Understanding the Glycemic Index
The body must convert the sta
rches and sugars in foods into blood glucose to meet basic energy needs. “Glycemic index” (GI) is the term commonly used to describe how fast the body breaks down starches and sugars after a particular food or beverage is consumed.
Bodybuilders tend to avoid foods that are considered to have a high glycemic index in fear of an abnormally high rise in blood glucose or “glycemic response” which then triggers an excess production of insulin. The idea is that consuming low GI foods will provide a slower release of carbohydrate into the bloodstream, result in stable insulin levels, increased rate of fat utilization and promote satiety (feelings of fullness).
Based on this rationale, bodybuilders eliminate white potatoes, rice, breads and other higher GI starches and replace them with high-fiber whole grains like oatmeal, brown rice, or yams. However the reality is there are several important practical limitations to the glycemic Index that should be considered when making food selections.
Limitations of Glycemic Index
Blood glucose levels depend not only on how much and what types of carbohydrates are eaten but also on how much fat or protein is eaten WITH the carbohydrates. When macronutrients are combined in a typical bodybuilding meal of chicken, rice and vegetables, the glycemic index of the selected starch (in this case rice) is altered. Protein, fat and fiber all slow the release of glucose into the bloodstream. So the more important factor is the glycemic effect of the entire composition of the meal.
Another limitation of the glycemic index is that it does not take into account the amount of carbohydrate actually consumed. So a related measure, the “glycemic load”, factors this in by multiplying the glycemic index of the food by the carbohydrate content of the actual serving. It is possible to get high insulin responses with low GI eating. Since glycemic response is a combination of GI multiplied by carbohydrate concentration (glycemic load), more grams of carbohydrate consumed will result in higher blood glucose and insulin levels.
Cooking method and amount of processing will also affect glycemic index. For example, the GI of boiled potatoes is substantially lower than microwaved potatoes.
Finally, the glycemic response varies from one individual to another and even in the same person from day to day. Blood glucose levels, insulin resistance, and other factors can affect the rate of glucose released into the blood.
Below is a chart indicating the glycemic index and glycemic load of many popular foods. The lower a food's glycemic index or glycemic load, the less it affects blood sugar and insulin levels. Note the rather low glycemic index of ice cream (57). While ice cream typically has high sugar content, the added fat reduces the glycemic index. It’s also interesting to note that pastas—which are believed by many to be high—are actually rather low on the glycemic index.
How Bodybuilders can benefit from high GI foods
The Glycemic Index can be a useful tool to help bodybuilders
and other athletes select the right type of foods to eat before, during, and after exercise. Choosing foods that are high or low GI can speed-up or slow-down the availability of carbohydrates (Manore et al., 2004). Bodybuilders can use a low GI meal prior to exercise to better maintain blood glucose during training and increase the rate of fat oxidation (Bernard et al., 2005).
Eating a high GI meal immediately (within 45 minutes) after exercise elevates blood glucose concentrations (Ivy and Portman, 2004). Muscle glycogen re-synthesis is critical for the exercised muscles to replenish depleted glycogen stores. Higher glucose levels from high GI foods also stimulate the secretion of insulinwhich helps to promote glycogen storage and protein synthesis. Keep in mind that fat, fiber and protein slow the release of carbohydrate into the bloodstream so it would be prudent to limit these three nutrients in the post workout meal.
The glycemic index does have value for bodybuilders and other athletes although it’s important to understand the many practical limitations when making food choices. When selecting foods it’s also important to consider not only the glycemic index of a carbohydrate but also the nutrient value of the food as well as the method of preparation, and glycemic load of the composition of each meal.
References:
Kaye Foster-Powell, Susanna HA Holt, and Janette C Brand-Miller International table of glycemic index and glycemic load values: 2002 ; Am J ClinNutr. January 2002 vol. 76 no. 1 5-56
G Jerry J. Mayo, Ph.D., R.D. and Len Kravitz, Ph.D.; Glycemic Index: Weight Loss Sham or Sensation
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