The level of insulin in your body changes throughout the day. This change is triggered largely by how recently you have eaten and what you ate. When your blood sugar rises -- which it typically does after a meal -- your body releases insulin. When insulin levels rise rapidly, you experience an insulin spike. One way to predict the likelihood of an insulin spike is to consider the glycemic index (GI) of a food. The GI of a given food is a number from 1 to 100. Foods lower on the GI scale tend to have less of an impact on your blood sugar and insulin levels than foods ranked more highly. The combination of foods you eat in a meal, serving sizes and the other nutrients found in these foods also affect your insulin level after eating. Therefore, there is no specific GI level that can reliably be used to predict an insulin spike.
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Glycemic Index Factors
Foods are divided into high, intermediate and low GI categories. A GI of 0 to 55 is low. Intermediate GI foods have a value of 56 to 69, and 70 or above is considered high. Many factors influence a food’s glycemic index, including: -- Type and amount of sugar, starch, fiber, protein and fat. -- Extent of food processing, cooking method and ripeness. -- Ease of digestion and absorption from the intestine.
Some foods, like meats, have no GI ranking because they don’t contain any carbohydrates. But the GI scale can help differentiate carb-containing foods that seem quite similar, as the difference between low- and high-GI foods may be difficult to discern without this measure. For example, oatmeal and sweet potatoes -- low GI foods -- may not appear that different from cornflakes and russet potatoes, which are high on the GI scale.
The idea behind the GI scale is that carbohydrates have a larger impact on insulin levels than other nutrients. Therefore, the GI scale is at the forefront of determining how much of an impact a food has on insulin levels. However, many other factors also influence insulin response -- how much insulin is released. Proteins in foods can have a major impact on insulin response. Fats typically have a lesser effect. For example, a July 2001 study published in the "American Journal of Clinical Nutrition" found that milk products may have a greater impact on insulin than the glycemic index would suggest. This is because milk proteins stimulate insulin release. Studies like this highlight the limitations of the glycemic index as a standalone measure.
Glycemic Index Limitations
The GI scale has long been an important tool for individuals with diabetes who are working to control their blood sugar levels. It does have limitations, however. In a January 2014 report published in "Diabetes Care," the American Diabetes Association reminded that, while some studies have found maintaining of a low-GI diet helpful for managing diabetes, other studies have found that it has little or no effect. This observation is at least partially explained by the fact that people typically eat a mixture of foods when sitting down for a meal. The combination of foods eaten greatly affects both blood sugar and the insulin response after a meal. So while the GI scale can be useful, it cannot predict insulin response precisely.
The glycemic index isn't the only measure you can consult when trying to calculate the impact a food will have on your blood sugar and insulin levels. The glycemic load is another potentially useful measure. Like the GI scale, this measure reflects how much a food will raise blood sugar. However, glycemic load also takes serving size into account.
The food insulin index (FII) is another potentially useful measure of the effect of various foods on insulin levels. While similar to the GI scale, the FII determines effects on blood insulin levels rather than blood sugar levels. As discussed in a June 2015 report published in "Diabetes Care," the FII may provide a more accurate picture of a meal’s impact. This is because the FII can be used to calculate the impact of both individual foods and meals containing mixtures of foods. Additional work needs to be done in investigating the effectiveness of the FII, however.