If you check your blood sugar against the carbohydrate foods you eat, you will find that certain carbohydrate foods, even at the same amount, will raise blood sugar faster and spike insulin levels more than others. This is because not all carbohydrates are of the same quality. Frequent insulin spikes can worsen diabetes condition and promote weight gain. In 2004, Professor Jennie Brand-Miller from University of Sydney, Australia, introduced a system to address this phenomenon and named it as the glycemic index, or GI.
Defining Glycemic Index
Miller explains that GI measures how quickly carbohydrates raise blood sugar levels. It compares carbohydrate foods weight for weight. The quicker the carbohydrate food raises blood sugar, the higher the GI value of the food. For example, a 50 g white bread increases blood sugar levels faster than a 50 g whole grain bread. White bread has a higher GI than whole grain. GI ranks individual carbohydrate foods mostly between 0 to 100 and divides them into three categories: low GI is 55 or less, medium GI is between 56 to 69 and high GI is 70 or more. High-GI foods induce insulin spikes due to the rapid conversion of those foods into blood sugar.
Foods with High GI
Harvard Health Publications lists foods with GI, serving size and carbohydrate availability, also called glycemic load. High-GI foods include dates, fruit roll-ups, baguettes, baked russet potatoes, oven-baked pretzels, corn flakes, rice cakes, waffles, bagels, microwave popcorn, wafers, crackers and grape nuts cereals.
Factors affecting GI
Many factors affect GI, such as the amount of added fat, fiber and how the food is prepared will all change the values. Whole milk has a lower GI than lowfat milk because the higher fat content slows down the digestion of lactose. The GI of pasta is is lower when cooked al dente than when it is overcooked. You do not have to completely eliminate a food just because it is a high GI food, though. You can bring down the GI of a food by adding healthy fats, or combine with a low GI food to make your meal low to moderate GI.
GI should only be used adjunctively to carb counting and a good knowledge of healthy eating; proper meal planning is still required. If you only use the index as a guide for food choices, you may be choosing more unhealthy food items than you realize. For example, regular yogurt, which has a higher amount of unhealthy saturated fats, places lower on the GI than healthier lowfat yogurt. Most importantly, you still have to look at serving size and count total grams of carbohydrates because portion has the most impact on blood sugar, regardless of the GI.
- "The Low GI Diet Revolution"; Jennie Brand-Miller; 2004
- Harvard Health Publications: Glycemic Index and Glycemic Load of 100+ Foods