The Glycemic Index
Not all carbs are created equal. Different foods have varying impacts on blood sugar, changing how they affect athletic performance. In this article, we will explore the glycemic index and how athletes can use it to choose the right foods for their athletic goals.
What is the glycemic index?
The glycemic index (GI) is a scale used to measure how much a food changes blood glucose levels after it is consumed. The GI is used to better manage blood sugar levels and avoid large fluctuations. Each food is ranked on a scale from 0-100, with foods closer to 0 having less of an effect on blood sugar than foods closer to 100. There are three levels on the glycemic index: low (0-55), medium (56-69), and high (70-100).
The glycemic index is related to a similar measure, the glycemic load (GL). This scale takes into account the amount of carbohydrates found in a portion to provide a more accurate idea of how the food will impact blood glucose levels.
What factors affect a food’s ranking on the glycemic index?
Foods that contain more refined carbohydrates and sugars often have a higher GI and are processed a lot quicker. Foods higher in protein and fat have a lower GI. Foods without carbs, such as meat, fish, nuts, seeds, and oils do not have a GI. Additionally, the structure of the food, how it’s cooked, and its fiber content can impact a food’s GI.
Glucose spikes and insulin sensitivity:
Glucose spikes occur when there is an excess of glucose in the bloodstream that the body’s cells cannot take in. High-glycemic foods, which are found higher on the GI, are more likely to cause glucose spikes (if they also have a high glycemic load). Glucose spikes cause negative effects on sleep, mood, and attentiveness, and can result in hormonal imbalances. Frequent dips and spikes in blood glucose can lead to insulin resistance. This occurs when insulin, a molecule released in response to an increase in blood glucose, is constantly released and begins to lose its effectiveness.
Benefits of a low-glycemic diet:
A low-glycemic diet avoids foods that are high on the glycemic index. Here are some benefits attributed to a low-glycemic diet:
Better regulation of blood sugar
Increased short-term weight loss
Lower risk of diabetes and heart disease
Less inflammatory response from food
High, medium, and low GI foods:
The International Tables of Glycemic Index and Glycemic Load Values: 2008 contains a list of various carbohydrate-rich foods and their ranking on the glycemic index. Here are some examples of foods from this list that fall into the three categories of the glycemic index:
High:
Processed foods
Baked goods
White bread
White rice
Breakfast cereals
Potatoes
Medium:
Pineapples
Brown rice
Honey
Oatmeal
Low:
Sweet potatoes (boiled)
Apples
Oranges
Bananas
Lentils
Blueberries
**Note that GI can vary depending on the cooking method and other factors**
What’s best for athletes?
While high-glycemic foods generally come with many negative health effects, for athletes they can be helpful. The body utilizes carbohydrates as fuel during exercise, meaning athletes will need to replenish their carbs after working out. It is recommended that athletes stick to low-glycemic carbohydrates before a workout, to prevent a glucose spike that will lead to hyperglycemia (high blood sugar) during exercise. These low-glycemic carbs will release sugar slowly, ensuring that the athlete will still have enough energy during exercise. During and after the workout, high-glycemic carbs are recommended, as long as it is consumed in moderation. These foods are absorbed rapidly and will replace the carbs used up by exercise.
Conclusion:
By using the glycemic index, athletes can gain better control of their blood sugar levels and improve their performance in competitions and workouts. By being aware of how different foods rank on the glycemic index, athletes can choose foods that will support their nutrition and allow them to have the energy they need to perform at their best.
Sources:
Fiona S. Atkinson, Kaye Foster-Powell, Jennie C. Brand-Miller; International Tables of Glycemic Index and Glycemic Load Values: 2008. Diabetes Care 1 December 2008; 31 (12): 2281–2283. https://doi.org/10.2337/dc08-1239
“Glycemic Index and How It Affects Your Diet.” Cleveland Clinic Health Essentials, 21 October 2021, https://health.clevelandclinic.org/glycemic-index.
“Glycemic Index and How It Affects Your Diet.” Cleveland Clinic Health Essentials, 21 October 2021, https://health.clevelandclinic.org/glycemic-index.
Morgan, Kendall K. “Glycemic Index: How to Determine High- vs. Low-Glycemic Foods.” WebMD, 26 August 2024, https://www.webmd.com/diabetes/glycemic-index-good-versus-bad-carbs.
Peres M, Costa HS, Silva MA, Albuquerque TG. The Health Effects of Low Glycemic Index and Low Glycemic Load Interventions on Prediabetes and Type 2 Diabetes Mellitus: A Literature Review of RCTs. Nutrients. 2023 Dec 10;15(24):5060. doi: 10.3390/nu15245060. PMID: 38140319; PMCID: PMC10746079.
“What is a Glucose Spike?” Abbott, https://www.abbott.com/corpnewsroom/nutrition-health-and-wellness/what-is-a-glucose-spike.html.