Understanding the Glycemic Index

UNDERSTANDING THE GLYCEMIC INDEX & GLYCEMIC LOAD.

Introduction.

In relation to physique enhancement & weight loss, the scientific community has focused on counting calories for many years. Then, it focused on fat, & the “low-fat diet” movement was born. For the past few years, however, the focus has moved onto carbohydrate ingestion/restriction. Because of advances in nutritional biochemistry, many physiologists (as well as people wanting leaner physiques) have learned that various types of carbohydrates affect the body differently.

Interestingly, some types of carbohydrates are preferentially converted to fat, raise blood glucose levels into the danger zone, & are linked to many health problems like diabetes, cancer, obesity etc. Other types of carbohydrates are not converted to fat easily & are not considered harmful to good health.

To understand the differences between the various types of carbohydrates, it’s good to have a knowledge of the “glycemic index” & the “glycemic load”, & how they are related.

THE GLYCEMIC INDEX.

The glycemic index was developed by Dr. David Jenkins in 1981 & 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 & performance.

On the index, carbohydrates that are listed below 55 are more slowly absorbed & subsequently cause a small increase in blood sugar & insulin. Quite simply, the glycemic index is a numeric ranking of carbohydrate-containing foods based on their potential to raise blood sugar levels. Carbohydrates that are high on the index (above 70), are quickly digested & absorbed. These carbohydrates tend to cause a rapid rise in blood glucose &, in most cases, a quick rise in insulin.

On the other side, carbohydrates that are low on the glycemic index (55 & below) are more slowly absorbed & therefore cause a relatively small increase in blood sugar & insulin. Hence, the GI index allows an individual to indirectly estimate both blood glucose & insulin levels. This is important for diabetics & anyone looking to help control their weight. It’s also good to determine what types of carbohydrates to eat around exercise workouts for improved performance.

HIGH GI FOODS.

Generally speaking, foods that rank high on the glycemic index include products made from finely ground flours like bread & baked goods, processed breakfast cereals, baked, mashed & French fried potatoes, snack foods like chips & pretzels, & sticky rice. Foods that rank lower on the glycemic index include most fruit & vegetables, sweet potatoes, minimally processed foods like oatmeal, oat bran, barley, bulgur wheat, long-grain brown rice, pasta & dairy products. What follows is a list of some common carbohydrate foods & their glycemic index:

HIGH GI (70+) :

Boiled potato – 101

Baked potato -85

Pretzels – 83

Corn flakes – 80

Shredded wheat – 75

Cheerios – 74

Bagels – 72

Watermelon – 72

White rice – 72

MODERATE GI (70-56):

Croissant - 67

Brown rice – 66

Wholemeal bread -65

Raisins – 64

Ice-cream – 61

Bran flakes – 61

Sucrose – 59

Coke – 58

Fruit cocktail -55

LOW GI (55-):

Wheat bread – 53

Potato chips – 51

Peas – 51

White pasta -50

Apple Juice – 40

Oranges – 40

Skimmed milk – 32

Whole milk – 27

Fructose – 20

Peanuts – 13

HOW DO NUTRITION RESEARCH SCIENTISTS WORK OUT THE GI OF A FOOD?

Researchers measure out a portion of food that contains 50 grams of carbohydrate. For example, 4 ½ slices of bread, 1 ¼ cups of rice, 1 ½ pounds of carrots, & 3 medium apples contain about 50 grams of available carbohydrate. A food is fed to a group of test subjects & their blood sugar responses are measured. – The test subjects’ blood sugar response to the food is then compared to their response to eating 50 grams (about 3 tablespoons of glucose) of pure glucose.

To illustrate this point, I’ll look at oatmeal. Oatmeal on average, is approximately 49 on the GI 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 (eg 50 grams) of pure glucose is consumed.

There are, however, some flaws with the glycemic index. So whenever you consider using the glycemic index as a guide, the glycemic load should also be considered:

GLYCEMIC INDEX Vs GLYCEMIC LOAD.

The glycemic load uses the glycemic index as well as the actual amount of carbohydrate (eg the serving size) to determine the overall effect of a carbohydrate-containing food in relation to blood sugar & insulin levels.

As mentioned previously, the glycemic index compares different food sources that contain carbohydrates of the same quantity (eg 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 portions.

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

How about a ‘real-life’ example. – A boiled potato has a glycemic index of around 101. A Mars chocolate bar has a glycemic index of around 65. Just looking at the glycemic index, you might assume that the Mars bar is the ‘better’ choice of the two options. However, the average serving of a baked potato is about 150 grams, which contains 17 grams of carbohydrate. – A mars bar serving size is only 60 grams but contains 40 grams of carbohydrate. – Therefore, the Mars Bar has the greatest glycemic load & has a larger effect on blood glucose & insulin. The boiled potato has a glycemic load of 17, while the mars bar is 26. So even though the potato has a higher glycemic index, the mars bar has more effect on blood glucose despite being half the size!

So, in conclusion, both the glycemic index & the glycemic load provide information relative to the impact that carbohydrate has on the blood sugar & insulin response. However, the glycemic load is a much more practical scale. It’s also important to remember that the glycemic index & glycemic load only refer to the food when it is 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’s just one of the many factors to consider when planning an effective diet.