The Glycemic Index - Which Carb is right for you?
Carolyn Classick-Kohn,MS,RD

Low Glycemic Index Diets - Which Carbs?Carbohydrates are made up of small sugar molecules, which once absorbed into the bloodstream, raises blood sugar levels, so that the body can have a source of fuel for energy. People who have the right amount of insulin in their bodies will clear the blood sugar produced after eating carbohydrate. The glucose (blood sugar) enters the cells with the help of insulin so that the body can use the glucose for fuel and will be "burned" so that for most people, blood sugar levels return to normal fairly quickly after a meal. For people who have Type II diabetes, or have "insulin resistance" due to obesity or other factors, the body must work harder to produce more insulin to cover the blood sugar that is produced following a meal. This is one reason that many popular diets emphasize reducing the amount of carbohydrate in the diet, and promote the use of the glycemic index to help choose good and bad carbohydrates.  But do you really need to reduce carbohydrates to very low levels to lose weight and improve insulin resistance?

The simple answer is no. A healthy diet is based upon eating a variety of healthy foods, and in fact most cultures have diets based upon carbohydrate sources. Examples of this are rice in India and Asia, tortillas and beans in Central America, bread and potatoes in the U.S. and Europe, and root vegetables in Africa. China, with one of the lowest incidences of obesity, has a diet based upon rice, a carbohydrate.

Are Low Glycemic Diets Right for Diabetes?The recommended diet for people with diabetes
(a disease in which the body cannot produce insulin or cannot use the insulin it produces normally to lower blood glucose) includes about 50% carbohydrate. Your recommending eating plan at PersonalDiets,  for weight loss, weight maintenance, is at least 50% carbohydrate. 

Do not be concerned that you might be eating too much carbohydrate on your diet plan. The reality of a weight loss diet is that, for the most part, it is lower in everything, compared to a diet that maintains your body weight! Although you may be following a diet that is 50% carbohydrate (sounds like a lot), 50% of the calories on a 1400 Calorie diet (or your particular calorie level) is probably a smaller amount of carbohydrate than the total amount of carbohydrate you were eating when you were gaining or maintaining your body weight at a higher calorie level.

For more basic information about carbohydrates, please read the archived newsletter in your member's area "Carbohydrates - Not So Simple."

The Glycemic Index 
The glycemic index has shed new light on how carbohydrates are absorbed, and how they affect blood sugar. It turns out that some foods made from simple sugars actually raise blood sugar more slowly than some “complex” carbohydrates.The glycemic index is one way to categorize foods by how rapidly they increase blood glucose levels, causing insulin to be released by the pancreas. This can be a useful tool in evaluating foods, especially for people who have insulin resistance.

The higher the glycemic index, the more quickly blood sugar elevates after eating that food. Low glycemic index foods have a glycemic index of 55. High glycemic index foods have a glycemic index of 70 or more. This rating is all based upon glucose being given an arbitrary value of 100. Low glycemic index foods are considered more healthy because the energy released is slow and sustained, not quick, stimulating a quick release of insulin that stresses the body.

Fast or Slow Carbohydrates?

There are times when people need a quick source of fuel (those carbohydrates with a high glycemic index). One of these times is when blood sugar is very low and needs to be raised quickly. That's why it's important for people with diabetes, who often have widely fluctuating blood sugar levels, to always have a quick source of carbohydrate (like glucose tablets) to eat in case blood sugar levels fall too low. Eating a quick source of carbohydrate (like hard candy) must be eaten alone, because fat and protein will delay the absorption of the sugar. (That is why a chocolate bar, which contains fat, is not a good choice at times like these).

Another good time to choose high glycemic carbohydrate foods is when you want to quickly restore the body's carbohydrate stores that are used up during intense exercise.

Slow carbohydrates are generally the best choice for the everyday diet, to avoid rapid spikes in blood sugar levels, especially if the body is insulin resistant because of extra body fat. So, the glycemic index is typically used to help people choose low glycemic index carbohydrates for the day to day diet.      

Some Things to Consider

The reason I do not use the glycemic index to plan your custom diet is that your plan emphasizes choosing carbohydrates based upon their total nutritional value, not just the blood sugar raising potential of the food. The glycemic index is helpful, but is complicated for the average person to use correctly to plan a healthy diet for these reasons:

  1. Although the glycemic index provides some very useful information, it should not be the only measure of the value of the food. For example, a can of Coca-Cola has a glycemic index of 63, while 5 dried dates has a glycemic index of 103. Which is the more nutritious food? (Hint: not the coke!).

  2. Factors that influence how quickly blood sugar is raised by a food include its chemical composition, how long the food is cooked (to break down the carbohydrate molecules, making them more quickly absorbed), and what other foods are eaten with the food. For example, bread by itself might be quickly absorbed, but bread and margarine takes longer to break down because of the presence of fat. So, if you eat a food that has a high glycemic index along with some fat or  protein, it will change how the food is absorbed and reduce the importance of the glycemic index.

  3. Foods are not typically eaten by themselves, they are eaten along with other foods, which affect how quickly that food is digested. When you eat high glycemic foods together with low glycemic foods, you can average the effect.

  4. In some cases, the glycemic index of a food is based upon unrealistic amounts of foods. To get 55 grams of carbohydrate from bread, it takes about 3 1/2 average slices. To get 55 grams of carbohydrate from carrots, it takes about 3 cups of carrots!

In Summary:

  • The glycemic index helps us understand how specific carbohydrates affect blood sugar levels.

  • It is one piece of information that can be helpful, but should not be used exclusively to determine your diet.

  • A healthy diet, both for weight loss and for weight maintenance includes a variety of nutrient-dense carbohydrates – not junk foods!

  • The glycemic index can be a little complex for most people to be very practical, but some may find it helpful in evaluating foods.

  • Lastly, if you really need to know how a carbohydrate affects your blood sugar (as in the case of diabetes), you should test your blood sugar after eating the food, following the instructions from your physician or your diabetes educator.

See a sample of the author's diets today!
A Personal Dietitian