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Low Glycemic Foods

What Are the Health Benefits of Low Glycemic Foods?

Salmon Low Glycemic FoodSalmon, a low glycemic food option
Atkins, Zone, South Beach, ketogenic, low-carb… Despite their differences, all of these diets have one thing in common: an emphasis on low-glycemic foods. Long before low-carb diets became popular, diabetics have needed to pay attention to something called glycemic control, which in laymen’s terms, means how well you manage your blood sugar. But this concept isn’t just important for diabetics. Whether you maintain your blood sugar in a healthy range (or not) will affect your energy levels, sleep quality, hormone balance, and body weight, just to name a few. In this article we will explore the following:

​There are a host of factors that affect your glycemic control, the most important being insulin secretion and sensitivity, and the types and amounts of food you eat. You’ve likely heard the distinction between simple and complex carbs. Simple carbs (like maple syrup and white table sugar) contain lots of small, rapidly digestible sugar molecules that will spike your blood sugar rather quickly. Complex carbs on the other hand (think butternut squash or kidney beans) contain sugar molecules bound up in large carbohydrate chains (a.k.a. starch), which take longer to digest and therefore have a dampened effect on your blood sugar compared to simple carbs. In the early ‘80’s, researchers from the University of Toronto decided to find out exactly how much certain foods independently affected blood sugar, and so the glycemic index was born.

The Glycemic Index 

The glycemic index is basically a measure of how much the carbohydrates in a certain food item affect blood sugar. To determine a food's glycemic index, it is fed to test subjects in an amount containing 50 grams of digestible carbs (total carbs minus fiber) after a 12 hour fast. The extent to which the food increases blood sugar is compared to how much 50 grams of pure glucose affects blood sugar. For ease of reference, glucose is given a standard glycemic index value of 100. So, if a food’s effect on blood sugar is greater than pure glucose, it’s given a glycemic index of greater than 100. Conversely, if a food’s effect on blood sugar is less than pure glucose, it’s given a glycemic index of less than 100. A glycemic index of 55 or below is considered low, 55-69 is considered moderate and 70 or above is considered high. 

A major drawback of the glycemic index is that it doesn’t account for portion size. Remember, it tells you how much your blood sugar will be affected by the amount of a food item that contains 50 grams of digestible carbs. Depending on the food, this may be a completely unrealistic serving size. Take carrots, which have a glycemic index of 35. This is still low, but considering that apples have a glycemic index of 39 and taste much sweeter than a carrot, something doesn’t seem to quite add up. Here’s the key—in order to obtain 50 grams of digestible carbohydrates from carrots, you would need to eat 12 medium-sized carrots (which few of us do in one sitting, unless you’re Bugs Bunny). To get 50 grams of digestible carbs from apples, you only need to eat two and half (medium-sized). So the question then becomes: to what extent will a standard serving size of a certain food affect your blood sugar? Enter the concept of glycemic load.

Glycemic Load 

The glycemic load essentially combines the glycemic index of a food with its carbohydrate density to give you a more practical basis for judging how it will affect your blood sugar. Continuing with our carrot example, a standard serving of carrots contains about 7.5 grams of digestible carbs, which gives us a glycemic load of 3.5. One medium-sized apple, on the other hand, contains about 21 grams of digestible carbs, giving apples a glycemic load of 6. Even though carrots and apples have similar glycemic index values, the glycemic load of apples is almost double that of carrots. A glycemic load of 10 or below is considered low, 11-19 is considered moderate, and 20 or above is considered high. For those of you who are curious, the formula for calculating glycemic load is: 

                 Glycemic Load  =  [Glycemic Index of food] x [grams of digestible carbohydrates per serving] 

Some foods with a high glycemic index have a low glycemic load, because they have a low carbohydrate density. For example, watermelon has a glycemic index of 72 (considered high), but a glycemic load of only 4. Likewise, pineapple has a glycemic index of 59, but a glycemic load of 7. Very starchy foods like pasta, white potatoes, white rice, and bread typically have a moderate to high glycemic index and a high glycemic load, because of their high carbohydrate density. You can see a table showing the glycemic index and glycemic load values for a variety of foods here:

​Again, here are the cutoffs for the glycemic index and glycemic load: 
low glycemic foods cutoff
Glycemic Index and Glycemic Load cutoffs

Factors that influence Glycemic Index and Glycemic Load 

While the glycemic index and glycemic load provide a basis to evaluate how a particular food affects blood sugar, there are some factors that complicate their interpretation. First, the glycemic load of a food may change when consumed with other foods. Let’s take those carrots again, with a glycemic index of 35. Say you eat those raw carrots with some hummus, which contains fat from the sesame tahini and fiber from the garbanzo beans. Fat delays the movement of food from the stomach into the small intestine (called gastric emptying), and soluble fiber increases the viscosity of the food mixture as it passes through your GI tract. Both the fat and soluble fiber will decrease the glycemic load of the carrots. Generally, fat, fiber, and protein consumed along with a food will reduce its glycemic load.  

Alternatively, say you make a curry carrot soup, first boiling the carrots to soften them and then blending them with low-fat coconut milk and curry spices. What you’ve done is disrupted the “food matrix” of the carrots—instead of being solid roots, they’re now a creamy orange mush. As a result, when that soup hits your small intestine, your digestive enzymes will be able to start breaking apart the starch molecules much more quickly than if the carrots were raw, and so you will have increased the glycemic load of the carrots. In almost all cases, cooking and processing a food will increase its glycemic load. 

What the Glycemic Load doesn’t tell you

Since the development of the glycemic index, low glycemic diet advocates have recommended that diabetics or anyone wanting to lose weight reduce the overall glycemic load of their diet. Generally speaking, this is a good recommendation, especially if it means that people cut out added sugars and refined starches. However, there is one carbohydrate that often slips under the radar when talking about glycemic load: fructose. 

Fructose is the sweetest simple sugar occurring in nature, but interestingly, it doesn’t have much of an effect on blood sugar, with a very low glycemic index of only 19. However, even though fructose doesn’t spike blood sugar by itself, it does have adverse health effects when over consumed. While glucose is absorbed into the bloodstream and transported to tissues and cells where it is used for energy, fructose is shuttled to the liver where it is metabolized and used to make triglycerides (fat molecules). These triglycerides are either stored in the liver or transported to and stored as fat tissue. This phenomenon is called fructose-induced lipogenesis, which simply means that at a certain intake level, fructose may lead to fat accumulation. 

“Now hold on a second, isn’t fructose the main sugar in fruit? Does that mean fruit causes fat accumulation?” Not necessarily. Remember, table sugar (sucrose) is actually 50% fructose. Fructose by itself is neither “good” nor “bad,” it’s all about the context! Fresh fruits contain fructose alongside fiber, vitamins, minerals, and phytonutrients, which have health benefits and affect how the fruit is metabolized. However, most snacks or beverages sweetened with sucrose or high-fructose corn syrup have little or none of these healthful compounds. Even fruit juices, which are often touted as healthy, contain little if any fiber and huge doses of fructose. A 12-ounce serving of unsweetened apple juice contains about 23 grams of fructose, versus 11 grams in a medium-sized apple. This is why it’s always better to eat fresh fruit compared to fruit juices. Still, we don’t recommend eating five peaches or two cups of raisins in one sitting. That much fructose, eaten on a regular basis, can lead to excessive production of triglycerides and fat accumulation. But the point is, concentrated sources of fructose like soda, highly sweetened snack foods, and fruit juices will lead to fructose-induced lipolysis. 

How does this apply to a Low Glycemic Diet?

The take away is that the glycemic index and glycemic load can be useful tools in your tool-belt of nutrition knowledge, but they shouldn’t be the only tools that you use to evaluate a food product or choose low glycemic foods. A Snickers bar actually has a lower glycemic load than a sweet potato (18 compared to 22), but we trust you know which is a healthier choice. It’s important to consider the glycemic load of a food in context. It’s likely that you’d eat a Snickers bar by itself, and much more likely that you’d eat a sweet potato along with a meal containing protein, fat, and fiber, which would reduce the effective glycemic load of the sweet potato (just in case you needed convincing that the sweet potato would be a better choice). 

Again, the spirit behind a low-glycemic diet is to improve blood sugar regulation, which given the current pandemic of diabetes, prediabetes, and impaired glucose tolerance, is definitely a good thing. Those attempting to lose weight would also do well to consider a low-glycemic diet, given that better glycemic control will likely normalize insulin levels. But that’s a subject for another day.