchers measure out a portion of food that contains 50 grams of carbohydrate. For instance, 4 1/2 slices of bread, 1 1/4 cups of rice, 1 1/2 pounds of carrots, and 3 medium apples each contains about 50 grams of available carbohydrate⁵. A food is fed to a group of test subjects and their blood sugar responses are measured⁵. The test subjects' blood sugar response to the food is then compared with their response to eating 50 grams (about three tablespoons) of pure glucose⁵.

To illustrate this point, let's look at oatmeal. Oatmeal on average is approximately 49 on the glycemic index. This means that when plain oatmeal that contains 50 grams of carbohydrate is eaten, it will produce an increase in blood sugar approximately 49% of that obtained when the same amount (i.e., 50 grams) of straight glucose is consumed.

There are, however, some shortcomings with the glycemic index. So whenever you consider using the glycemic index as a guide, the glycemic load should also be considered. Let me explain…

Glycemic Index vs. Glycemic Load

The glycemic load uses the glycemic index as well as the actual amount of carbohydrate (i.e., the serving size) to determine the overall effect of a carbohydrate-containing food has on blood sugar and subsequent insulin values.

As mentioned earlier, the glycemic index compares different food sources that contain carbohydrates of the same quantity (i.e., 50 grams of glucose is compared to 50 grams of carbohydrate in oatmeal). However, this is not always practical or realistic because many foods are not consumed in 50-gram (1.76 ounces) portions.

Barley also has a low glycemic index.

So the glycemic load is calculated by multiplying the amount of carbohydrate in a given serving of food by the glycemic index of that same food and then dividing that number by 100.

Let's us look at a real-life example. A boiled potato has a glycemic index of ~101. A Mars® candy bar has a glycemic index of ~65. Just looking at the glycemic index, you might be surprised that the candy bar appears to be the "better" choice between those two foods.

However, the average serving size of a baked potato is about 150 grams (5.3 oz), which contains 17 grams of carbohydrate. Conversely, a Mars candy bar serving size is only 60 grams (2.1 oz) but contains 40 grams of carbohydrate.

Which one of these two food items has the greatest glycemic load and hence the greater effect on blood glucose and insulin? You guessed it, the Mars® candy bar! The boiled potato has a glycemic load of 17, while the Mars bar is 26. Thus, even though the potato has a higher glycemic index, the Mars® candy bar has more effect on blood glucose than the potato even though the size of the Mars® candy bar is less than half that of the potato.

Dr. Jeukendrup, a respected sports nutrition researcher, reports that foods with a glycemic load of > 20 are high, 11-19 are medium, and < 10 are low⁶. The following table lists some common foods with their corresponding glycemic index and glycemic loads⁵.

Table 2. Comparison of glycemic index and glycemic load for common foods.

Food	Glycemic Index	Carbohydrates (g)	Glycemic Load
1 medium carrot	71	8	6
1 cup watermelon	72	11	8
1 cup pasta	41	39	16
1 cup brown rice	55	44	24
12-oz soda	68	37	25

Both the glycemic index, and perhaps more importantly, the glycemic load can help you determine how any carbohydrate food can help you maintain weight and/or boost performance.

Conclusion

While both the glycemic index and the glycemic load provide information relative to the impact that carbohydrates have on the blood sugar and subsequent insulin response, the glycemic load is a much more practical scale for reasons mentioned above.

For more scores on individual foods, the complete list of the glycemic index and glycemic load for 750 foods can be found in the article "International tables of glycemic index and glycemic load values: 2002," by Kaye Foster-Powell and colleagues (see website below in reference list)⁷.

There's one last important caveat, however. It is also important to realize that both glycemic index and glycemic load only refer to the food when it's eaten alone. When you add some fat or protein to a meal containing carbohydrates, the total impact of either score goes down. So it's wise to take glycemic load into account, but don't be a slave to it. It is just one of the many factors to consider when planning an effective diet.

References

1. Augustin LS, Dal Maso L, La Vecchia C, et al. Dietary glycemic index and glycemic load, and breast cancer risk: a case-control study. Annals of Oncology. 2001 Nov;12(11):1533-8.
   
   
2. Franceschi S, Dal Maso L, Augustin L, et al. Dietary glycemic load and colorectal cancer risk. Annals of Oncology. 2001 Feb;12(2):173-8.
   
   
3. Barkoukis H, Marchetti CM, Nolan B, et al. A high glycemic meal suppresses the postprandial leptin response in normal healthy adults. Annals of Nutrition & Metabolism. 2007;51(6):512-8.
   
   
4. Radulian G, Rusu E, Dragomir A, Posea M. Metabolic effects of low glycaemic index diets. Nutrition Journal. 2009 Jan 29;8:5.
   
   
5. Woodruff, S. "Glycemic Index". http://www.tshc.fsu.edu/he/nutrition/nutrition_ specialneeds/glycemic_index.htm. Accessed 7-17-09.
   
   
6. Juekendrup A and Gleeson M. Sports Nutrition: An Introduction to energy Production and Performance. Human Kinetics. 2004.
   
   
7. Foster-Powell K, Holt S, and Brand-Miller J. "International tables of glycemic index and glycemic load values: 2002". http://www.ajcn.org/cgi/content/full/76/1/5. Accessed 7-17-09.

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