Posted on April 27, 2026 at 06:00 AM
It’s been more than 40 years since researchers at the University of Toronto developed the idea of the glycemic index. The glycemic index (GI) was initially created as a nutritional tool for diabetics who needed to be especially careful about their blood glucose (sugar) levels. Diets with a high glycemic index It could be a risk factor To develop diabetes. But over the years, it’s been seen as a way for us all to regulate our diets to eat better carbohydrates for improved metabolic health and perhaps even fitness gains.
when Eat carbohydratesYour body eventually breaks it down into glucose, which enters your bloodstream. This is what fuels your mind and muscles. However, some carbohydrate foods cause a rapid rise in blood sugar, while others provide a slower, more steady release. This is where GI comes into play.
So what exactly is this nutritional index, and should you use it to form your own? Carbohydrate options? Here’s an in-depth look at the glycemic index and a summary of how you can leverage it to improve your performance and nutrition.
How does the glycemic index work?
In layman’s terms, the glycemic index (GI) is a measure of how quickly a food or drink containing carbohydrates raises a person’s blood sugar after consuming a specific amount. “When you eat carbohydrates, your body converts them into glucose — but not all carbohydrates work the same way,” he says Carissa Gallowayregistered dietitian and marathon broadcaster. “High GI foods cause a rapid increase in blood sugar, while low GI foods create a slower, more sustained response, thus lowering blood sugar.”
Everything from rice to bread to apples is rated on a scale from 0 to 100, and lower numbers indicate that a particular food takes longer to digest and absorb, causing a slower rise in blood glucose than foods with a higher number which can cause blood sugar to rise more quickly. For example, carrots, chickpeas and oats are considered low GI with a rating of 55 or less. White bread, rice cakes and ripe bananas are considered to have a high glycemic index rating of 70 or higher. White rice delivers carbs faster than a bowl of quinoa.
Here are some key points to consider regarding your digestive system when it comes to nutrition and performance.
Choose healthy carbohydrates
On the whole, it can provide a GI rating Some insight In how a food or drink is processed, because many carbohydrate-containing items like candy, cookies, and refined grains that are high on the GI scale have undergone some processing that has stripped away much of their nutrition and increased how quickly your blood sugar can rise. Or food manufacturers may take a food and pump in extra sugar, which affects the digestive system. Plain yogurt will have a lower GI compared to most flavored versions because the latter have been further processed to add sugar to the mix.
As for daily nutrition, we can confidently say that foods with a low glycemic index are generally the best choices. They are whole grains, legumes, and vegetables that provide fiber, along with a range of vitamins and minerals that will help you meet many of your nutritional needs.
“Beyond training, focusing on low-GI carbohydrates like whole grains, beans, fruits, and vegetables can help with energy stability, recovery, and long-term health,” says Galloway. “Research consistently links these foods to a lower risk of chronic disease, and I recommend runners build their daily diet around lower GI carbohydrates and use higher GI carbohydrates to support their training and endurance needs.”
Remember that foods like beans, nuts, leafy greens, and whole grains digest slowly, keeping you feeling full longer. This makes it easier to stick to a healthy eating plan without feeling deprived.
Some research It suggests that runners who consume a high-carbohydrate diet that is generally lower on the GI may experience improved performance metrics, including increased aerobic capacity.
Not all high-glycemic foods are bad
Labeling all high-glycemic foods as unhealthy is not the best solution. “The glycemic index only measures how a food affects blood sugar, and does not necessarily reflect its overall nutritional value,” Galloway says. She explains that some high-GI foods, such as potatoes and watermelon, provide important nutrients for runners, including potassium, vitamin C, and antioxidants. Beets are higher in natural sugars than most other vegetables, and surprisingly they have a fairly high glycemic index, but I can’t imagine many nutritionists warning you against eating them – their overall nutritional profile outweighs any potential effect on blood sugar. On the other hand, adding isolated proteins and fiber to highly processed foods like cereals and crackers can significantly lower their blood sugar, but that doesn’t make them nutritional champions.
Like all things related to nutrition, some perspective is needed when it comes to the digestive system. Focus on the overall nutritional value of your foods, not just the glycemic number.
Factors that affect the glycemic index
Some may think that the glycemic index causes more confusion than it’s worth when it comes to the way most people eat. The reason is that the glycemic index of a single food or multi-ingredient meal is affected by several factors, including:
- How much food is eaten: The index is based on a serving size of 50 grams (200 calories) of carbohydrates, which is often not the serving size we eat. That much cantaloupe is a lot of watermelon.
- What food is eaten: Adding protein, fat, and fiber to a meal greatly affects how quickly carbohydrates enter your system, causing your digestive system to slow down. Fiber is a big factor, Galloway explains, as high-fiber foods slow digestion and thus reduce the blood sugar response to a meal compared to eating carbohydrates alone. For example, adding peanut butter (fat/protein) to white bread or milk and high-fiber berries to Cheerios reduces the overall GI of the meal.
- How to prepare and cook food: Cooking your spaghetti only to “al dente” (undercooked) will lower the GI, or serving cooked potatoes cold, which increases resistant starch levels, making the potato lower in the GI rating.
- Food doneness: Ripening, such as a very ripe banana versus a slightly green banana, can change how quickly carbohydrates are absorbed, which can raise their glycemic index.
- How the same food is processed: Processing methods that strip away fiber will increase the GI of the food. For example, a whole orange has a lower glycemic index than orange juice because of the fiber it contains. Likewise, steel-cut oats have a lower GI than instant oats because they remain whole and take longer to digest, even if their overall nutritional profile is similar.
- What to eat first: The order of what we eat during a meal changes how the GI of foods affects blood sugar. For example, eat non-starchy vegetables like broccoli before eating high-GI foods like white rice or dinner rolls. can reduce High blood sugar after a meal.
- Who are you: There could be Great contrast In individual glycemic responses to foods, including potatoes, rice and grapes, based on everything from genetics to body weight and fitness level. Just because a bowl of Special K can cause one person’s blood sugar to spike doesn’t necessarily mean it will do so for another.
All of this means that there are many limitations that prevent the glycemic index from being the be-all and end-all of healthy eating. There are a lot of variables at play here.
Go higher when you exercise…
“Research shows that slow rises in blood sugar can support better energy stability and metabolic health over time; however, there are times, such as during endurance exercise, when high-GI foods are beneficial,” says Galloway. She explains that when you’re in the middle of a run or race, especially anything intense, your body prioritizes carbohydrates it can use immediately — so high-GI sources make the most sense. “It helps keep blood sugar stable in the moment and supports performance.”
This means that using the glycemic index to see how quickly carbohydrate foods and drinks raise your blood sugar can help you better plan fuel for improved performance. Sports drinks, gels, beans, and honey are all high-GI items that can help you stay strong. They are easy to digest and provide quick energy without weighing you down. Just heed Galloway’s warning that eating large amounts of high-GI carbohydrates at once can overwhelm your intestines, leading to bloating, cramping or nausea. Space it out and train your gut.
“For all-day or all-day efforts, relying solely on high-GI fuel can feel like a rollercoaster,” Galloway warns. “Adding some low-GI foods can smooth out energy levels and provide more staying power over time.” Another win for Slim Jim at 50 miles.
…but less before running
You may think that high-GI foods before exercise are the perfect solution because they give you a quicker boost of energy. but Research indicates Eating foods with a low glycemic index can provide an even greater boost. Because moderate to low GI foods stabilize blood sugar, endurance runners may find that they provide them with more sustained energy throughout their run. On the other hand, high-GI pre-workout fuel can cause a sharp spike in blood sugar and an equally rapid drop, leading to fatigue early during your workout.
As with all things sports nutrition, it’s best to experiment and find out what foods work best for you before heading out for a run.
Glycemic guidelines for post-workout nutrition
Post-workout nutrition is crucial to recovery. “After exercise, your body is ready to absorb carbohydrates, and higher glycemic index options can speed up glycogen recovery,” Galloway says. High GI foods, such as chocolate milk and rice cakes, help restore glycogen levels faster than low GI foods, such as a bowl of bulgur. This speeds up muscle repair and prepares the body for the next session. But Galloway explains that this is only useful if you exercise regularly and have shorter periods before training sessions, say 24 hours or less. If you have a longer time frame between runs or don’t plan to exercise at a high intensity, you can stick to low-GI foods like whole grains for recovery as long as you eat adequate amounts of carbohydrates overall. In other words, you don’t necessarily need to down a gallon of Gatorade to improve your recovery.
If anything, understanding the glycemic index helps you be more aware of your food choices to support your health and performance goals. A daily sugary Frappuccino habit probably isn’t the best idea. But it’s good to know that your favorite white pasta doesn’t have to be off the table, especially when you bring the meat sauce.
