The Blood Sugar Factor: Glycemic Index vs Glycemic Load

The glycemic index is a measure of how quickly and how high your blood sugar rises after eating food.

But it’s not nearly as important as a less famous measure called the glycemic load. And the glycemic load is something worth knowing about.

When you eat any food- especially carbohydrate and to some extent protein- your blood sugar goes up. (It hardly goes up at all when you eat fat.) In response to the rise in blood sugar, your pancreas secretes insulin, whose job is to act as a traffic cop and escort the excess sugar out of the bloodstream and into the cells where- in an ideal world- it can be used for fuel. Blood sugar (and insulin) both gradually go back down to pre-eating levels, and in a few hours you repeat the whole process.

Problem is, this is anything but a perfect world.

We overeat high sugar carbohydrates, which quickly drives our blood sugar up into the stratosphere. The pancreas sends out a ton of insulin in an attempt to lower blood sugar, but most of us are pretty sedentary, so our muscle cells aren’t interested in taking it in. Insulin knocks on the doors of the muscle cell walls and the cells say, “sorry dude, we don’t need any sugar, our guy’s going to be sitting at the computer all day, go somewhere else”. (Sugar winds up going to the fat cells, which are far more welcoming.) Meanwhile both blood sugar and insulin have been raised, setting you up for hypertension, fat storage, hunger, cravings and mood crashes when your sugar eventually does fall.

Not a great situation by any means.

To measure the effect of food on blood sugar, scientists came up with the idea of the glycemic index. Using pure glucose as a standard (with an index of 100), they tested 50 gram portions of digestible carbohydrate and measured how quickly and how high blood sugar rose in reaction to eating them. By eating low-glycemic index foods you presumably could avoid the blood sugar roller coaster.

But there are two big problems with using the glycemic index as a guide to eating.

One, it only applies to a food eaten alone- in other words, a banana, not a banana with peanut butter.

Two, and more important- the glycemic index doesn’t take into account portion size.

The glycemic index of 50 grams of spaghetti is “moderate”, but no one eats 50 grams of spaghetti- at least they don’t at the Olive Garden, or at any home cooked Italian meal I’ve ever seen!

And the glycemic index of 50 grams of carrots is “high” but no one eats 50 grams of carrots (there’s 3 grams of carbohydrate in a carrot).

Glycemic load takes into account portion size. Carrots- which have a high glycemic index- actually have a very low glycemic load. Spaghetti- which has a moderate index- has a very high glycemic load.

Glycemic load is all you need to pay attention to, because it tells you what’s going to happen to your blood sugar in the real world. (Even then, it still refers to food eaten alone. Add some fat to your carbs– peanut butter on an apple, for example– and you’ve just lowered the glycemic load.)

Glycemic index is a pretty useless indicator of anything, but glycemic load is meaningful. (You can find a definitive of glycemic index and glycemic load of food here.) Bottom line: eat as little sugar as possible and go easy on the foods that turn into sugar quickly- like cereals, breads, pastas and anything white (except chicken, cauliflower and mushrooms!)

When it comes to sugar one thing is very clear: Less is more and zero is better.

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  • Judy Cox

    Thank you for this explanation and clarification. It makes sense to me and I had no knowledge of the differences between the two.

    • Adrienne

      Thank you so much for this understandable explanation. My blood results have come back as pre diabetic. I need to make changes to the way I eat, and really had absolutely no idea where to start. I have driven myself nearly mad, trying to decipher all the information so readily available on the internet.
      Your explanation is just so clear, and I get it…
      Very grateful.

  • Paleo Huntress

    The index isn’t based on the weight of the food, it’s based on the carbohydrate content. In other words, the portion contained as many carrots as was necessary to equal 50 grams of carbohydrate. In the case of carrots, that’s over a pound. In the case of pasta, that’s just a couple ounces.

    Your conclusion is still accurate, but the description of the method is off.

  • Thank you so much for this explanation! I have looked multiple times in the past for an understanding of the differences between glycemic index and glycemic load, and I finally understand! Thanks again!

  • […] Less movement means you get to eat less, but that only works for me if I can become less hungry, which requires mastering the art of maintaining stable blood sugar. Researching how to calculate glycemic index and glycemic load gave me flashbacks of flunking organic chemistry; basically, different foods affect your blood sugar to dramatically different degrees. And the equation for each food changes in conjunction with what else you eat that food and its portion size. For example, the glycemic load of eating an apple changes if you eat that same apple with almond butter. For an explanation regarding everything glycemic that won’t give you a migraine, read Jonny Bowden’s blog, The Blood Sugar Factor Glycemic Index vs. Glycemic Load. […]

  • […] Index vs Glycemic Load – Try this article on for size: (The whole thing about eating high sugar foods is really not the obesity epidemic, or the cancer […]

  • JH

    Hi Jonny,

    Thanks for the great description of GI vs. GL. Unfortunately there is so much emphasis on GI, and that is so wrong. We all need to get the word out that GL is the one to watch – stop thinking that bread, pasta, rice, oats, corn, and potatoes are just fine as long as you choose the lowest GI ones. With that said, there are a few additional points worth noting, as Paleo Huntress started on:

    1. Put the GL in terms of familiar measures – in the case of the carrots, you’d have to eat about 6-7 carrots at once to get the same effect as just a few ounces of pasta. But, how much is a few ounces of pasta? I’m bright and educated, but I certainly don’t know offhand. And, is this cooked or dry weight? If it were put in terms of n carrots = 1/2 c of dry macaroni (for GL), that would be much more of an eye-opener for a lot of people.

    2. You have to pay attention to the GL chart serving sizes! If you choose to eat pasta, thinking that you’ll just have one cup and maybe get a reasonable GL from it, then actually measure it! It’s easy to look at the pile of pasta on your plate and underestimate just how much is there, accidentally eating two cups instead of the one you thought you were eating. Because the GL is related to serving size, people have to keep in mind that if you eat e.g. twice as many graham crackers as the standard serving, the GL will also double from that food. I also found the Harvard GL tables rather laughable – their serving sizes can be quite unrealistic, so if someone chooses a food based on it’s GL, then eats THEIR usual serving not Harvard’s, they will have much more of a blood sugar effect than they think.

    3. People should stop thinking that “healthy whole grains” are okay – the GLs of these are just as high or higher than their white counterparts. People need to realize that eating “healthy whole grains” is essentially eating “teaspoons of sugar”, something they’d never do. Let’s call all grains what they really are – starches which digest into massive amounts of sugar. In spite of the enormous amount of reading I do and my large interest in nutrition, I literally had no idea until recently that a whole wheat pasta lunch was really the same as eating 15 or 20 teaspoons of sugar, and really, most other people probably don’t know this either. Think of all the moms who send their kids a “healthy” whole wheat sandwich for lunch, while carefully never letting their child eat candy “because candy is bad for them”. (Now, since I’ve mostly stopped eating the highest GL foods, if I eat something with a teaspoon of sugar on or in it, I don’t worry – I’m still far ahead of where I would have been had I eaten even a single piece of bread!)

    4. We should emphasize that it’s not just diabetics who should be concerned about raising blood sugar – it’s bad for all of us, for many reasons, even for our thin healthy active children. This goes for doctors too – my mother-in-law is prediabetic, and when she got her blood sugar checked by her doctor, it was “It’s okay, it’s low enough for you to not be diagnosed as diabetic, but you should lose weight.”. So, for her it was “Ok! No changes necessary, I’ll just go ahead eating starches as usual – since I’m not diabetic I don’t have to worry.”.

    Great article!

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