The glycemic index (GI) measures how quickly a food converts to sugar in your body and raises your blood sugar. Higher-glycemic foods spike your blood sugar quickly, whereas lower-glycemic foods are absorbed more slowly. What the glycemic index doesn't measure is how much of a food you eat. That’s where the glycemic load (GL) comes in: It measures quality and quantity.
It takes a bit of math to put these tools to work. You can determine a food’s glycemic load by multiplying the glycemic index by the number of grams of carbohydrate in the food and dividing the total by 100.
So while carrots have a glycemic index of 47, whole-wheat spaghetti clocks in at just 32. So that means you’re better off eating the spaghetti, right? Nope. Carrots carry far fewer carbs than pasta, thus the glycemic load number is much lower:
Carrots: 47 x 6/ 100 = 2.82
Pasta: 32 x 48/ 100 = 15.36
As you can see, this can become confusing, yet nutrition experts continue to trot out this data. As a health coach, I disagree with its value as a health-promoting tool. Here are five reasons to ditch the glycemic index and load (along with those so-called experts):
1. The GI and GL look at foods as singular entities.
One big problem: We don’t eat foods in isolation, and these measures couldn’t possibly look at every food combination. So, for instance, while a white baked potato has a high glycemic index of about 76, you’ll probably throw in some butter, which buffers the potato’s blood sugar spike.
2. The GI and GL don't assess the quality of a food.
A sweet potato and graham crackers both have a GI of about 70. Graham crackers actually have a lower GL than a sweet potato (14 versus 22), yet that sweet potato comes packed with beta-carotene and other nutrients plus fiber. The graham crackers are just a processed, sugary train wreck. But if you were looking only at the GI and GL, you would assume graham crackers are a better pick — which is not the case.
3. The GI and GL don't analyze fructose levels.
The GI and GL look at how a food raises your blood sugar. All sugar breaks down to glucose and fructose. Glucose raises your blood sugar; fructose doesn’t. Thus, high-fructose foods register low on the GI and GL scales. Yet this type of sugar increases inflammation, stresses out your liver, and converts to fat. What's more, processed foods often contain high-fructose corn syrup, making them low on the GI (as manufacturers proudly tout) but still not great for your health.
4. The GI and GL don't account for your personal biology.
The GI and GL assume your metabolic machinery works correctly. Sorry, not everyone falls into that “average, healthy adult" category. Depending on your body, foods will have an entirely different effect on your blood sugar and how your body handles that sugar load. The GI and GL couldn’t possibly account for such biochemical individuality.
5. The GI and GL are inconsistent.
One study found that athletes should eat low-glycemic carbs 30 to 60 minutes before exercise, high-glycemic carbs during exercise, and high-glycemic carbs for post-exercise meals. Other studies yield much different conclusions. One looked at how seven male athletes performed during high-intensity interval training (HIIT) using either high-glycemic or low-glycemic foods. Researchers concluded that though “the relationship between GI and sporting performance has been a topic of research for more than 15 years, there is no consensus on whether consuming [carbohydrates] of differing GI improves endurance performance.” In other words: Nobody has much of a clue whether or how GI and GL work.
I gave up on the GI and GL numbers years ago because they’re too confusing, and really, who wants to tally up numbers or reference charts? Instead, I focus on whole, quality, nutrient-dense foods. Those include leafy and cruciferous greens, lower-sugar fruits like berries and apples, complete protein sources like grass-fed beef, and healthy fats like nuts and seeds. Focus on nutrition — instead of numbers — and you'll establish a healthy diet you can stick to.