Carbs can be confusing. There are “simple carbs” and “complex carbs”, “good carbs” and “bad carbs” (and of course plenty of diets that tell you to simply cut them out). But there’s another measure of carb quality you may have heard of, especially if you’re trying to prevent or control diabetes: the glycemic index. Wondering if it’s worth using? Here’s the scoop.
The glycemic index is a ranking of carbohydrate foods on a scale of 0-100 in terms of how they affect your blood sugar after eating them. It’s calculated by feeding a certain amount of the particular food to healthy people, then measuring how their blood sugar responds over the next two hours.
Low GI foods (ranked 55 or less) are more slowly digested and absorbed by the body, so they raise your blood sugar levels more slowly too. Apples, carrots, nuts, but also pasta and brown rice are considered low-GI. High GI foods (over 55) are more quickly metabolized and boost your blood sugar (and insulin) levels faster. High-GI foods include white bread and candy, but also watermelon and oatmeal.
The idea is that by choosing low-GI foods more often, you’ll avoid spikes in your blood sugar and insulin levels, which may help prevent type 2 diabetes or help keep your blood sugar in better control if you have diabetes. In a position statement, the American Diabetes Association said that substituting low-GI foods for high ones may help control blood sugar. There’s also some research suggesting that a low-GI diet can help reduce cholesterol levels and is better for weight management in the long-term.
But truth is, the glycemic index is not a perfect system--and not as straightforward as it may seem. For starters, blood sugar responses to a carbohydrate food can vary widely between people and even vary in the same person under different circumstances. A food’s official GI ranking only requires ten people. In my mind, that’s a pretty small number that can affect whether that food is perceived as “good” or “bad” to others. The ranking also depends on a lot of factors, like ripeness, temperature, and amount of processing (for instance, diced boiled carrots have a higher GI than raw).
What’s even more worrisome for me as a dietitian is that the rankings can make some foods appear unhealthy, when they’re actually quite nutritious. For instance, the GI of potatoes is higher than potato chips. Ditto for other healthy, higher-GI foods like popcorn and oats. I’d hate to see people cutting out healthy foods they love because of their number on the Index. On the flip side, it can make some foods seem healthier than they are. Case in point: Coconut sugar is held up by some as a healthy sweetener because of its GI ranking, even though it’s an added sugar just like table sugar or honey and has no significant nutritional value in the amount most people would use.
Bottom line: The glycemic index may be a helpful tool, especially if you’re trying to control your blood sugar, but you need to use common sense too. Just because a food has a low-GI doesn’t mean it should be a staple. And just because a food has a higher-GI doesn’t mean you shouldn’t eat it. With high-GI foods, watching portion size and having it with other foods (especially protein foods) as part of a snack or meal can help prevent blood sugar spikes.