{"id":27695,"date":"2021-10-01T10:00:00","date_gmt":"2021-10-01T17:00:00","guid":{"rendered":"https:\/\/foodrevolution.org\/?p=27695"},"modified":"2025-11-24T13:53:57","modified_gmt":"2025-11-24T21:53:57","slug":"what-is-the-glycemic-index","status":"publish","type":"post","link":"https:\/\/foodrevolution.org\/blog\/what-is-the-glycemic-index\/","title":{"rendered":"What Is the Glycemic Index & How Should You Use It?"},"content":{"rendered":"

The glycemic index is often associated with diabetes control, but it has also has uses in the management of other chronic conditions like heart disease, obesity, and even epilepsy. If you\u2019ve been diagnosed with one of these conditions, especially diabetes or prediabetes, your healthcare provider may recommend you use the glycemic index as a tool for dietary planning.<\/p>\n

But what is the glycemic index? How exactly can it help you with your health? What qualifies as a low-glycemic versus high-glycemic food? And what does the evidence say about the index\u2019s usefulness?<\/p>\n

What Is the Glycemic Index?<\/h2>\n
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The <\/b>glycemic index<\/b><\/a> (or GI) assigns a number to carbohydrates on a scale from 0 to 100 based on how much they raise blood sugar (or glucose) levels after eating.<\/b> Foods that have little effect on blood sugar have lower GI values, while those that tend to spike blood sugar the most have higher ones. The GI scale is calibrated with pure glucose assigned the value of 100.<\/p>\n

The GI scale was developed<\/a> by two physicians, David Jenkins and Thomas Wolever, in 1981. They assigned the first values by measuring how a specific amount of glucose raised study participants\u2019 blood sugar over a two-hour time frame.<\/p>\n

Here\u2019s how the test<\/a> goes: Ten or more people are given a particular food \u2014 an apple, say, or piece of watermelon, or a pretzel \u2014 and their glucose is monitored for the next two hours to see how high it goes. The same cohort is then also fed pure glucose sugar as a comparison. If the apple raises blood sugar half as much as the sugar, it\u2019s assigned a value of 50. If the pretzel spikes blood glucose 73% as much as the sugar, its GI value is 73. And so on.<\/p>\n

However, you might be thinking, what about volume? Surely more of a food will raise blood sugar levels than less of it. Are they comparing apples and oranges here, or, more starkly, apples and watermelons?<\/p>\n

Well, it\u2019s complicated. Jenkins and Wolever did attempt to account for portion size by standardizing the test portions. But they didn\u2019t do it by comparing equal volumes (say, half a cup) or equal weight (like, four ounces). Instead, they decided that each test food must contain 50 grams of carbohydrates.<\/p>\n

How useful is this, really? Well, in real life, many foods don\u2019t typically get eaten in whatever quantity equates to 50 grams of carbohydrates.<\/p>\n

The Difference Between Glycemic Load & Glycemic Index<\/h2>\n
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That\u2019s why the glycemic load (or GL) was created. The GL is used in nutrition research and dietary advice to factor quantity in addition to carbohydrate quality. Glycemic load measures how much a typical serving of a food impacts blood sugar (as opposed to 50 grams of carbohydrates\u2019 worth).<\/b><\/p>\n

The GL is different from<\/a> the GI, but you may see both numbers when looking up a food as both are used. The GL takes into consideration how much of the food people typically eat, and thus the likely impact on blood sugar levels. Some experts believe that the GL gives a more realistic picture of how foods affect blood sugar.<\/p>\n

One way to think about this is to consider a riddle I heard when I was a kid: What\u2019s heavier, a ton of feathers or a ton of lead? The answer (they weigh the same; a ton is a ton) is a little counterintuitive if you\u2019re just thinking of the relative weights of feathers and lead. After all, a ton of lead can fit into a carry-on bag, while a ton of feathers could fill about 1,000 queen-size bed comforters.<\/p>\n

When it comes to the glycemic index, foods high in water and fiber are like feathers, and processed carbs are like lead. That is, it takes a lot more apples to reach 50 grams of carbohydrates (about two large apples, which weigh close to a pound) than Pepperidge Farm Milano cookies<\/a> (6 cookies, or roughly \u2153 of a pound).<\/p>\n

Calculating Glycemic Load<\/h3>\n

When you know a food\u2019s GI, you can calculate its GL by multiplying the GI by the number of carbohydrates you\u2019re eating and dividing by 100.<\/p>\n

GL = (GI x the amount of carbohydrate) \u00f7 100<\/p>\n

Here\u2019s an example. Sweet raw cherries have a GI of 62<\/a>. If you eat a cup of pitted cherries, you calculate their glycemic load by first looking up the carbohydrate grams in one cup. You can do this at various online food databases, such as NutritionData.self.com.<\/a> There you\u2019ll discover that one cup of pitted cherries delivers 25 grams of carbohydrates. Now, you can plug the two variables into the equation to find out the GL:<\/p>\n

GL = (62 x 25) \u00f7 100 = 15.5<\/p>\n

But when you calculate the number, what does it actually mean? For optimal health, and to support blood sugar levels, the Glycemic Index Foundation \u2014 an Australian nonprofit raising awareness about a low GI diet \u2014 recommends<\/a> keeping your daily glycemic load under 100. So a cup of pitted cherries still leaves you room for 84.5 more GL points (100 – 15.5 = 84.5).<\/p>\n

Still, the GI continues to be more widely used than the GL, despite being less relevant to how we actually consume food.<\/p>\n

What They Mean for You<\/h3>\n

So what can GI and GL tell you? In theory, the GI gives you a way to identify which foods contribute slower-acting \u201cgood carbs\u201d versus faster-acting \u201cbad carbs\u201d in terms of their impact on your blood sugar.<\/b><\/p>\n

Multiple factors<\/a> are involved in how fast a specific food will raise your blood sugar. And two foods with the same carbohydrate content can have different GI numbers<\/a>. Some examples include how refined or processed the carbohydrate is, the cooking method used to prepare the food, the chemical and physical properties of the food, and its fiber, protein, fat, and acid content.<\/p>\n

In general, the more a food has been cooked or processed, the higher the GI<\/a> will be. This is because physical and temperature changes made to the food before you eat it cut down on some of the time your body has to spend on digesting it. For example, mashed potatoes have a higher GI than a baked potato, which is also higher on the GI than a raw, untouched potato (not that we recommend eating raw potatoes to lower your GI, just to be clear). The American Diabetes Association even says that al dente pasta has a slightly lower GI<\/a> than pasta that has been cooked longer.<\/p>\n

One way to think about this is to imagine taking a match to a pound of wood. If that wood is in one piece, it may not catch fire at all. If, on the other hand, that wood has been turned into a pound of crinkled newspaper, it could ignite rapidly upon ignition. Same substance, but differently processed.<\/p>\n

The GI of fruits also increases<\/a> as they ripen. A green banana has a lower GI than a ripe banana that\u2019s starting to develop brown spots. This explains why a ripe banana has a sweeter flavor, and tastes a whole lot better, than a green one. We\u2019ve evolved to prefer foods that give us a big sugar spike because they tend to have more calories, which can be a handy tendency in a world of constant food insecurity and intermittent famine.<\/p>\n

Glycemic Index, Glycemic Load, and Health<\/h2>\n
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Research shows that the glycemic index and glycemic load can both be useful tools to help you eat for health \u2014 and to manage specific conditions. Below are how the GI and GL can be best used for certain health conditions.<\/p>\n

Diabetes<\/h3>\n

The GI and GL are primarily used as tools for managing diabetes and prediabetes. Specifically, they help individuals with diabetes gain awareness of how certain foods can impact their blood sugar readings. For instance, high GI and GL foods can spike blood sugar quickly, which can be dangerous for someone with diabetes. Plus, the American Diabetes Association says the glycemic index may be useful to help fine-tune blood sugar<\/a> when adjustments are needed in a diabetes management regimen.<\/p>\n

Research has confirmed that the GI and GL can be useful tools for optimal glycemic control. A 2019 meta-analysis<\/a> published in the American Journal of Clinical Nutrition<\/i> examined 54 randomized controlled trials in adults or kids with impaired glucose tolerance, type 1 diabetes, or type 2 diabetes. They found that low GI diets were effective at reducing glycated hemoglobin (HbA1c), fasting glucose, BMI, total cholesterol, and LDL \u201cbad\u201d cholesterol, but didn\u2019t impact fasting insulin, HDL \u201cgood\u201d cholesterol, triglycerides, or insulin requirements. Overall, current evidence suggests that low GI diets may be helpful in blood sugar management and may even help in achieving a healthy body weight among people with diabetes.<\/b><\/p>\n

Other studies support this finding, too. A 2018 review<\/a> found that a low GI diet is more effective for controlling fasting blood glucose in comparison to a higher GI diet among people with type 2 diabetes.<\/p>\n\n \n

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Cardiovascular Disease<\/h3>\n

Research shows that consuming a diet based on foods that contribute a lower GI and GL may be better for your heart health as well.<\/p>\n

In a 2021 study<\/a> published in the New England Journal of Medicine<\/i>, diets with a high glycemic index were associated with an increased risk of a major cardiovascular event or death, both among participants with preexisting cardiovascular disease and without.<\/p>\n

And in a large prospective study<\/a> involving 338,325 participants over approximately 13 years, researchers aimed to determine whether GI and GL are associated with heart disease risk in both sexes. They concluded that a high GL, or a diet that triggers a high glucose response, is associated with a greater risk for developing heart disease.<\/p>\n

Lastly, an expert analysis<\/a> of the Prospective Urban Rural Epidemiology (PURE) study published by the American College of Cardiology<\/i> in 2021 concluded that among adults with established heart disease, a diet based on higher GL foods was associated with higher risk of both heart disease events and all-cause death.<\/p>\n

Weight Management<\/h3>\n

The GL and GI trends in your diet can also be important for helping or hindering healthy weight management goals.<\/p>\n

A 2019 meta-analysis<\/a> published in the American Journal of Clinical Nutrition<\/i> examined data from 54 randomized controlled trials in adults or children with impaired glucose tolerance, type 1 diabetes, or type 2 diabetes. They found that diets with a lower GI may help lower body weight among people with prediabetes or diabetes.<\/b><\/p>\n

A 2015 systematic review<\/a> and meta-analysis examined how high or low glycemic foods affected weight of overweight or obese children and adolescents. Overall, they found that a primarily low GI or GL diet was more beneficial for weight management for this population than a higher GI or GL diet.<\/p>\n

And in a 2015 Brazilian study<\/a>, 19 participants were randomly assigned to either eat two daily low-GI or high-GI meals, for 45 days in a row. Their normal everyday food intake was assessed before beginning, and then their intake, body composition, and other anthropometric measurements were evaluated every 15 days. At the end of the 45 days, other biochemical and metabolic markers were also assessed. The authors found that consumption of two daily low GI meals for 45 consecutive days had a positive effect on obesity control, whereas, the consumption of high GI meals had the opposite effect.<\/p>\n

Epilepsy<\/h3>\n

While you may have heard that a strict ketogenic diet<\/a> can help manage epileptic seizures in children, there\u2019s also evidence that a low GI or GL diet can also offer therapeutic benefits for this condition. One of the reasons this is attractive to some people is that while the ketogenic diet may have benefits for people with epilepsy, it is also associated with a new set of problems, including<\/a> lower life expectancy. A diet that is low on the glycemic index offers a less restrictive approach, making it easier to incorporate many of the healthy foods that tend to be left out of a ketogenic diet.<\/p>\n

The low glycemic index treatment<\/a> (LGIT) is a form of dietary therapy for epilepsy. It was first described as such in 2005, after doctors observed that some children were experiencing noticeably more seizures after eating high GI foods.<\/p>\n

Researchers have helped identify that stabilizing blood glucose seems to help control seizures in some children, as well as adults. For instance, a 2017 study<\/a> among 36 children with epilepsy were treated with LGIT for one year, and their seizure outcomes and side effects were observed. The authors found that while few children on LGIT received total freedom from their seizures, this dietary approach was effective for reducing seizure frequency.<\/p>\n

And a 2018 review<\/a> examined eight studies on LGIT and epilepsy management, concluding that while currently available research has found mixed results, this approach does appear to be beneficial for patients with intractable epilepsy.<\/p>\n

How to Use the Glycemic Index<\/h2>\n
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The glycemic index can be a useful tool if you\u2019re diabetic, suffering from cardiovascular disease, obese, or epileptic.<\/b> But even if you don\u2019t have one of these conditions, you can still use the index and benefit from it. Keeping a steady blood sugar<\/a> is important for good health both in the short-term and long-term.<\/p>\n

If you\u2019re curious about the glycemic index of a food you like, you can easily search for it on the official GI website<\/a> maintained by the University of Sydney. You can search by food name, category of food, country of origin, GI number, GL number, serving size, and carbs per serving.<\/p>\n

All of the foods in the GI database are categorized into GI and GL ranges<\/a>, which are outlined below. The range<\/a> indicates how much of an impact the food is expected to have on your blood sugar after you eat it, with low being the least impact.<\/p>\n

Glycemic index ranges:<\/p>\n