GI Load

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Glycemic Index (GI)

The new carbohydrate-classification system known as the Glycemic Index rates the carbohydrate quality in foods according to its immediate effect on blood glucose level.

Thus carbs that break down quickly into glucose during digestion, causing a rapid rise in glucose levels, have a High GI value. Those carbs that break down more slowly, are given an Intermediate or Low GI value.

Designed For Diabetes Treatment

Invented in 1981 by David Jenkins and Thomas Wolever of the University of Toronto, as a tool for the treatment of diabetics who need to maintain stable blood sugar, the Glycemic Index (GI) has now replaced the older method of classifying carbohydrates according to their "simple" or "complex" chemical structure.

GI Shows Us Which Foods Are Best/Worst For Blood Sugar Levels

In order to "use" food, our body first converts it into glucose. This glucose then enters our bloodstream and can be used as needed.

We have a safety mechanism to ensure our glucose level remains relatively balanced. It works like this. If levels fall too low, the brain makes us feel hungry, so we eat food that is turned into glucose. If levels rise too high, the brain tells the pancreas to release insulin into the blood to "mop up" excess glucose.

So far so good. However, the human body was designed in the Stone Age - long before the existence of modern super-refined carb-foods. Some of these super-refined carb-foods are converted into glucose very fast - too fast for comfort. As a result, our blood-glucose shoots up (called a "sugar-spike"). This fools the body into releasing too much insulin.

This mops up too much glucose and our level falls so low that the brain makes us feel hungry again!

Thus, not only do we overeat, but also we can experience excessively high levels of insulin which can over time cause health problems.

The glycemic index helps us to understand which foods are best and worst for controlling our blood glucose levels.

Details of Glycemic Index (GI)

The GI Scale

The glycemic index uses a scale from 1 to 100, which indicates the rate at which 50 grams of carbohydrate in a particular food is absorbed into the bloodstream as blood-sugar. The main reference food (rated 100) is glucose.

GI Rating Categories

The glycemic index divides carbohydrate foods into three categories:

  1. High GI Foods (GI value 70+) - These foods cause a rapid rise in blood-sugar levels.

  2. Intermediate GI Foods (GI value 55-69) - These lead to a medium rise in blood-sugar.

  3. Low GI Foods (GI value 54 or less) - These lead to a slow rise in blood-glucose.

GI Food Testing is Ongoing

Not all foods have been given a GI value, although most food-types are covered. However, due to the way GI is measured using volunteer subjects, results can vary, so GI values for some specific foods are not yet uniformly established.

GI - Diabetes and Weight Control

Although the glycemic index was first designed to assist diabetes patients manage their blood-sugar levels, dietitians and weight experts now use it as a tool to help treat obesity, food cravings and appetite swings, and improve eating habits.

GI Measurement

Measuring the glycemic index or GI rating of a food is conducted under strict conditions, although sampling methods can vary slightly.

  • Portions of GI Food Being Tested - Typically, 10 or more volunteers are given a serving of the test-food containing 50 grams of digestible (available) carbohydrate. The actual portion or serving size of each tested food varies according to how much carbohydrate it contains, based on official food composition tables.

    The smaller the percentage of carbs in the food, the larger the portion needs to be in order to provide the standard 50 gram amount of digestible carbs. Thus in practice, if a food contains a very small proportion of carbohydrate, necessitating a very large test serving size, the test serving is typically scaled down.

  • Blood Tested For Glucose - A sample of blood is then taken from each subject every 15 minutes during the first hour and thereafter every 30 minutes. These blood samples are laboratory-tested for glucose content and the results recorded.

  • Interpretation of Results - The glucose level is plotted on a graph and the results are interpreted using a computer program.

Test Food Results Compared Against Glucose Results

The volunteer's blood-glucose reaction to the food being tested is compared with his/her response to 50g of pure glucose. These comparative tests using pure glucose are typically conducted several times, on several occasions, to provide a mean response.

  • Results Averaged - The average blood sugar response from 8-10 volunteers determines the GI value of that food.

  • GI Rating Categories :

  • Low GI Food - These are foods with a GI rating below 55.

  • Intermediate GI Food - These are foods with a GI rating between 55 and 70

  • High GI Food - These are foods with a GI rating above 70

  • Glycemic Load - Both the type AND quantity of carbohydrate in our food influence the rise in blood glucose. But the glycemic index only rates a standard 50 gram serving size of digestible carbohydrate in a particular food, which may not be appropriate for all foods.

    For example, foods whose serving size contains only a small amount of carbohydrate may in practice be better for blood sugar control than foods whose normal serving size contains a large amount of carbs. Therefore, to provide a more meaningful GI-rating system, researchers at Harvard University invented the term Glycemic Load, which applies the glycemic index to normal food serving sizes.

GI Values: Determining Factors

As we have seen (How Carbs are Digested) the speed at which carbohydrate is broken down in the intestinal tract into simple sugars and ultimately glucose, is usually dependent on the specific structure of the carb in question (meaning: how easy is it for the digestive enzymes to gain access to the carbohydrate) but can also be affected by other factors which interfere with the action of enzymes.

  • Physical Structure

  • The physical characteristics of the carbohydrate is a major factor in determining its likely GI value.

  • The small particle size of finely ground flour gives digestive enzymes great surface area to attack and metabolize the bread. By comparison, stone-ground flour has a larger particle size and consequently a lower GI value.

  • A "puffed up" or "swollen" carbohydrate is more rapidly metabolized to glucose and has a higher GI value than less enlarged carbs. For example, fluffy white bread typically has a much higher GI value than denser rye breads.

  • A carbohydrate surrounded by fiber, like that in vegetables, beans, nuts and seeds, is better protected from rapid attack by digestive enzymes and has a lower GI value than other carbohydrates.

  • Very refined carbs (eg. many breakfast cereals) typically have most of their 'natural' fiber and other indigestible constituents removed. Result? These carbs tend to be rapidly metabolized into glucose.

  • Molecular Structure - Carbs with a simple molecular structure, like monosaccharide, are metabolized to glucose much more rapidly than more complex polysaccharides.

  • Starches - An interesting example of how a carb's chemical structure can affect GI rating is seen in various starches. Starch comes in two forms, amylase and amyl pectin. Starchy carbs typically contain a mixture of the two types, but the molecular structure of amylase is tighter and more compact, thus less easy to breakdown than amyl pectin, whose structure is more extended and more vulnerable to attack from digestive enzymes. Thus, carbohydrates like beans, lentils, basmati rice with a high ratio of amylose-to-amylopectin tend to have lower GI values.

Other Factors That Influence GI Rating

  • Cooking - Pasta has a medium-glycemic-index value of 40-50. This may be lowered by cooking it for less time (al dente). Al dente pasta resists the effect of digestive enzymes more than regular cooked pasta and so has a lower GI.

  • Presence of Soluble Fiber in the Gut - Soluble fiber in the stomach or small intestine inhibits interaction between carbohydrate and the digestive enzymes, whose job is to break down the carb into glucose. One reason why it's a good idea to include a high fiber food with every meal. It helps reduce the GI value of the meal.

  • Presence of Acid - Acid in the stomach during digestion (eg. in the form of lemon juice) tends to slow down stomach emptying and thus the conversion of carbs to glucose.

  • Presence of Fat - The same applies to fat. Like acid, fat retards stomach emptying and thus glucose metabolism. This explains why certain candy bars have relatively low GI values, despite their refined nature and simple physical structures.

  • Presence of Sugar - A concentration of sugar in the stomach and intestine typically inhibits the effects of digestive enzymes, as it attracts water which would otherwise help in glucose metabolism.

Glycemic Load Explained

  • Glycemic Index Rates 50 Gram Portions of Carbs - As we have seen (How GI is measured) the glycemic index rates how rapidly a particular food raises blood-glucose. The test is performed using a food-serving that contains 50 grams of digestible carbohydrate. While providing valuable comparative data on the glycemic effects of different foods, this test is not ideal. Why not? Because it doesn't take into account the fact that some foods contain a lot more carbohydrate than others.

  • Different Percentages of Carbohydrate - Take two foods: assume both have GI values of 80, making them high GI foods. On this basis, we should eat both relatively sparingly. But suppose one of them contains 75 percent carbohydrate, whereas the other is only 5 percent carbohydrate. These foods are now quite different. The 75 percent carb food should be eaten more sparingly. The glycemic index does not allow for different carb percentages.

  • Glycemic Load Applies GI to Food Serving Sizes - In response to this problem of carbohydrate percentage, researchers at Harvard University invented the idea of Glycemic Load, which applies the glycemic index to normal food serving sizes. The glycemic load of a particular food rates the effect of a normal serving-size of that food on blood glucose levels.

How Glycemic Load is Calculated

The formula for calculating glycemic load is simple. Multiply the GI value of a food by the amount of carbohydrate per serving and divide the result by 100.

Example No 1

Spaghetti has a GI value of 40

A serving (1 cup) contains 52 grams of carbohydrate.

The glycemic load of spaghetti is: (40 X 52) divided by 100 = 20.8

Example No 2

An apple has a GI value of 40

A serving (medium size apple) contains 15 grams of carbohydrate.

The glycemic load of an apple is: (40 X 15) divided by 100 = 6

Calculating GI Values For Meals

Most of the time we don't eat servings of individual carbohydrate-type foods: we eat meals with a variety of foods containing varying amounts of carbs, as well as protein, fat and fiber. Thus in practice, for optimum blood-glucose management, we need to know the glycemic value of a meal, rather than simply the GI of individual foods.

How to Measure the Glycemic Index Value of Meals

To calculate the GI value of a meal, you need to know two things:

  • The total grams of carbohydrates in the meal.

  • The percentage of the carb-total contributed by each food.

Once you know this data, which is typically obtainable from most food composition or nutrition tables, the GI calculation for a meal is simple:

Multiply the GI value of each food by their percentage of total carbohydrate. Add up the totals, to get the GI value for the meal.

Calculating GI For a Simple Meal

Suppose you eat 2 slices (2oz) of toast and a glass (4oz) of milk.

The toast contains about 26g of carbohydrate; milk about 6g of carbs.

The total carb content is 32g. (81% from bread; 19% from milk)

The GI of bread is about 70; the GI of milk is about 28.

Calculation = GI X Percentage of carb contribution

Toast: 70 X 81% = 57

Milk: 28 X 19% = 5

Total: 57 + 5 = 62

The GI value of the meal is 62.

Calculating GI Value of Meals Not Always Possible

If we eat meals with non-standard foods that either do not have a GI rating, or are cooked in ways that have not been tested for GI effect, it is not possible to calculate a precise GI value for them. Even so, by using food composition tables and GI rating lists, it is possible to arrive at ballpark GI values for most meals.

Reduce GI of Your Meal

First of all, remember that GI values only apply to foods containing carbohydrate. Therefore, if the only carbohydrate in a meal has a high GI, then the GI of the whole meal is high. For example, if the only carb in your meal is bread, the GI of that meal will be 70. Therefore, to reduce the GI value of a meal, you must include lower-GI carbs. Here are some healthy suggestions for lowering GI value.

  • Low-GI Breakfast Suggestions

    • Add All-Bran or oats to your breakfast

    • Eat bread with a lower-GI, like rye or any whole grain variety

    • Add low-fat fruit yogurt

  • Low-GI Lunch Suggestions

    • Add chopped vegetables (eg. celery, carrot sticks, tomatoes)

    • Add nuts (eg. peanuts, cashews) or dried fruit (eg. apricots)

    • Add fruit (eg. apple, berries)

    • Add low-fat fruit yogurt

  • Low-GI Dinner Suggestions

    • Add plenty of vegetables (treat meat as an extra, not the main item)

    • Add beans, lentils

    • Add (or finish with) fruit (fresh, stewed or baked)

How to Lower Glycemic Effect of a Meal Even Further

As we have seen (What Determines Glycemic Effect), the presence of certain substances in the stomach and intestinal tract, during digestion (eg. fiber, acid or fat), can reduce the speed at which carbs are converted to glucose and thus reduce glycemic effect. By adding these items to our meal, we can lower it's glycemic impact on our system.

  • Add Soluble Fiber to Your Meal - Soluble fiber (eg. from oats, apples, citrus fruits) in the stomach or small intestine inhibits interaction between carbohydrate and the digestive enzymes, whose job is to break down the carb into glucose.

  • Add Food Acids to Your Meal - Acid (eg. from lemon juice or vinaigrette) in the stomach during digestion slows down stomach emptying and thus the conversion of carbs to glucose.

  • Add a Little Healthy Oil - Like acid, fat/oil retards stomach emptying and thus glucose metabolism. However, all oil is high in calories, while not all oil is healthy. So choose carefully, and add any oil sparingly. The best fats/oils are uncooked and unrefined. Choose ones like extra virgin olive oil, wheat germ oil, canola, flaxseed (linseeds).

Creating Lower GI Meals: Summary

The GI effect of high-GI foods can be reduced by eating them together with low GI foods in a balanced meal. Adding soluble fiber and/or food acids also helps lower GI. When using fats or oils, choose carefully.

Low Carb vs. Low GI

  • Low Carb Diet Plans Vary - There is considerable variation in the level of carbs permitted by popular low-carb diet plans. Some, like Atkins Diet, are deliberately ketogenic - they starve the body of carbohydrate in order to force it to burn fat for fuel. For severely overweight or obese patients who prefer high protein eating, this approach might be fine. Even for moderately overweight people, the Atkins ketogenic method can be highly effective in reducing weight in the short term and good for motivation. Other low-carb plans, like the Zone Diet or South Beach, are not ketogenic like Atkins. They permit a wider intake of carbs and may be regarded as healthier. See Recommended Low Carb Diet

  • All Carbs Are Not Bad For Weight Loss Health - The low carb diet craze is fuelled by the idea that "all carbs are bad for weight control". Therefore the less carbs we eat, the better. But this notion is misleading, even dangerous. The truth is, the leanest and longest living people in the industrialized world are the Japanese whose diet is dominated by carbohydrates and is low in fat. High carb foods like grains, rice, and vegetables are daily staples of the Japanese diet, and intake of high protein, high fat animal products is minimal. Yet Japan has one of the lowest rates of obesity, heart disease, cancer and diabetes in the world. Promoters of the "all carbs are bad for weight loss" viewpoint know this perfectly well - they know the problem lies in high-GI carbohydrates and junk food - but this does not get attention-grabbing headlines.

  • Low-GI Diet Plans Tackle the Real Issue - A low-GI eating plan does not seek to improve your health and weight by restricting how much carbohydrate you should eat. Instead, it advises what type of carbohydrate to eat. It recommends lower-GI carbs that boost health and therefore weight reduction. Unlike the low-carb method, the low-GI dietary method is backed by a wide range of clinical studies, conducted all over the world, that demonstrate it is good for long term health.


A healthy type of low-carb diet is fine for fast initial weight loss. Rapid weight reduction (even if largely water) can boost motivation and diet compliance. However, significant carb-restriction should be short-term.

Most experts consider a low-GI diet to be healthier than regular low-carb diets, as it delivers all the benefits of healthy carbohydrate without the blood-glucose problems and other health risks of high-GI carbs.

The above opinionated views and information serves to educated and informed consumer .  The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. .It should not replaced professional advise and consultation.  A licensed physician should be consulted for diagnosis and treatment of any and all medical conditions 

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