Many alternatives have been developed to evaluate how foods affect blood sugar, including glycemic load.
The human diet consists of three macronutrients: protein, fats, and carbohydrates. For most people eating a Standard American Diet, carbohydrates make up the bulk of what’s consumed, and that’s as it should be. The 2015-2020 Dietary Guidelines for Americans recommends that 45 to 65 percent of your diet is made up of carbs.
Carbs and blood sugar
In recent years, carbohydrates have gotten a bad rap as a culprit in the obesity epidemic and the concurrent and related spike in cases of type 2 diabetes and cardiovascular disease. People who have type 2 diabetes are cautioned against consuming too many and the wrong kind of carbs. But carbohydrates are an essential part of your diet because they are the primary source of energy for cells in your brain and muscles. Without them, your body will turn to protein from your muscles for fuel.
There are basically three kinds of carbs — starch, fiber, and sugar — and not all are created equal. Most carbohydrates occur naturally in plant-based foods, for example vegetables and grains, but carbs are also added to many processed foods in the form of sugar or starch. So what’s the best way to decide which ones are OK to eat?
Too simple to be helpful
Sometimes carbs are classified as either simple or complex. Simple carbohydrates are sugars (for example, fructose and glucose) and are so called because they have simple chemical structures that your body can quickly turn into fuel, leading to a rapid rise in blood sugar when you eat them.
As their name implies, complex carbohydrates have a more complex chemical structure and so take longer to digest. This leads to a slower, sustained rise in blood sugar. Complex carbs are commonly found in whole plant foods, including:
- Beans, lentils, and peas
- Whole grains and foods made from them
- Starchy vegetables such as potatoes and winter squash
But simply dividing carbs into simple or complex doesn’t really provide enough information about which ones are better or how they will affect your blood sugar. Technically, complex carbohydrates are any kind of starch, which would include many processed foods such as white bread, cookies, pastries and cakes, and a variety of other foods considered unhealthy, like white potatoes and rice.
The role of the glycemic index
To address this shortcoming, the glycemic index (GI) was developed. GI places food on a spectrum of low (1 to 55), medium (56 to 69), and high (70 to 100). A food is ranked according to how much it raises your blood sugar level compared with pure sugar (GI of 100). Foods with a low GI are digested slowly, causing a gradual and sustained rise in blood sugar, and are therefore favorable over high GI foods, especially for people with type 2 diabetes.
However, GI doesn’t tell you how much “digestible carbohydrate” — the food’s carbohydrate content minus the fiber — is in a particular food. This is important because when you eat, your body responds to both the type of carb (where it falls on the GI) and the amount of carbohydrate consumed.
According to the Academy of Nutrition and Dietetics, a food’s GI ranking is calculated based on a serving that contains 50 grams of carbohydrate minus the fiber. That makes sense for a serving of white rice (GI of 64), which contains 53 grams of carbs per cup. But beets, which also have a GI of 64, only contain 13 grams of fiber per cup. So you’d have to eat a whopping 4 cups of beets to get 50 grams of fiber, and that’s unlikely.
A more useful alternative
Another way to evaluate the quality of a carbohydrate is its glycemic load, also known as GL. The formula used to determine glycemic load corrects for the shortcomings of the GI system by combining portion size and GI into a single number. The carbohydrate content of an actual serving of food is multiplied by that food’s GI. That number is then divided by 100.
To figure out the glycemic load for the previously mentioned cup of beets you’d use the following formula: 13 × 64 = 832 ÷ 100 = a GL of 8.3.
A glycemic load ranking of more than 20 is considered high, between 11 and 19 is moderate, and 10 or less is considered low. So although beets are have a medium GI ranking, they have a low glycemic load ranking, which is more reflective of the amount you’re actually likely to eat.
Although glycemic load values may provide a more realistic idea about how a particular food is going to affect your blood sugar, it assumes that the GI of any given food is known, but in reality, that information may not be readily available. One resource that may help is the international GI database, a searchable database that ranks thousands of foods based on their GI and GL.
Why it’s important
The food you eat has an impact on your blood sugar levels. With the exception of recovering from sustained, strenuous physical activity (for example a really hard workout), a big, rapid spike in blood sugar is a shock to your system that results in a drop that can leave you feeling weak and drained of physical and mental energy. If you are diabetic, it’s especially important to keep you blood sugars level, which means you need to avoid foods that cause these spikes.
There are a variety of tools available to help you monitor how your food may affect your blood sugar. But if you find you don’t have the time or aren’t motivated to track the numbers, eating a healthy diet rich in fresh (not processed) food will go a long way toward maintaining your energy and your health.
June 16, 2016
Christopher Nystuen, MD, MBA