Good Carb, Bad Carb: Do You Know the Difference?

It’s important to track the quality of your carbohydrates—as well as the quantity—if you have diabetes.

Good Carb, Bad Carb: Do You Know the Difference?

Which do you think will raise your blood sugar more gently: Eating a whole orange or downing a glass of orange juice? The answer comes down to the quality of the carbohydrates in each.

High-quality carbs contain more fiber, which helps slow your digestion and, in turn, keeps your blood sugar from spiking. Low-quality carbs have usually been processed or refined in some way, which may strip away most of that helpful fiber.

This means that, in this example—you guessed it—the whole orange is the way to go.

What are low-quality carbs?
Low-quality carbs often lurk in refined, “white” foods (such as bread, rice and pasta), and in foods that have added sugar (which constitute up to 75 percent of packaged foods in America, according to a study published in 2012.)

In many cases, those choices also contain a lot of fat and not much nutritional value. Even if you didn’t have diabetes, they wouldn’t be smart options.

Discerning high-quality carbs
To identify a high-quality carbohydrate food, check the nutrition facts statement on the label for the amount of fiber the food contains. Multiply the number of grams of fiber per serving by 10.

Is that number greater than the grams of total carbs per serving? If so, you’re good to go.

Let’s use the orange/orange juice comparison as an example:

Take the orange, for starters:

  • An orange has 3 grams of fiber and 17 grams of total carbohydrates.
  • 3 grams of fiber x 10 = 30, which is far greater than 17.
  • Upshot: The whole fruit counts as a high-quality carb.

Now let’s look at the orange juice:

  • An 8-ounce glass of orange juice has 0.7 grams of fiber and 29 grams of total carbohydrates.
  • 0.7 grams of fiber x 10 = 7, which isn’t even within spitting distance of 29.
  • Result: That glass of OJ is definitely low-quality.

Understanding glycemic index
The glycemic index (GI) offers another way to measure the quality of carbohydrates in a food. The index assigns foods a number from 0 to 100 to reflect how quickly it boosts your blood sugar when consumed. The higher the number, the more dramatic the effect. A score of 100 represents pure glucose.  

Going back to our example, the GI of an orange is 43, while the GI of orange juice is 50.

But it’s important to note that the index works only in comparison to other foods. To predict how drastically a serving of something will affect your blood sugar, you need to consider the glycemic load (GL). That number looks at both the quality and the quantity of the carbs.

To return to the orange example, the GL of an orange is 4, while the GL of a glass of orange juice is 12.

It’s good information to be aware of, but the problem is that neither of these numbers will be readily available when you’re food shopping.

What’s the easiest way to avoid low-quality carbs?
Short answer: choose whole foods.

That orange may have sugar, but it also has some fiber and other nutrients that your body needs. Regular oatmeal—made from old-fashioned rolled oats—will affect your blood sugar less than a packet of instant oatmeal, which has been processed to make it cook quickly.

This doesn’t mean you can’t eat foods that contain low-quality carbs. If you pair them with high-quality carbs and plan your meals carefully, you should be able to enjoy them occasionally.

You can also be heads up when you’re in the supermarket aisle. When you shop for packaged foods, look for “unsweetened” on the label, which means no sweeteners—whether sugars, fruit-based or artificial—have been added.

What’s the deal with sugar alcohols?
You may also want to be on the lookout for sugar alcohols, a type of sweetener that often appears in foods labeled “sugar-free,” “no-sugar added” or “reduced-calorie.” Sugar alcohols provide fewer calories than regular sugar, but they’re not entirely calorie-free. (Rest assured, despite their name, they contain no alcohol.)

You can sleuth whether a packaged food contains sugar alcohols by looking for ingredients ending in “-ol” on the label. Common examples include mannitol, sorbitol, xylitol and erythritol. One reason to go easy on sugar alcohols? They may cause gastrointestinal distress—such as cramps, bloating and gas—for some people.

Since sugar alcohols are technically carbohydrates—albeit chemically-adjusted and derived from plant foods—they do hold the potential to raise blood glucose levels, particularly if eaten in excess. In short, just as you would with foods made with added sugars, it’s also important to consider the overall carb content of foods that contain sugar substitutes.

Medically reviewed in November 2020.

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