When you eat carbs<\/a>, your body eventually breaks them down into glucose, which enters your bloodstream. This is what fuels your brain and muscles. However, some carb-containing foods cause a fast rise in blood sugar, while others provide a slower, steadier release. This is where the GI comes into play.<\/p>\n So what exactly is this food index, and should you use it to shape your carb choices<\/a>? Here\u2019s an in-depth look at the glycemic index and a rundown on how you can leverage it to improve your performance and nutrition.<\/p>\n How does the glycemic index work?<\/p>\n In layman\u2019s terms, the glycemic index (GI) is a measure of how quickly a carbohydrate-containing food or drink causes a person\u2019s blood sugar to rise after a set amount is consumed. \u201cWhen you eat carbohydrates, your body converts them into glucose \u2013 but not all carbs act the same, says Carissa Galloway<\/a>, a Registered Dietitian Nutritionist and a marathon race announcer. \u201cHigh-GI foods lead to a rapid increase in blood sugar, while low-GI foods create a slower, more sustained response, thus a lower blood sugar number.\u201d<\/p>\n Everything from rice to bread to apples is ranked on a scale of 0 to 100, with lower numbers indicating that a certain food takes longer to digest and absorb, causing a slower rise in blood glucose compared to foods with a higher number that can spike your blood sugar more rapidly. For example, carrots, chickpeas, and steel-cut oats are considered low-GI with a ranking of 55 or less. White bread, rice cakes, and ripe bananas are considered high GI with a ranking of 70 or more. White rice delivers faster carbs than a bowl of quinoa.<\/p>\n Here are some key points to consider regarding the GI when it comes to nutrition and performance.<\/p>\n Choosing healthier carbs<\/p>\n On the whole, the GI ranking can provide some insight<\/a> into how processed a food or beverage is, because many carb-containing items like candy, cookies, and refined grains that are high on the GI scale have undergone some processing that has stripped away a sizable chunk of their nutrition and increased how fast they can shoot up your blood sugar. Or food manufacturers have taken a food and pumped in extra sugar, which impacts the GI. Plain yogurt will have a lower GI compared to most flavored versions because the latter have been further processed to have sugar added to the mix.<\/p>\n For day-to-day nutrition, we can pretty confidently say that foods with a lower GI are generally the best choices. They are the whole grains, legumes, and vegetables that provide fiber, along with an array of vitamins and minerals that will help you meet many of your nutritional needs.<\/p>\n \u201cOutside of training, focusing on lower-GI carbs like whole grains, beans, fruits, and vegetables can help with energy stability, recovery, and long-term health,\u201d says Galloway. \u201cResearch consistently links these foods with reduced risk of chronic disease, and I recommend that my runners build their daily diets around lower GI carbs and use higher GI carbs to support their training and endurance needs.\u201d<\/p>\n Remember that foods like beans, nuts, leafy greens, and whole grains digest slowly, keeping you full longer. This makes it easier to stick to a healthy eating plan without feeling deprived.<\/p>\n Some research<\/a> suggests that runners who consume a high-carb diet that is overall lower on the GI index may experience improved performance metrics, including increased aerobic capacity.<\/p>\n Not all high-glycemic foods are bad<\/p>\n Labeling every high-GI food as unhealthy is not the way to go. \u201cGI only measures how a food affects blood sugar \u2013 it doesn\u2019t necessarily reflect its overall nutritional value,\u201d Galloway says. She explains that some high-GI foods like potatoes and watermelon provide important nutrients for runners, including potassium, vitamin C, and antioxidants. Higher in natural sugars than most other veggies, beets are surprisingly fairly high on the GI, but I can\u2019t imagine too many nutritionists warning you against eating them \u2013 their overall nutritional profile outweighs any potential impact on blood sugar. On the flipside, adding proteins and isolated fibers to highly processed foods like cereals and cookies can significantly lower their GI, but that doesn\u2019t make them nutritional heroes.<\/p>\n Like all things with nutrition, some perspective is needed when it comes to the GI. Focus on the overall nutritional value of your foods, not just the GI number.<\/p>\n Factors that affect the glycemic index<\/p>\n Some will believe that the glycemic index causes more confusion than it is worth when it comes to the way most people eat. The reason is that the GI of an individual food or multi-component meal is influenced by several factors, including:<\/p>\n How much of the food is eaten: The index is based on a portion size of 50 grams (200 calories) of carbohydrate, which is often not the serving size we eat. That much cantaloupe is a lot of melon. All of this is to say that there are several limitations that prevent the glycemic index from being the end-all and be-all of healthy eating. There are just too many variables at play here.<\/p>\n Go higher when working out\u2026 \u201cResearch shows that slower 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,\u201d Galloway says. She explains that when you\u2019re in the middle of a run or race, especially anything intense, your body prioritizes carbs it can use immediately \u2013 so high-GI sources make the most sense. \u201cThey help keep blood sugar stable in the moment and support performance.\u201d<\/p>\n This means using the GI to learn how quickly carb-containing foods and drinks can raise your blood sugar can help you better plan your fuel to optimize performance. Sports drinks, gels, jelly beans, and honey are all high-GI items that can help keep you going strong. They\u2019re easy to digest and provide quick energy without weighing you down. Just heed Galloway\u2019s warning that consuming large amounts of high-GI carbs all at once can overwhelm the gut, leading to bloating, cramping, or nausea. Space it out and train the gut.<\/p>\n \u201cIn ultras or all-day efforts, relying only on high-GI fuels can feel like a rollercoaster,\u201d cautions Galloway. \u201cAdding in some lower-GI foods can smooth energy levels and provide a bit more staying power over time.\u201d Another win for a Slim Jim at mile 50.<\/p>\n \u2026but lower before your runs<\/p>\n
\nWhat food is consumed: Adding protein, fat, and fiber to a meal greatly impacts how fast carbs enter your system, sending the GI on a nosedive. Galloway explains that fiber is a big factor, as high-fiber foods slow digestion, thus lowering the glycemic response of a meal compared to consuming a carb alone. For example, adding peanut butter (fat\/protein) to white bread or milk and high-fiber raspberries to Cheerios reduces the meal\u2019s overall GI.
\nThe way a food is prepared and cooked: Cooking your spaghetti only to al dente (undercooked) will reduce its GI, or serving cooked potatoes cold, which increases resistant starch levels, makes the spud lower on the GI ranking.
\nRipeness of a food: Ripeness, such as that of a very ripe banana versus a slightly green one, can shift how quickly carbs are absorbed, potentially moving its GI upward.
\nHow the same food is processed: Processing methods that strip away fiber will increase a food\u2019s GI. For instance, a whole orange has a lower GI than orange juice due to its fiber. Similarly, steel-cut oats have a lower GI than instant oats because they remain more intact and take longer to digest, even if their overall nutritional profiles are similar.
\nWhat you eat first: The order of what we eat during a meal changes how the GI of foods impacts our blood sugar. For instance, eating non-starchy veggies like broccoli before digging into higher GI foods like white rice or dinner rolls can reduce<\/a> the post-meal blood sugar spike.
\nWho you are: There can be a large variation<\/a> in individual glycemic responses to foods, including potatoes, rice, and grapes, based on everything from genetics to body weight to fitness level. Just because a bowl of Special K can cause one person\u2019s blood sugar to soar does not necessarily mean it will for another individual.<\/p>\n
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While sports drinks are extremely valuable during endurance training and racing, you might not need them post-workout when they are more likely to spike your blood sugar. (Photo: Challenge Family)<\/p>\n