What is the Glycemic Index?

Navigating the realm of dietary choices to manage blood sugar levels and tackle conditions like diabetes can feel daunting. The starting point is often clouded with uncertainty and conflicting advice, leaving individuals grappling with the question: What truly constitutes the "right" diet? 

Far from being a passing dietary trend, the glycemic index is a scale that ranks foods based on their effect on blood sugar levels. It is a scientifically validated tool that empowers individuals to make informed, conscientious choices about what they eat, guiding them toward stable blood sugar control.

[signup]

What Is the Glycemic Index (GI)?

The glycemic index (GI) is a numerical ranking system that categorizes carbohydrate-containing foods based on their ability to raise blood sugar levels after consumption compared to a reference food, usually glucose or white bread. This index assigns a value (0 to 100) to each food, indicating how quickly or slowly it causes blood sugar levels to rise. Foods with a high GI are rapidly digested and absorbed, rapidly increasing blood sugar levels. In contrast, those with a low GI are digested and absorbed more slowly, resulting in a gradual and sustained release of glucose into the bloodstream. (3) 

The GI serves as a valuable tool for understanding how different foods affect blood sugar levels and overall health. By incorporating GI into dietary choices, individuals can make informed decisions to select food options that minimize blood sugar spikes, helping achieve better glycemic control.

Low-GI diets have been proven effective in preventing and treating diseases where glycemic control is important, particularly diabetes, weight management, and cardiovascular disease. 

• Research suggests that low-GI diets reduce hemoglobin A1c (HbA1c) levels, fasting glucose, and postprandial blood sugar levels (13, 32).  

• Studies have also found that low-GI diets facilitate healthy weight management through various mechanisms, including reducing appetite and food cravings, promoting fullness, and decreasing insulin resistance. These effects culminate in a lower overall caloric intake and weight loss. (12, 24)  

• Furthermore, low-GI diets benefit cardiovascular health and reduce the risk of cardiovascular disease by improving lipid profiles and markers of inflammation (4, 21). 

The glycemic index is also relevant for individuals seeking to maintain stable energy levels throughout the day. Blood sugar instability, characterized by blood sugar highs and lows, is closely tied to mental and emotional health, causing symptoms like irritability, anxiety, worry, and energy crashes. (5, 14) High-glycemic diets are more likely to cause higher depressive symptoms, lack of motivation, and fatigue than low-glycemic diets.

What Is a High Glycemic Index?

The GI scale categorizes foods into three main categories based on their effect on blood sugar:

Balancing high-GI foods with low-GI alternatives is key to maintaining a balanced diet that supports stable blood sugar levels and overall health. When in doubt, use this Swap It Tool, but here are some examples: 

Instead of eliminating high-GI foods altogether, pair them with low-GI options to mitigate their impact on blood sugar levels. For example, if you're having a serving of white rice, balance it with vegetables and lean protein to achieve a moderate total GI. 

Pay attention to portion sizes, especially when consuming higher-GI foods. Smaller portions of high-GI foods combined with larger portions of low-GI foods help balance the overall glycemic load of the meal. Use your plate as a visual to help portion your food choices accordingly: at each meal, fill half your plate with vegetables and salads, a quarter with low-GI carbohydrates, and the final quarter with lean proteins. 

How to Calculate Glycemic Index

The GI of a food is measured through a standardized testing procedure that involves feeding at least ten healthy individuals a portion of the food containing 50 grams of digestible carbohydrate and measuring their blood glucose levels over the next two hours. On a separate occasion, the same individuals consume an equal-carbohydrate portion of glucose (the reference food), and their blood glucose response is also measured. (10) 

The changes in blood glucose concentrations are plotted as a curve, and the GI is calculated as the incremental area under the glucose curve (iAUC) after the test food is eaten, divided by the corresponding iAUC for the reference food. The value is then multiplied by 100. (10) 

GI = (iAUCtest food/iAUCglucose) x 100

Several factors influence the GI of a food:

1. How refined the carbohydrate is (degree of processing)
2. The physical and chemical structure of the carbohydrate
3. Cooking method
4. Fat, protein, acid, and fiber content of the food

Generally speaking, cooked refined carbohydrates low in fiber, protein, and fats are metabolized into glucose and absorbed into the bloodstream quickly, translating to a higher GI value.

What Effect Do Foods With a High Glycemic Index Have On The Body?

High-GI foods are quickly digested and absorbed, causing a rapid spike in blood sugar levels after consumption. In response to the sudden rise in blood sugar levels, the pancreas releases insulin to help transport glucose from the bloodstream into cells for energy or storage. As insulin shuttles glucose out of the bloodstream and into cells, blood sugar can rapidly drop, causing symptoms like fatigue, mood swings, headaches, difficulty concentrating, and dizziness. Over time, these dysglycemic patterns contribute to the development and progression of insulin resistance and diabetes.

While high-GI foods can provide quick energy, their frequent consumption may negatively affect blood sugar control, energy levels, and overall health. Prolonged consumption of high-GI diets has been associated with chronic inflammation and, subsequently, an increased risk of chronic disease, including type 2 diabetes, cardiovascular disease, obesity, and cancer. 

Can You Lower the Glycemic Index of Food?

It is possible to alter the GI of a food. We know that the following factors influence the GI of a given food (2, 29): 

• Cooking and processing raises GI
• Riper foods have a higher GI
• Fiber, protein, acid, and fat lower the GI

Taking these into consideration, incorporating these strategies into dietary and cooking habits can help lower the total GI of meals and promote more stable blood sugar levels:

• Choose low-GI carbohydrates, such as whole grains, legumes, fruits, and vegetables
• Pair carbohydrates with lean proteins (poultry, fish, tofu, beans), healthy fats (nuts, seeds, olive oil), and acids (lemon, vinegar, pickles). For example, enjoy whole grain bread with nut butter or avocado.
• Include a variety of fiber-rich foods, such as berries, avocados, leafy greens, and beans, in your meals and snacks.
• Cook foods for shorter periods to help preserve their natural fiber content. For example, pasta cooked al dente has a lower GI than pasta that is overcooked.

Incorporating GI Into Healthy Eating

While GI provides valuable insights into how foods affect blood sugar levels, a balanced diet encompasses more than just GI values. Nutrient density, fiber content, and overall macronutrient composition are just as important to consider.

One helpful concept to consider alongside GI is glycemic load (GL), which takes into account both the GI of a food and the amount of carbohydrate consumed. This provides a more practical way to assess the impact of a particular food on blood sugar levels in real-life scenarios. Foods with a moderate-to-high GI may actually have a low GL, such as parsnip and watermelon. The Glycemic Index Foundation recommends keeping your daily GL under 100 for optimal health.

Applying GI information to your everyday life involves planning meals, strategically swapping high-GI foods for low-GI alternatives, and combining different foods to mitigate their glycemic impact. When meal planning, consider the overall GL of meals by balancing high-GI foods with lower-GI options and controlling portion sizes. When shopping, read food labels and choose products with lower GI values whenever possible. The Glycemic Index Foundation offers several free tools that can help you begin making low-GI food choices:

• Low GI Shopping List
• Glycemic Index Swap It List
• Top 10 Low GI Pantry and Fridge Foods List

[signup]

Key Takeaways

• The GI is a valuable tool in understanding how different foods affect blood sugar levels and overall health. 
• Evidence shows that a low-GI diet is one strategy for preventing and treating inflammation, diabetes, cardiovascular disease, and obesity.
• While GI provides important insights into the speed at which carbohydrates are digested and absorbed, overall diet quality, nutrient balance, and portion sizes also promote optimal health and healthy blood sugar. Incorporating the concept of GI into dietary choices can help guide you toward a balanced and nutritious diet that supports long-term health.