As you digest carbohydrates, the resulting sugars will enter the bloodstream for transport across the body. As your blood sugar levels rise, the pancreas releases insulin, a hormone that signals the cells to absorb this sugar for energy production or storage .
When you consume simple carbohydrates, blood sugar levels will rise rapidly as they are easily digested and absorbed by the body . Insulin levels rise to accommodate this change, and the cells are signalled to absorb a large amount of sugar. Once energy demands are met, and glycogen stores are full, the excess sugar is stored as fat .
On the other hand, complex carbohydrates take longer to digest, so sugars are released slowly into the bloodstream. The gradual supply of sugar will cause less insulin to be released, and cells will absorb the sugar slower . Our cells will gradually use the sugar as normal metabolic functions demand it, and less excess will be available to convert and store as fat.
The interaction between the digestion of carbohydrates and blood sugar levels is described by the term glycemic index (GI). Effectively it provides a rating for carbohydrates (from 0-100) based on the rate at which they will raise sugar levels in the blood . The lower the GI score, the slower it will raise your blood sugar levels. Low GI is below 55, medium GI is 56-69, and high GI is greater than 70.
It is worth noting that the glycemic index only reflects the rate at which carbohydrates raise blood sugar levels, not the amount. The quantity of carbohydrates in food is also an important factor that determines how high your blood sugar levels may rise after a meal . Glycemic load (GL) is a term that accounts for both of these elements. It effectively takes the GI score and multiplies it by the amount of carbohydrates in a given food . Similarly to GI, there are three categories for glycemic load; low being ten or less, medium being 11-19, and high being 20 or more.