What is the glycemic index?
Last week, we talked about carbohydrates as the main energy source for our bodies. All carbohydrate-containing foods have a different ability to raise our blood glucose levels. The glycemic index (GI) is a measurement for exactly this ability of different foods to increase our blood sugar levels.
Therefore, the glycemic index shows the relative rise in blood glucose after consuming 50g of a particular food compared to 50 g of glucose. So, foods that have a high glycemic index cause a higher blood glucose level than those with a low GI.
The GI was originally designed for people with diabetes as a guide to food selection. People suffering from diabetes were given the advice to select foods with a low GI.
How do we determine the glycemic index of food?
The glycemic index of food is determined by the type of carbohydrates, food composition, and other macronutrients. Plus, GI tables often show just a number and imply that the GI is constant for a particular food. In fact, the GI depends on variety, ripeness, cooking methods, and processing. Foods are ranked on a scale of 0 to 100, with pure glucose (grape sugar) given a value of 100. The rule of thumb is: The more processed food is, the higher its GI. And, the more fiber, protein, or fat in a food, the lower its GI.
Furthermore, the glycemic index may also vary between individuals, and within an individual, depending on the time of the day, prior food consumption, etc. Therefore, you should know, that the GI of a food can vary slightly. But, in general, the GI will show you the average response in blood glucose levels.
Foods with a low or high glycemic index
Foods with large amounts of simple carbohydrates compared to protein and fat appear to cause a higher rise in your blood sugar level. Therefore, foods with a high GI (more than 50) are white bread, white rice, potatoes and sugar such as glucose. For example, boiled white rice has a GI of 72, baguette has a GI of 95 – quite the same as sugar with GI 100!
Foods with complex carbohydrates, protein and fat appear to increase your blood sugar levels just slightly. Foods with a low GI (up to 50) are e.g. beans, lentils, seeds, nuts, most fruits and vegetables, meat and fish. For example, peanuts have a GI of 13. Fiber-rich foods generally have a low glycemic index. Although not all foods with a low GI necessarily have high fiber content. Here is a GI-table provided by the Harvard Medical School with 100+ foods.
The “Second-Meal Effect” of beans and lentils
Beans have a predominant role: Eating beans has even a positive influence on food consumed later the day. Therefore, if you eat beans for lunch, your blood sugar levels won’t increase as expected after eating dinner. Studies have shown that people eating beans have at least 45% lower blood sugar levels when drinking sugar water compared to people eating other foods instead of beans. Even the next day. Lentils appear to have the same effect. This effect is also known as the “Second-Meal Effect”.
Our gut bacteria love beans and lentils because they have loads of fiber. While digesting fiber, they produce propionate which has a beneficial effect on our sugar and fat metabolism. At the same time, it reduces our appetite and strengthens the feeling of satiety. Good teamwork!
Why is it important to measure blood sugar levels?
Your blood sugar level is linked to several diseases and even more important for your friends and family: your mood. Having a high blood sugar level because of eating food with a high glycemic index means that your blood sugar level will fall at quite the same speed. Then, you feel tired and exhausted and you crave something sweet to raise your blood sugar level again. Just like a vicious circle – see here my blogpost on sugar.
Having this high peak of blood sugar followed by a rapid decrease is linked to food cravings, overeating because of eating too many snacks, etc. Even worse, the higher your blood sugar level is, the more insulin needs to be produced by your pancreas. This is one of the main factors why people get diabetes. It’s just like having a car you ride too often, especially the cold start: After driving thousands of kilometers, your engine will break down sooner or later. The more often you start your engine cold, the sooner your engine will probably say goodbye. That’s the same with your pancreas, the more it has to produce insulin, the earlier it will lose its ability to provide this essential hormone.
Blood sugar vs. insulin
Insulin lowers our blood sugar levels by getting glucose out of our bloodstream into our cells. Plus, it converts glucose into body fat. Consequently, the higher your blood sugar level, the more body fat is stored.
Following a low-carb diet is quite the same as eating just foods with a low glycemic index. The lower the GI, the lower your blood sugar levels, and the lower your insulin response. In the extreme case with empty carbohydrate stores, your body starts burning fat to get energy. This effect is also called “ketosis”. More on this topic is coming soon.
The glycemic load is more precisely
There are still some limitations:
The glycemic index is only defined for specific food and not in combination with other food. Plus, the amount of food eaten is not taken into consideration.
Because of this, the glycemic load (GL) was introduced. It represents the multiplication of the glycemic index of the food combined with the carbohydrate content of the serving.
The glycemic load is determined by multiplying the grams of carbohydrates in a serving by the GI, then divided by 100. A glycemic load of 0-10 is considered low, 20 or above is considered high. For example, watermelon has a high glycemic index (72). But a serving of watermelon (120g) has so little carbohydrates (6g) that its glycemic load is only 4.
GL = GI x amount of carbs in your serving: 100
Try to avoid processed food
To sum up, the more processed food is, the higher the glycemic index and glycemic load will be. Following a diet with consuming unprocessed, natural foods rich in fiber will help you have stable blood sugar levels and get rid of food cravings. That’s quite the way I nourish myself. I try to avoid processed food such as white bread, white rice, and added sugar. I love fruits and vegetables, and I’m nuts about nuts 🙂 So, I eat a lot of antioxidants and fiber, drink a lot of water and unsweetened tea, and keep an eye on my vitamin B12-intake. Since I’m doing so, I feel better than ever. The reaction of my internist on my blood count some days ago: “This is the best blood count I’ve seen for months!” 😉
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Here is the scientific evidence used for this blog post
Brighenti, F./Benini, L./Del Rio, D./Casiraghi, C./Pellegrini, N./Scazzina, F./Jenkins, D. J./Vantini, I. 2006: Colonic Fermentation of Indigestible Carbohydrates Contributes to the Second-Meal Effect, in: American Journal of Clinical Nutrition, Vol. 83, 2006, No. 4, pp. 817-822.
Jenkins, D. J./Wolever, T. M./Taylor, R. H./Barker, H. M./Fielden, H. 1980: Exceptionally low blood glucose response to dried beans: comparison with other carbohydrate foods, in: British Medical Journal, Vol. 281, 1980, No. 6250, pp. 578-580.
Khan, S. H./Fazal, N./Manzoor, S. M./Asif, N./Rafi, T./Yasir, M./Niazi, N. K. 2017: Insulin Resistance and Glucose Levels in Subjects with Subclinical Hyperthyroidism, in: Journal of the College of Physicians and Surgeons, Vol. 27, 2017, No. 6, pp. 329-333.
Mattei, J./Hu, F. B./Campos, H. 2011: A higher ratio of beans to white rice is associated with lower cardiometabolic risk factors in Costa Rican adults, in: American Journal of Clinical Nutrition, Vol. 94, 2011, No. 3, pp. 869-876.