Does the Glycemic Index Really Matter When Managing Your Blood Sugar?

If you don't have diabetes, you probably don't give your blood sugar much thought. No matter how much you eat, drink or exercise, your body is going to maintain normal levels of blood glucose (sugar).

But for people with diabetes, managing blood sugar can be a daily struggle. Practically anything and everything can affect blood sugar levels — excess stress, illness, lack of sleep, not enough water, too much or too little exercise, even sunburns. Diet, however, remains one of the main ways people with diabetes can effectively manage their blood sugar, and controlling carb intake is one of the most important aspects of a diabetic-friendly diet.

But not all carbs are created equal. The glycemic index (GI) is one such tool that measures the impact of carbohydrate-containing foods on your blood sugar. Low-glycemic foods are digested more slowly compared to high-glycemic foods, which can raise blood sugar levels fast.

Therefore, it makes sense for people with diabetes or prediabetes to follow a low-glycemic diet, right? Not necessarily, says Kelly Gaines, a registered dietitian nutritionist at Houston Methodist.

"For people with diabetes, there is a benefit to choosing foods that have less of an impact on blood sugar levels," she says. "A low-glycemic diet has been shown to reduce the risk of type 2 diabetes and coronary heart disease. But just because something is a low-glycemic food doesn't mean that it's necessarily a healthy choice."

While the glycemic index can be a useful tool, it's not without limitations, according to Gaines, who here explains its benefits, drawbacks and potential alternatives.

What is the glycemic index?

"The glycemic index is a database comparing foods to see how they impact blood sugar or glucose levels," says Gaines. "The foods are ranked on a scale from 0 to 100 based on how much of an impact they have on blood glucose, zero being the most minimal impact with 100 being the most."

Low-glycemic foods have a GI between 1 and 55. These foods are digested at a slower rate and are typically — but not always — higher in fiber, protein, fat or a combination of these nutrients, says Gaines. Medium-glycemic foods have a GI between 56 and 69, and high-glycemic foods have a GI from 70 up to 100. High GI foods typically have less fiber, protein or fat and more carbohydrates (sugars), she says. Since the glycemic index measures only carbohydrates (sugar), foods without carbs like meat and fat are not included.

The glycemic index of certain foods

Examples of low-GI foods (0 to 55) include:

• Agave nectar
• Apples
• Corn tortillas
• Dried apricots
• Grapefruit
• Hummus
• Low-fat ice cream
• Mango
• Most beans and legumes
• Oranges
• Peanuts
• Pearl barley
• Pears
• Pistachios
• Raw carrots
• Sweet corn
• Vanilla cake (with frosting)
• Whole milk

Examples of medium-GI foods (56 to 69) include:

• Beets
• Couscous
• Dates
• Dried cranberries
• Figs
• Grapes
• Honey
• Kiwi
• Peaches
• Persimmons
• Pineapple
• Potatoes
• Pumpkin
• Raisins
• Ripe mango
• Ripe yellow bananas
• Watermelon

Examples of high-GI foods (70 to 100) include:

• Baked sweet potatoes
• Boiled yams
• Brown rice
• Cassava
• Fully cooked pasta
• High fructose corn syrup
• Most breakfast cereals
• Overripe bananas
• Pretzels
• Refined sugar
• Rice cakes
• Ripe plantains
• White bread
• White rice
• Whole wheat bread

Certain factors can alter a food's glycemic index

Both how you process and prepare a food can change its glycemic index score, according to Gaines. In other words, the more you process and handle a food, the more quickly it's going to raise your blood sugar levels.

"Cooking to a degree makes food easier to digest, so that can raise the glycemic index of something," says Gaines. "Ripeness can also affect how quickly a food is digested. For example, a ripe banana will raise your blood glucose faster than an unripe, green banana."

Another example is al dente pasta (Italian for "to the tooth"). By undercooking the pasta by a few minutes, you can slow the digestion down and lower the glycemic index of it.

"The way I like to think about [the glycemic index] is how much effort your body is putting into processing an ingredient," says Gaines. "For example, you can just tell by chewing al dente pasta that it takes more time for you to physically break it down, and so from a digestion standpoint, the same thing is happening in your body. Your body is having to put more effort to break it down to extract its glucose."

This is also why ultra-processed foods — given that they're "ultra" processed — tend to be easier to digest and often have a high glycemic index. They're going to raise your blood sugar faster than less processed foods, according to Gaines.

The glycemic index is a useful but limited tool

There are a few pitfalls when it comes to the glycemic index, which is why Gaines believes it's getting phased out in favor of other eating patterns.

"The studies about the glycemic index are about eating that specific food by itself, but how often are we eating a food completely by itself, like a piece of white bread with nothing on it?" she says. "Even at breakfast, you usually have cereal with milk or oatmeal with fruit. So it doesn't make much sense to be overly concerned that a food's GI is low or high because you're pairing it with other foods that likely are going to slow down digestion and lower its score."

Food pairings involving fat, protein and acid all help to slow digestion and can lower the GI of foods, according to Gaines.

Another limitation is how the glycemic index is standardized, says Gaines. The glycemic index doesn't take into account the portion sizes people typically consume. Rather, it's standardized by the amount of available carbohydrates (total carbs minus undigestible fiber and starch) present in each food tested.

For example, 50 grams of carbs from white bread is about two to three slices, whereas 50 grams of carbohydrates from blueberries is about three cups. Most people don't eat three cups of blueberries in one sitting, notes Gaines.

"Two slices of white bread or a cup of rice is very common to eat at a meal, but 50 grams of carbs from certain fruits or vegetables would be a lot," says Gaines. "It would be like eating an entire cantaloupe, five cups of beets or three cups of blueberries. It's just a much larger portion than we would typically consume in one sitting."

This, says Gaines, is why vanilla cake (with frosting, mind you) has a low glycemic index score of 46, while boiled yams and baked sweet potatoes have a glycemic index of 75 and 94, respectively.

"You can still have less nutritious foods that are low on the glycemic index, but there are foods with a high glycemic index that are going to have more vitamins, minerals and fiber than something like vanilla cake," she says.

Finally, the glycemic index doesn't include all foods — only the ones that have been studied. Therefore, there could be perfectly healthy fruits and vegetables out there that haven't been studied at all or in a very specific way (for example, cooked vs. raw)

that might be higher or lower on the index than how you'd prepare them yourself.

Glycemic load might be a good alternative

The glycemic load is a measure that considers both the glycemic index and portion size of a food, says Gaines. This formula, according to Gaines, helps put a food's glycemic index into a realistic perspective. After all, she notes, no one's going to eat five cups of beets in one sitting, but beets are still an otherwise incredibly healthy vegetable, and its glycemic load reflects that.

To calculate glycemic load, multiple a food's glycemic index by the number of available carbohydrates (total carbs minus fiber) in a serving and then divide by 100.

Glycemic load = glycemic index x grams of available carbohydrates in one serving / 100.

For a cup of cooked beets, that would be: 6.7 x 64 ÷ 100 = 4.3

A glycemic load between 0 and 10 is low, 11 through 19 is medium and anything 20 and above is considered high. Therefore, a cup of cooked beets has a very low glycemic load, despite having a medium-high glycemic index score.

What to focus on rather than glycemic load or index

Prioritize minimally processed and whole foods

"Rather than someone trying to focus on the glycemic index or load of each individual food, I'd much rather have people focus on eating more minimally processed, whole foods," says Gaines. "I think a lot of people would benefit their health more if they could move away from ultra processed foods, which would still help from a glycemic index standpoint."

"For example people ask me if they shouldn't eat carrots because they're too high in sugar," she adds. "Eating too many carrots isn't going to contribute to you developing diabetes, but eating too many ultra-processed foods like cakes, sweets, snacks and chips can."

So, what's the difference between minimally processed and ultra-processed foods? A "processed" food is simply any food that's been altered from its natural state, whereas an ultra-processed food typically has ingredients on the nutrition label that you can't pronounce and wouldn't otherwise be something you'd have in your kitchen, such as emulsifiers, colorings and preservatives. In other words, you couldn't recreate an ultra-processed food at home.

For example, fresh strawberries in the produce section would be considered a "whole" food, a pack of frozen strawberries would be considered "processed" and a strawberry toaster pastry would be considered ultra-processed.

Canned vegetables and beans are also examples of processed foods that aren't necessarily ultra-processed. You can cook beans and boil vegetables at home with ease.

Try the 'plate method' pattern of eating

"I have a lot of clients telling me that their doctors are recommending the Mediterranean diet," says Gaines. "While the Mediterranean diet is very healthy, you're often asking people to overhaul their food choices since it focuses a lot on seafood, whole grains and very low amounts of red meat, and it can be harder to fit into your lifestyle."

After all, we live in Texas; not along the Mediterranean, cites Gaines.

The plate method gives you more flexibility than the Mediterranean diet while still incorporating the principles of balanced eating, says Gaines.

"The plate method help you visualize your portions, regardless of what foods you're choosing from the different food groups to help you create more balanced meals," Gaines says. "Second, it takes away the burden of having to count and track things that can easily become tedious and overwhelming for people."

The plate method works like this. Using or visualizing a standard 9-inch dinner plate:

• Fill half the plate with nonstarchy vegetables
• Fill a quarter of the plate with whole grains, starchy vegetables or beans and lentils
• Fill a quarter of the plate with lean protein
  

This is also the approach recommended by the American Diabetes Association as the "easiest way to create healthy low-carb meals that can help you manage your blood glucose."

"The plate method is great because you can even translate it to when you're eating out," says Gaines. "This is still what I need my plate to look like."

The plate method can even still apply to meals that don't neatly fit within the quadrants of a plate like sandwiches or one-pot meals, says Gaines.

"There are so many ways we can make a sandwich healthy, even from a glycemic index perspective," says Gaines. "Yes, you can choose to use whole wheat bread, but even if you were to use white bread, you could focus on pairing it with other things like a lean protein source, some avocado for a healthy fat and vegetables to increase the fiber content. Then maybe it doesn't really matter so much whether it's on white bread or whole wheat bread."

"It just gives you a bit more flexibility rather than trying to avoid high-glycemic foods," says Gaines.

(Related: How to Build a Healthy Sandwich)