How to calculate glycemic index?

The Bigger Picture: Glycemic Load and a Good Diet

The glycemic index shouldn’t be the only thing you consider when making choices about what to eat. The fact a food has a low glycemic index doesn’t mean it’s super-healthy, or that you should eat a lot of it. Calories, vitamins, and minerals are still important.

For example, potato chips have a lower glycemic index than oatmeal and about the same as green peas. But oatmeal and green peas have more nutrients.

Portion sizes matter, too. The more of whatever kind of carbs you eat, the more they’ll affect your blood sugar. That’s what the glycemic load tells you. It’s a number you may see along with the glycemic index in lists. Think of it as the glycemic index for a specific amount of that food.

Glycemic load helps you account for both the quantity and the quality of your carbs at the same time. Less than 10 is low; more than 20 is high.

For a diet with a lower glycemic load, eat:

  • More whole grains, nuts, legumes, fruits, vegetables without starch, and other foods with a low glycemic index
  • Fewer foods with a high glycemic index, like potatoes, white rice, and white bread
  • Less of sugary foods, including candy, cookies, cakes, and sweet drinks

You can still eat foods with a high glycemic index. Just enjoy them in smaller portions, and offset them with nutritious, low-glycemic index foods when you do.

Glycemic Load: The Key to a Smarter Diabetes Diet


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Once you’ve mastered counting carbs, just a little more math will let you fine-tune your diabetes diet plan. Figuring out the glycemic load of a food can help you craft a menu that won’t put your blood sugar on a roller coaster.

Understanding Glycemic Index vs. Glycemic Load

Beyond carbohydrate counting, you might already be looking at the glycemic index (GI) number, which tells you how quickly your blood sugar might spike after eating a certain type of food. The GI of carb-based foods is a measurement of how quickly blood sugar rises after eating in comparison to a slice of white bread, which has a GI of 100. In general, the lower the GI number, the less dramatically the food will affect blood sugar. Low-GI foods are generally 55 or less.

However, calculating the glycemic load (GL) can provide an even more accurate picture of what that food will do to your blood sugar. “Glycemic load accounts for carbohydrates in food and how much each gram of it will raise your blood sugar level,” says Krista Wennerstrom, RD, food and nutrition services director at Thorek Memorial Hospital in Chicago.

To find a food’s GL, multiply its GI by the number of carbohydrate grams in a serving, and then divide by 100. A low GL is between 1 and 10; a moderate GL is 11 to 19; and a high GL is 20 or higher. For those with diabetes, you want your diet to have GL values as low as possible.

As an example, an average cake-type doughnut has a GI of 76 and 23 carbohydrate grams. Multiply 76 by 23 and then divide by 100, and you get 17.48, which is close to the top of the moderate range for glycemic load.

Taking the GL of carb-rich foods into account can have a direct impact on diabetes control. There’s a strong correlation between eating a high-GL diet and the risk for ongoing high blood sugar, according to research in the April 2014 issue of the European Journal of Clinical Nutrition, which reviewed the dietary habits of 640 adults with type 2 diabetes.

Putting Glycemic Load to Work for You

The strategy for effectively using glycemic load to evaluate your diet requires some research and math — this is where the trusty calculator on your smartphone can come in handy. Begin by focusing on the carb-rich foods you eat most often. Assess the GL of your favorite foods and, where needed, find lower GL substitutions where possible, says Patrice Atencio, MEd, RD, CDE, a dietitian with the East Carolina University Physicians Endocrinology Program in Greenville, N.C. “I have worked with some clients who want to have very good blood sugar control, and this is a great approach for them.” You can also use existing tables to make this easier, such as the one listed in the journal Diabetes Care.

Here are some sample meal swaps based on the GL of common foods:

Breakfast: Choose a serving of an all-bran cereal, which has a GL of 12, instead of corn flakes, which has 24 GL. Add a serving of milk, with 3 GL, and berries.

Lunch: Instead of a ham-and-cheese sandwich on white bread, which has a GL of more than 10 per serving, go for a wheat tortilla with refried beans and salsa, which comes in at a 6 GL. Add a side salad or fruit, such as an orange with 4 GL, to fill out the meal.

Dinner: Skip the two slices of pizza — 18 to 24 GL — and have instead a serving of baked fish, a side of whole grains at 17 GL (rather than the 23 GL of white rice) and cooked vegetables.

Snacks: Consider a serving of cashews with 3 GL rather than the GL of 15 in some chocolate bars.

Wennerstrom emphasizes that calculating GL isn’t for everyone, and it’s not always easy, such as when you’re out somewhere and faced with new foods. In those instances, the closer you can get to choosing fresh whole foods, such as salad, the more favorable your GI and GL numbers are likely to be. But when in doubt, ask, she says. Many facilities have a dietitian who can be reached for advice, or your diabetes educator can help.

Glycemic load is a measure that takes into account the amount of carbohydrate in a portion of food together with how quickly it raises blood glucose levels.

Should people with diabetes eat a Glycaemic Index diet?

Whereas the Glycemic Index is a good way of making food choices, Glycemic load helps to work out how different sized portions of different foods compare with each other in terms of their blood glucose raising effect.

How is Glycemic load worked out?

The Glycemic load (GL) isworked out by the following formula:

  • GL = GI x carbohydrate / 100

To work with this equatio, you will need to know:

  • The Glycemic Index (GI) of the food found by referring to a table of Glycemic Indexes for different foods
  • The amount of carbohydrate in that quantity of food

Example: What is the Glycemic load of a slice of whole grain bread?

  • Glycemic Index of whole grain bread = 45
  • Carbohydrate content of a slice of bread = 18g

Note these figures are examples.

The GI and carbohydrate values may vary slightly between different types and slice sizes of whole grain bread.

What counts as a high and low Glycemic load?

The University of Sydney defines low, medium and Glycemic loads as follows:

  • Low Glycemic load (low GL): 0 to 10
  • Medium Glycemic load (med GL): 11 to 19
  • High Glycemic load (high GL): 20 and over

How useful is Glycemic load?

Glycemic load can be useful for people with diabetes to assess which quantities of which foods are likely to be suitable for maintaining good blood glucose levels.

Example of calculating Glycemic load

This can be illustrated by another example: Jim is going to have roast chicken for dinner and is thinking of having it either with white rice or couscous.

Jim has enough white rice to make a 130g (when cooked) portion of rice which will provide 40g of carbohydrate. White rice has a Glycemic index value of 85. He also has enough couscous to make a 200g serving of couscous which will also provide 45g of carbohydrate. Couscous has a Glycemic index value of 60.

  • Glycemic load of white rice portion
    = GI x carbohydrate / 100
    = 85 x 40 /100
    = 34
  • Glycemic load of couscous portion
    = GI x carbohydrate / 100
    = 60 x 45 /100
    = 27

So, Jim sees that even though the smaller portion of white rice has less carbohydrate, the portion of couscous actually has a lower Glycemic load. The Glycemic load calculation tells Jim that the portion of couscous, despite being larger and containing slightly more carbohydrate, is less likely to cause as sharp a rise in his blood sugar levels as the portion of white rice.

Making use of Glycemic load

Glycemic load can involve a certain amount of calculation which may not be practical for everyone, however, those with time to get the calculations correct may find Glycemic load to be a helpful extra tool in choosing which foods and which portions are suitable for maintaining good blood glucose levels

Assessing the Glycemic load of foods can be particularly useful if you have a specific meal quite often or if you are thinking of trying a new meal but are not sure how it may impact on your blood glucose levels.

Note that different people with diabetes will have different tolerances to the carbohydrate in food. Some people may be able to comfortable tolerate meals with a medium Glycemic load, whereas other people may find that they can only tolerate low Glycemic load values.

If you have access to blood glucose testing supplies, you may wish to test which Glycemic load values allow you to keep your sugar levels within the recommended guideline blood glucose values A good way to assess the effect of a particular meal is to test your blood glucose before eating, 2 hours after eating and again 4 hours after eating.

  • Read more about pre and post meal blood glucose testing

Glycemic Index & Load Diet Assistant is an app that lets you easily browse, search for, and display the Glycemic Index for different foods. The application also helps in keeping a body weight and blood glucose levels measurement logs. Additionally you can access Glycemic Load and carbohydrates contents in foods. There’s also a calculator of the Glycemic Load in a given serving. Knowing these values and following a low-carb diet like Montignac, Paleo, Atkins, low-GI and similar, helps avoid weight gain or obesity and lower the risk of diabetes, coronary heart and age-related health diseases.
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The free features of the app are:
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GI means Glycemic Index. It is a number associated with a particular type of food to indicate the food’s effect on a person’s blood glucose (blood sugar) level. The number typically ranges between 50 and 100, where 100 represents pure glucose, an equivalent amount of pure glucose.
The Glycemic Load (GL) of food is a number that estimates how much the food will raise a person’s blood glucose level after eating it. It can be used to apply the Glycemic Index to dieting by connecting the GI number with carbohydrates content in a given serving. It gives an estimation on how much a serving size of food is likely to increase blood-sugar levels.
Net carbs are total carbs minus fiber which is indigestible thus it is considered not to raise blood sugar levels.
BMI is used to assess health risks and body structure but does not take in consideration muscular mass so it can sometimes be inaccurate, for instance in the case of athletes or pregnant women.
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Glycemic Index Calculator

About the tool

The glycemic index calculator offers information about the effect of food on blood sugar levels through the glycemic value of aliments from different categories: fruits, vegetables, legumes, nuts, grains, pasta, bread, bakery products, dairy, meals, sugar types, treats and beverages.

Once some foods are selected, the calculator will offer the GI value of each of them. For each category of foods, one item can be selected at a time.

The GI value offered refers to an average portion which for fruits and vegetables would be around 150 g, for other foods would be 100 g and for beverages, about 250 mL.

What is the glycemic index?

The GI is a scale that rates carbohydrate rich foods based on their effect on blood glucose levels. Pure glucose is taken as reference for the GI of 100.

Whilst foods with high GI increase blood glucose levels fast, those with low GI absorb glucose slower.

In the case of the first, the body is subjected to serious travail to absorb the glucose while in the case of the second, the body has time to adapt the regulatory measures to make use of the absorbed glucose.

The three categories of GI are:

■ Low GI: values below 55;

■ Medium GI: between 56 and 69;

■ High GI: values above 70.

The glycemic index of foods is most commonly used in the management of diabetes, however, health conscious people can use the calculations to keep their sugar levels constant.

During periods of increased mental and physical activity, high GI aliments can help the body meet the increased demands. However, their consumption should not become a habit.

Table of GI values

Category GI range Product GI value
Fruits Low Cherries 22
Medium Banana 58
High Watermelon 72
Vegetables Low Sweet potato 48
Medium Beetroot 64
High Parsnips 97
Legumes&Nuts Low Red lentils 26
Medium Broad beans 63
Grains&Pasta Low Fettuccine pasta 32
Medium Sweet corn 60
High White rice 76
Bread&Bakery Low English Muffin bread 45
Medium Croissant 67
High Wheat flour pancakes 80
Dairy&Egg Low Whole milk 27
Medium Yoghurt 57
Meals Low Baked beans in tomato sauce 48
Medium Mashed potato 67
High French fries 75
Sugar&Treats Low Maple syrup 52
Medium Sugar 65
High Waffles 72
Beverages Low Apple juice 40
Medium Lemonade sweetened 58
High Rice milk drink 92

1. Atkinson FS, Foster-Powell K, Brand-Miller JC International tables of glycemic index and glycemic load values: Diabetes Care 31. 2008.

2. Glycemic Research Institute. (2006-2010) Glycemic Index Defined.

How can I calculate the glycemic index (GI)?

The glycemic index (GI) provides a numerical value that expresses the rise in blood glucose after eating a particular food item. The GI is computed in two ways because there are two standards of comparison. The first standard to be developed was based on the rise in blood sugar seen with the ingestion of glucose, which was given a value of 100. Today, this glucose standard has largely been abandoned by the scientific community in favor of the more accurate starch standard. In the starch standard, a 50 gram portion of white bread made using refined flour (the bread most commonly eaten in the United States) is given the value of 100. White bread was selected as the new standard because the glycemic response to white bread is more reliable than the response to glucose. This is because glucose attracts water, an effect called osmolarity, which can delay gastric emptying and misrepresent the insulin response. In addition, white bread stimulates more insulin activity than glucose. Using either standard, the glycemic index ranges from about 20 for fructose and whole barley to about 98 for a baked potato. The insulin response to carbohydrate-containing food is similar to the rise in blood sugar.
The glycemic load (GL) takes the glycemic index into account but gives a more complete picture of the effect that a food item has on the blood sugar level because it also considers the amount of carbohydrate in the food.

Glycemic Index, Glycemic Load, and Glycemic Response Are Not the Same

The paper by Hodge et al. (1) published in the November 2004 issue of Diabetes Care aptly contrasts the potential benefits of moderately high-carbohydrate diets with a low glycemic index (GI) versus diets that have a lower glycemic load (GL) by virtue of a low carbohydrate content. In their prospective analysis of a cohort of ∼36,000 adults followed for 4 years, Hodge et. al found that higher-carbohydrate diets were associated with a lower risk of development of type 2 diabetes. However, the type of carbohydrate was equally important: low-GI carbohydrates reduced the risk, while high-GI carbohydrates increased the risk. Thus, low GI and low GL are not equivalent and produce different clinical outcomes.

Because this issue may be confusing to some readers, it is important to clarify the difference between GI and GL. Both the quality and quantity of carbohydrate determines an individual’s glycemic response to a food or meal (2). By definition, the GI compares equal quantities of available carbohydrate in foods and provides a measure of carbohydrate quality. Available carbohydrate can be calculated by summing the quantity of available sugars, starch, oligosaccharides, and maltodextrins. As defined (3), the GL is the product of a food’s GI and its total available carbohydrate content: glycemic load = /100.

Therefore, the GL provides a summary measure of the relative glycemic impact of a “typical” serving of the food. Foods with a GL ≤10 have been classified as low GL, and those with a value ≥20 as high GL (4). In healthy individuals, stepwise increases in GL have been shown to predict stepwise elevations in postprandial blood glucose and/or insulin levels (5).

It can be seen from the equation that either a low-GI/high-carbohydrate food or a high-GI/low-carbohydrate food can have the same GL. However, while the effects on postprandial glycemia may be similar, there is evidence that the two approaches will have very different metabolic effects, including differences in β-cell function (6), triglyceride concentrations (7), free fatty acid levels (7), and effects on satiety (8). Hence, the distinction has important implications for the prevention and management of diabetes and cardiovascular disease. Our concern is that the use of the GL or “glycemic response” in isolation may lead to the habitual consumption of lower-carbohydrate diets.

The simplest way to consume a moderately high-carbohydrate, but low-GI diet is to follow the new 2005 Dietary Guidelines for Americans (9) and to incorporate the recommendations of the World Health Organization/Food and Agriculture Organization (10); that is, the GI should be used to compare foods of similar composition within food groups. By choosing the lower-GI options within a food category (breads, breakfast cereals, etc.), an individual automatically chooses those with a lower GL. Because most fruit and vegetables, other than potatoes, are not major contributors to carbohydrate intake, their GI should not be the basis for restriction.

The important message for clinicians, nutritionists, and food industry professionals is that the evidence, as it stands, suggests that for preventing type 2 diabetes, we ought to encourage low-GI carbohydrate foods but not those that simply have low “net carbs,” low GL, or produce a low glycemic response.


  1. ↵ Hodge AM, English DR, O’Dea K, Giles GG: Glycemic index and dietary fiber and the risk of type 2 diabetes. Diabetes Care 27: 2701–2706, 2004
  2. ↵ Sheard NF, Clark NG, Brand-Miller JC, Franz MJ, Pi-Sunyer FX, Mayer-Davis E, Kulkarni K, Geil P: Dietary carbohydrate (amount and type) in the prevention and management of diabetes: a statement by the American Diabetes Association. Diabetes Care 27: 2266–2271, 2004
  3. ↵ Salmeron J, Manson JAE, Stampfer MJ, Colditz GA, Wing AL, Jenkins DJ, Wing AL, Willett WC: Dietary fiber, glycemic load, and risk of non-insulin-dependent diabetes mellitus in women. JAMA 277: 472–477, 1997
  4. ↵ Brand-Miller JC, Holt SHA, Petocz P: Reply to R. Mendosa. Am J Clin Nutr 77: 994–995, 2003
  5. ↵ Brand-Miller JC, Thomas M, Swan V, Ahmad ZI, Petocz P, Colagiuri S: Physiological validation of the concept of glycemic load in lean young adults. J Nutr 133: 2728–2732, 2003
  6. ↵ Wolever TMS, Mehling C: High-carbohydrate/low-glycaemic index dietary advice improves glucose disposition index in subjects with impaired glucose tolerance. Br J Nutr 87: 477–487, 2002
  7. ↵ Wolever TMS, Mehling C: Long-term effect of varying the source or amount of dietary carbohydrate on postprandial plasma glucose, insulin, triacylglycerol, and free fatty acid concentrations in subjects with impaired glucose tolerance. Am J Clin Nutr 76: 5–56, 2002
  8. ↵ Ball SD, Keller KR, Moyer-Mileur LJ, Ding YW, Donaldson D, Jackson WD: Prolongation of satiety after low versus moderately high glycemic index meals in obese adolescents. Pediatrics 111: 488–494, 2003
  9. ↵ Dietary Guidelines for Americans 2005 . Department of Health and Human Services and the U.S. Department of Agriculture. Available from Accessed 16 January 2005
  10. ↵ Food and Agriculture Organization/World Health Organization: Carbohydrates in human nutrition: report of a Joint FAO/WHO expert consultation. FAO Food and Nutrition Paper 66: 1–140, 1998

The Lowdown on Glycemic Load

Every food you eat affects your body differently, and not just in terms of your long-range health, but also in the way it is processed and the effect it has on your energy level and blood sugar.

Glycemic Load and Diet: The Basics

The glycemic load is a classification of different carbohydrates that measures their impact on the body and blood sugar. The glycemic load details the amount of carbohydrates a food contains and its glycemic index, a measurement of its impact on blood sugar. “The glycemic index ranks foods based on how quickly they’re digested and get into the bloodstream,” says Sandra Meyerowitz, MPH, RD, a nutritionist and owner of Nutrition Works in Louisville, Ky. “Its glycemic load takes into consideration every component of the food as a whole, so it’s a different number. It changes everything.”

Because the glycemic load of a food looks at both components, the same food can have a high glycemic index, but an overall low glycemic load, making it better for you than it originally might have appeared.

Glycemic Load and Diet: The Effect on Your Health

Foods with a low glycemic load keep blood sugar levels consistent, meaning that you avoid experiencing the highs and lows that can be caused by blood sugar that jumps too high and quickly drops — the candy bar effect.

Watching the glycemic load of the foods you eat can have a big impact on your health in many ways. A diet focused on foods with a low glycemic load can:

  • Make it easier to lose weight and avoid the dreaded diet plateau
  • Keep blood sugar levels more consistent
  • Burn more calories
  • Help prevent insulin resistance and diabetes
  • Lower heart disease risk

“It makes more sense to use the glycemic load because when you eat a food you don’t just eat one food by itself — you eat a whole bunch of foods together,” says Meyerowitz. Looking at the total picture of foods you eat, rather than just the individual pieces, gives you a clearer and more accurate picture of the foods that make up your diet.

Glycemic Load and Diet: Glycemic Loads in Favorite Foods

It’s tough to figure out on your own if a food has a high or a low glycemic load, but as a general guideline, the more fiber a food has the better. Here is a glycemic load reference list with many common foods to let you know which are low, medium, and high.

Foods with a low glycemic load of 10 or less:

  • Kidney, garbanzo, pinto, soy, and black beans
  • Fiber-rich fruits and vegetables, like carrots, green peas, apples, grapefruit, and watermelon
  • Cereals made with 100 percent bran
  • Lentils
  • Cashews and peanuts
  • Whole-grain breads like barley, pumpernickel, and whole wheat
  • Whole-wheat tortillas
  • Tomato juice
  • Milk

Foods with a medium glycemic load of 11 to 19:

  • Whole-wheat pasta and some breads
  • Oatmeal
  • Rice cakes
  • Barley and bulgur
  • Fruit juices without extra sugar
  • Brown rice
  • Sweet potato
  • Graham crackers

Foods with a high glycemic load of 20 or more:

  • High-sugar beverages
  • Candy
  • Sweetened fruit juices
  • Couscous
  • White rice
  • White pasta
  • French fries and baked potatoes
  • Low-fiber cereals (high in added sugar)
  • Macaroni and cheese
  • Pizza
  • Raisins and dates

Focusing on the glycemic load of foods is particularly important for people with diabetes to help maintain a steady blood sugar, but everyone can benefit from understanding and monitoring the glycemic load in their diet.

Your blood glucose levels rise and fall when you eat a meal containing carbohydrates. How high it rises and how long it stays high depends on the quality of the carbohydrates (the GI) as well as the quantity. Glycemic Load (or GL) combines both the quantity and quality of carbohydrates. It is also the best way to compare blood glucose values of different types and amounts of foods. The formula for calculating the GL of a particular food or meal is:

Glycemic Load = GI x Carbohydrate (g) content per portion ÷ 100.

For example, a single apple has a GI of 38 and contains 13 grams of carbohydrates.

GL= 38 x 13/100 = 5

A potato has a GI of 85 and contains 14 grams of carbohydrate

GL=85 x14/100 = 12

We can therefore predict that the potato will have twice the glycemic effect of an apple.

Similar to the glycemic index, the glycemic load of a food can be classified as low, medium, or high:

Low: 10 or less

Medium: 11 – 19

High: 20 or more

The GL of a mixed meal or diet can simply be calculated by summing together the GL values for each ingredient or component. For example, if breakfast was composed of 2 wheat biscuits (GL = 15), ½ a cup of milk (GL = 4) and 2 teaspoons of sugar (GL = 6), its overall GL would be 25 (15 + 4 + 6).

For the whole day, a low GL diet has a GL less than 100 g/% for people consuming 8,700 kJ. Therefore, for people consuming 3 meals per day, a low GL meal would have a GL ≤ 33 g/%.

For optimal health, you should aim to keep your daily glycemic load under 100.

Should I use GI or GL?

Although the GL concept has been useful in scientific research, it’s the GI that’s proven most helpful to people with diabetes and those who are overweight. That’s because a diet with a low GL, unfortunately, can be a ‘mixed bag’ full of healthy low GI carbs in some cases, but too high in protein and low in carbs and full of the wrong sorts of fats (i.e., saturated) such as those found in some ‘discretionary foods’. If you use the GI as it was originally intended – to choose the lower GI option within a food group or category – you usually select the one with the lowest GL anyway because foods are grouped together for a reason because they contain similar nutrients, including amounts of carbohydrate. So, if you choose healthy low GI foods, at least one at each meal, chances are you’re eating a diet that not only keeps blood glucose ‘on an even keel’ but contains balanced amounts of carbohydrates, fats and proteins.

What is the Glycemic Response?

After eating a meal, the digestible or available carbohydrates are absorbed into the blood stream, producing an increase in blood glucose concentration. In time and in response to its tissue disposal, facilitated by the hormone insulin, the blood glucose concentration falls back to or below fasting levels. The magnitude of the rise and fall of blood glucose and the duration over which it occurs has been termed the glycemic response. More slowly digestible carbohydrates or minimally processed starchy foods produce a different response. Compared with rapidly digestible carbohydrates they show a slower and more prolonged increase in blood glucose, rising to a lower peak. Other factors include how much food you eat, how much the food is processed and even how the food is prepared For example, pasta that is cooked al dente has a slower glycemic response than pasta that is overcooked.

Glycaemic Load (GL)

  • What is the glycaemic load (GL)?
  • How is the glycaemic load calculated?
  • Factors affecting the glycaemic load
  • Metabolism and glycaemic load
  • Medical conditions and glycaemic load
  • Lowering dietary glycaemic load

What is the glycaemic load (GL)?

The concept of the glycaemic load is one that is becoming more used and referred to in the food industry. We may have all heard of the glycaemic index (GI) – a value that is obtained by measuring the effect that a carbohydrate containing food has on blood sugar levels, compared to the effect of the same amount of pure sugar on blood sugar levels. However, the problem with the GI is that it doesn’t provide an accurate picture of the entire blood sugar raising potential of the food. The blood sugar response depends on both the quantity and quality of carbohydrates consumed. The GI only provides us with an idea of how rapidly a carbohydrate turns into sugar, but not how much of that carbohydrate is in a food serving.

The glycaemic load (GL) is an extension of the GI, taking into account the quantity of carbohydrates as well. The GL is obtained by multiplying the GI value by the carbohydrate content of the food. This provides us with a more accurate picture of the overall effect that the food product has on blood sugar levels. Clinical studies have shown that the dietary GL is linked to risk factors for heart major vessel disease, and obesity, although data is still being collected.

How is the glycaemic load calculated?

The glycaemic load of a food ranks the effect of a specific serving size of that food on the blood sugar levels. It is calculated by multiplying the GI value of the food by the amount of carbohydrate the serving of food contains, divided by 100. The GL uses white bread as a baseline standard, where each unit of GL reflects the glycaemic effect of 1g of carbohydrate from white bread. If we take a common fruit such as an apple for example, the GL is determined as follows:

GI of a standard apple = 40
Carbohydrate content of a standard apple = 15
GL = (GI x Carbohydrate content) / 100
= (40 x 15) / 100
= 6

If we take two foods with the same GI value, but Food A contains 5% carbohydrates and Food B contains 80% carbohydrates, Food B has a much higher GL and should be eaten in lesser proportions. In general terms, foods with high carbohydrate levels and low fibre contents have high GI and GL values, whereas those with high fibre contents have lower GLs.

Factors affecting the glycaemic load

There are various factors that affect the GL of a food. Many of these are similar to those that also influence the GI of a food product. These include: the types of sugar and starches in the food, the way it is prepared, its fat, fibre and carbohydrate content, and the serving size. The rate of absorption and digestion of food products also influences the GI and GL.

The following ranges are usually applied to determine the GL of a particular food:

  • Low GL – 10 or less
  • Medium GL – 11 to 19
  • High GL – 20 or more

The following values are applied to define the GL per day:

  • Low GL – less than 80
  • High GL – more than 120

Foods with a low GL means that they cause a steadier and lower rise in blood sugar levels. These foods include many fruits and vegetables. Foods with a high GL means that they cause a faster and higher rise in blood sugar levels.

High GL foods include white rice and refined snack foods such as chips and sweetened drinks. By consuming foods that have a low GL, there is an overall slower and lower rise in blood sugar levels.

The usefulness of the GL has been demonstrated, particularly in relation to diabetic patients – if you suffer from diabetes, the GL has been shown to be a more accurate and reflective predictor on blood sugar levels. By adhering to a diet with a low GL, diabetics can reduce their average blood sugar levels and lower their risks of developing complications such as eye, kidney and nerve damage.

Table 1: List of foods and their GL

Glycaemic load Fruits / Vegetables Carbohydrates Others
Low Fruits: Apples, pears, oranges, grapes, peaches, strawberries, tomatoes, watermelon, cantaloupe

Vegetables: Beans, peas, carrots, sweet corn

All grain cereal

Bread: Whole wheat, grain, multi-grain, whole grain crackers

Dairy products: Low fat yoghurt, whole/low fat/skim milk

Eggs, Milo

Medium Fruits: Bananas, apple juice, orange juice

Vegetables: Navy beans, sweet potatoes

Wholemeal bread, white bread, brown rice, rice cakes, Cornflakes Coke, chocolate
High Sultanas, dates, raisins, tomato juice, potatoes Bagels, spaghetti, macaroni, white rice, refined cereal products Chips/french fries, jellybeans, lamingtons

Metabolism and glycaemic load

The GL is a bit more complex than the GI. Carbohydrates vary in terms of quantity and quality (ie GI values) in different foods. Let us compare the GI values of foods with different carbohydrate densities.

The GI of a baked potato is classified as medium-high, which places the potato on the list of foods to avoid or eat less of. The GI of watermelon is also high. However, a serving of watermelon contains high levels of water and a low level of carbohydrates – a 100g serving of watermelon contains 5g of carbohydrates. This gives the watermelon a low GL value. The potato is packed with more carbohydrates, which gives it a high GL value. Therefore, consuming a serving of watermelon has a much smaller impact on blood sugar levels than a serving of potatoes.

In summary, the GI of potatoes is not a misleading value because potatoes are carbohydrate dense, thus their GL is also high. Watermelon on the other hand contains only a small percentage of carbohydrates, so although they have a high GI level, their GL is low.

Medical conditions and glycaemic load

Looking at over 75,000 healthy middle aged women involved in the Nurse’s Health Study, the impact of carbohydrate consumption on long term heart and major vessel health was assessed. They found that diets with a high GL value correlated with increased risk of heart and major vessel disease, regardless of whether the women had conventional risk factors for heart disease or not (ie high blood pressure, high cholesterol levels, family history, smoking, etc). There was also a strong association with weight – particularly in overweight women, a strong positive association was seen between dietary GL and cardiovascular disease. In lean women, there was little association between the two. Another study was performed in 280 postmenopausal women, which showed that dietary GL was inversely related to the level of good cholesterol (HDL) and directly related to bad cholesterols such as LDL and triglycerides.

If you have diabetes, blood sugar levels and insulin resistance is important in understanding and management of your disease. A chronically high blood sugar level after meals has been linked to increased insulin resistance and decreased production of insulin. Some studies performed in patients show that there is a lower rise in blood sugar levels if a meal with a low glycaemic index or glycaemic load is consumed. In the Framingham Study, diets high in total fibre and whole grain were associated with decreased insulin resistance. Elevated dietary glycaemic index and glycaemic load were associated with insulin resistance. A higher glycaemic intake and lower intake of fibre were also shown to be linked to an increased risk of the metabolic syndrome.

Lowering dietary glycaemic load

Some ways to achieve a lower dietary GL include:

  • Replace carbohydrates with protein;
  • Eat low GI carbohydrate foods instead of high GI carbohydrate foods;
  • Try and have at least 3 low GL foods throughout the day, with each meal.

More information

For more information on nutrition, including information on types and composition of food, nutrition and people, conditions related to nutrition, and diets and recipes, as well as some useful videos and tools, see Nutrition.
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