Glycemic Response

The glycemic index (GI) concept was developed in 1981 as a way to rank carbohydrate-containing foods based on their potential to raise blood glucose.(1) GI measures the extent to which a specific carbohydrate-containing food raises blood glucose. Carbohydrate foods are classified based on how they compare to a reference food which is either pure glucose or white bread. Foods classified as “high GI” raise blood glucose more than a food with a “medium GI” or “low GI”. Rapidly digested and absorbed carbohydrates generally have a fast and high impact on blood glucose, resulting in the highest GI and the sharpest rise in blood glucose after they are eaten. High GI foods would be appropriate to have after an endurance exercise or for someone suffering from hypoglycemia, or low blood sugar. Slowly or incompletely digested carbohydrates such as pasta or legumes have a low GI. In these cases, glucose is released gradually into the blood with a slow and steady increase in blood glucose after eating.(2)

 

 

Foods that contain fat and/or fiber affect the overall glycemic response of a food by slowing down gastric emptying which in turn slows down the digestion of carbohydrates.  This is similar to the lower glycemic response observed when a meal contains fat, protein and/or carbohydrate. Cooking or processing of a food expands and softens starch based foods, which speeds up the rate of digestion. Cooking or processing foods may raise the GI of that food, e.g. cooked carrots have a GI of 92 which is considered high, where raw carrots have a GI of 16 which is considered low.(3) Other factors contributing to a higher GI include ripeness and storage time, cooking method and type of carbohydrate.

 

The overall glycemic response of a meal may be affected by the type of food that is eaten with the carbohydrate. If a high GI food (such as white bread) is combined with a low GI food (such as low fat yogurt) blood glucose will benefit by a more balanced fluctuation of blood glucose and a lower GI.

 

Although GI can represent a carbohydrate-containing food’s effect on blood glucose, portion sizes are still an important consideration for blood glucose management and for losing or maintaining weight. Glycemic load measures the degree of glycemic response and insulin demand elicited by a given amount of a certain food. Glycemic load reflects both quality and quantity of dietary carbohydrates.(4)  GI is one factor which may be used to evaluate the nutritional quality of foods and ranks carbohydrates based on immediate blood glucose response.(4) There are other factors that contribute to nutritional quality as well and all of these factors should be considered when determining overall healthfulness. Many healthy food choice options may have a higher GI than their less nutritive counterparts.

 

 

Low GI foods have a GI range of 55 or less and include most fruits and vegetables, pasta, legumes, milk, and pumpernickel bread. Medium GI foods have a GI range of 56 – 69 and include foods such as whole wheat products, brown rice, table sugar, sugar confections, regular soda and cheese pizza. High GI foods have a GI range of 70 – 99 and include baked potatoes, watermelon, and graham crackers. A GI of 100 represents pure glucose.(3) For a full list on foods and their GI value, visit: www.glycemicindex.com.

 

 

The concept of GI is most frequently used in diabetes patient education and is presented in different ways, either as table values or otherwise integrated into dietary recommendations. In 2008, the American Diabetes Association (ADA) published a position statement on “Standards of Medical Care in Diabetes.” ADA states among its recommendations for medical nutrition care for people with diabetes:

 

“Monitoring carbohydrate intake, whether by carbohydrate counting,exchanges, or experience-based estimation, remains a key strategyin achieving glycemic control.  For individuals with diabetes,the use of the glycemic indexand glycemic load may providea modest additional benefit forglycemic control over that observedwhen total carbohydrateis considered alone.”(5)

 

The significance of low GI food to healthy people is still an ongoing discussion within the scientific community and official bodies in different countries. Health problems associated with being overweight are a major concern for countries all over the world. The World Health Organization and Food and Agriculture Organization of the United Nations (WHO/FAO) have stated that, globally, overweight is a bigger problem than undernourishment. They have recommended that people in industrialized countries base their diets on low GI foods to prevent lifestyle-related diseases.(6)

 

Conversely, the 2005 US Dietary Guidelines Advisory Committee concluded that “Although the use of food with a low-glycemic index may reduce postprandial glucose, there is not sufficient evidence of long-term benefit to recommend general use of diets that have a low-glycemic index.”(7) Thus, the clinical and practical value of the GI merits to be further studied, and more evidence is needed before adding information regarding low GI food to public recommendations on an evidence-based level.

 

Consistent consumption of high GI foods may increase risk factors associated with obesity, type-2 diabetes, and heart disease. Conversely, the consumption of foods that elicit low glycemic responses may help to reduce such risk factors. A lower glycemic response is thought to correspond to less insulin release, better long-term blood glucose control and a reduction in blood lipids. While there is no definitive proof that reducing glycemic impact will prevent disease on an individual basis, some research suggests that reducing the glycemic effect of the diet may reduce disease risk. A growing number of studies suggest that reducing the glycemic impact of the diet may help consumers eat fewer calories, however not all investigators and reviewers have reached the same conclusion.(8)

 

Two papers in Obesity Reviews addressed the question of whether obese patients should be advised to follow a low glycemic index diet. Pawlak et al. concluded that obese patients should be advised to follow a low GI diet based on a concern that the reduction in fat intake widely advocated in the prevention and treatment of obesity has the potential to encourage an increase in the consumption of high GI carbohydrates. (9) 

 

Raben concluded that obese patients should not be counseled to follow a low GI diet because there is no evidence at present that low-GI foods have a better or different effect than high-GI foods when considering long-term body weight control. However, long-term studies where ad libitum intake and fluctuations in body weight are permitted, and the diets are similar in all variables except GI, have yet to be conducted.(10) Raben noted that low GI is recommended in the management of diabetes. A systematic review was undertaken of intervention studies comparing high and low GI foods and diets on appetite, food intake, energy expenditure and body weight.  Of 31 short-term studies, low GI was associated with a greater feeling of fullness or reduced hunger in 15. No difference was seen in 16.  In 20 longer term studies, weight loss occurred in four low GI and two high GI trials however it should be noted that many of the diets had the same number of calories.(10) 

 

A 2007 literature review, “Glycaemic response to foods: Impact on satiety and long-term weight regulation,” published in Appetite, analyzed 32 short and long-term studies relating to GI and satiety. The review concluded, “While there is evidence from short-term studies that low-glycaemic foods (low-GI in particular) have higher satietogenic properties than high-glycaemic foods, the available long-term studies do not allow conclusion about the regulation of energy intake and body weight. The demonstration of the long-term benefit of low-GI foods and diets with respect to their effect on satiety requires further studies.” The results further conclude, “Based on these data, one can legitimately say that wordings such as, ‘This is a low-GI food. Low-GI foods help one to feel fuller for longer than equivalent high-GI foods’ are substantiated health claims. By contrast, claims on a longer-term health benefit of low-glycaemic diets based on energy intake and body weight regulations remain unsubstantiated.”(11)

 

In summary, the low GI diet has emerged as in interesting tool in reducing risk of lifestyle diseases. Although there is some evidence supporting a potential protective role of low GI foods against chronic diseases, more evidence is needed to further evaluate its clinical significance and value in healthy people.  Finally, it should always be kept in mind that the GI concept is only one measure of many factors which together indicate a healthy diet. 

 

 

Sugar alcohols (polyols) such as lactitol, xylitol, isomalt, erythritol and maltitol produce a low glycemic effect, as do fructose, isomaltulose, oligofructose, inulin, polydextrose, resistant starches and other dietary fibers. These ingredients may be used to completely or partially replace sucrose, glucose and high GI carbohydrates such as starch and maltodextrin in a wide range of processed foods, including dairy products, baked goods and confectionery. 

 

 

Traditionally, GI has been used as a tool to assist people with diabetes in controlling their blood glucose. In recent years it has gained popularity among the general population as an effective means of monitoring carbohydrate intake.

 

GI should not be seen as a diet, but rather a strategy to achieve quality nutrition that becomes a lifestyle. With a reduction in the glycemic impact of the diet, a reversal in the trend towards ‘lifestyle’ related diseases may be observed. A low GI diet may play a key role in the prevention of lifestyle related diseases and conditions as well as help maintain steady post meal blood glucose levels. More well-controlled clinical trials are needed to establish the association with greater certainty.

 

 

Glycemic Index (GI) – Glycemic Index (GI) is a ranking of carbohydrate containing foods according to their effect on blood glucose levels. Carbohydrate foods that are digested quickly and rapidly release glucose into the blood stream have a high GI; those that are digested slowly or partially and gradually release glucose into the blood stream have a low GI.

 

Glycemic Load (GL) – Glycemic load is a measure of the degree of glycemic response and insulin demand elicited by a given amount of a certain food. Glycemic load reflects both quality and quantity of dietary carbohydrates.

 

Glycemic Response – Glycemic responseis not formally defined, but generally refers to the changes in blood glucose after consuming a carbohydrate-containing food.