When it comes to making smart food choices, you probably already think about calories and carbs, fast foods and fats. Now you can add one more thing to the list: the glycemic index (GI).
How it works
Developed in 1981, the GI was originally for diabetics, but it’s useful for all of us. The GI is a measurement of how much a set amount of food has the potential to raise your blood sugar. When you eat, you convert a food’s digestible carbohydrates into glucose. Glucose energizes your cells and tells your pancreas to produce insulin, and this helps your cells absorb glucose.
Depending on the food, you digest and convert its carbohydrates at different rates. The lower the GI of a particular food, the more slowly you digest it, which gradually increases your blood sugar and insulin. Good. The higher the GI, the faster your blood glucose rises. Not good. Here’s why:
“Eating foods that cause rapid increases in blood sugar triggers the rapid release of insulin. This causes your blood sugar to lower quickly, which results in hunger, sleepiness and the desire to eat again,” says Lauri Ek-Watson, clinical nutrition manager at Providence Alaska Medical Center. “Studies suggest that if this persists for years, you have higher post-meal blood sugar and excessive insulin secretion. This can contribute to obesity, irreversible Type 2 diabetes, heart disease and gall bladder disease.”
GI by the numbers
The GI of foods is ranked on a scale of 0-100:
- Low GI – 55 or less (100 percent stone-ground whole wheat, sweet potatoes, peas, other non-starchy vegetables and most fruits)
- Medium GI – 56-99 (whole wheat and rye breads, quick oats and brown rice)
- High GI – 70 or more (white bread, corn flakes, russet potato, melon and pineapple)
Generally, the more food is cooked or processed, or the more ripe it is, the higher its GI.
Paleo and gluten-free diets
“The Paleo diet—mostly fruits, vegetables and meat—tends to have a lower GI,” says Ek-Watson. “Gluten-containing foods (wheat, rye and barley) have a lower GI, if they are eaten in the most unprocessed form possible (whole-grain cooked barley, whole-wheat bread). Gluten-free foods made of rice or potato flour have a higher GI than wheat products. If you eat gluten-free, choose whole grains, like oatmeal and quinoa; they have a low GI. However, just because a food has a low GI doesn’t mean it’s more healthful. Some low-GI foods, like ice cream and chocolate cake with frosting, are loaded with sugar and/or bad fats.”
Look out for limitations
As a measurement of healthy eating, relying just on the GI goes only so far regarding the following:
- Combining foods. You may start with a high-GI plain, baked potato, but top it with margarine and you lower the GI. “Mixing foods together changes the way you digest them, which in turns changes the GI of them, overall,” Ek-Watson says.
- Portion sizes. The GI is based on 50-gram amounts. For some foods, that’s a lot on your plate at once. At this unit of measurement, the GI of watermelon and a donut are the same. But they’re really not when you sit down to eat them. A cup of watermelon has 7 grams of carbohydrate (GI of 72) and a slice of chocolate cake with frosting has 52 (GI of 38).
- Type vs. total amount of carbs. The GI deals only with individual foods, not the total amount in a meal.
Enter the glycemic load (GL)
Like the GI, the GL affects glucose and insulin, but it goes a step further. “The GL considers not only the GI of a single food, but also its typical-portion size,” says Ek-Watson. “What’s referred to as dietary GL is the total of GLs consumed in a meal.”
- Low dietary GL – 10 or less
- Medium dietary GL – 11-19
- High dietary GL – 20 or more
That serving of watermelon? It has a GL of 7, while the slice of chocolate cake with frosting has a GL of 12.5. “Obviously, the watermelon is healthier,” says Ek-Watson. But these numbers don’t mean the same thing for everyone.
We’re all unique
“Recently, an Israeli study published in Cell, a scientific journal, looked at blood sugar levels in 800 people after they all ate the same meals for a week. It found that each person metabolized the meals differently,” says Ek-Watson. “That’s because their ages, BMIs (body mass index) and other factors affected their blood sugar levels differently. This study points to the need for people to have individualized diet plans.”
Be a healthful eater
For a list of foods with their GIs and GLs, Ek-Watson suggests the University of Sydney’s site. And she urges:
- Eat a balanced diet of fresh fruits and vegetables, whole grains, legumes, fish, a little red meat and poultry, and good fats.
- Eat fewer foods with simple carbs, but don’t pass up the ones rich in vitamins, minerals and fiber.
- Watch your portion sizes.
- Choose foods more often with a low-to-medium GI and GL.
When you eat healthfully and in moderation you can’t go wrong with the food choices you make—whatever the number.
If you want help finding your GI and GL numbers or have other questions about healthy eating, talk to a nutritionist. You can find a Providence provider in this multistate directory.