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Glycemic Index
February 16, 2008 | 15 Comments
Glycemic Index (GI) refers to the ability of the body to metabolize food and is typically denoted with a number between 0 and 100. A high GI reflects a fast breakdown of the food and sharper spike in the blood sugar and vice versa.
The concept has been around for a quarter of a century, and lot of research has been done both in the medical and sport circles. My interest in GI was rekindled as my preparation for an endurance race started to heat up.
Majority of our caloric needs are met through carbohydrates. GI allows us to categorize these carbohydrates so that we may be able to choose the right carb for our dietary needs. A person wishing to lose weight may want to focus more on low GI foods but after a strenous bout of exercise will need to reload the system with some high GI foods. Diabetics may also see the benefit of a low GI diet as the spikes in blood glucose are muted with low GI foods, however, diabetics need to be aware of the Insulin Index as well. During competition, endurance athletes also pay a lot of attention to GI to keep their performance levels at an even keel.
Breakfast cereals made from oats, barley or bran are low GI (adding copious amounts of sugar will make it high GI as glucose has a GI of 100 
). Breads made with wholegrain, stoneground flour, or sourdough are low GI. Quinoa, Pasta, and noodles are typically low GI – but avoid the refined flour varieties. Potatoes are high GI.
The product of the GI of the food and the net carbs consumed is referred as the Glycemic Load (GL). Higher the GL, greater the rise in blood sugar levels. So one could have a huge glycemic response by eating large quantities of low GI foods. When you have a meal which results in a disproportionately large and rapid glycemic response vis-a-vis the needs of the body, initially the energy levels may increase but this could be followed by a cycle of increased fat storage, lethargy, and more hunger as the body responds by cutting the insulin.
Data on the GI and GL levels of specific foods can be found at Nutrition Data and at the Home of Glycemic Index
Simple searches on the above sites yielded very interesting observations. There is a wide range in GI for the same type of food and in addition the nature of cooking can greatly alter the GI. The table below shows a simple example for white potatoes and sweet potatoes.
| Food | GI |
Serving(g) |
Carb per Serving (g) |
GL
|
|---|---|---|---|---|
| Potato, white, boiled |
54
|
150
|
19.5
|
10.5
|
| Potato, White, Instant mashed |
97
|
150
|
22.8
|
22.1
|
| Sweet potato (Ipomoea batatas),boiled |
44
|
150
|
26
|
11.4
|
| Sweet potato, kumara, boiled |
77
|
150
|
21.2
|
16.3
|
One study on the GI of potato had the following observation to make:
..both the method of cooking and variety of potato can affect glycemic index. What was most interesting was that when a red potato was boiled, refrigerated, and consumed cold the next day, the glycemic index plummeted 37%, from the upper end of a high glycemic index food (89) to one point away from classification as a low glycemic index food (56).
When potatoes are cooked, the starch granules absorb water. This is called gelatinization, and it tends to change the structure of the starch, making it more susceptible to the digestive enzymes. When the cooked potato starch is cooled, the molecules bond in an irregular fashion, making it more difficult to be hydrolyzed by enzymes. The authors mention that repeating the cooking-cooling cycle will continue to result in a more resistant starch. The more resistant a starch is, the longer it will take the body to break it down, digest, and absorb it.
A study published in the Indian Journal of Physiology and Pharmacology corroborates the above view and showed that the GI of boiled, salted potato dropped from 76 to 23 when consumed after refrigeration and reheating.
Potatoes and Puris : A High GI Double Carb Whammy
Refrigerating these potatoes overnight after boiling them and then making the final dish will reduce the GI.
Potatoes and sweet potatoes are very versatile and we use them a lot in our cooking. Now we also can make the same dish high and low in GI as well !!
-Jai
Filed Under: carbohydrate, fitness, Glycemic Index, Glycemic Load, NUTRITION, Potato, Sweet Potato, Vegetarian Athlete
|
15 Comments
Very useful & informative article. I didn’t know about refrigerating potatoes to lower GI. That’s what I am going to do now on. Thanks! most of the foods make sense for high GI, the only I do not understand is watermelon. Why on earth does it have high GI of 72? I have been thinking about it from a long time. Isn’t it full of water? If you know the reason, please kindly let me know. Thanks again for a wonderful article.
GI only pertains to how quickly something gets metabolized and is not related to calories or solid/liquid ratio. Water does not need to get metabolized. I would imagine that anything sweet (sugary) such as fruit will have high GI. Fiber content has an effect of lowering GI, and watermelon is not super high on fiber. –j
Thanks for this post J! Been reading around GI quite a bit these days, and the potato refrigeration info is very useful. Do you know anything about giving other veggies like carrots the same treatment to lower GI?
Don’t have any similar studies that I have looked for carrots. Let us know if you find anything. -j
Wow hey, thanks for sharing that piece of research-news! I just might be eating potatoes more often (I be a hypoglycemic).
Thats a lot of good information in this post. Thanx a lot for sharing..
I also read that the more the pasta gets cooked, the higher the GI. GI is interesting, although it is not proven beyond doubt. There is still some controversies.
Certainly a good concept…but not a theory. My opinion is that there are way too many variables to measure and take into account that the concept may never be fully realized. -j
These days even I am cooking with GI consciouseness. Liked the info here.
Very informative post…thanks Jai…and I also love the new entry form for Click :yes:
Glad that you like the form. Makes the process much easier. Thanks for the feedback. -j
Excellent post Jai! That bit about boiling and cooling potatoes is very useful and will come in handy. Thanks.
Have been reading about this. Nice write up all the same.
Very user friendly form for Click. Thanks.
Jai that is a very informative post. One more tip for lowering GI. Any starchy vegetable/tuber/ fruit if kept immersed in water for atleast half hour lowers GI. This is caused by starch sedimenting into the water. This water can be used as stock for cooking or can be discarded. Thus allowing most people to consume their favorites like potatoes.
thanks for the tip. -j
so now I know that what Amma has been doing all these years is such a good thing!! And I should start doing the same too
Thanks
Ever since I read this post I have been trying to remember where I read that cooking potatoes with the skin on also affects the GI just like refrigerating it. But so far I’ve been unsuccessful. I think I am mixing up some unrelated information(s) here!
And Jai, congratulations on the marathon. (I missed the post about it.)
Thank you for this information—I’m always smiling when I come here because I’m always learning/seeing new things.
Very informative read. Acyually i didn’t know nothing about these.
I love the timing of this post, just spent a couple of hours reading about carb and protein combinations/intake and the impact on workout regimes.
Thanks, Jai!