5 Things Your Athletes Should Know About the Glycemic Index

#1 The GI wasn’t created for athletes to use

The GI was initially developed 40 years ago3 with the goal of helping people with type 1 diabetes build their meals and snacks with blood sugar control in mind. Subsequently, three GI categories were developed: high (>70), medium (55-69) or low (<55)—and published in a popular book.4 This gave foods high in starch (e.g., breads, pasta, rice and “starchy” vegetables like potatoes) a “high-GI” label. For this reason, some people began to associate high-GI foods with negative impacts on health and low-GI foods with beneficial impacts on health. 

More than 750 nutrition professionals surveyed by Today’s Dietitian agree the GI of potatoes depends on a number of factors, is highly variable, and they do not rule high-GI foods out when working with patients and clients on meal planning. For example, the GI of potatoes can change by boiling and cooling them, as a result of the type of starch in the potato. Potatoes are a quality carb for athletes to fuel and recover with irrespective of their GI value. They’re also an ideal performance produce providing high-quality complex carbohydrates, potassium, and vitamin C that your athletes need to perform at their best.

#2 Solely using GI as a dietary planning tool may cause athletes to exclude perfectly healthy foods from their performance plate

Nutrition professionals surveyed believe that the GI leads to misinformation about the healthfulness of fruits and vegetables. For example, some nutrient-dense fruits (e.g. pineapple, watermelon and ripe bananas) and vegetables (e.g. potato, carrots, beets) are assigned a moderate- to high-GI value. Your athletes may already be struggling to consume enough of the fruits and vegetables5 that provide them with important nutrients like vitamin C and potassium. Confusion around the healthfulness of these foods and others in the context of GI may be another barrier to adequate consumption. Training or going into games and events with low carbohydrate or micronutrient intake may make athletes fatigued, reduce their ability to train hard, impair their competition performance, and reduce their immune system function.1 

#3 The connection between GI, health and athletic performance has not been clearly established

Your athletes should be choosing nutrient-dense carbohydrates based on what fuel they personally enjoy and what they tolerate best (e.g., tailoring to their digestive system) during each stage of activity. If your athletes are choosing their pre-, during- and/or post-exercise carbohydrates based solely on the GI, it’s important to remind them that the connection between GI and health, as well as GI and athletic performance, is not clear. For example, a 5-week randomized controlled feeding study of 163 U.S.-based overweight adults found that diets having either a low- or high-GI did not result in improvements in insulin sensitivity, lipid levels, or systolic blood pressure.6 Thus, in the context of this study, using GI to select specific foods did not improve health outcomes. The findings of this study cannot be extrapolated to represent athletes. When it comes to guiding your athletes on using GI to benefit sports performance, let them know there is no clear consensus on whether consuming carbohydrate-containing foods, beverages or meals of differing GI values improves performance. Interestingly, one recent randomized cross-over study of 10 male amateur-level athletes from Singapore found consuming either a high-GI or low-GI meal 45 minutes before exercise did not differently affect physiological, subjective and intermittent sprint and endurance performance outcomes.7 Always consider your athlete’s individual goals when providing dietary guidance. 

#4 The majority of nutrition professionals surveyed do not use the GI or glycemic load (GL) when providing dietary guidance or recommendations

The Today’s Dietitian survey revealed that nearly three-quarters (73%) of nutrition professionals report that they do not use the GI when working with patients or clients. What’s more, 86% of all nutrition professionals report they do not use the glycemic load (GL) with patients and clients. The GL is a tool that evaluates the quality and quantity of carbohydrates in a serving of food and was developed to be a solution to the limitations of the GI, which only evaluates the quantity of carbs of a standardized amount of a food. In fact, nearly half (48%) of all surveyed believe there is conflicting or misleading research on the GI of certain food items and their relationship to clinical outcomes or general health.

#5 There are more important criteria to pay attention to than GI values when your athletes choose a carbohydrate-containing food, beverage or meal plan

There are a number of other criteria of greater importance than GI for determining the quality of a carbohydrate-containing food to benefit athletic activity. It’s more practical and sustainable for your athletes to pay attention to the combination of foods and beverages needed to meet total daily carbohydrate requirements than the individual GI of those items. Remember, there are characteristics of foods, beverages and meals that are better for your athletes to consider than their GI such as the total nutritional content of a food or meal and how it compares to daily needs, cost, taste, shelf stability, palatability, versatility, familiarity, practicality, and gastric comfort. Your athletes should choose meals and snacks according to the goals and needs of each training or competition situation.