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Spotlight on Carbs: The Difference Between the Glycemic Index and Glycemic Load

Spotlight on Carbs: The Difference Between the Glycemic Index and Glycemic Load


First things first.

Right off the top, you should know that highly processed foods (pre-packaged salty and sugary snacks, breakfast cereals, frozen or instant meals, soft drinks, fruit juices, white bread, etc.) have a high glycemic index (GI). This is because they’re full of simple carbohydrates, which are sugars made up of one or two molecules that can be digested and released into the blood stream quickly. On the other hand, whole foods such as fresh fruits and vegetables, legumes, and whole grains tend to have a low GI because they’re complex carbohydrates made of long strings of molecules, and heavy processing and refining have not removed their fiber and nutrients. Fiber in particular slows digestion and therefore slows down the release of sugar into the blood stream.



So, what is the glycemic index anyway?

Glycemia is the presence of sugar in the bloodstream, and the glycemic index is a measure of how quickly particular foods, specifically carbohydrates, get digested and release sugar into the bloodstream. David Jenkins, M.D., is a scientist at the University of Toronto who led the team that introduced the glycemic index in 1981. (Shamard Charles, 2022) It’s graded on a scale from 0 to 100. 55 or lower is considered low, 56 to 69 is medium, and 70 or above is high, with 100 being equivalent to pure glucose.

A low GI correlates with lower spikes in blood sugar. Foods that have no carbs, such as meats, fish, poultry, seeds, and nuts, are excluded from the glycemic index. The ideal, especially for people at risk or already dealing with blood sugar issues such as diabetes, is to eat more foods with a low GI and fewer with a high GI. However, GI can present a misleading picture of how likely a food is to affect your blood sugar levels, so looking at glycemic load provides a more practical yardstick.



What, then, is glycemic load?

Some limitations of GI are that it doesn’t account for portion sizes or the overall nutritional contribution of foods. Because portion sizes aren't considered, GI can’t estimate how much a particular food will raise your blood sugar, which is really what you want to know. Glycemic load (GL) partially rectifies this by considering the typical serving sizes of different foods, together with their GI, to quantify the expected effect on blood sugar levels when foods are eaten in a real-world situation.

GL is calculated as GI multiplied by the grams of carbs in a serving size divided by 100, or GL = GI x available carbs (g) ÷ 100. A GL of 10 or less is low, 11 to 19 is moderate, and 20 or more is high. (Michelle Severs, 2023) The result is that many foods, such as fruits and vegetables, with a high GI turn out to have a low GL, meaning they’re not likely to suddenly spike your blood sugar levels. See the tables below, and you’ll get the idea.

Graphs: Comparison of GI and GL for various sources of carbs. Source: Reproduced unmodified from Harvard Health. (Harvard Health Publishing, 2021)



Do I need to be concerned about glycemic ratings every time I eat?

It depends. If your dietary preferences skew heavily towards refined carbs and sugar, and ultra-processed foods in particular (fast food, white bread, soda, pasta, breakfast cereal, pastries, fruit juice, pretzels, TV dinners, etc.), then monitoring your blood glucose levels could help to lower your risk of developing diabetes. Of course, if you already have diabetes, then monitoring and managing your blood glucose levels is a necessity, and it would be wise to have some knowledge of the GI and GL of specific foods. This also applies if you’re not necessarily diabetic but simply trying to lose weight.

If you are interested in managing your GI and GL more intently, pay attention to the characteristics and methods of preparation of the foods you eat. While they are not hard-and-fast rules, below are some general guidelines:

  • High-fiber foods (peas, beans, lentils, fruits, vegetables, nuts, and seeds) tend to have lower glycemic ratings because fiber slows down digestion and the release of glucose into the bloodstream.

  • Highly processed foods (i.e., junk food and fast food) tend to have higher glycemic ratings.

  • The riper a fruit becomes, the higher its glycemic rating is likely to be because the amount of resistant starch decreases. (Resistant starches are carbohydrates that resist being digested in the small intestine and pass into the large intestine, where they ferment and nourish healthy gut bacteria.)

  • Fats and proteins, which are digested more slowly, tend to have lower glycemic ratings.

  • The method of cooking can also affect a food’s glycemic ratings.



Harvard Health Publishing. (2021, November 16). Glycemic index for 60+ foods. Retrieved October 5, 2023, from www.health.harvard.edu: https://www.health.harvard.edu/diseases-and-conditions/glycemic-index-and-glycemic-load-for-100-foods

Michelle Severs, M. (2023). Glycemic Index vs. Glycemic Load: What’s the Difference? Retrieved September 28, 2023, from www.veri.co: https://www.veri.co/learn/glucose-glycemic-index-and-glycemic-load-explained

Shamard Charles, M. M. (2022, February 2022). Difference Between Glycemic Index and Glycemic Load. Retrieved September 27, 2023, from www.verywellhealth.com: https://www.verywellhealth.com/glycemic-index-vs-load-5214363

*This newsletter has not been authored in whole or in part by any artificial intelligence tools.
*No content on this site, regardless of source or date, should ever be used as a substitute for direct medical advice from your doctor or other qualified clinician.



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