For many years, food scientists have advocated the use of the Glycemic Index as a useful tool in avoiding certain foods which might cause blood sugar to rise. It is a ranking system that tells you how fast the sugar content of a food is released into your bloodstream.
The concept behind the GI was developed by Dr. David J. Jenkins and colleagues at the University of Toronto in 1980 while researching which foods were best for people with diabetes. Jenkins began testing how quickly 50 grams of specific foods like beets and oatmeal convert to glucose (blood sugar), and compared them to either white table sugar or white bread. His team set a standard measure. Today, when you follow a GI diet, you use a chart that scores food on a range from 1-100. A high GI score indicates foods to avoid; a low GI score, the ones to eat.
There have been some problems with the GI rankings. If following the GI, you might be tempted to think that a cola, with a GI of 90, is better than cranberry juice, which carries a GI of 105. You might also think you should eliminate carrots from your diet due to their extremely high GI value. (A newly updated figure has Canadian carrots listed at 97 GI per serving.). Another problematic example is ‘fructose’, which has a very low glycemic index, and yet has been established as a major reason why so many people are overweight.
Common sense, however, tells you that cranberry juice should be better than a sugar-based soda, and that carrots are good for you.
GI and GL – Does it matter which one I use?
Glycemic Index food scores, while useful, only provide half the picture. While the GI value tells you how rapidly the carbohydrate in a food turns into sugar, it does not tell you the quantity of carbohydrates in a serving. You need to know both sets of data in order to understand how that food will impact your blood sugar. The Glycemic Load measures both and combines this data into “one figure”.
Questions around juicing and blood glucose Levels
The newer Glycemic Load concept, developed by Harvard School of Public Health Professor Walter Willett and his associates in 1997, sheds light on whether ‘juicing’ of fruits and vegetables is really the high-sugar culprit it has long been made out to be. Yes, an 8-ounce serving of carrot juice contains approximately 11 grams/3 teaspoons of sugar, but you need to keep in mind that it is about half the amount found in a large apple. Carrots are an excellent food for your body’s cells. They are full of dietary fibre and contain many important vitamins and minerals. In short, you need to look at the whole picture. You never want to cut a natural form of beta-carotene from the diet, especially since you would be missing out on its pro-vitamin A, important for immune system health, for skin repair, and for maintenance of the retinas of your eyes.
Calculating Glycemic Load easily:
An often-used example of watermelon is given here: Watermelon contains fast-releasing carbohydrates; for this reason, it has a high GI score of 72. However, only 1/8 oz (6g) of carbohydrate per 3 ½ oz (100g) of watermelon is present. The rest of the fruit is mainly water. The impact of the fast-releasing sugar is very low; therefore, the “high glycemic index” watermelon actually has a low GI score of only 4.
Here’s how to calculate the GL of any given food: take the GI value and multiply it by the actual number of carbohydrates in a serving. So…Quantity of Carbohydrate X Quality of Carbohydrate. Then simply divide by 100.
The GL score of watermelon is therefore calculated as:
72 X 6 = 4.32
100
(Rounded down you get = 4 GL)
GL food scores – What’s a safe range?
The glycemic load of a food varies according to portion size, and the range of measures runs from 0-35. Anything over 15 is to be avoided. Here is an easy guideline you can follow:
LOW GL – a score of 10 is good.
MEDIUM GL – 11-14 is OK in moderation
HIGH GL – 15 or more is “bad” and to be avoided. (Contrast that with the GI, where a score of 55 is considered low.).
If this sounds very complicated, do not worry. Many calculations have been done for you by trusted sources such as the University of Sydney http://www.glycemicindex.com. For a free, “2008 International Table of Glycemic Index and Glycemic Load Values”, see http://www.mendosa.com/GI_GL_Carb_data.xls and http://www.mendosa.com/gilists.htm. Mendosa.com is a well-respected resource for people living with diabetes. (Normally, this information is available only via a subscription to the Journal of Diabetes Care, or to the American Journal of Clinical Nutrition.)
Examples of low GL foods include:
- Oatcakes, whole wheat bread, baked beans, quinoa, all vegetables (except for potatoes and parsnips), fish, white meat, eggs, fermented soy, and dairy.
Medium GL foods are healthy in moderation:
Healthy Habits at Home
They release glucose into the bloodstream at a slower rate than high GL foods, but still raise blood sugar to a level where it is likely to overproduce glucose, and some is turned into fat. If you want to lose weight, they should be limited and eaten alongside low GL foods. Examples include:
- Rye crispbread, rice noodles, parsnips, boiled potatoes, rice milk.
High GL foods are to be avoided:
- High GL foods release glucose into the bloodstream fast and raise sugar levels too quickly for the body to cope. The body cannot use all the glucose produced and deposits a large proportion of glucose for storage as fat. Your blood sugar level then crashes, leaving you hungry again (and so the cycle continues). Examples include:
White baguette, muffins, cornflakes, all rice (except for brown basmati), couscous, puffed rice cakes, all potatoes (except boiled new and fingerling potatoes), and honey.
Why do we need to limit high GL foods?
Blood sugar levels are linked to hunger and the way you eat. High-glycemic-load foods cause a sharp, rapid rise in blood glucose, especially if you do not ‘space’ them over the day. Once in the cell, any glucose that is not used for energy is converted into fat. Insulin then blocks the enzyme that breaks fat into free fatty acids that are used up as an energy source.
Low GL foods are preferable because glucose is released into the bloodstream slowly, helping blood sugar to remain more stable. Maintaining blood sugar at a stable level is the key to steady, long-term weight loss as well as preventing diseases such as diabetes and heart disease. Keeping blood sugar steady also prevents the energy slumps that trigger food cravings.
Several factors come into play when calculating the GL of a food:
Amount of cooking:
Amount of processing:
Amount of fibre:
Amount of fat:
What can you do to stay healthy at home?
MENU SWAPS
| Boxed breakfast cereal | Oatmeal, or teff porridge |
| Fried egg and bacon | Scrambled eggs on rye toast |
| Croissant with jam | Egg pancake with chia seed fruit gel |
| Burger and French fries | Turkey or chickpea burger, and salad |
| Spaghetti carbonara | Zucchini pasta with cauliflower or broccoli, parmesan sauce |
| Doner kebab | Greek pita bread filled with aubergine |
| Chicken Biryani | Brown rice pilaf with curried chicken |
| Smoked salmon and cream cheese sandwich | Cottage cheese with smoked salmon and cucumber |
| Tea, coffee, or cola | Rooibos tea, herb teas, freshly made lemonade with stevia, and fresh ginger tea |
If you keep to the low GL guidelines:
References
1. 8 principles of low-glycemic eating. Harvard Health. (2014, February 15). https://www.health.harvard.edu/healthbeat/8-principles-of-low-glycemic-eating
2. Glycemic index and Glycemic Load. Linus Pauling Institute. https://lpi.oregonstate.edu/mic/food-beverages/glycemic-index-glycemic-load
3. Jenkins, D. J., & Willett, W. C. (2024). Perspective on the health value of carbohydrate-rich foods: glycemic index and load; fiber and whole grains. The American journal of clinical nutrition, 120(3), 468–470. https://www.sciencedirect.com/science/article/pii/S0002916524005999?via%3Dihub
4. Jenkins, D. J., Wolever, T. M., Taylor, R. H., Barker, H., Fielden, H., Baldwin, J. M., Bowling, A. C., Newman, H. C., Jenkins, A. L., & Goff, D. V. (1981). Glycemic index of foods: a physiological basis for carbohydrate exchange. The American journal of clinical nutrition, 34(3), 362–366. https://www.sciencedirect.com/science/article/abs/pii/S000291652342816X?via%3Dihub