Chapter One
Part I The Secrets of the Glycemic Index
1. All Carbohydrates Are Not Created Equal
If you're confused about carbohydrates, you're not alone. Over the past severalyears, opinions about the role of carbohydrates in a healthy diet have rangedfrom "eat more for optimal health" to "nothing could be worse for your health."The truth about carbohydrates, however, lies somewhere in between. The fact isthe type of carbohydrates that we eat is one of the foremost predictors ofhealth. As you will see, a diet high in the wrong kinds of carbohydrates canlead to obesity, insulin resistance, diabetes, cardiovascular disease, and manyof the other health problems that are so pervasive today. On the other hand, adiet that includes the right carbohydrates can help prevent these same diseasesand put you on the road to excellent health.
Over the past couple of decades, the medical establishment has paid littleattention to the impact of carbohydrates on health and wellness. But a growingbody of evidence has made this a topic that can no longer be ignored. The factis there are good and bad carbohydrates, and making the right choices is crucialto your pursuit of a healthy body weight and optimal health.
What makes some carbohydrate-containing foods better choices than others?One of the most important factors is the rate at which they raise blood sugarlevels-or their glycemic index. This chapter will introduce you to thisrevolutionary way of looking at carbohydrates and show you why all carbs are notcreated equal. The following chapters will help you apply the glycemic index toyour everyday life and create simple and satisfying meals that will enhance yourhealth for years to come.
A Brief History of Carbohydrates
To truly understand how carbohydrates affect our health, it's important to lookat how the carbohydrates we eat have changed over time. Throughout most ofhistory, the only carbohydrate foods that were available were the wild roots,tubers, fruits, vegetables, and nuts that people foraged for. These foods wereloaded with fiber and nutrients, and they were slowly digested and absorbed toprovide a slow-release, sustained form of energy.
With the advent of agriculture about 10,000 years ago, people learned tocultivate grains such as wheat, rice, corn, oats, and barley. These foods, whichquickly became mainstays in the human diet, were consumed in their naturalunprocessed forms. Whole, cracked, or coarsely ground grains were made intoporridges or baked into hearty whole-grain breads. These foods, too, were highin fiber and nutrients.
While the introduction of cereal grains substantially changed the humandiet, the past 200 years have had an even greater impact on the types ofcarbohydrates available in the food supply-starting with the invention ofhigh-speed grain mills in the early 1800s. Using this technology, millerslearned to remove the fibrous bran and nutritious germ from grains and to makefinely ground flour from just the starchy endosperm portion of the grain. Peopleeagerly adopted this new flour, which had a very long storage life and madesofter and lighter breads, cakes, and pastries. Unfortunately, this new whiteflour was also virtually devoid of the vitamins, minerals, and fiber found inwhole grains. And its superfine texture makes it quickly digested and absorbedin the body, causing a rapid release of glucose and insulin into the blood. Thepast fifty years have brought the most dramatic changes of all to our foodsupply. For instance:
Products made from quickly digested white flours-such as breads, bagels,crackers, pretzels, and baking mixes-have become staples in most people's diets.
New technologies for processing grains-such as explosion puffing, extruding,and flaking-have been developed. Products made using these technologies,including breakfast cereals, snack foods, and a wide variety of "instant" and"quick-cooking" foods, are also rapidly digested, causing a fast rise in bloodglucose and insulin levels. Like white-flour products, these foods make up alarge part of many people's diets.
Consumption of refined sugars is at an all-time high.
The serving sizes of refined-carbohydrate foods like muffins, bagels, candybars, and sodas have grown to enormous proportions.
This deluge of quickly digested nutrient-poor carbohydrates represents muchof what's wrong with today's diets. Currently, about 85 percent of all grainproducts eaten by Americans are refined. And together, refined grains and sugarscompose close to 40 percent of all calories eaten! What can you do to bring yourdiet back into balance? Learning about the glycemic index is a great place tostart.
What is the Glycemic Index?
The glycemic index (GI) is a ranking of foods based on their potential to raiseblood sugar levels. The higher the GI of a food, the faster the resultant risein blood sugar after eating it. And the higher the GI, the higher the body'sinsulin response tends to be. Why is this important? High levels of blood sugarand insulin in the body have been linked to many of the health problems that areso common today.
The glycemic index has been the subject of scientific research for overtwenty years. It was originally developed as a dietary strategy to help peoplewith diabetes gain better control over their blood sugar levels. Today the GI iswidely accepted in Canada, Australia, and much of Europe, and its use hasexpanded to include roles in treating obesity, cardiovascular disease, andvarious other health problems. Health professionals in the United States havebeen slow to adopt this revolutionary way of classifying carbohydrates. However,this is rapidly changing as mounting evidence on the benefits of the GI makethis a topic that can no longer be ignored. The health effects of high- versuslow-GI foods are summarized below:
High-GI Foods
Are quickly digested, causing a rapid rise in blood sugar and insulinlevels.
Provide short bursts of energy that may be quickly followed by hunger and aroller-coaster pattern of overeating.
Promote excess insulin secretion, which may increase the risk for diabetes,cardiovascular disease, and some types of cancer and may contribute to a varietyof other health problems.
Low-GI Foods
Are slowly digested, allowing for a gradual rise in blood sugar and insulin.
Provide a slow-release form of energy that sustains you between meals andpromotes a healthy body weight.
Protect the body from the harmful effects of too much insulin.
You might look at this comparison and deduce that you should eliminateentirely foods that have a high glycemic index and eat only low-GI foods.Fortunately, going to extremes is not necessary. And as you will discover, justbecause a food has a low GI does not necessarily mean it is a healthful choice.However, replacing some of the high-GI carbohydrates in your diet with healthfullower-GI carbohydrates should be a primary strategy for anyone who wants toachieve a healthy body weight and maximize his or her health.
Ranking Foods on the Glycemic Index
Determining the GI of a food is a fairly complicated process (see the inset "HowDo Researchers Determine the GI of a Food?" on page 11 for details), so the GIof every food is not known. However, researchers have tested a variety of commonfoods, some of which are shown on page 9. A more extensive listing of the GIvalues of foods can be found in the appendix. These tables list the glycemicindexes of foods when compared to pure glucose, which has a GI of 100. Whencomparing foods, the following scale will help you put the GI in perspective:
Very low G1 = 39 or lower
Low GI = 40 to 54
Moderate GI = 55 to 69
High GI = 70 or higher
A look at Table 1.1 may surprise you. Many foods that are often thought ofas "health foods"-rice cakes and baked potatoes, for instance-have very highindexes, while "junk foods" like potato chips and chocolate have relatively lowindexes. Is there any rhyme or reason to the glycemic index? Yes. The GI of afood is influenced by a variety of factors, including the degree to which thefood is processed; how long the food is cooked; the kind of starch, sugar, orfiber the food contains; and the food's acidity. In general, anything thatspeeds the rate at which a food is digested and absorbed will increase the GI ofa food. The section "Factors That Affect the Glycemic Index of a Food" on page13 provides more details about what factors can raise or lower the GI of a food.
Of course, the glycemic index cannot be the only factor that determineswhich foods you should eat. As you can see from looking at Table 1.1, justbecause a food has a low GI does not necessarily mean it is good for you. It'simportant to consider all the nutritional qualities of a food when planning yourdiet. This book will help you make the best choices based on this philosophy.
While the GI should not be the only criterion used for choosing foods, somegeneralities can be drawn from Table 1.1 that can help guide you in choosingfoods:
Foods That Raise The Glycemic Index Of Your Diet
Bread
Potatoes
Breakfast cereals
Processed snack foods like chips, crackers, and pretzels
Foods That Lower The Glycemic Index Of Your Diet
Vegetables
Fruits
Legumes
Minimally processed whole grains
Pasta
Dairy products
Realize that some variation exists within these lists. For instance, not allkinds of bread and potatoes have a high GI. The remaining chapters of this bookwill help you make these distinctions and help you to plan varied and satisfyingmeals and snacks.
What effect do sweets have on the glycemic index of your diet? Many candies,cakes, cookies, and sodas have a moderate GI. However, these foods are veryconcentrated sources of carbohydrate, and the workload they place on thepancreas is considerable. Since sweets are often high in calories and low innutritive value, they should be eaten with your total carbohydrate and nutritiongoals in mind.
Perspective on Portions
How do portion sizes affect the glycemic index? The more carbohydrate you eat ina meal, the more insulin your pancreas must secrete to process the carbohydrate.For instance, eating a 4-ounce bagel will cause twice the insulin response aseating a 2-ounce bagel. Choosing low-GI foods will minimize the amount ofinsulin that you secrete when you eat carbohydrates, but portions are stillimportant. Chapter 2 will give you an idea of how much carbohydrate is right foryou.
Glycemic Index Versus Glycemic Load
Recognizing that both the GI of the carbohydrate-containing food and the amountof carbohydrate eaten affect blood insulin levels, researchers have coined theterm glycemic load to describe these two factors considered together. Glycemicload is a better indicator of total insulin demand and the workload of thepancreas than just glycemic index by itself. This term is becoming more popularin the scientific literature, so when you see it, just realize that it reflectsboth the type and the amount of dietary carbohydrate.
Factors That Affect the Glycemic Index of a Food
Table 1.1, which lists the glycemic index of a variety of common foods,reinforces the statement that all carbohydrates are not created equal. However,at first glance, the glycemic index may not seem to make much sense. Why do twostarchy foods like pasta and potatoes have such different indexes? And why doesfruit have a lower GI than bread? Differences in cooking and processing methods;the chemical structure of the starches, sugars, and fibers in foods; and thepresence of fat, protein, or acid can all markedly affect the GI of a food.Knowing more about how these factors affect the digestibility of foods will helpyou make sense of the GI.
Milling, Grinding, And Processing Of Grains
Modern food-processing techniques, such as grinding, pulverizing, puffing,extruding, and otherwise destroying the natural intact form of whole grains,make whole grains easier to digest and absorb. This is why most breads,breakfast cereals, snack chips, and crackers have such a high glycemic index.This is also why thinly cut instant oats have a higher GI than thicker cutold-fashioned oats.
Cooking
During cooking and baking, the starches in foods like grains, pasta, breads,and muffins absorb water. This causes the starch granules to swell and rupture,a process known as gelatinization. Gelatinized starch is readily attacked bydigestive enzymes and very quickly digested and absorbed. Bread has a high GIpartly because the starch in the finely ground flour used to make bread iseasily gelatinized. And soft, overcooked pasta has a higher GI than firm, aldente pasta because the overcooked pasta absorbed more water during cooking.
Many of the processing methods used to make extruded, flaked, or puffedcereals and snack foods involve steam-cooking at very high temperatures andpressures. This fully gelatinizes the starch in these foods and contributes totheir high glycemic indexes.
The Type Of Starch Present
Starch is a storage form of glucose found in plant foods. Because starch iscomposed of hundreds or thousands of glucose molecules that are strung togetherin chains, it is often referred to as complex carbohydrate. Scientists have longbelieved that because starch has a complex structure, it is more slowly digestedthan simple sugars. However, the glycemic index has proven this notion to befalse.
There are two main kinds of starch present in plant foods-amylose andamylopectin. When these starches are digested, their glucose molecules areliberated and absorbed, causing a rise in blood sugar. However, because of thedifferences in their chemical structures, these two starches have very differenteffects on blood sugar.
Amylopectin's structure resembles the branches of a tree and so it is easilyattacked by digestive enzymes. Starchy foods that contain a high proportion ofamylopectin-like baking potatoes and sticky short-grain rice-are quicklydigested and produce rapid rises in blood sugar levels. Amylose, on the otherhand, consists of a long, straight chain of tightly packed glucose moleculesthat resists digestion. Foods high in amylose-such as new potatoes and basmatirice-are absorbed more slowly and have lower glycemic indexes.
The Type Of Sugar Present
Many people are surprised to learn that with the exception of glucose (GI =100), most sugars have low to moderate glycemic indexes. Fructose, the sugarthat occurs naturally in fruits, is very slowly absorbed, giving it a GI of only23. Lactose, the sugar naturally present in milk and dairy products, has a GI of46. This is one reason why most fruits and dairy products have such low glycemicindexes. Sucrose (white table sugar), a combination of equal parts fructose andglucose, has a GI of 65. The fact that sucrose is part fructose is one reasonwhy many sweets have a moderate GI.
Acid
The naturally occurring acids in fruits, as well as the acids in fermentedfoods like yogurt, buttermilk, and sourdough bread, slow the rate of digestionand contribute to the low GI of these foods. Likewise, adding just 4 teaspoonsof vinegar or lemon juice to a meal can lower the GI of the meal by about 30percent. For this reason, using vinegar and lemon juice to flavor foods can be apowerful way to lower the GI of your diet.
Copyright © 2001 Sandra Woodruff. All rights reserved.
