Classifying Foods using the Glycemic Index

We know that foods are not created equal. It is healthier to eat a Granny Smith apple than a slice of Grandma’s apple pie. Foods are often classified as “good” or “bad” and that is one way to label foods. Countless other types of classifications exist (proteins, carbs, fats, fruits, vegetables, meats, and dairy). A different way to categorize food is based on the scientific system known as the glycemic index. What does the glycemic index mean to you as an athlete?

The glycemic index (GI) is a tool that provides you with information about the unique nature of that particular food. The GI scores the rate at which carbohydrates are broken down and converted to glucose (blood sugar). A quick release of sugar from a meal triggers the release of the hormone insulin from the pancreas. This results in a rapid decrease in the blood sugar level.

Carbohydrates can be classified by their glycemic responses. Low GI foods are associated with low blood glucose levels and a slow insulin response, while high GI foods have the opposite effect. You can learn a food’s GI by consulting a GI Index Table. Examples of high GI foods include bagels, certain cereals (Cheerios, Chex, Cornflakes) and potatoes. Some low GI foods are skim milk, lentils and beans, certain fruits and vegetables (apples, pears and peas). A food’s GI must be measured scientifically in a lab. The GI cannot be calculated based on glancing at the ingredients alone.

There is not just one factor that determines a food’s GI. The effect of the GI on the body can be adjusted by the foods we consume together. Rarely are meals eaten with just one ingredient. By combining foods together we adjust the body’s response. If we add fiber to a meal, we reduce the GI effect of the food. Similarly, if we add protein to a meal it will slow down the spike in blood sugar levels. Fat also reduces the raising of blood sugar levels. Some of the low fat or non fat, heavily processes foods (non fat cookies and cakes) tend to have a high glycemic index due to the addition of simple sugars when fat is removed. The GI is also influenced by how the glucose molecules in the food are connected, the form of the food and the degree of food processing

There is conflicting information about the value of GI in meal timing for runners. Some studies show that athletes may benefit from choosing low GI foods before a workout, and high GI foods during and after a workout. Other studies indicate that the nature of the carbohydrate is not as important as long as sufficient amounts of carbohydrate are consumed. So what’s a runner to do? Given the conflicting studies, the GI might serve as a useful guide to help fine tune food choices. One should also consider a food’s nutritional content and the practical uses of palatability, portability, cost, gastric comfort and ease of preparation.

Ultimately it is up to you to decide what works best for your unique body. Athletes should evaluate their responses to high carbohydrate foods with both low and high glycemic indexes in training to find out what works the best. I recommend taking the time to learn what makes the most sense for you nutritionally. The results could show themselves in your next race performance.