Glycemic Index Diet

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KEY POINTS

• The glycemic index (GI) ranks foods that contain carbohydrates based on how the food affects blood glucose. A food with a high GI raises blood glucose more than a food with a medium or low GI. You need sugar in your cells for energy, but too much sugar in your blood is not good for your health.
• Many things can affect the GI of a food. It’s best to work with a dietitian if you want to try this kind of diet.

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What is the glycemic index?

Carbohydrates, or carbs, are the main source of energy for the body. Carbs get digested quickly, and the body converts them easily into blood glucose. Your body uses insulin to help move sugar from the blood into the cells. You need sugar in your cells for energy, but too much sugar in your blood is not good for your health. If your blood glucose runs too high over time (months or years), it can cause problems with your heart, eyes, kidneys, nerves, and blood vessels.

Carbohydrates are the foods that affect blood glucose the most. Examples of carbs are fruits, starchy vegetables, breads, pastas, rice, sugar, syrup, and honey. The glycemic index (GI) ranks foods that contain carbohydrates based on how the food affects blood glucose. A food with a high GI raises blood glucose more than a food with a medium or low GI.

The glycemic index measures blood glucose effect per gram of carbohydrate in a food, not per gram of the food. This can be confusing, because a large serving of a low GI food will raise blood glucose.

Examples of foods with a low GI include most beans and lentils, vegetables such as broccoli, lettuce, and peppers, some starchy vegetables like sweet potatoes, most fruit, and many whole grain breads and cereals. Meats and fats don’t contain carbohydrates, so they don't have a GI.

What affects the GI of a food?

Many things can affect the GI of a food:

• The GI of a food is different when eaten alone than when you eat it with other foods. For example, eating protein with a high GI food slows down the rate of digestion and can cut the GI effect by about one third. Combining high GI foods with low GI foods helps balance out the effect on your blood glucose.
• The size of food particles affects GI. Fruit juice has a higher GI than whole fruit. Mashed potatoes have a higher GI than a baked potato.
• Whether you cook foods, and how long you cook them affects the GI. For example, cooking pasta until it is soft raises the GI, while lightly cooked or “al dente” pasta has a lower GI.
• The form of the food makes a difference. For example, long-grain white rice has a lower GI than brown rice. However, brown rice has a lower GI than short-grain white rice.
• Foods high in fiber take longer to digest and therefore affect your blood glucose more slowly. For example, All-Bran cereal is a low GI food, while Puffed Wheat is a high GI food.
• The higher the fat content of a food the lower its GI. Fat slows digestion, so foods such as Snickers candy bars affect your blood glucose less quickly than food such as rice cakes.
• When a fruit or vegetable is ripe, it has a higher GI than when it is slightly green.
• Acids in foods slow down digestion. Having meals that include some vinegar, lemon or lime juice, or pickled vegetables can lower the GI for the meal.

Following a glycemic index diet may have health benefits for people with diabetes, and possibly acne and heart disease. It has not been shown to help with weight loss. It is also important to look at the nutrient value of foods, not just the GI, when making food choices. Ask your healthcare provider for a referral to a dietitian to learn more about whether the GI diet is right for you.