By David Mendosa
Are there Other Important Diet Considerations? Most definitely. The glycemic index should not be your only criteria when selecting what to eat. The total amount of carbohydrate, the amount and type of fat, and the fiber and salt content are also important dietary considerations.
The glycemic index is most useful when deciding which high-carbohydrate foods to eat. But don't let the glycemic index lull you into eating more carbohydrates than your body can handle, particularly if you have diabetes. The number of grams of carbohydrate we consume is awfully important. Make sure you know the carbohydrate content of the foods you eat—study the nutritional information on the package But first you need to decide the composition of your diet in terms of carbohydrate, fat, and protein.
Almost all the experts agree that we should minimize our intake of saturated and trans fat and eat a lot more fiber than we do. Some other fats, particularly those from cold-water fish, seem to be beneficial. Beyond that, the battle rages between those who would have us eat more protein and those who say that carbohydrates should provide most of our calories. I'm no expert and am genuinely puzzled myself, although I have begun to cut back on my carbohydrates and eat more protein. Generally, foods high in fat and protein have lower glycemic indexes than foods high in carbohydrate. In a real sense, the glycemic index is not applicable to high-fat and/or high-protein foods.
The problem is that even among the complex carbohydrates not all are created equal. Some break down quickly during digestion and can raise blood glucose to dangerous levels. These are the foods that have higher glycemic indexes. Other carbohydrates break down more slowly, releasing glucose gradually into our blood streams and are said to have lower glycemic indexes.
Before the development of the glycemic index, scientists assumed that our bodies absorbed and digested simple sugars quickly, producing rapid increases in our blood glucose levels. This was the basis of the advice to avoid sugar, a proscription recently relaxed by the American Diabetes Association and others. Contrary wise, the experts thought that our bodies absorbed starches such as rice and potatoes slowly, causing only small rises in blood glucose. Clinical trials of the glycemic index have also proven that assumption to be false. Factors such as variety, cooking, and processing may affect a food's GI. Foods particularly sensitive to these factors include bananas, rice, and potatoes (for a fuller discussion of the GI of rice and potatoes see the section below). A 1992 study by Hermansen et al. reported that the GI for under-ripe bananas was 43 and that for over-ripe bananas was 74. In under-ripe bananas the starch constitutes 80-90 percent of the carbohydrate content, which as the banana ripens changes to free sugars.
Particle size is also an important factor, according to a 1988 study by Heaton et al. The researchers found that the GI of wheat, maize, and oats increased from whole grains (lowest GI), cracked grains, coarse flour, to fine flour (highest GI) In addition, the glucose response to a particular food may be somewhat individual. So it is probably a good idea to carefully watch your own blood glucose level after eating foods you have questions about and determine if they have high or low GI for you.
So, the idea of glycemic index is a very useful one. But if you find a specific food produces an unexpected result, either high or low, take note of it and incorporate that into your meal planning. Also note that the numbers vary from study to study. This may be due to variations in the individuals in a particular study, other foods consumed at the same time, or different methods of preparation, since your body can absorb some foods better when they are well cooked. Most, but not all, of the foods tested are high in carbohydrates. Some may wonder at the gaps—why other high-carbohydrate low-calorie foods like celery (or tomatoes or similar foods) have never been tested. The problem is a technical one for the testers, because they would be so hard put to get anyone to volunteer to eat 50 grams of carbohydrate from celery—it's just too much celery to think about!
Essentially, from a glycemic index standpoint, celery and foods like it can be considered as free foods. I now have a list of the common vegetables and fruits that are free foods on-line at http://www.mendosa.com/freefoods.htm. Mixed Meals Some people wonder if the glycemic index can predict the effect of a mixed meal containing foods with very different indexes. Studies have shown that it does that job very well. More than fifteen studies have looked at the glycemic index of mixed meals. Twelve of them showed an excellent correlation between what was expected and what was actually found. You can quite readily predict the glycemic index of a mixed meal. Simply multiply the percent of total carbohydrate of each of the foods by its glycemic index and add up the results to get the glycemic index of the meal as a whole.
What about Protein and Fat? But what if the meal contains protein and fat too, as it usually does? How does that affect our mixed meal calculations? The conventional wisdom holds that between 50 to 60% of protein becomes glucose and enters the bloodstream about 3 to 4 hours after it's eaten. It's generally accepted that fat has little affect on blood glucose In fact, recent studies indicate that neither protein nor fat have more than a minuscule affect on blood glucose. This seems to be true for people both with and without diabetes. The protein studies are particularly interesting. A 50-gram dose of protein (in the form of very lean beef) resulted in only about 2 grams of glucose being produced and released into circulation. Neither does adding protein to carbohydrate slow the absorption or peak of the glucose response.
Fat delays the peak but not the total glucose response, according to these new studies. Therefore, it looks like you can simply ignore protein and fat in mixed meal calculations "Of much greater concern is how protein and fat affect blood glucose levels in the long term," Jennie Brand-Miller of the University of Sydney writes me. "High fat and high protein diets have the distinct potential to induce insulin resistance, which would mean that any carbohydrate eaten would raise blood glucose and insulin levels to greater heights on a day to day basis. However, the type of fat may be important here. A recent study in Diabetologia showed that moderately high MUFA [monounsaturated fatty acids] diets improved insulin sensitivity, if the fat was less than a certain level (higher than 37% was associated with insulin resistance.
Many people have noticed that pizza seems to keep their blood glucose level high longer than just about any other food. While the reason remains a mystery, this folk wisdom now has scientific confirmation. Ahern et al. compared the effect on insulin-dependent patients of a pizza meal with a control meal that included high glycemic index foods. They found that although the initial glucose increase was similar for the two meals, the GI continued to rise and was significantly increased from four to nine hours after the pizza meal compared with the control meal.
Rice and Potatoes: Rice and potatoes are some of the foods most tested for their glycemic indexes. They are important both because most of us tend to eat a lot of rice and potatoes and because they can have a high glycemic index. Professor Brand-Miller reports the results of 49 studies of rice and 24 studies of potatoes. The results for rice ranged all the way from 54 to 132 and for potatoes from 67 to 158. What could possibly cause such tremendous variation? According to Professor Brand-Miller, for rice one of the most important considerations is the ratio of amylose to amylopectin. She says that "the only whole (intact) grain food with a high G.I. factor is low amylose rice, such as Calrose rice...However, some varieties of rice (Basmati, a long grain fragrant rice, and Doongara, a new Australian variety of rice [which is not available in the United States] have intermediate G.I. factors because they have a higher amylose content than normal rice.
The three other types of rice have lower glycemic indexes Of course, each of these three types of rice may be brown or white. Brown rice has a lower glycemic index than white rice, everything else being equal. Therefore brown long-grain rice—or if you can find it—brown Basmati rice—will probably have a lower glycemic index. White Basmati rice had a glycemic index of 83 in one study. Brown Basmati rice can be expected to have a somewhat lower index, but we don't know precisely what it is, because the studies haven't been done yet.
Fructose is not the same as high fructose corn syrup, Professor Jennie Brand-Miller emphasized, "The former is pure fructose; the latter [high fructose corn syrup] is a mixture of fructose and glucose," she wrote. "In high fructose corn syrups, the fructose content is about 50 percent. Thus the GI of high fructose corn syrups is about the same as sucrose, i.e. 60-65 (if glucose = 100)." When white bread = 100, the GI of high fructose corn syrups is 85-92.
Soy Milk: Soy milk has a low glycemic index of 43, according to e-mail from Professor Brand-Miller. The tested soy milk, she writes, has 4.5 grams of carbohydrates, 3.5 grams of fat, and 3.5 grams of protein per 100 ml. A low factor for soy milk isn't surprising, since soybeans have a GI of 25. But consumers in the United States—where many different brands and flavors are available—need to be aware that not all soy milks are created equal. I recently discovered that my blood glucose rose dramatically after a large cup of chai made with soy milk. That's when I paid attention for the first time to how many grams of carbohydrate that particular soy milk had. So then I looked through the nutrition information on the dozens of brands and flavors of soy milk (and rice milk and almond milk and oat milk, etc.) in our local natural foods store I was amazed to find that the carbohydrate content of these beverages varied from 4 grams per 8 oz. to 36 grams. At least five brands have no more than 4 grams of carbohydrate per 8 oz. serving and are made from nothing but water and organic whole soybeans. WestSoy Organic Unsweetened Soymilk has 5 grams of carbohydrate per 8 oz. serving, of which 4 grams are fiber, which means it has only 1 gram of available carbohydrate per serving.
Thanks to Professor Jennie Brand-Miller for authorizing me to reproduce her glycemic index and glycemic load table. Thanks too to Tere Griffin who began the collection of information for what turned into this Web page and originally got me interested in this fascinating subject.
Too Complicated There's nothing on my Web site that draws more visitors (and more e-mail questions) than my articles on the glycemic index. Ever since I reviewed the first Australian edition of The G.I. Factor by Jennie Brand-Miller and her associates at the University of Sydney for Diabetes Interview in August 1996 (online at http://www.mendosa.com/gifactor.htm), Jennie and I have maintained a close albeit long-distance relationship.
High blood glucose levels are a risk factor for diabetes and cardiovascular disease. Dozens of studies have shown improvements in a variety of clinical outcomes with free-living subjects consuming self-selected low glycemic index diets.
Like the calorie content of food, the glycemic index deserves some consideration. The foods that provide the most carbohydrate in the diet are the ones that need close attention (potatoes, breakfast cereals, breads, soft drinks), not carrots, honey or over-ripe bananas. For an extended bibliography please go to the website at mendosa.com.
Copyright Jewish Diabetes Association. Last updated June 2017©