Carb Ranking Glycemic Index
For a number of years, particularly since the 1980s, when rates of overweight and obesity in the United States began to climb rapidly, experts have been concerned by the effects of different foods on appetite and blood sugar regulation. Scientists became interested in how different foods affect blood sugar, insulin release, and, in turn, energy usage and fat storage. In exploring the impact of foods on blood sugar, scientists constructed the glycemic index (GI), a scale for measuring and classifying foods based on how quickly they raise blood sugar. The best foods, according to these scientists, are foods that rank low on the index: foods that are digested slowly, cause a gradual rise in blood sugar, and lead to a moderate insulin response. The least favorable foods in terms of glucose response are those that elevate blood sugar levels quickly and lead to a rapid insulin response that results in a burst of energy that drops off rapidly.
Using the GI doesn't play much of a role in sports nutrition according to the research, despite the water-cooler chatter. Many experts have criticized the GI for a number of reasons, including reference foods not being well-defined and variations in foods that are often culture-dependent.
According to scientists, the cons for using the GI include:
- It is not applicable to exercising individuals, since the tests are conducted at rest and in a fasted state.
- GI tests actually show a high rate of variability of more than 30 percent, between individuals, and within the same individual.
- Studies have not consistently shown any performance benefit in consuming low- versus high-GI foods before, during, or after exercise.
- It is an unreliable and impractical way of measuring foods and making recommendations to athletes.
- The GI of a food varies from person to person and even in a single individual from day to day, depending on blood glucose levels, insulin resistance, and other factors.
- The GI is not the same as rate of digestion and absorption, which has a greater impact on athlete performance and GI distress during exercise.
- Once you mix foods together, the GI is invalidated, since foods are all mixed in the digestion process.
Research at the Australian Institute of Sport, in conjunction with researchers at Deakin University and the University of Melbourne, has examined the use of the GI in sports. Here's a summary of their findings:
- The jury is still out on the use of the GI in sports. It should not be used, and is not intended to be the overall ranking system, for carbohydrates. Foods should be selected to meet a variety of criteria based on taste, tolerance, convenience, and nutritional value.
- There is not enough evidence to recommend use of low GI foods prior to prolonged exercise. The best practice is to enlist your fueling strategies during exercise to avoid depleting your muscles' fuel supplies. You are better off using foods that are tried and true. Both high- and low-glycemic foods can work just fine.
- A very small percentage of the population (about 5 percent) have a condition called rebound hypoglycemia. For those individuals, a lower GI meal before exercise may be a better option.
- For prolonged exercise, athletes should consume carbohydrate during the event to fuel active muscles and thereby enhance performance. The choice of carbohydrate type seems to be more related to gut tolerance, hydration requirements, type of sport, previous experience, and individual tastes.
- There is some evidence that moderate and high-glycemic foods appear to help glycogen recovery after exercise compared to low-glycemic foods. The reason is not clearly understood. It is more important for the athlete to have adequate total carbohydrate intake than a specific glycemic index of food, with practicality being emphasized.
Research on the GI is preliminary at present for use with weight control. There is some evidence that limiting high-GI foods can be helpful for weight control in some people, perhaps those with a predisposition for overweight or obesity. The GI also may help delve into the ways in which low-fat but nutritionally empty foods such as potato chips and some crackers and cookies can lead to overeating and weight gain from the added calories in some people. The GI may be a useful tool for some diabetic individuals, since such individuals must control insulin response closely.
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