What Is Glycemic Index? 

The glycemic index (GI) ranks a carbohydrate containing food based on how much it raises postprandial blood glucose levels in comparison with reference food (ie, white bread or pure glucose).^1,2 The GI is on a scale of 1 to 100: low GI is <55, moderate GI is 56-69, and high GI is >69. Foods with slower absorption and digestion have a low GI while foods with rapid absorption and digestion have high GI.³ Various factors such as macronutrients consumed in conjunction and cooking methods can affect the GI of a food.⁴

What Is Glycemic Load? The glycemic load (GL) of a food multiplies the GI by the total available carbohydrate content (g) in the serving divided by 100.^1,4 This measurement is used to assess a food’s overall effect on blood glucose and insulin levels.

What Are Low & High Glycemic Index Foods?

 Examples of low-GI foods include:^1,4,5

• Whole grains
• Nuts
• Legumes (eg, chickpeas, kidney beans, lentils)
• Fruits (eg, apples, oranges, peaches)
• Non-starchy vegetables (eg, broccoli, cucumber, celery, carrots)

Examples of high-GI foods include:

• Sugary foods (eg, soft drinks, candies, cookies)
• White bread
• White rice
• Potato

What Are the Benefits of Low Glycemic Index on Diabetes?

Current guidelines heavily emphasize the importance of intensive lifestyle management as a fundamental aspect of diabetes care.^6,7 Lifestyle management of diabetes includes healthy eating patterns that can facilitate glycemic control and healthy weight loss. Studies are showing that a low glycemic load dietary pattern may have beneficial effects in achieving glycemic control in individuals with diabetes by improving their carbohydrate quality and quantity.¹

As individuals with prediabetes, type 1 diabetes mellitus (T1DM), and type 2 diabetes mellitus (T2DM) have diminished or no ability to control postprandial blood glucose levels without medical care, low-GI diets that have lower postprandial blood glucose excursions have shown to improve glucose control in diabetic individuals.⁸

Several recent systematic reviews and meta-analyses have demonstrated that low-GI diets are effective in improving various parameters of diabetes.^1,8–10 A 2018 review of 6 randomized controlled trials (RCTs) studying the effect of dietary GI in adults with T2DM found that low-GI diets were more effective in improving hemoglobin (Hb) A1c and fasting blood glucose levels than high-GI diets.¹⁰ Similarly, a 2019 review of 54 RCTs on low-GI diets in adults and children with T1DM or T2DM concluded that low-GI diets effectively lowered HbA1c and fasting glucose levels, with reduction in their levels being inversely correlated with body weight.⁸ The study also found improvements in body mass index (BMI), low-density lipoprotein (LDL) cholesterol, and total cholesterol levels. Most recently, a 2021 review of 29 RCTs on the effects of low-GI diets on cardiometabolic factors in adults with type 1 or 2 diabetes found small but significant improvements in HbA1c, fasting glucose, LDL cholesterol, triglycerides, BMI, and systolic blood pressure.¹

Despite none of these studies finding improvements in blood insulin or insulin resistance, the favorable outcomes in HbA1c, fasting glucose, and BMI show that low-GI diets may be useful for diabetes management.^1,8,10 Some of these outcomes show very modest improvements, but even small improvements in these numbers can result in clinically significant benefits. For instance, studies have shown that a 1% and 0.67% reduction in HbA1c levels resulted in a respective 37% and 21% reduction in diabetes-related microvascular complications.^11,12 The US Food and Drug Administration has also recognized a 0.3-0.4% reduction in HbA1c as clinically significant for pharmaceutical treatments for diabetes.¹³ As such, even small improvements in HbA1c levels and potentially other parameters from low-GI diets may result in clinical value in diabetes management.