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Diabetes Diet - Glycemic Index and Glycemic Load

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Glycemic Index and Glycemic Load

By Nina Nazor

What happens after you eat?

Your blood glucose levels after a meal are most affected by the amount of carbs in your diet and the amount of insulin secretion and its action on your tissues.

The nutrient that has the greatest effect on blood glucose is carbohydrate. Fat and protein, for example, don't affect so much glucose levels and fat, on the contrary, slows glucose absorption.

Both, the quantity and the type or source of carbs of the food you eat, influence your glucose levels after having a meal.

In recent years, two methods have been shown to be good tools for meal planning and diabetes, they are the glycemic index and the glycemic load.

What is the glycemic index?

The glycemic index measures the change in blood glucose concentrations after eating foods that contain carbs. Some foods cause a very rapid increase in glucose levels while others have smaller effects.

The glycemic index ranks food containing carbs comparing them according to the increase in blood glucose (over the fasting level) that is observed in the 2 hours after eating certain amount of carbs in an individual food. This value is compared with the response to food of reference like glucose or white bread, which contains the same amount of carbs

What is the glycemic load?

The glycemic load of a food takes into account the glycemic index of a specific food as well as the amount of carbs in a serving of that food. In summary, the glycemic index is a qualitative measure and the glycemic load is a quantitative one.

How can you calculate the glycemic effect of a food?

Both, the amount of carbs as well as the type of carbs in a food have an influence on blood glucose level.

This means that the specific type of carb (e.g., starch versus sugar) of a specific food does not always predict its effect on blood glucose levels.

Different factors in each food can affect its influence on blood glucose concentrations. For example, the physical form (i.e., juice versus whole fruit, mashed potato versus whole potato), the ripeness, the degree of processing, the form of preparation and the specific variety of the food.

The more natural and less processed the food is, the low seems to be the effect on glucose levels.

You might like to try the Glycemic Index and Glycemic Load Calculator from the University of Sidney, in Australia.

Is the type or the total amount of carbs more important?

Both the amount and the source of carbs account for after meals glucose levels. In a recent study carb content (total grams) alone explained 68% of the variation in glycemic load, while the glycemic index of the food explained 49% in a recent study.

Another study showed that the amount of carbohydrate ingested (whether in a single food or as part of a meal) accounted for 57–65% of the variability in glucose response, while the glycemic index of the carbohydrate explained a similar amount (60%) of the variance.

Together, the amount and the glycemic index of carbohydrate accounted for 90% of the total variability in blood glucose response, indicating the cumulative effect of both factors on postprandial blood glucose concentration.

Does the glycemic index work for only one food and not for mixed meals?

The glycemic index takes into account only the type of carbs, ignoring the total amount of carbs in a typical serving, although both the type and amount of carbohydrate influence after meals glucose levels and insulin response of a given food.

The glycemic index only measures the response to an individual food consumed in isolation and does not predict blood glucose concentrations when that food is part of a meal.

The glycemic effect of mixed meals can be calculated with some accuracy by summing up the glycemic index of the component foods individually, although some studies have not found a direct relationship between calculated and measured glycemic index of mixed foods.

Are there research studies about the glycemic index and diabetes?

Brand-Miller and colleagues recently conducted a meta-analysis of available studies on this topic. Their findings indicate that implementing a low–glycemic index diet lowered A1C values by 0.43% when compared with a high–glycemic index diet. The findings were similar in both type 1 and type 2 diabetes.

These findings are also consistent with the results of the EURODIAB study, a cross-sectional study involving nearly 3,000 subjects with type 1 diabetes in 31 clinics throughout Europe.

Are there research studies about the glycemic load?

Recently, Brand-Miller and colleagues published data that examined the relationship between glycemic load, blood glucose level, and insulin response following ingestion of individual foods. Stepwise increases in glycemic load for a range of foods produced proportional increases in blood glucose and insulin. In addition, the investigators demonstrated that portions of different foods with the same glycemic load produced similar glycemic responses.

These findings demonstrate that calculated glycemic load can predict the blood glucose response to individual foods across a range of portion sizes. These are important findings in establishing a physiological basis for glycemic load; however, it will be necessary to examine the effect of the glycemic load of a mixed meal on postprandial glucose and insulin levels, as well as the effects on day-long glucose and insulin levels.

Why not eliminate all carbs in the diet of people with diabetes?

Dietary carbohydrate are very important because they are the main source of fuel in our bodies as well as sources of many nutrients, like vitamins and minerals as well as fiber.

Low carb diets are not recommended for people with diabetes. Recently, the National Academy of Sciences–Food and Nutrition Board recommended that diets provide 45–65% of calories from carbohydrate, with a minimum intake of 130 g carbohydrate/day for adults.

What is the conclusion then?

·  Low carb diets are not recommended. 45 – 65% of total calories should come from carbs and a minimum of 130 g a day. If you want to cut carbs, try not to reduce more than 45% of your total calories.

·  Both the amount (grams) of carbohydrate as well as the type of carbohydrate in a food influence blood glucose level.

·  If you have diabetes, carbohydrates are not so bad for you, unless of course you are eating way too many and your blood glucose levels get very high. Choosing fresh vegetables and fruits, whole-grain foods, checking the portions you eat and learning how to count your carbs will help you keep diabetes under control.

Source: Nancy F. Sheard, et al. A statement by the American Diabetes Association, Dietary Carbohydrate (Amount and Type) in the Prevention and Management of Diabetes, Diabetes Care 27:2266-2271, 2004.