What Does “Glycemic” Mean, Anyway?

“Glycemic” is a word that gets tossed around a lot these days. It’s important to eat “low on the glycemic index,” or a healthy “low-glycemic diet.” But what does “glycemic” mean, exactly?

Glycemic: It’s all about sugar

The concept is actually pretty straightforward: The glycemic index measures how quickly different foods dump sugar into your bloodstream.

Here’s an example. Drink a cup of apple juice, and your body gets a speedy jolt of sugar. Eat a whole apple, though, and that doesn’t happen. What’s the difference? Fiber. It slows the whole process, keeping sugar delivery from the apple nice and slow. But without fiber, the apple juice gets an express pass into your bloodstream.

Glycemic index charts (like this one from Harvard) rank foods by their glycemic load—how much your blood sugar will actually rise after eating it. Apple juice packs five times the glycemic load of an apple.

Why Does the Glycemic Index Matter?

Blood sugar spikes aren’t healthy. They wreck your metabolism, forcing your liver to store the extra sugar as fat. They set off a dangerous chain reaction of insulin surges, high blood pressure, and high triglycerides, too. High-glycemic eating makes you more likely to get heart disease or several types of cancer.

Eat low-glycemic and you’ll soothe your insulin response, lose more weight—and keep it off, studies show.

So What Should I Eat?

It’s pretty simple. Low-glycemic-load foods tend to be whole, unprocessed foods—fresh fruits and veggies, whole grains, beans, and lentils—the only type of carbs you’ll find in The Fast Metabolism Diet. (You won’t find meats and fats on the glycemic index, because they don’t contain any sugar.)

Don’t get too wrapped up in the numbers, though. Watermelon has a high glycemic index (72 out of 100), but the amount of sugar in a serving of watermelon is so minuscule that it’s barely a blip in your blood sugar: it works out to a tiny glycemic load of 4. Sponge cake is technically lower-glycemic than a sweet potato, but obviously, the sweet potato is healthier.

Try these low-glycemic swaps:

Instead of this: Eat this:
Orange juice Orange
Instant oatmeal Steel-cut oats
White rice Brown rice
White potato Sweet potato
White bread Sprouted grain bread