When you eat carbohydrates, your blood sugar rises. It also matters what kind of carbohydrates you eat. A big baked potato can have the same effect on your body as pure table sugar — a fast, sharp spike in blood sugar and insulin. In the form of lentils, the same amount of carbs acts more slowly and has a smaller impact.
Avoiding those spikes is good for your health. Even if you don’t have a blood-sugar issue, choosing your carbs carefully will help you steer clear of various cancers and heart disease as well as type 2 diabetes. The glycemic index (GI) measures how much a food boosts blood sugar, comparing its effect to either table sugar or white bread. A food with a glycemic index of 100 has the same effect as table sugar (or bread). On the other hand, lentils have a GI around 30, compared to sugar. So do nuts.
When you look at GI tables, you’ll also see information on the glycemic index per serving. Remember that the tables are based on averages, which can include big variations. This list, for example, covers 62 foods, while this one breaks out the differences among more than 1,800 foods from around the world! It’s also important to remember that the tables are based on the reactions of people with normal blood-sugar responses. If you’re diabetic or prediabetic, you may experience bigger spikes. (You can also use this GI calculator to search for a food.)
You already know the foods that are heavy in starch. The glycemic index tables will help you realize just how starchy they are. A big baked russet potato has a GI of 111, compared to sugar, and 158 compared to bread. Sushi rice is just slightly better.
There are some fine points you’ll learn from the chart of 1,800 foods. Brown rice has a lower glycemic index than the potato or most white rice but isn’t necessarily a low-GI food; depending on the rice, it may have a GI from 50 to 90, compared to sugar. Converted long-grain rice can be healthier. (Carbs with a low GI (55 or less) are digested more slowly and cause a lower and slower rise in your blood sugar.)
Unless it helps make healthy eating fun, you don’t need to get too involved with the math. The main message: choose foods with a low GI, eat small amounts of the foods in the middle, and save high GI foods for treats. Meats and fats don’t have a GI because they do not contain carbohydrate. You can lower the total GI of a meal by eating less of the higher-GI foods and combining them with low-GI food. Healthy fats are your friends; they add calories to fill you up and won’t add to your GI count at a meal.
Low GI foods have a glycemic index, compared to sugar, of 55 or less. This group includes nuts, beans, legumes, most fruits and vegetables, al dente pasta, dairy foods, and nuts.
Moderate GI foods run from 56 to 69. You’ll find corn, some kinds of rice, and small potatoes or yams and some breakfast cereals in this group.
The high GI foods, those with a glycemic index of 70 or higher, are the problem. This group includes all the “white” foods, including bread, rice cakes, bagels, most crackers, and packaged breakfast cereals. Add in sugar in cakes and cookies and GIs soar.
When you’re preparing meals for a family, you can swap out white rice and potatoes for brown rice and yams, and substitute peas or pasta for corn.
Fat and fiber tend to lower the GI of a food. In general, the more cooked or processed a food, the higher the GI. Juice has a higher GI than whole fruit, for example. Choose a whole grain over a refined grain. As you’d expect, a sweeter riper fruit has a higher GI than if the fruit is less ripe. Cooking can increase GI by reducing fiber, so al dente pasta has a lower GI than soft pasta.
GI isn’t the only consideration. You’re looking for nutritious foods and meals that are healthy as a whole. You may feel compelled to eat more meat to make up for the missing potato. However, there’s some evidence that a vegetarian diet is helpful for type 2 diabetics, so try not to load up on steak. Gradually move towards more beans, legumes, and vegetables.
If you’re like most Americans, you’re eating too many starchy or sugary snack foods. The GI index is another reminder of why that’s a habit to break.
June 02, 2016
Christopher Nystuen, MD, MBA