Understanding the Glycemic Index: Navigating Healthy Food Options

Unhealthy behaviors, such as eating the wrong foods or lack of sufficient exercise, can have detrimental impacts on a wide range of health outcomes. By choosing low-glycemic meals, you may control your weight better, decrease your risk of diabetes mellitus, or improve diabetes management. Further, eating foods with low glycemic indices may reduce the risk of heart disease, high cholesterol, and even stroke.

Meals with a low glycemic index are characterized by their ability to prevent abrupt increases in blood glucose or insulin levels. Considering the glycemic index while selecting meals could lead to favorable health results.

Using the glycemic index for healthy food choices

Healthy food choices help minimize our risks of obesity, diabetes mellitus (DM), heart disease, and more. Food selection can be based on various factors for those already classified as pre-diabetic, those with DM, or those wanting to eat healthier and lessen their disease risks. One, the glycemic index (GI), can help us evaluate foods relative to their effects on blood sugar levels.

What is the glycemic index?

The GI compares a meal’s effect on blood sugar to pure glucose. For example, a meal classified as 20 GI increases blood sugar by 20% less than pure sugar (glucose). Compare that to a GI of 98, which raises the blood sugar about the same as pure glucose.

When thinking about the GI, how does this work? Because foods with high GI scores (high glycemic foods) (e.g., a candy bar or a tablespoon of sugar) cause the blood sugar in your body to spike, this causes a fast spike in insulin release. However, when eating lower GI foods, insulin and blood sugar increase gradually and have a smaller overall effect. This is especially important in those with pre-diabetes and DM who don’t have enough insulin to respond to the spikes.

Low glycemic index foods

When using the GI to evaluate foods, we look at scores from 0 to 100. The lower the number, the less impact it will have on blood sugar.

Low glycemic foods or foods with GI≤55 include:

• Most fruits and veggies
• Minimally processed grains
• Nuts
• Beans
• Low-fat dairy products (but watch other ingredients)

Low glycemic index fruits

Generally, fruits have relatively low GI values, with a few exceptions, including pineapples (66), watermelon (75), and some dried fruits. Low GI fruits range from black currants (15) to raw red and green grapes (45) to bananas (48). Fruit color, ripeness, and freshness (canned vs. fresh vs. processed/cooked) all contribute to the GI.

Low glycemic index veggies

Most vegetables have low GI values, with a few exceptions, including potatoes (boiled 70), sweet potato/yams (70), and pumpkin (75). Veggies with low GI levels (10–20) include avocado, artichoke, broccoli, squash, capers, cauliflower, black olives, cucumber, sweet peppers, rhubarb, and zucchini. Cooking can drastically change the GI level of vegetables.

Moderate glycemic index foods

Moderate GI foods are those with GI levels from 55-69. Examples include:

• White/sweet corn
• Boiled beets
• Dessert bananas
• Raw pineapple
• Raisins

High glycemic index foods

Foods that we associate with high GI levels (70 and above) include cakes, croissants, white bread, white rice, rice cakes, bagels, doughnuts, many packaged breakfast cereals, and the majority of crackers. Canned pumpkin, cooked turnips, and parsnips are also high. It isn’t just processed foods or sweets.

What about grains?

Where do grains fall in the GI mix? When we think of carbohydrates, grains are at the top of the list. Some grains spike blood sugar faster than others. Grains with high GI scores include amaranth (70), yellow corn (65), potato flour/starch (95), corn starch (85), rice noodles (65), rice flour (95), white wheat flour (85), and sticky rice (90).

Pros and cons of a low-GI diet

Selecting food based on a low GI diet may be beneficial. The possible benefits of a low-GI diet have been well-researched. However, some of these benefits are thought to be partly due to a low GI level in combination with the high-fiber and/or nutrient-rich foods used in the research. So, benefits may not solely be due to a low-GI diet.

Benefits of a low-GI Diet

Benefits may include weight management, improved cholesterol control, a lower risk of developing heart disease or DM, lower blood pressure, and better DM management for those with DM.

Additional considerations and references

When evaluating a food’s GI (a carbohydrate’s potential to spike blood sugar), we must consider additional food components, including added sugars, dietary fiber, and starch-to-sugar ratio.

Make sure you are using the most up-to-date references for GI values. According to a 2021 systematic review by Atkinson et al., these values are updated and re-evaluated periodically. If you are looking to evaluate the foods you commonly eat to see where they score on the GI, resources that may be helpful to you include the Glycemic Index Foundation and The University of Sydney’s Glycemic Index search engine. The University has developed its GI database by compiling the results from numerous global scientific studies.

Limitations to a low-GI diet

A meal being Iow GI does not imply that it is healthy or cannot have negative health impacts. While the GI may assist people concerned with blood sugar levels in meal choices, it cannot be the sole metric used.

Remember that while the GI of a food may be low uncooked, or alone, food preparation, including any processing or added ingredients, can impact the GI.

Another drawback of utilizing the GI to guide meal selections is that while the GI helps us to understand how rapidly a specific food or ingredient will increase our blood sugar, it doesn't address a food's portion size. Just because a food has a low GI doesn’t mean you can eat a ton of it without ill effects. The GI does not indicate the recommended serving size or safe portion of a meal to consume. For this, we can turn to the glycemic load (GL).

The glycemic load

The GL helps tell a person the effects of blood sugar after eating an acceptable portion. Ultimately, the GL equates to the glycemic index multiplied by the carbohydrate in grams in one food serving divided by 100. This number ranges from 1 to 20 and above, with a low GL from 1 to 10, a medium from 11 to 19, and anything 20 or above representing a high GL value.

As a result, a meal with a higher GL is expected to increase blood glucose and insulin activity per serving size by greater amounts than a food with a lower GL. Thus, consuming both low-GI and low-GL foods may improve health outcomes. Let's take potatoes and carrots as an example. In contrast to starchy foods like potatoes, which have a high GI and a high GL, carrots have a high GI but low GL. Thus, eating a carrot will impact blood sugar and insulin levels less than a potato.

Research suggests that eating foods regularly with high GLs and GIs increases one’s risk of developing DM and possibly other conditions. The GI and GL may help guide decisions when selecting fruits and vegetables because many fruits may have higher than desired GI levels. However, when evaluated based on portion size and compared to lower GI foods, their blood sugar/insulin impacts may still be less significant.

While numerous research studies have provided a large database of foods and GI and GL levels, it is not all-inclusive. So, use the GL and GI indices cautiously and only as a guide to healthier food choices. Ensure appropriate portion control, monitor additional ingredients, and don't forget that drink choices and not just foods contribute to one's carbohydrate load and must be considered. Further, remember that portion sizes vary with geographical locations and culture, so you must interpret the GL carefully.

Reasons to follow a low-GI/GL diet

Using glycemic control (choosing foods that are less likely to spike blood sugar) to select food choices is a diet management strategy often associated with diabetes management. However, choosing foods with a low GI can also help people looking to:

• Maintain an ideal body weight
• Lose weight
• Lower one’s risk of developing DM, stroke, or heart disease
• Help in meal planning as part of a healthy diet
• Help prevent people diagnosed as pre-diabetic from developing DM
• Decrease fasting blood sugar levels

GI & GL guiding healthy food choices

For those who want to improve their overall health via nutrition, eating foods with low GIs and GLs helps lessen the spikes and troughs of blood sugar and insulin levels and may help enhance DM management or prevent the onset of DM. However, remember that carbohydrates are only one part of our diet. Our diet also includes fats and proteins along with needed vitamins and minerals.

Healthy eating is about striking a balance between calories in and calories out and between carbs, proteins, and fats. Ensuring a well-rounded diet is necessary to improve overall health and health outcomes. For advice on how to achieve a healthy food balance tailored to your specific needs, preferences, and routine, talk to a dietitian or medical professional.