| Glycemic Index
For many years we have learned that carbohydrates fall into two major categories: simple (including sugar, honey and maple syrup) and complex (including whole 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 also important when differentiating between various types of carbohydrates is how rapidly a particular carbohydrate will get metabolized into sugar and impact blood sugar (glucose) levels. Sugars are 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 partly derived from the carbohydrates in the foods that we eat. A food with a low glycemic index (GI) typically raises blood sugar levels only moderately, while a food with a high GI may cause blood sugar levels to increase more than desired. When we look at the GI figures associated with various carbohydrates, we find that some of the foods traditionally classified as complex carbohydrates - such as peeled, boiled potatoes - can increase our blood sugar levels more rapidly than some of the simple carbohydrates like table sugar! Because GI values can help us predict the functional effects in our bodies of the carbohydrates we eat, the GI has become an important tool for helping us select the right foods to help stabilize our blood sugar levels.
What Is Glycemic Index?
The Glycemic Index (GI) is a numerical scale used to indicate how fast and how high a particular food can raise our blood glucose (blood sugar) level. A food with a low GI will typically prompt a moderate rise in blood glucose, while a food with a high GI may cause our blood glucose level to increase above the optimal level.
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, starchy vegetables, and legumes, can have an affect on blood glucose.
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, etc.)
- Sugars, such as those naturally found in fruits and dairy products as well as packaged 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 (except sometimes very late in the digestive process by bacteria in the large intestine), does not directly raise blood glucose levels.
After we eat carbohydrate-rich foods, our digestive process usually breaks them down, and eventually turns them into glucose, which can then enter our bloodstream. (Since most proteins and fats from food are not turned into glucose by this same process, they typically have much less of an immediate effect on our blood sugar).
The presence of glucose in the bloodstream usually 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, extra glucose still remaining in the bloodstream can 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 can help our body store this excess sugar 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. However, too much insulin secretion 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 certain combination of these disease-promoting factors is present all at once, the constellation of symptoms is called Metabolic Syndrome. The presence of these symptoms also raises a person's risk of cardiovascular disease, diabetes, and prostate 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 the continual eating of 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 were twice as high as the levels that resulted from consumption of a low glycemic load meal. These high blood sugar levels triggered the synthesis and release of insulin, our key hormone for getting sugar back out of the bloodstream and into the cells.
While a single, high-GI meal might not cause significant health problems for our body, frequent consumption of high glycemic load meals can result in perpetually high insulin levels. When insulin levels stay high, our endocrine system can start out on a rollercoaster ride in which the body tries to adjust to its perpetually high insulin level with changes in other hormone levels that can leave us both tired, hungry, and on a course toward increased risk of cardiovascular disease and type 2 diabetes.
By contrast, many or all of these unfavorable hormonal shifts become less likely when a meal with low glycemic load is eaten. Since low glycemic meals take longer to digest and absorb, and nutrients are released gradually, blood sugar levels tend to remain more stable and insulin levels tend to rise in a non-risky fashion. As an added benefit, a low glycemic way of eating is associated with lower levels of LDL-cholesterol and triglycerides. 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 healthy eating plan that enables you to maintain a low to moderate Glycemic Index has great potential importance in treating and preventing chronic disease. 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 often 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. Most of these foods have a low GI and will nourish, satisfy and energize you, while helping keep 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 lower GI fruits) with your oatmeal rather than a banana (a fruit with a higher GI), and toss a few nuts or seeds over the oatmeal (nuts and seeds tend to have extremely low GIs). Finally, sprinkle a little cinnamon over your oatmeal. Recent studies have found that compounds in cinnamon can stimulate our cells' insulin receptors, increasing the cells' ability to absorb and use glucose. In this way, you can reduce the GI of your oatmeal 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 higher 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.
Foods high in protein, while not necessarily high in fiber, typically score lower on the glycemic index scale. Some foods - like legumes - are rich in both fiber and protein, and give you a doubly safe glycemic margin. 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.
Fats do not immediately cause a rise in 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. Combine high GI foods with low GI foods to help 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 help keep your blood sugar at a healthy level all day or the next day. For your best chances of good blood sugar control, you will need to consistently choose "complex" meals and snacks with a good overall low-GI. You will need a healthy way of eating that surrounds each meal or snack in both directions.
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.
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FOOD ITEMS
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Glycemic Index
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VEGETABLES*
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Spinach
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15-50
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Turnip Greens
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15-50
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Lettuce
|
15-50
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Water Cress
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15-50
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Zucchini
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15-50
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Asparagus
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15-50
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Artichokes
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15-50
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Okra
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15-50
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Cabbage
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15-50
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Celery
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15-50
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Cucumbers
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15-50
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Dill Pickles
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15-50
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Radishes
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15-50
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Broccoli
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15-50
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Brussels Sprouts
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15-50
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Eggplant
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15-50
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Onions
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15-50
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Tomatoes
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15-50
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Cauliflower
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30
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Bell Peppers
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40
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Green Peas
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40
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Squash
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50
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Heart of Palm
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50
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GRAIN ITEMS
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Barley
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Pearled barley, cooked (average of 5 samples)
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35
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Barley kernel bread (50% kernels) (average of samples
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64
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Barley flour bread (80% barley, 20% white wheat flour
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94
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Whole meal barley porridge
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95
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Buckwheat
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Buckwheat bread (50% dehusked buckwheat groats, 50% white flour)
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66
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Buckwheat, cooked (average of 3 samples)
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76
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Corn
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Corn, yellow
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78
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Corn tortillas
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78
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Cornmeal, boiled in salted water 2 minutes
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95
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Taco shells
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97
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Millet
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Millet, boiled
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99
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Oats
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Oat bran bread (45% oat bran, 50% white wheat flour
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66
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Oatmeal (thick, dehulled oat flakes
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77
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Oat bran cereal
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78
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Museli
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80
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Oatmeal (rolled oats), cooked
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81
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Oat bread (80% intact oat kernels, 20% white wheat flour)
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91
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Oatmeal (one-minute oats
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92
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Rice
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Wild rice
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81
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Rice cakes
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81
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Rice noodles, cooked
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85
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White, boiled (average of 12 saamples)
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90
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Parboiled rice
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100
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Rice bread
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100
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Rye
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Whole kernels, cooked (average of 3 samples)
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48
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Rye kernel bread (80% kernels, 20% white wheat flour) (average of 6 samples)
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70
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Whole meal rye bread (average of 4 samples)
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81
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Wheat
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Spaghetti, whole meal (average of 2 samples)
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52
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Whole wheat kernels, cooked (average of 4 samples)
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57
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Spaghetti, white, boiled 10-15 minutes (average of 7 samples)
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62
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Cracked wheat, bulgar, boiled (average of 4 samples)
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67
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Wheat kernel bread (80% intact kernels, 20% white wheat flour
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73
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Couscous (from semolina-durham wheat) boiled 5 minutes
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91
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Whole wheat bread (average of 13 samples)
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95
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White flour bread (average of 6 samples)
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100
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Gluten-free
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129
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Spelt
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Whole meal spelt bread
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88
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Multi-grains
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Multi-grain bread
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60
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FRUITS
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Grapefruit
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35
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Apples, Dried (average of 2 samples)
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40
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Prunes
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41
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Apricots, Dried (average of 2 samples)
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43
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Apples, Raw (average of 6 samples
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53
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Pears (average of 4 samples)
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53
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Plums (average of 2 samples
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55
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Strawberries
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56
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Oranges (average of 6 samples)
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59
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Pineapple juice
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64
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Grapes (average of 2 samples)
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64
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Orange juice (average of 3 samples)
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73
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Bananas (average of 10 samples)
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73
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Kiwi (average of 2 samples)
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74
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Apricots, Raw
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80
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Papaya (average 3 samples)
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83
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Pineapple (average of 2 samples)
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83
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Figs
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85
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Raisins
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90
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Cantaloupe
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91
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Watermelon
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100
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STARCHY VEGETABLES
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Yams (average of 3 samples)
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52
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Carrots (average 4 samples)
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66
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Potatoes, Boiled 15 minutes, cubed, peeled
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81
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Sweet potatoes (average of 5 samples)
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85
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Beets
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64
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Potatoes, Baked (average of 4 samples)
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119
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Mashed (average of 3 samples)
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104
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LEGUMES
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Soybeans, cooked (average of 2 samples)
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25
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Lentils, red, cooked (average of 4 samples)
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36
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Garbanzo beans, dried, soaked, boiled 35 minutes (average of 4 samples)
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39
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Kidney beans (average of 8 samples)
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39
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Lentils, green, cooked (average of 3 samples)
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42
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Split peas, yellow, cooked
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45
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Soymilk, full fat, with maltodexdrin, calcium-fortified
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50
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Navy beans, cooked (average of 5 samples)
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53
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Pinto beans, cooked
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55
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Pinto beans, canned
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63
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DAIRY
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Yogurt, low fat, plain
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20
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Whole fat milk
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39
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Skim milk
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46
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Yogurt, low fat, with fruit
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47
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SWEETENERS
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Honey (average of 11 samples)
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77
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Sucrose (white sugar)
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95
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*We cannot find published research studies to confirm the GI of vegetables. Most commentators we've read 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 but treat any alcoholic beverage as a problematic food since alcohol itself can be de-stabilizing of blood sugar. To some extent, red wine may be an exception, but the jury is still out.
Practical Tips
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
- Bell SJ, Sears B. Low-glycemic-load diets: impact on obesity and chronic diseases. Crit Rev Food Sci Nutr. 2003;43(4):357-77.
- Brand-Miller, JC. "Glycemic index and obesity." AJCN 76:1, p. 281S-285S, July 2002.
- Brasco, J. Low Grain and Carbohydrate Diets Treat Hypoglycemia, Heart Disease, Diabetes, cancer and Nearly ALL Chronic Illness, www.mercola.com
- Broadhurst CL, Polansky MM, Anderson RA.Insulin-like biological activity of culinary and medicinal plant aqueous extracts in vitro. J Agric Food Chem 2000 Mar;48(3):849-52.
- Foster-Powell, K. et al. "International table of glycemic index and glycemic load value: 2002." AJCN 76:1, p. 5-56, July 2002.
- Goldbeck N, Goldbeck D. The Healthiest Diet in the World, Penguin-Putman: NY, 2001.
- Imparl-Radosevich J, Deas S, Polansky MM, Baedke DA, Ingebritsen TS, Anderson RA, Graves DJ. Regulation of PTP-1 and insulin receptor kinase by fractions from cinnamon: implications for cinnamon regulation of insulin signalling. Horm Res 1998, Sep;50(3):177-82.
- Jenkins, DJA, et al. "Glycemic index: overview of iimplicait5ons in health and disease." AJCN, 76:1, 266S-273S, July 2002.
- Leeds, A.R. "Glycemic Index and heart disease." AJCN 76:1, p. 286S-289S, July 2002.
- Mendosa, R. Revised International Table of Glycemic Index (GI) and Glycemic Load (GL) Values - 2002. www.mendosa.com/gilists.htm
- Pi-Sunyer, FX. "Glycemic index and disease." AJCN 76:1, p. 290S-298S, July 2002.
- Willett, W. "Glycemic index, glycemic load and risk of type 2 diabetes." AJCN 76:1, p. 274S-280S, July 2002.
- Wolever, T. The Glycemic Index: Flogging a Dead Horse? Diabetes Care, 20:3, p 452-456, 1997.
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