“My father, mother, wife, husband, child, I have just been diagnosed with diabetes. How and what do I eat?” “What is carbohydrate counting?” “What is the glycemic Index and do I need to know about it?”
For these reasons we update the nutritional guidelines for you as soon as they come out. We talk about carbs and how to count them, and this month, we will re-examine the glycemic index thanks to an excellent article in JAMA, May 8, 2002.
We found this article titled The Glycemic Index; physiological mechanisms relating to obesity, diabetes, and cardiovascular disease by David S. Ludwig, MD, Ph. D. The glycemic index was first proposed in 1981 as an alternative for classifying carbohydrates and only carbohydrates.
Since then many diet books and articles have been published on the subject and using the ideas of the Glycemic Index. This article is a review of the subject as it relates to obesity, diabetes, and cardiovascular disease, all of which are of interest to those of us with diabetes; however, we will deal mostly with diabetes.
We will also include one of the many indexes so that you will understand how various carbohydrate foods fit into an index.
Before we look at this article, it is important to understand that the glycemic index has its share of controversy. The American Diabetes Association has a position on the index. The ADA places priority on the amount rather than the source of the carbohydrate source.
At least some people have taken this to mean that all carbohydrates produce the same glycemic response. In fact the ADA booklet on carbohydrate counting counsels “Studies have proven that…all carbohydrates have nearly equal impact on blood sugar”. The ADA has also had concerns about the difficulty of using the Glycemic Index and the extra discipline needed to adhere to it.
The organization was cautious because some studies were done on single meal or two meals. They have not however, researched the effects on larger populations over time. With all of this in mind, we can begin to look at the article with open eyes.
The glycemic index was proposed in 1981 as an alternative system for classifying carbohydrate-containing foods. Since then several hundred books have been written on the topic, but as we stated before, it remains a subject of debate.
To better understand, we need to understand that all carbs, from starches to just plain table sugar, share a basic biological property: They can be digested and converted into glucose. From the beginning of this century, digestion rate and therefore the blood glucose response, has been commonly thought to be determined by the saccharide chain length, which is the basis for the terms complex carbohydrate and simple sugar.
Diabetic diets based on this are high in starches and low in sugar. During the last 25 years the relevance of chain length in carbohydrate digestion has been questioned. The physiological effects of carbohydrates may vary substantially, as demonstrated by marked differences in glycemic and insulinemic responses to ingestion of isoenergetic amounts of white bread vs. pasta. For this reason Jenkins et al proposed the glycemic index as a system of classifying carbohydrate-containing foods according to the glycemic response.
The body has an obligatory requirement for glucose, approaching 200g/d, determined largely by the metabolic demands of the brain. Those of us with diabetes know the effects of hyper- and hypoglycemia on our brains.
We know that blood glucose levels below 40 mg/dL can cause coma, seizure or even death. We also know that blood glucose levels above 180 mg/dL are associated with long term complications of diabetes.
Hyperglycemia stimulates insulin secretion, promoting uptake of glucose from muscle and adipose tissue. Hypoglycemia elicits secretion of glucagons, epinephrine, cortisol, and growth hormone, counter-regulatory hormones that antagonize insulin action and restore normoglycemia.
We will concentrate in this review on the glycemic response and diabetes. It is hypothesized that calorie for calorie a high-glycemic index meal stimulates more insulin secretion than low-glycemic index meals because of relative postprandial hyperglycemia and increased incretin levels.
This state of primary hyperinsulinemia may in turn cause insulin resistance, as demonstrated by whole-body glucose disposal after insulin infusion under glucose infusion under euglycemic conditions in humans. Insulin resistance may also occur with high-glycemic index diet because of the direct effects of hyperglycemia, hormone secretion, and increased postprandial serum-free fatty acid levels.
Several studies demonstrate how increased demand for insulin and hyperinsulinemia itself can directly compromise beta cell function. In addition, high dietary glycemic index may impair beta cell function through the direct effects of elevated blood glucose and free fatty acid levels.
Hyperglycemia is known to cause beta cell dysfunction, a phenomenon that has been called glucotoxicity. A variety of genetic and environmental factors is known to affect risk for type 2 diabetes. Proponents of using the glycemic index suggest that a high-glycemic index diet might increase risk susceptible individuals by over- stimulation, glucotoxicity, and lipotoxicity, three critical metabolic factors thought to contribute to beta cell failure.
In terms of management of diabetes, a low glycemic index diet may theoretically appear to improve postprandial hyperglycemia and decrease the risk of hypoglycemia. A number of studies have been done on the subject. Some have shown improvement in hemoglobin A1c.
However, as stated before, the ADA citing methodological issues with some of these studies still concluded that there is insufficient evidence of substantial long-term benefit to recommend use of the glycemic index in the management of diabetes. The author makes the follow conclusions about his review of studies. Do read the entire article to get all of this research and to understand the effect of high and low glycemic foods on obesity and cardiovascular disease. There is not space here to report all of this in detail and add an index for you to read.
Conclusions include the following:
- The rate of carbohydrate absorption after a meal, as quantified by the glycemic index, has significant effects on postprandial hormonal and metabolic responses.
- High-glycemic index meals produce an initial period of high blood glucose and insulin levels, followed in many people by reactive hypoglycemia, counter-regulatory hormone secretion, and elevated free fatty acid concentrations.
- These can cause excessive food intake, beat cell dysfunction, dislipidemia, and endothelial dysfunction.
- Thus, eating high glycemic meals over the long term can raise the risk for obesity, type 2 diabetes and heart disease.
We found this Glycemic Index on the net on the Nutrition Science News Page. Brand-Miller J et al Glucose Revolution N.Y. Marlow & Co 1999: How fast the carbohydrate food gets into the blood stream to glucose (=100).
We have adapted it for this article. It is general and you can find more food included on other glycemic indexes. Also note that some indexes are based on white bread and some on sugar so the numbers may vary. It is the relativity that counts. (Maybe that’s one of the reasons why we have controversy here)
80-90=corn flakes, crisp bread
70-79= raisin bread, vanilla wafers, graham crackers, waffles, white and wheat breads, bagel, cakes
60-69= taco shells, shredded wheat, arrowroot, cookies, shortbread
50-59= All Bran, ground whole wheat, buckwheat, brown and white rice, blueberry muffin, pita and sourdough bread
40-49= noodles, sponge cake, spaghetti, oatmeal, banana bread
90-99= parsnips, baked white potato, dried dates
80-89= red skinned potato
70-79= French fries, pumpkin, watermelon
60-69= beets, new potatoes, cantaloupe, pineapple, raisins
50-59= sweet corn, sweet potato, banana, kiwi, mango, papaya
40-49= grapes, carrots, orange, green peas
30-39= apple, apricot, pear, plum
70-79= broad beans
50-59= pinto beans, black-eyes peas
40-49= baked beans
30-39= butter beans, chick peas, lentils, navy beans
20-29= kidney beans
10-19= soy beans
60-69= soft drink, syrup
50-59= orange juice
40-49= apple, grapefruit juice, soy milk
30-39= chocolate milk
20-29= whole milk
Have you noticed that some low-glycemic foods are not included in your diabetic diet? Whole milk is certainly one of them. On the other hand, eating pasta is not so bad. The problem then becomes what you put on your pasta. If you still have questions feel free to e-mail us or talk to your health care team. We’re here to help and so are they.