What is the Glycemic Index?

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Introduction

For many years we have learned that carbohydrates fall into two major categories: simple (including sugar, honey and maple syrup) and complex (including grains, starchy vegetables and legumes). We have been encouraged to eat plenty of the complex and only moderate amounts of the simple carbohydrates. However, an increasing amount evidence indicates that distinguishing which carbohydrates are good for you is more complicated than this simple dichotomy suggests. What is important when differentiating between various types of carbohydrates is how rapidly a particular carbohydrate will turn into sugar and raise blood sugar (glucose) levels, the body’s source of energy for most activities.

The blood sugar (glucose) that is delivered to the cells throughout our bodies via our bloodstream is primarily derived from the carbohydrates in the foods that we eat. A food with a low glycemic index (GI) only raises blood sugar levels slightly, while a food with a high GI will cause blood sugar levels to spike. When we look at the GI figures associated with various carbohydrates, we find that some of the foods classified as complex carbohydrates in the old system, such as white potatoes, increase blood sugar levels faster than some of the simple carbohydrates, such as table sugar! Because of GI’s more accurate description of the functional effects in our bodies of the carbohydrates we eat, the GI has become an important and much more accurate tool for helping to select the right foods to stabilize our blood sugar levels while providing the energy our bodies’ need and promoting both short-term and long- term health.

What Is Glycemic Index?

The Glycemic Index (GI) is a numerical scale used to indicate how fast and how high a particular food raises blood glucose (blood sugar) levels. Glucose, the body’s source of energy for many activities, is delivered to cells throughout our bodies via our bloodstream, and is primarily derived from the carbohydrates in the foods we eat. A food with a low GI causes just a small rise in blood glucose, whereas a food with a high GI can cause blood glucose levels to spike.

An awareness of foods’ Glycemic Index can help you control your blood sugar levels, and by doing so, may help you prevent heart disease, improve cholesterol levels, prevent insulin resistance and type-2 diabetes, prevent certain cancers, and achieve or maintain a healthy weight. A substantial amount of research suggests a low GI diet provides these significant health benefits. So, it’s worth taking a look at the basic principles of a low GI way of eating.

High Carbohydrate Foods Can Raise Blood Glucose Levels

High carbohydrate foods, even wholesome foods that are high in carbohydrates such as satisfying whole grain breads, delicious fruits, certain starchy vegetables, and legumes, can affect blood glucose levels.

Carbohydrate-rich foods include:

  • Starches, which are found in foods such as
    • Grains (foods made from wheat, barley, rice, etc.)
    • Legumes, (split peas, lentils and dry beans such as pinto, kidney, black, etc.)
    • Starchy vegetables (potatoes, winter squash, yams)
  • Sugars, such as those naturally found in fruits and dairy products as well as sweeteners, and sugars added in processing.
  • Fiber—the indigestible portion of carbohydrates. However, even though fiber is considered a carbohydrate, since it is not digested, it does not raise blood glucose levels.

After we eat carbohydrate-rich foods, our digestive process breaks them down, eventually turning them into glucose, which enters the bloodstream. (Since most proteins and fats from food are not turned into glucose in this way; they have little effect on glucose levels.)

The presence of glucose in the bloodstream triggers the production of insulin, a hormone that helps glucose get into cells where it can be used for energy. Once our immediate energy needs have been met, any extra glucose still remaining in the bloodstream will first be stored in our muscles and liver for later use. If our muscle and liver stores of glucose are full, but we still have extra glucose floating around in our blood, then insulin helps the body store it as fat.

Too Much Insulin Can Cause Problems

Since insulin helps glucose get into cells where energy is made, insulin is vital to fueling the body, but too much insulin over long periods of time can cause problems. Research shows that prolonged exposure to elevated levels of insulin can cause:

  • high triglycerides
  • high “bad” LDL cholesterol
  • low “good” HDL cholesterol
  • high blood pressure
  • insulin resistance
  • increased appetite
  • obesity
  • risk of developing or exacerbating type-2 diabetes
When a person has most of these disease-promoting factors at the same time, this constellation of symptoms is called the Metabolic Syndrome or Syndrome X. The presence of these symptoms raises a person’s risk of cardiovascular disease, diabetes, obesity and prostrate or breast cancer. In studies reported in the American Journal of Clinical Nutrition in 2002, diets high in carbohydrates that had a high GI were linked to a greater risk of coronary heart disease. Several prospective observational studies have shown that continually eating foods with a high GI is linked to an increased risk of developing chronic conditions such as cardiovascular disease, type 2 diabetes and certain cancers. In a recent study that evaluated more than 65,000 American women, a high dietary GI was positively associated with an increased risk for type 2 diabetes.

An article appearing in the October 2003 issue of Critical Reviews in Food Science and Nutrition by Drs. Stacey Bell and Barry Sears explains in detail what happens metabolically when a high glycemic load meal or snack is eaten. (The glycemic load represents the food's glycemic index multiplied by the quantity of the food consumed by weight.)In their study of healthy volunteers, Bell and Sears found that two hours after eating a high glycemic load meal, blood sugar levels can be twice those found after eating a low glycemic load meal. High blood sugar levels trigger insulin, which causes blood sugar levels to drop, triggering hunger.

Frequent consumption of high glycemic load meals can result in perpetually high insulin levels. When insulin levels are high, the hormone responsible for triggering sugar breakdown, glucagon, is suppressed as is the breakdown of fats for energy. After four hours, this imbalance between insulin and glucagon results in further lowering of blood sugar levels, sometimes to levels near hypoglycemia (low blood sugar).

Because blood sugar (glucose) is the only form of fuel used by the brain, signals are sent that intensify hunger pangs. As mentioned, high insulin levels also prevent the breakdown of fats, so free fatty acids, an alternate source of fuel for most bodily functions, are also rendered unavailable. Between 4-6 hours after eating a high glycemic load meal, the body will release growth hormone and adrenalin (epinephrine) to try to restore free fatty acids, but the actions of these hormones are also suppressed by high levels of insulin. The result is that the individual is almost perpetually hungry, a hunger which he or she try to appease by over-consuming calories at the next meal or snack, continuing a viscous cycle that leads to obesity, cardiovascular disease and type 2 diabetes.

In contract, none of these unfavorable hormonal shifts occur after a low glycemic load meal is eaten. Low glycemic meals take longer to digest and absorb, so nutrients are released gradually, blood sugar levels remain stable and insulin levels rise minimally. The liver continues to make and release glucose, so the brain has a continual source of fuel, and hunger returns slowly. In addition, a low glycemic way of eating is associated with lower levels of LDL-cholesterol and triglycerides—two major risk factors for cardiovascular disease. Bell and Sears suggest that an optimal glycemic load diet would keep the glycemic load under 50 and be made up of 40% low glycemic index/glycemic load carbohydrates, 30% low-fat protein, and 30% fat.(December 3, 2003)

A Low Glycemic Healthy Way of Eating Protects Against Disease

A healthy eating plan that enables you to maintain a low to moderate Glycemic Index has great potential importance in treating and preventing chronic disease and Syndrome X. In studies in which persons with type-2 diabetes were given a low GI diet, their risk predictors of heart disease such as total cholesterol and “bad” LDL cholesterol fell. In other short-term human studies, individuals with a high intake of high GI carbohydrates had more insulin resistance than those who ate diets based upon low GI carbohydrates.

Persons with diabetes, in particular, can reap significant benefits from a low to moderate GI way of eating. In persons with diabetes, an uncontrolled glucose level—which means blood glucose levels are often too high—can lead to severe health complications including heart disease, blindness, kidney failure and limb amputations. Fortunately, an individual with diabetes who controls his or her blood glucose levels most of the time has little risk of these complications.

People without diabetes will also find it helpful to choose a low to moderate GI way of eating since it can help them to:

  • more carefully regulate their blood glucose and avoid developing the health risk factors noted above
  • reverse Syndrome X conditions
  • maintain a healthy energy level and avoid feelings of low energy and fatigue

Have you ever noticed that you feel lethargic after eating foods that stimulate a large insulin response, such as donuts or candy? This happens because too much insulin is produced in response to such foods, and this excess insulin causes blood sugar levels to drop below normal, resulting in low blood sugar (hypoglycemia) and fatigue.

When this happens, people who are unaware that the high sugar food they just ate is the reason for their sudden drop in energy reach for another sweet or high carbohydrate food, which starts the cycle all over again. When our blood sugar is bouncing from too high to too low repeatedly throughout the day, we certainly don’t feel our best. On the other hand, when our food choices help us maintain consistent normal blood sugar levels, we feel great and have the energy we need to enjoy long, active days.

Eating the Low Glycemic Way

A helpful way of looking at high and low GI carbohydrates is explained by Robert Crahyon, M.S., promoter of the “Paleolithic Diet.” Crahyon divides carbohydrates into two groups:

  • Paleocarbs. The carbohydrates that sustained early mankind, the hunter-gatherers: vegetables, fruits and possibly tubers. All these carbohydrates are rich in fiber, vitamins and minerals—plus, most have a low GI.
  • Neocarbs. Carbohydrates that developed as a result of agriculture: grains, legumes and flour products, then eventually, processed grain products such as those made with white flour and sugar, which have a high GI.

The majority of the World’s Healthiest Foods are paleocarbs. These foods have a low GI and will nourish, satisfy and energize you, while keeping your blood sugar levels on an even keel.

The wholesome members of the World’s Healthiest Foods that do have a higher GI can also be enjoyed in moderation, eaten along with low GI foods to balance their potential effect on your blood sugar levels.

For example, for breakfast, you might want to have oatmeal. Choose thick, dehulled oat flakes to make your oatmeal (these have a lower GI than rolled oats or one-minute oats), then eat grapefruit (one of the low GI fruits) with your oatmeal rather than a banana (a fruit with a high GI), and toss a few nuts or seeds over the oatmeal (nuts and seeds have a GI so low it’s not even charted). Finally, sprinkle a little cinnamon over your oatmeal. Recent studies have found that compounds in cinnamon stimulate cells’ insulin receptors, increasing almost 20-fold cells’ ability to absorb and use glucose. In this way, you can minimize oatmeal’s high GI, and enjoy a nourishing breakfast that will provide you with plenty of energy all morning.

How to Estimate a Food’s GI

Glycemic index is somewhat counter-intuitive—not all foods that you might think would have high values do have them, while other foods you might expect would have low values actually have high values. To get the most precise idea of whether your typical meals are high or low on the GI scale, it’s best to look over a Glycemic Index list of foods (check our GI listing of the World’s Healthiest Foods below) and see where your favorite foods fit. However, these following basic principles can help you estimate a food’s GI and eat healthfully:

Foods that are white tend to have a high glycemic index. This includes processed foods made with white flour and white sugar—but even white potatoes have a high GI.

Concentrate on eating foods that are high in fiber. In general, high-fiber foods take longer to digest and therefore produce a slower rise in blood glucose levels. Whole, unprocessed foods that still contain their original amounts of fiber move more slowly through the gastrointestinal tract than those whose fiber has been removed. These fiber-rich foods more fully engage the digestive process, thereby slowing release of sugar into the blood. This provides a feeling of satiety, or fullness, which helps prevent overeating. Many of the World’s Healthiest Foods are high in fiber and can be relied upon to maintain healthy blood glucose levels. These include most vegetables, whole grains, legumes, nuts, seeds, and even fruits such as apples and pears when eaten with their skin and not as juice. Citrus fruits, in particular, have a lower GI than most other fruits.

Protein foods, while not high in fiber, are typically low in glycemic index. A healthy exception is legumes, which are rich in both fiber and protein. In addition to legumes, excellent protein choices include nuts, seeds, fish and lean meats. If possible, choose organic meats from free-range or wild animals since these meats will not only have less fat, but the fat they contain will have a much larger percentage of beneficial omega-3 fatty acids. Conventionally raised animals are fed grain-based diets, which result in their meat containing much more saturated and omega 6 fats, but virtually no omega 3 fats. This fat profile can set the stage for health problems such as cardiovascular disease, certain cancers and high insulin levels. (To learn more about the importance of consuming omega-6 and omega-3 fatty acids in proper ratio, click A New Way of Looking at Proteins, Fats and Carbohydrates.

Fats do not raise glucose levels—but stick with healthy fats such as those found in olive and flaxseed oils, fish, and nuts. The monounsaturated and omega-3 fats in these foods provide a wide variety of health benefits. Decreasing your intake of these healthy fats and increasing the amount of carbohydrates you consume, especially when those carbohydrates have a high GI, actually increases cholesterol and triglyceride levels, raising your risk of cardiovascular disease. The healthy fats in the World’s Healthiest Foods should not be feared, but enjoyed! These fats play essential roles that contribute to the health of every cell in your body.

A person’s glycemic response to a food also depends on the other foods eaten along with it, so when eating a meal or snack, make sure it is “complex.” A complex meal or snack is one that contains complex carbohydrates (e.g., whole grains, vegetables, and whole fresh fruits), protein, healthy types of fat, and of course, plenty of fiber. Complex meals and snacks help keep blood glucose levels on an even keel. Keep this in mind when looking at the GI list of foods; rarely would you eat a high GI food by itself. Just combine high GI foods with low GI foods to moderate the effect on blood sugar levels and reduce the overall GI of the meal.

Choosing a healthy way of eating each day will naturally ensure that you maintain a healthy GI. Not only is your glycemic response to a food dependent upon the other foods you eat along with it, but also on your most recent meals. For example, your previous night's dinner can alter the next-morning’s GI. So, using GI as a guideline to help you control your blood sugar means eating healthfully day-by-day, week by week. Choosing low-GI foods at just one meal will not keep your blood sugar at a healthy level all day or the next day. For good blood sugar control, you need to consistently choose “complex” meals and snacks with a good overall low-GI. You need a healthy way of eating that surrounds each meal or snack in both directions.

A Closer Look at Glycemic Index Values

There are two ways of computing glycemic index because there are two standards of comparison. The earliest standards used glucose. A dose of glucose given to a patient was used to establish the baseline response. This response was arbitrarily given a value of 100. If you would like to look at a reliable resource that has used this standard in testing foods to determine how quickly they cause blood glucose levels to rise, we refer you to a list of 750 international foods at www.mendosa.com/gilists.htm. This list of international foods from verified sources was first published in The American Journal of Clinical Nutrition in 2002.

Today, however, the scientific community has largely abandoned the glucose standard for a starch standard. At the World’s Healthiest Foods, we believe that this standard provides a more accurate assessment of GI. Using this newer standard, a 50 gram portion of white bread (made using the 60% extraction process for wheat flour) is used as the standard and given a value of 100. Such bread, made from refined flour, is the bread most commonly eaten in the standard American diet. White bread (a starch) has been chosen as the new standard because the glycemic response to white bread is more reliable than the response to glucose, and more insulin activity is stimulated by white bread than by glucose. In addition, glucose tends to attract water. This effect, called osmolarity, can delay gastric emptying and misrepresent the insulin response. So, when looking over GI numbers, it's critical to know whether glucose or white bread was used as the standard. Keep in mind that the white bread values are the most accurate. The GI values of the World’s Healthiest Foods—based on the more reliable starch standard—are listed below.

The majority of the World’s Healthiest Foods have a low GI. Those that don’t—because they are naturally rich sources of carbohydrate—are listed below and can still be enjoyed in moderation when eaten along with other foods. The exact species of a food, and even the specific variety of that species, impacts GI, as does cooking and processing—for instance, cubed potatoes have a lower GI than do mashed potatoes. So, in the list below, an average of several types of a food is provided whenever available, and the cooking method is listed, if available.

Glycemic Index of World’s Healthiest Foods

In the table below, we’ve listed the Glycemic Index values primarily for the World’s Healthiest Foods that are high in carbohydrates—plus a few comparative foods. If a World’s Healthiest Food is not on this list, it is because it does not have a high carbohydrate value and therefore, even if eaten alone, will not cause blood sugar levels to spike.

The values in our table are based on the more reliable white bread (starch) index rather than the glucose index. Should you compare these values to a GI table based on the glucose index, divide those values by 1.4.

FOOD ITEMS Glycemic Index
VEGETABLES*
Spinach 15
Turnip Greens 15
Lettuce 15
Water Cress 15
Zucchini 15
Asparagus 15
Artichokes 15
Okra 15
Cabbage 15
Celery 15
Cucumbers 15
Dill Pickles 15
Radishes 15
Broccoli 15
Brussels Sprouts 15
Eggplant 15
Onions 15
Tomatoes 15
Cauliflower 30
Bell Peppers 40
Green Peas 40
Squash 50
Heart of Palm 50
GRAIN ITEMS
Barley
Pearled barley, cooked (average of 5 samples) 35
Barley kernel bread (50% kernels) (average of samples 64
Barley flour bread (80% barley, 20% white wheat flour 94
Whole meal barley porridge 95
Buckwheat
Buckwheat bread (50% dehusked buckwheat groats, 50% white flour) 66
Buckwheat, cooked (average of 3 samples) 76
Corn
Corn, yellow 78
Corn tortillas 78
Cornmeal, boiled in salted water 2 minutes 95
Taco shells 97
Millet
Millet, boiled 99
Oats
Oat bran bread (45% oat bran, 50% white wheat flour 66
Oatmeal (thick, dehulled oat flakes 77
Oat bran cereal 78
Museli 80
Oatmeal (rolled oats), cooked 81
Oat bread (80% intact oat kernels, 20% white wheat flour) 91
Oatmeal (one-minute oats 92
Rice
Wild rice 81
Rice cakes 81
Rice noodles, cooked 85
White, boiled (average of 12 saamples) 90
Parboiled rice 100
Rice bread 100
Rye
Whole kernels, cooked (average of 3 samples) 48
Rye kernel bread (80% kernels, 20% white wheat flour) (average of 6 samples) 70
Whole meal rye bread (average of 4 samples) 81
Wheat
Spaghetti, whole meal (average of 2 samples) 52
Whole wheat kernels, cooked (average of 4 samples) 57
Spaghetti, white, boiled 10-15 minutes (average of 7 samples) 62
Cracked wheat, bulgar, boiled (average of 4 samples) 67
Wheat kernel bread (80% intact kernels, 20% white wheat flour 73
Couscous (from semolina—durham wheat) boiled 5 minutes 91
Whole wheat bread (average of 13 samples) 95
White flour bread (average of 6 samples) 100
Gluten-free 129
Spelt
Whole meal spelt bread 88
Multi-grains
Multi-grain bread 60
FRUITS
Grapefruit 35
Apples, Dried (average of 2 samples) 40
Prunes 41
Apricots, Dried (average of 2 samples) 43
Apples, Raw (average of 6 samples 53
Pears (average of 4 samples) 53
Plums (average of 2 samples 55
Strawberries 56
Oranges (average of 6 samples) 59
Pineapple juice 64
Grapes (average of 2 samples) 64
Orange juice (average of 3 samples) 73
Bananas (average of 10 samples) 73
Kiwi (average of 2 samples) 74
Apricots, Raw 80
Papaya (average 3 samples) 83
Pineapple (average of 2 samples) 83
Figs 85
Raisins 90
Cantaloupe 91
Watermelon 100
STARCHY VEGETABLES
Yams (average of 3 samples) 52
Carrots (average 4 samples) 66
Potatoes, Boiled 15 minutes, cubed, peeled 81
Sweet potatoes (average of 5 samples) 85
Beets 90
Potatoes, Baked (average of 4 samples) 119
Mashed (average of 3 samples) 104
LEGUMES
Soybeans, cooked (average of 2 samples) 25
Lentils, red, cooked (average of 4 samples) 36
Garbanzo beans, dried, soaked, boiled 35 minutes (average of 4 samples) 39
Kidney beans (average of 8 samples) 39
Lentils, green, cooked (average of 3 samples) 42
Split peas, yellow, cooked 45
Soymilk, full fat, with maltodexdrin, calcium-fortified 50
Navy beans, cooked (average of 5 samples) 53
Pinto beans, cooked 55
Pinto beans, canned 63
DAIRY
Yogurt, low fat, plain 20
Whole fat milk 39
Skim milk 46
Yogurt, low fat, with fruit 47
SWEETENERS
Honey (average of 11 samples) 77
Sucrose (white sugar) 95

*We cannot find published research studies to confirm the GI of vegetables. Some consider them so low that they are not detectable while most place their value between 15-50 and we suspect that this range is right on target based on their low carbohydrate and high-fiber content.

**The standard value for beer is 110, based primarily on the malted aspect, and maltose has a GI value of 110. Although it has been suggested that red wine has a low GI value, we cannot confirm this claim and treat any alcoholic beverage as a high GI food since alcohol itself is, without question, de-stabilizing of blood sugar. Red wine may be somewhat of an exception, but the jury is still out.

Practical Tip

A food is generally considered to have a high GI if it is rated above 60.

Individuals who have problems with maintaining proper blood sugar levels should restrict their selection to foods with a GI of 40 or less. These include those who have low blood sugar (hypoglycemia) and high blood sugar (hyperinsulemia) as well as those who have a high sensitivity to sugar. Sugar includes not just simple sugars, honey and maple syrup but also fruits, fruit juices, starchy vegetables and grain products or foods with a high glycemic index.

For a healthy person without any problems with blood sugar levels all of the foods in a meal do not have to have a low GI. For example, consider a bean-and-cheese filled tortilla. The corn tortilla has a high GI (78), as do pinto beans (GI of 63), but the tomatoes (GI of 15) onions (GI of 15), lettuce (GI of 15) and cheese (GI so low it is not recorded) balance out the overall GI effect. The result is a healthy meal that will not destabilize blood sugar levels.

When planning your healthy GI meals, keep the following simple guidelines in mind:

  • Main components should have a GI of no more than 70
  • Half of all components should have a GI below 50

References

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This page was updated on: 2004-11-18 22:23:43
© 2002 The George Mateljan Foundation