Bringing balance to the glycemic index

By Linda Blarjeske, RD, CD, LDE, Providence Nutrition Services

Newcomers to the glycemic index often ask: Do I have to stop eating potatoes, since they have a high glycemic index? The short answer is: not necessarily. Rather than eliminating certain foods altogether, it’s more important to focus on balancing your diet overall. 

The long answer gets more complicated, but I hope it clears up some of the confusion about this often-misunderstood tool.

The glycemic index, or GI, is a comparison of how quickly different foods – specifically those that contain carbohydrates – raise blood sugar.

To understand the GI, you first need to understand carbohydrates. We all need carbs – they act as fuel for the brain, for the nervous system and for physical activity. Adults need about half of their energy (calories) to come from healthful carbs – that is, whole grains, fresh vegetables, fruits and low-fat dairy. Athletes who engage in strenuous activity often need even more. 

For people who don’t have diabetes or prediabetes, it’s not necessary to obsess about the specific types of carbohydrates you eat. As long as you generally minimize sweets and stick mostly to whole grains, fruits and vegetables, your body will produce the appropriate amount of insulin to manage whatever carbs you eat.

For people who have diabetes or who are insulin resistant, however, it’s useful to understand which types of carbs tend to raise blood sugar more. The glycemic index was developed as a tool for this purpose, allowing people with diabetes to avoid “high-GI foods” – foods that tend to be digested quickly and to raise blood sugar faster – and to focus their carbs on “low-GI foods” – foods that tend to be digested and absorbed more slowly, so their impact on blood sugar is subsequently less pronounced.

Although it was developed for people with diabetes, the GI was quickly adopted by the diet industry, spawning several popular weight-loss programs. While it can be useful for both blood sugar control and weight loss, however, it is far from a perfect science. 

Understanding the numbers

The GI number for a given food is calculated by analyzing the increase in blood sugar after eating 50 grams of that food on an empty stomach. Pure glucose is given 100 points on the index, and other foods are indexed in comparison to that. High-GI foods come closer to 100 (baked potatoes have an average GI of about 85, for example), and low-GI foods fall farther down on the index (apples have a GI of about 38). By the way, you won’t find every food on the index – only foods that contain enough carbohydrates to affect blood sugar. If you don’t see broccoli on the index, that’s because it has little to no impact on blood sugar.

One problem with the index is the arbitrary quantity of 50 grams used for all foods. While it does lend consistency for comparison’s sake, it doesn’t reflect the actual amount of each type of food that you would probably eat in a sitting. For a better understanding of that, you need to look at a second number: the glycemic load, or GL. This number starts with a food’s GI and multiplies it by the number of carbohydrates in the recommended serving size for that food. The GL for a baked potato, for example, is about 26. 

Balancing the load

But there’s another problem with these numbers: Both GI and GL measure the blood-sugar impact of individual foods eaten all by themselves. In the real world, we rarely eat foods in isolation. We eat them in combinations, which significantly changes the way they are absorbed – and that changes their impact on blood sugar. That baked potato might raise your blood sugar quickly if it were the only thing you ate. But if you had it with some chicken and a green salad with a little dressing (and better yet, if you ate only half a potato), its effects on your blood sugar would be moderated.

To get the best use out of these tools, then, it makes sense to focus less on individual foods and more on the way we eat them – as meals. For a low-GL diet, aim for the sum of all of your daily carbohydrates to come to less than 80 GL, and try to balance those carbs evenly across all of your meals. 

Looking at that potato again, with a GL of 26, it does consume a hefty chunk of your day’s 80-GL budget. But if you love baked potatoes, there is no reason why you can’t have one – or part of one – every now and then as part of a balanced meal whose overall glycemic load is on the moderate side.

Other considerations

When you use GI and GL, be aware of these issues, as well:

  • Not all potatoes are created the same. Type “potato” into the search window at www.glycemicindex.com, and you’ll get 12 pages of results. The GI and GL of potatoes – and many other types of food – can vary greatly depending on the variety and how they’re cooked. A baked Burbank russet, for example, has a sky-high GI of 111 (GL 33), while a baked white potato has a GI of only 69 (GL 19). Boil the same white potato, however, and the GI rises to 96 (GL 24) – but choose boiled new potatoes instead and the GI falls to 54 (GL 11).
  • Not all people are created the same. Different people have different blood-sugar reactions to different foods.
  • GI is not a perfect indicator of the nutritional value of foods. Potato chips have a lower GI than potatoes, but whole, natural, unprocessed potatoes are certainly a better choice for good health. 
  • Low-GI also does not necessarily mean low-calorie. Some low-GI foods, such as chocolate cake (GI 38), are high in calories. When using GI for weight management, you still need to take calories and portion sizes into account.

As I said – it’s complicated. Eating low-glycemic foods can be a good thing to consider, especially if you have diabetes or insulin resistance. But it’s not easy, it’s not always practical, and it’s not a perfect path to a healthy diet.

Choosing a balanced approach

Does eating really have to be that complicated? Not really. Good health and quality of life mean finding the right balance that works for you.

If you like the structure of the GI diet, it certainly has benefits to offer for blood sugar control and weight management – just be aware of its limitations. 

But if you prefer your food – and your life – a little less complicated, there’s a simpler way. For optimal glycemic control, the American Diabetes Association recommends that, rather than focusing on individual carbohydrates, people with diabetes focus on getting a similar total amount of carbs at each meal. A dietitian can help you determine the appropriate level of carbohydrate to aim for based on your age, weight, gender, activity level, medications and other factors. 

Choosing a wide variety of fresh vegetables and fruits (these should make up half your plate), moderate amounts of whole grains or starchy vegetables (a quarter of your plate), and lean proteins or legumes (a quarter of your plate) will generally yield the same benefits for weight loss and glycemic control as following a more structured GI diet – but with less stress and more flexibility to choose foods that fit your personal tastes and cultural traditions.


More information

Diabetes: Eating a Low-Glycemic Diet

American Diabetes Association

www.glycemicindex.com