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Carbohydrate Counting, Glycemic Index, and Glycemic Load: Putting Them All Together
Meal planning is often called a cornerstone of diabetes management, but there are many ways to plan a meal, and not all of them will help to keep blood glucose levels in target range. Among those that will is carbohydrate counting, and when the glycemic index of carbohydrate-containing foods is also taken into account, the results may be even better.
Carbohydrate counting involves identifying which foods contain carbohydrate, then assessing how much carbohydrate a serving of food (or an entire meal) contains. For some people, the next step is to match the premeal insulin dose with the amount of carbohydrate. Accurately counting the amount of carbohydrate in your meals can help with blood glucose management, because carbohydrates (with the exception of fiber) raise blood glucose levels. However, some forms of carbohydrate raise blood glucose levels more and faster than others. This is where the glycemic index comes in.
The glycemic index of a food is a ranking (from 0 to 100) of how much it raises blood glucose level after it is eaten. A number of things affect a food’s glycemic index, including the type of starch it contains, the type of fiber it contains, and how finely milled or broken down the grain kernels, beans, or seeds are. Luckily for consumers, lists of commonly consumed foods and their glycemic index values are readily available.
The glycemic load of a serving of food puts together its carbohydrate content and its glycemic index to give a more accurate estimate of how much it will affect blood glucose level. Once you know a food’s glycemic index and the carbohydrate content of the amount you plan to eat, it’s fairly easy to calculate your portion’s glycemic load.
The amount of carbohydrate found in menu items at chain restaurants can usually be found on the restaurant Web sites (such as www.subway.com or www.applebees.com) or on some general health Web sites such as www.dietfacts.com and www.sparkpeople.com. A variety of free apps for smart phones, iPads, iPod touches, and tablets also list carbohydrate grams in thousands of foods, including restaurant meals. Some examples include MyFitnessPal, Diet and Food Tracker by SparkPeople, and Calorie Counter by Fat Secret.
The total carbohydrate listed on food packages (and on Web sites, in books, etc.) is the sum of starches, added sugars, natural sugars, and fiber. Since the nutrition information is listed “per serving,” the carbohydrate gram information will need to be adjusted accordingly if more (or less) than one serving is eaten. Since fiber is not absorbed by the body and is therefore not broken down to glucose, the grams of dietary fiber can be subtracted from the total carbohydrate for a more accurate estimate of how the portion of food will affect blood glucose level.
Most people need between 30–75 grams of carbohydrate per meal and 15–30 grams for snacks. The amount depends on a person’s age, activity level, sex, health status, and weight. You will want to work with a registered dietitian to determine your carbohydrate targets at each meal and snack.
Some people prefer to count grams of carbohydrate, while others prefer to count carbohydrate “choices,” or servings. Each carbohydrate choice contains 15 grams of carbohydrate. When using this method of meal planning, it’s handy to have a resource that lists the serving sizes of various foods that contain 15 grams of carbohydrate. One example of such a resource is the booklet Choose Your Foods: Exchange Lists for Diabetes, published by the American Diabetes Association. The booklet groups carbohydrate-containing foods in categories of fruits, starches, milk, and other carbohydrates. For the purposes of carbohydrate counting, items in one list can be swapped with items in the other lists.
The right number of choices per meal depends on the person; a common range is 2–5 servings per meal and 1–2 servings for snacks. The table “Same Carbohydrate, Different Glycemic Load,” shows the portion sizes of a variety of carbohydrate foods that equal 1 carbohydrate choice, or about 15 grams of carbohydrate.
Most sweets and desserts contain carbohydrate, but typical portion sizes usually contain more than 15 grams of carbohydrate. Desserts are often high in calories and fat, and they should ideally be consumed in moderation to control not only blood glucose levels, but also weight and blood fats (cholesterol and triglycerides). See “Sweets and Desserts” for a sampling of sweets’ and desserts’ carbohydrate content.
Foods with little effect on blood glucose
So-called free foods are foods or beverages that contain no more than 20 calories per serving and no more than 5 grams of carbohydrate. The following are some examples of free foods. Note that the foods listed with a serving size are only “free” if no more than three servings are eaten per day.
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Protein alone does not raise blood glucose, but few if any foods contain only protein. Most foods that are high in protein also contain fat, such as meat, poultry, fish, dairy products, and nuts, and some contain carbohydrate, including dairy products, nuts, and beans. Those that contain carbohydrate will have a glycemic index value; those that don’t will not.
Fat alone or in combination with protein does not raise blood glucose, so foods such as butter, margarine, oil, and meat do not have a glycemic index value. When fat is combined with carbohydrate, it tends to lower the glycemic index value of the food, since fat slows digestion. This is why potato chips have a lower glycemic index than boiled white potatoes — and this in turn is an illustration of why a food’s glycemic index value is not the only the only thing to consider when deciding what to eat. Choosing foods that are lower in saturated fat and higher in monounsaturated and polyunsaturated fatty acids is important for heart health, regardless of glycemic index. Examples of healthier fats and fatty foods include olive oil, canola oil, liquid margarine, nuts, and avocado.
To determine a food’s glycemic index value, researchers give 10 or more volunteers a portion of the food being tested that contains 50 grams of carbohydrate. The volunteers’ blood glucose levels are checked before they eat the food and periodically during the two hours after they eat it. On another occasion, those same volunteers consume a portion of glucose (or sometimes white bread is used) that contains 50 grams of carbohydrate, and the same blood glucose measurements are taken. The two sets of measurements are then compared. Ten or more volunteers are used in these tests, and their results are averaged, because each person responds to food slightly differently.
Not only does the glycemic index of a food vary slightly from person to person, but it also depends on whether the food is eaten in isolation or with other foods. Consuming a food along with protein, fat, or other carbohydrates that have a lower glycemic index effectively lowers its glycemic index value. Other things that can affect a food’s glycemic index value include the ripeness of fruits (underripe fruits have a lower glycemic index than ripe fruit) and how foods are cooked or otherwise processed.
In people with diabetes, the glycemic index value of a food is additionally affected by a person’s premeal blood glucose level. If a person’s blood glucose level is elevated, the glycemic index of a food is lower than normal, and if a person’s blood glucose is low, the glycemic index of the food goes up.
In general, a serving of food with a glycemic load of 1–10 is considered to have a low glycemic load, 11–19 is a medium glycemic load, and 20 or higher is a high glycemic load. The table “Same Carbohydrate, Different Glycemic Load” shows the glycemic load for a variety of portions of foods.
A small study published in The American Journal of Clinical Nutrition in 2011 found that the glycemic load of a portion of a single food or of a meal (with a mix of foods) was a better predictor of after-meal blood glucose level than the carbohydrate content of the food portion or meal. However, the study subjects did not have diabetes, so it is not yet known whether the same would hold true for people with diabetes.
In the meantime, you may wish to experiment on yourself to see whether calculating the glycemic load of your meals and snacks helps you to anticipate your after-meal blood glucose levels better than carbohydrate counting alone.
Diabetes treatment. A meta-analysis of 14 studies that compared low-glycemic-index diets with conventional or high-glycemic-index diets found that study subjects who followed a low-glycemic-index diet had an HbA1c level of about 0.4 percentage points lower at the end of the study than those subjects following a higher-glycemic-index diet. This was true of both subjects with Type 1 diabetes and those with Type 2. Any reduction in HbA1c level lowers the risk of long-term diabetes complications.
Heart disease. People who follow diets with a high glycemic load tend to have increased triglyceride levels and lowered high-density lipoprotein (HDL) cholesterol levels, both of which raise the risk of heart disease. In a large study involving 750,000 female nurses, over a 10-year period, the women who followed the diets with the highest glycemic load were almost twice as likely to develop coronary heart disease as those following a diet with a lower glycemic load. Among the women who followed a high-glycemic-load diet, overweight and obese women were more likely to develop coronary heart disease than normal-weight women.
An Italian study involving almost 1,000 (nondiabetic) men and women compared a low-glycemic-index diet to a high-glycemic-index diet and found no overall increased risk of having a heart attack with the higher-glycemic-index diet. However, the researchers found an increased risk in overweight or obese volunteers and people over the age of 60.
Putting it all together
Choosing more carbohydrate foods with a medium or low glycemic index in place of foods with a high glycemic index is one way to lower the overall glycemic load of your meal plan. Another way is to consume less carbohydrate overall. A general rule of thumb for remembering which carbohydrate-containing foods have a lower glycemic index is the less processed a food is, the lower its glycemic index is likely to be.
Lowering your glycemic load has been shown to make a difference in blood glucose levels, weight control, and prevention of heart disease. Best of all, the benefits you reap can help you feel good and have more energy to do the things you enjoy. The menu here (along with these recipes) is an example of a low-glycemic-load day of meals. Use it to get started, then create more of your own.
Statements and opinions expressed on this Web site are those of the authors and not necessarily those of the publishers or advertisers. The information provided on this Web site should not be construed as medical instruction. Consult appropriate health-care professionals before taking action based on this information.