Why is the glycemic index so important?
For the past 30 years, the glycemic index (GI) has intrigued many athletes, doctors, and nutritional experts when discussing the effects of food on health and athletic performance. Thousands of research studies have been completed within the same timeframe to categorize foods based on their glycemic index, and to study the importance of the glycemic index. You may be asking why should you be paying attention to just another “food-related fad.” But, far from a fad, the concept behind the glycemic index is based on many years of scientific research. Unlike other food-related topics, the scientific concepts behind the glycemic index have not been outdated. In fact, more than 30 years after its conception, nutrition experts are now calling for more research on the glycemic index using larger groups of people. The American Institute for Cancer Research, in a report titled “The Glycemic Index: What It Is, What It Is Not,” also calls for more research:
“Although the glycemic index has the potential to be a valuable clinical tool, more research, including long-term clinical studies, are needed…”
Before the conception of the glycemic index, all carbohydrate-containing foods were thought to raise blood sugar levels rapidly. It was not until 1981 that a group of Canadian researchers led by Dr. David Jenkins systematically tested the effects of different carbohydrates on blood sugar levels. According to their observations, Dr. Jenkins and his team ranked the carbohydrates by what is now known as the glycemic index.
To give a single food item its appropriate glycemic index, scientists measure the blood sugar levels for two hours after eating a particular food item. The changes in blood sugar levels are then compared with the blood sugar levels after eating pure sugar (glucose) or white bread. The glycemic index of refined sugar is 100, and the effects of all other foods are compared to that of pure sugar. If the blood sugar levels increase rapidly, the food has a high glycemic index. On the other hand, foods with low glycemic index have slowly digested carbohydrates that release sugar slowly and gradually into the bloodstream. Nonstarchy foods like vegetables, fruits, and legumes have a low glycemic index, while refined sugars have a high glycemic index.
Keep it lean and sweet
The sugar in our bloodstream is incredibly essential for energy production in our bodies. That is the reason why sports nutrition experts and coaches pay very close attention to the amount and type of the carbohydrates that athletes consume before, during, and after sporting events. In addition to its relationship with energy production, the glycemic index can also be necessary for weight management in athletes and the general public. Many favorite weight-loss books blame high GI foods for excessive weight gain which can be detrimental to athletic performance. 
This idea is backed up by more than a dozen short-term research studies that showed that foods with high GI increased hunger and food intake when compared to food with low glycemic index. In one study, obese females who switched to a low glycemic index diet lost more weight in three months than those who ate a high GI diet. In another study by a French research team, obese men who ate mostly low glycemic index food has less body fat and healthier body weight. These studies have led the authors of some favorite diet books to advise against high GI food. It is important to remember that combining low GI food with high GI food can be even more beneficial for athletes. People who ingest only low GI foods may miss out on the nutritional benefits of wholesome foods, like vegetables and fruits, which happen to have higher GI values. On the other hand, some low GI foods, like fried potato chips, do not offer much health benefit. While unprocessed, low GI foods can be extremely beneficial, especially for endurance athletes. The timing and amounts of eating low GI foods are also essential for achieving maximum athletic performance.
Take advantage of the science
Some research indicates that ingesting low glycemic index foods improves endurance capacity. To confirm the results of these individual studies, a research group from Hong Kong combined the data from 15 studies that had measured at the effects of low GI food on athletic performance. The mixed results showed that endurance performance following a low glycemic index meal was superior compared to high glycemic index food. These results also showed that both trained and recreational athletes benefited from the little glycemic index food. Also, the improvement in performance was observed regardless of the type of exercise, like time trial or exercise to exhaustion.
The following reasons are why a low glycemic index diet can help you boost your athletic performance:
- Before exercise, endurance athletes benefit from eating low glycemic index foods. Immediately before exercise, eating low GI food is beneficial because these foods sustain blood sugar levels by releasing sugar slowly into the bloodstream during endurance activities. But the benefits of low GI food are not limited to the immediate timeframe before exercise. Research studies have shown that long-term consumption of low GI food, for example during training, may improve the ability of the body to utilize carbohydrates for generating sustained energy.
- Consuming foods or fluids that contain a mix of medium and high glycemic index help to maintain adequate blood glucose levels during prolonged exercise that takes longer than 2 hours. This helps sustained energy production by the body and prevents excessive cravings after the exercise.
- After exercise, foods and fluids that contain a mix of low and high GI should be consumed. The high GI food helps with the quick recovery of the depleted blood sugar levels, while the low GI food helps with keeping you satisfied for longs. Another benefit of consuming low GI food post-exercise is that they may help with the general recovery process. A research group from the University of Tokyo in Japan found that a diet that consists primarily of low-glycemic index food may increase the intake of micronutrients, which can boost recovery in endurance athletes.
Smart eating and consuming foods with the low glycemic index can increase your glycogen stores and, in the end, your performance and recovery. Eating foods with low glycemic index does not necessarily mean a monotonous diet. For example, coconut oil may be beneficial because it has high fiber and a low glycemic index. Cocao also has a low glycemic index and has high amounts of flavonoids, which have potent anti-inflammatory properties. Understanding the different types of carbohydrates and how your body uses them for energy production can help you achieve your maximum potential as an athlete.
This post was written courtesy of Dr Hani Ebrahimi, a former postdoctoral researcher who performed independent research in the fields of biochemistry, cell biology, genetics and molecular biology. His research has been published in several peer-reviewed scientific journals. He has worked at the National Institutes of Health, Cancer Research UK (London, UK), and University of Cambridge (UK). Recently, he co-founded Elucidaid to provide software solutions to research scientists.
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