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Glycemic Index, Glycemic Load, and Insulin Index – Explained!

high glycemic index foods assortment

Once low carb diets got popular, and everyone waged war on sugar, they needed more ways to state that certain foods were to be avoided. Looking at the amount of carbs and sugar in a certain food was too easy. That’s when we started seeing frequent references to the Glycemic Index, Glycemic Load, and Insulin Index.

The numbers are all related, but some are more important than others. Let’s look at each one in detail and see what, if any, role they should play in your life.

Glycemic Index

The Glycemic Index (GI) is a measure of how quickly a carbohydrate hits our bloodstream. The faster a carbohydrate gets digested and released as glucose into the blood, the higher it ranks on the index.

Foods are rated on a scale from 0 to 100. A GI of 1-55 is considered low, 56-69 is medium, and 70-100 is high. It’s all relative to pure glucose, which is rated at 100.

How is it calculated?

To determine a food’s GI, they take an amount of the food containing 50 grams of carbs and feed it to the test subjects, then monitor their blood glucose levels.

Why is it important?

Well, knowing the GI gives you an idea of how rapidly a certain food will spike your blood sugar. And since blood sugar spikes are usually followed by blood sugar crashes, which are followed by lethargy, you can see which foods you might want to avoid at certain times.

What’s missing?

What’s missing is the real life application. See, the measurements are done based on whatever amount of the given food contains 50 grams of carbohydrates. That works great for a control in a laboratory. But that’s not how we eat in real life. We eat food in portions. We eat serving sizes.

The Glycemic Index does not take portion size into account!

Also, it only applies to food eaten alone. That makes sense in the lab, but in real life, we typically eat meals. There’s a GI value for an apple, but there’s no GI value for apple slices with peanut butter, or baked potato with butter, or your mom’s secret family lasagna.

Fortunately, there’s something called Glycemic Load.

Glycemic Load

While the Glycemic Index is almost entirely useless, Glycemic Load (GL) actually has some meaning to it. Glycemic Load measures how much a serving of food will raise your blood sugars. It takes into account both how quickly the carbohydrate raises blood sugar and how much carbohydrate is found in whatever you’re eating.

A GL of 10 or less is low, 11 to 19 is medium, 20 or more is high.

How is it calculated?

Glycemic Load is the product of a food’s GI and its total available carbohydrate content (Net carbs.) So, if you know a food’s GI, and how many grams of carbs are in the serving you’re eating, you can calculate the GL.

First, multiply the GI of a food by the number of grams of Net carbohydrate in the specific serving. Next, that number is divided by 100. The result is the GL for your serving size.

Let’s look at watermelon as an example.

Watermelon has a GI of 72, and a 1 cup serving contains 11g Net carbs. So the calculation looks like this:

(72 x 11) / 100 = 8

Despite having a high GI, watermelon only has a GL of 8, which is low.

Why GL totally beats GI.

The Glycemic Index isn’t based on actual serving sizes, so it has little practical application in daily life. The only worthwhile application is using the values to calculate Glycemic Load.

GL has a real life application. It actually gives you an idea how much of an impact a serving of food will have on your blood sugar.

GI can actually give you the wrong idea.

The biggest problem with the Glycemic Index is that it spreads the idea that high GI foods are bad. Thus, people begin to think that many fruits and vegetables are unhealthy!

Here’s the thing though – if a food is high GI, yet low in carbs, it won’t have much affect on the body.

Watermelon and carrots are good examples.

Watermelon has a GI of 72, which is high. Higher than ice cream, sugar, and white bread! But if you look at watermelon in the perspective of 1 cup of watermelon balls, the GL is 8, which is low!

Now, I’d probably eat at least two cups of watermelon, which would be about 16 GL. Still though, that’s only a moderate GL from two servings!

Looking at carrots, the GI is 47. While not nearly as high as watermelon, it’s actually higher than the GI for spaghetti!

I like to eat baby carrots, and I might eat 10 of them, just over the typical serving size. But even though I’m surpassing the typical serving size, the GL is only 3. That’s about as low of an affect on your blood sugar as you can get!

Relying only on GI would have you eating spaghetti.

If you didn’t understand the numbers, and just took them at face value, you’d think that a plate of spaghetti (GI 42) was a healthier choice than a plate of carrots (GI 47.)

This dose of reality comes courtesy of Dr. Jonny Bowden:

“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!”

I can only imagine what the actual Glycemic Load would be of someone having even just two plates of spaghetti! I mean, one plate of spaghetti is probably double or triple the amount used when they calculated the Glycemic Index!

Insulin Index

What’s talked about even less is the Insulin Index. This measures your body’s insulin response to various foods.

It’s the same idea, but instead of looking at your blood glucose levels, it looks at blood insulin levels.

How is it calculated?

Test subjects are given a portion of food (equal to 1,000kJ, or roughly 240 food calories,) and blood insulin levels are tracked.

Though not based on serving sizes, it’s a much more relatable measure since we all understand calories!

Where the Insulin Index beats both GI and GL

Looking at the list, most foods that rate highly on the Glycemic Index rate highly on the Insulin Index. Breads, cereals, rice, potatoes, etc. But while most foods’s scores were highly correlated, not all of them were.

Certain foods, notably lean meats and other high-protein foods, will cause an insulin response despite their lack of carbohydrates.

You look up lean beef, or whey protein powder, and while you won’t even find them on the Glycemic Index, they produce surprisingly high insulin responses! Beef apparently produces more of an insulin response than pasta! (You gotta store those BCAAs!)

See the insulin index chart found here in The American Journal of Clinical Nutrition.

The Most Important Value: Nutritional Value

It’s easy to get caught up in the numbers and forget that you’re not eating numbers, you’re eating food. And why do we eat food? For the nutritional value!

And when it comes to nutritional value, none of the above ratings are particularly useful!

Consider baked potatoes.

White potatoes are often vilified due to their high GI. It’s actually on par with jelly beans!

1 medium baked potato with skin:

  • GI 76
  • GL 23

Compared to 1 oz. jelly beans:

  • GI 78
  • GL 22

What do we make of this?

Well, if you’re a stickler for Glycemic Load, you could reason that white potatoes and jelly beans are nearly equivalent foods. You might even consider a serving of jelly beans to be the better option.

But you’re forgetting that jelly beans are void of nutrients!

The lower (but still ‘high’) GL is not a good argument for eating jelly beans instead of a baked potato. You have to look at the nutrition profiles and see all the good stuff you’d get from that potato!

Eat your fruits and vegetables.

Yes, they’re typically high on the Glycemic Index. We saw that with watermelon and carrots. But when you consider serving sizes, you’re not getting enough carbs to make much of an impact. And it’s nearly impossible to overeat thanks to the high water and fiber content.

Unlike pasta, which is carbohydrate-dense and extremely easy to overeat!

And pasta doesn’t offer anywhere near the amount of vitamins, minerals, and other micronutrients found in fruits and vegetables.

How to Use This Information

For most endurance athletes, in daily life, this information is of little use.

It’s nice to know, to help you better understand food’s affect on the body, and it can help to reference the charts occasionally, but you don’t need to have it at the front of your mind.

Speaking of which, here’s the official list for the Glycemic Index, thanks to David Mendosa and Professor Jennie Brand-Miller of the University of Sydney. And if you check out NutritionData.com, you can find an estimated Glycemic Load for virtually any food you want.

When you want fast-acting carbs for energy or refueling.

Perhaps you’re wondering if you should eat a white potato or a sweet potato in your post-ride recovery meal. Going by the name alone, you’d think the sweet potato is going to be the ideal way to refuel your muscles quickly. But no – despite the name, the sweet potato is actually a low GL (10,) while the white potato is a high GL (23.)

So, the sweet potato is probably the better choice in a pre-ride meal, and you can load up on some baked white potatoes later.

More importantly, look at grams of carbs.

Most of the time, it’s more important to consume food containing the correct number of carbohydrates than it is to consume a food rated at a specific GI or GL.

That info is readily accessible on most food labels, on that NutritionData.com website, or in apps like MyFitnessPal.

Consider satiety.

There’s a myth that high GI foods wreck your appetite and cause cravings. But that’s not always the case. For example, a bowl of oatmeal or baked white potato. These are good choices (at least for most people) that fill you up so you feel satiated and maintain stable energy levels, despite a high GI.

You can gain weight no matter what choice you make.

Think that only eating low GI or low GL foods will help you lose weight? Perhaps. It sounds good, in theory. But one randomized clinical trial showed that it didn’t matter. Eating low GI carbs resulted in no increase in insulin sensitivity.

It boils down to the fact that if you’re eating more than you need to, you’ll probably get fat.

The Bottom Line

The numbers are helpful guidelines to be used in the greater context of your nutrition plan. They are not substitutes for n=1 testing. Remember, the numbers are only estimates and aren’t necessarily how your body will respond to a certain food.

It’s most important to find the foods that make you feel energized and satiated. That’s why you keep a food log with what you eat and how you feel, rather a list of foods and their GI values.

 

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6 Comments
  1. Nothing like a good sugar rush when you’re about to bonk!

  2. @Steve

    You got that right!

  3. Interesting in regards to the insulin response to protein. That should be used wisely by anyone on a low carb diet.

  4. @Eileen

    Like maybe someone is carb cycling or doing low carb, yet they want a good insulin response to shuttle muscle-building nutrients into cells, so they have protein? Yep, I like your thinking.

    Or just interesting reading for anyone that’s doing a high-fat diet.

    Regardless, the body is going to figure something out whether or not you analyzed the glycemic index or insulin index!

  5. Ok so you’re saying that even though the media reports that anything high on the glycemic index is bad, that’s hyperbole and we should think critically and logically before making dumb decisions? 🙂

  6. @Shelly

    Exactly!

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coach levi
Hi, I'm Coach Levi. I'm a USA Cycling Certified Level 3 Coach as well as Level 1 Certified with Precision Nutrition. Want to feel better, ride faster, and look great? Let's work together!

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