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July 2005 The
Highs and Lows of the Glycemic Index Many countries are gung-ho on the glycemic index, but it remains a bone of contention among U.S dietitians and diabetes educators. Are you wondering which side of the fence you should stand on when it comes to the glycemic index (GI) issue? Well, you’re not alone. Even though the GI is simply a ranking of how various foods affect blood sugar levels, the use of the GI as a diabetes management tool yields vastly differing opinions across the globe. In the not-so-distant past, the position of the American Diabetes Association (ADA) was that the total amount of available carbohydrate in meals or snacks was more important than the source or type, since it was felt that inadequate evidence was available to recommend a low-GI diet as a primary method for meal planning.1 Meanwhile, in Australia, Canada, France, New Zealand, and the United Kingdom, the GI was being widely used as a tool in diabetes education. The United Nations World Health Organization and the Food and Agriculture Organization recommended in their 1997 expert consultation report on carbohydrates in human nutrition that when looking at foods containing carbohydrate, the GI should be used to compare foods of similar composition with food groups.2 The European Association for the Study of Diabetes Nutrition Group recommended in their 1999 revision of guidelines for the management of diabetes that low-GI foods should be substituted when possible for those with a high GI.2 Diabetes Australia, the Juvenile Diabetes Research Foundation in Australia, and the International Diabetes Institute in Melbourne listed recommendations for the use of the GI in meal planning.2 The GI debate escalated when a meta-analysis of randomized controlled trials was published in Diabetes Care in 2003. The meta-analysis was performed to determine whether low-GI diets compared with conventional or high-GI diets improved overall glycemic control in people with diabetes. The results of the meta-analysis caused many to sit up and take notice, as the researchers concluded that choosing low-GI foods instead of conventional or high-GI foods had a small but clinically useful effect on glycemic control, similar to that offered by pharmacological agents targeted at postprandial hyperglycemia.3 It seems that opinions in the United States may be gradually softening when it comes to using the GI in diabetes management. A recent statement by the ADA reported in Diabetes Care in 2004 held that the use of the GI on overall blood glucose can provide an additional benefit over that observed when total carbohydrate is considered alone, noting that both the amount of carbohydrate and type of carbohydrate in a food effects blood glucose levels.4 Dietitians Dish on the GI Coopersmith seems to speak the sentiments of many U.S. dietitians in the field of diabetes management. Dietitians complain about the limitations of the GI as a tool for diabetes management, especially that the GI does not consider the effects of a typical amount of carbohydrate in a food portion on glycemia. “The GI can be misleading. It doesn’t look at what people realistically consume,” says Sally Brozek, MS, RD, LD, CDE, diabetes nutrition specialist at Piedmont Hospital in Atlanta, who believes that the bottom line for glucose management is total carbohydrates. This limitation of the GI has brought the use of the glycemic load (GL) more into favor with some experts, as GL is the product of the food and amount of carbohydrate in a serving. “Some feel that the glycemic load is more accurate, while others feel it is taking an imprecise method and magnifying it. It, too, is somewhat controversial,” says Brozek. Lauren Bronich-Hall, MS, RD, LD, CDE, diabetes educator at Johns Hopkins Bayview Medical, says, “Evaluating the glycemic load may be more beneficial than simply looking at the index, because it takes into account the quantity of the food consumed. Perhaps more randomized controlled trials that provide consistent benefits to GI and GL will increase its use in the U.S.” Experts call for further research comparing high-GL diets with low-GL diets to understand its relationship to glucose control.4 Dietitians also have issues about the variability that comes along with the GI. The glycemic response to a particular food is highly variable, both within individuals and between individuals, similar to what is seen in an oral glucose tolerance test. There are numerous factors that can affect the GI of a food, such as physical form of the food, ripeness, degree of processing, type of starch, style of preparation, and the specific type or variety of the food. Other variable factors include protein and fat with which the carbohydrate is eaten, prior food intake, preprandial glucose level, and degree of insulin resistance present.4 “The GI is looking at individual foods, not at what they are mixed with. You can see the GI for carrots, but what about when they are mixed with chicken and broccoli?” asks Brozek. Another concern dietitians point out regarding the GI is that some healthy foods are high-GI, spurring fears that patients will completely eliminate a nutrient-dense food from their diet. “Ice cream is a low-GI food, while carrots are high-GI. This can steer people towards unhealthy foods,” points out Brozek. “Patients may perceive or wish to perceive that they should choose potato chips over a baked potato because potato chips have a lower GI,” adds Bronich-Hall. To top it off, the GI does not predict postprandial blood glucose response in individuals with diabetes as well as it does for healthy people.4 “It depends on how the body is using insulin. It really depends on the person’s pancreas, liver, and how insulin is used in the body,” stresses Patricia Vasconcellos, RD, CDE, with the diabetes program at Falmouth Hospital in Massachusetts and ADA spokesperson. “It can be very different in individuals. There are lots of variables. The GI can be used as an education tool, but not all by itself.” Some dietitians who do use the GI as a tool stress the importance of educating patients on self-monitoring blood glucose by journaling their food intake and relating preprandial and postprandial blood glucose numbers to the carbohydrates consumed. “I think that everyone has to learn how their body works and functions by testing blood sugars two hours after they eat. I teach individuals that their best bet is to try it with their normal routine and see how it affects them,” says Vasconcellos. Brozek comments, “We teach patients to determine their own GI. They can check the blood sugar before and after meals and do their own little study.” Of course, this kind of mini self-study and recordkeeping is definitely not a one-size-fits-all approach. Brozek suggests that this method may work for some patients wanting an extra piece to help them fine-tune their diet, while others just simply won’t comply with the extra work. That brings up another complaint dietitians share about the GI and GL—that it is too complicated for a large number of patients who saunter into their diabetic classes. Andrea Conner, RD, CDE, with the University of California, Los Angeles’ Gonda Diabetes Center, suggests, “The GI can be broken down into manageable charts and steps; it can be very user-friendly.” Conner has developed her own exchange lists that she distributes to patients that group the foods into low, moderate, and high categories according to their GI. The Good News About the GI Dietitians also report that news about the GI is spreading, as patients with diabetes are coming into their appointments already asking questions about the GI. Vasconcellos credits the popularity of the GI on our carb-fearing culture. “Our society is so anti-carb, they are afraid to eat carbs,” Vasconcellos says. Brozek notes, “The GI comes up every time we teach a carbohydrate counting class, so more and more people are becoming aware of it.” Giving Good Advice on the GI
“We do discuss GI when a patient comes in who is familiar with it and can handle an extra level of complexity. It’s not an approach the ADA endorses as a sole means of meal planning, but rather used in conjunction with another approach, such as looking at total carbohydrate,” adds Brozek. Perhaps when it comes to making practical suggestions on GI use, we can look to our neighbors for guidance. The Canadian Diabetes Association offers a useful tool for diabetes educators to help patients with diabetes make choices to better control their blood glucose. The approach includes teaching clients that serving size still counts when making low-GI choices, to substitute low-GI carbohydrates for high-GI carbohydrates, to avoid choosing foods based solely on their GI values, and to individualize the educational approach.6 The Canadian dietitians are also getting involved in a project entitled Assessment of the Clinical Utility of the Glycemic Index in Diabetes Management, which seeks to determine the practices of dietitians and diabetes educators with respect to the GI in diabetes management and also hopes to determine the link between the GI and postprandial glycemia in individuals with type 1 diabetes. Part of this process will include a survey mailed to a random sample of dietitians, while other data will be collected from subjects provided with a Continuous Glucose Monitoring System and food records. The study designers believe this will be the first study of its kind.7 “The glycemic index does have some use in
diabetes education; however, like any education, use of GI should
be tailored to the audience,” emphasizes Bronich-Hall. Conner
takes it a step further in her practice. She has found that patients
having an especially difficult time managing their diabetes with
traditional carbohydrate counting may benefit with the added approach
of the GI. “A dietitian will know the positives and negatives
of the GI system and a dietitian is skilled at creating medical
nutrition therapy plans that are nutritionally sound and healthy
for patients with multiple medical conditions,” says Conner.
“If this method were to become more precise and standardized,
it would likely be used as a primary form of medical nutritional
therapy.”
Glycemic Load (GL): The GL of an individual food is the product of the GI of the food and the amount of carbohydrate in a serving.4 The GL builds on the GI to provide a measure of total glycemic response to a food or meal. A typical diet has approximately 100 GL units per day (range 60 to 180). GL = GI (%) x grams of carbohydrate per serving.8 Glycemic Database: The University of Sydney provides a GI database of both GI and GL values at www.glycemicindex.com.
Low-GI Foods — Source: Canadian Diabetes Association9
— Source: University of Sydney, The Glycemic Index8
2. Irwin T. New Dietary Guidelines from the American Diabetes Association. Diabetes Care. 2002;25:1262. 3. Brand-Miller J, Hayne S, Petocz P, et al. Low-glycemic index diets in the management of diabetes. Diabetes Care. 2003;26:2261-2267. 4. Sheard N, Clark N, Brand-Miller J, et al. Carbohydrate (amount and type) in the prevention and management of diabetes. Diabetes Care. 2004;27:2266-2271. 5. Anderson JW, Randles KM, Kendall CW, et al. Carbohydrate and fiber recommendations for individuals with diabetes: A quantitative assessment and meta-analysis of the evidence. J Am Coll Nutr. 2004;23:5-17. 6. Canadian Diabetes Association. The Glycemic Index Useful Tools for Professionals, October 2002. Available at: www.diabetes.ca/Section_Professionals/ng_glycemic.asp 7. Assessment of the Clinical Utility of the Glycemic Index in Diabetes Management, Letter of Intent. Available at http://www.dietitians.ca/cfdr/pdf/CFDR_Letter_of_Intent_MKalergis.pdf 8. The University of Sydney, Glycemic Index Web site. http://www.glycemicindex.com. 9. Canadian Diabetes Association. Glycemic Index - The Index in Depth. May 2002. Available at: http://www.diabetes.ca/section_about/glycemic.asp |
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