The Glycemic Index Science
The glycemic index (GI) was devised to rank the glycemic response of consumed foods, particularly carbohydrates, on blood sugar levels. The index ranges from 1 to 100. Essentially, the quicker the impact, the higher the ranking. Pure glucose and white bread are ranked at 100 on the index. Below 60 is considered low by the index. Between 60 and 85 is ranked as having a medium GI. High GI is any food ranked over 85. Typically, a rapidly elevated glucose level is followed by a rapidly decreased glucose level. Conversely, medium to slow increases in blood sugar results in sustained energy and reduced hunger for a longer period of time.
Influential Factors
Although the GI highlights carbs, since it is carbohydrates that are broken down into glucose, it does distinguish between the type or quality of carbohydrate. Refined sugars found in candies, sodas, corn flakes and honey have a high GI ranking. Whereas, fruits and vegetables, pasta and brown rice tend to rank lower, and are preferable. Also, at meals, the amount of fat, protein and fiber included can lower the impact a carbohydrate has on blood sugar. They assist in slowing the rate of absorption and digestion of sugars.
Measurement Administration
The measuring of a food's GI is done by feeding test subjects 50 g of carbohydrate of a particular food item. Blood glucose levels are monitored over the next two hours. The level of blood sugar is recorded at the 2-hour mark. On another occasion, the same test subjects are given 50 g of pure glucose, and the test process is repeated for 2 hours. Calculations are done on the results by dividing the test food response by the response solicited by the reference food. The average GI value for the 10 test subjects is the final value.
References
- "Sports and Fitness Nutrition," Robert Wildman and Barry Miller; 2004.
- "Nancy Clark's Sports Nutrition Guidebook, 3rd ed.," Nancy Clark; 2003.
