Discussion

Introduction

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.

A Low Glycemic Healthy Way of Eating Can Help Protect 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. 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. (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 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.

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, and carefully controlled amounts of this sugar were given to subjects in research studies to establish a baseline response. More recently, white bread has been used as a standard of comparison. (And just like the response to glucose, the response to white brad was given an arbitrary value of 100). There appear to be some advantages to the use of white bread over glucose in determining glycemic response, and for this reason, we recommend the use of GI values based on a bread versus glucose norm. One of the best free lists we're aware of for finding the GI value of many foods (about 750 on this website) has been compiled by David Mendosa in conjunction with the University of Sydney Glycemic Index Research Service. The GI values in this list are partly normed on glucose and partly normed on white bread. If you would like to consult this list of values, please visit 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.

GI values for the World's Healthiest Foods based exclusivelyon 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.