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Sugars and Endurance: Clearing up the Confusion

July 04, 2018 7 min read

Sugars and Endurance: Clearing up the Confusion

by Robert Kunz MS | Jul 1, 2018 | originally posted on First Endurance BLOG


By Robert Kunz MS

Endurance athletes put a strong emphasis on their training programs, their equipment, and their nutrition to ensure they reach their goals. First Endurance consults daily with endurance athletes, primarily on nutrition and how to best fuel your body for long distance racing. Through the hundreds of consultations with beginners, veterans, elite amateurs and professionals, it is quite clear that carbohydrates and their correct usage is vastly misunderstood. How to fuel during endurance events is a hotly debated topic which we have tackled with clear recommendations.

Much of what is misunderstood is likely driven by the media’s generalization of nutrition topics. You often hear ‘eating too much sugar makes you fat and is bad for you.’ Even as an endurance nutrition company we often get asked why we have sugar in our drinks. Clinical data performed on the general population and/or mice, though valid within this constraint, becomes irrelevant for athletes who are exercising aerobically. In other words, the physiology of sitting on a couch sipping on sugar is far different than the physiology when we are out training. This has led to misunderstandings and misconceptions about carbohydrates. Below are the four most common misconceptions.

#1 Misconception: Sugars are high glycemic* so they give a sugar high then crash.


Glycemic Index is a test that measures the blood sugar response to a food after it has been ingested. High glycemic means the food quickly increases blood sugar, whereas low glycemic raises it slowly. Generalizing all sugars into the category of high glycemic is simply incorrect. From the chart below you can see that the simple sugars glucose and fructose are vastly different in their effect on blood sugar. Some sugars are high glycemic, some are moderate, and some are low. Almost all foods have been tested for glycemic index and can be found using a simple internet search. The only way to truly know what a food’s glycemic index is, is to look it up or have it measured.



Below you will find the glycemic index of the more common sugars found in sports drinks:

Glucose                                                     High

Maltodextrin                                               High

Sucrose                                                     Moderate

agave nectar                                                Low

Cyclic Cluster Dextrin                                  Low (yet very fast gastric emptying)

Fructose                                                    Low

Glucose Scale 0-100

#2 Misconception:  Complex Carbohydrates like Maltodextrin are slow burning

This is one of the most common misconceptions and is also directly related to misconception #1 & #4.   Maltodextrin is one of the highest glycemic index carbohydrates available.  Because it has a high glycemic load, it actually works very well as a primary carbohydrate in energy drinks. Additionally, maltodextrin has a low osmolality which allows it to empty from the gut faster – another reason of why it is an effective carbohydrate to consume while exercising.

#3 Misconception:  Sugar is bad for my health.


What this should state is: Highly refined (empty calorie) high glycemic sugar during rest is bad for my health. Consider that fruits and vegetables and grains are primarily sugar, would one state that adding more vegetables, fruits and whole grain to one’s diet is bad? Of course not. Unfortunately, many consumers forget that these highly nutritious foods are almost all sugar. Sugar (as glucose) is the primary fuel that your body and brain runs on. Glycogen is our stored energy source and glucose is our circulating energy source. Nutrients like protein and fiber, and in extreme and rare cases even fat get broken down into glucose so your body can run efficiently. Trying to eliminate sugar is like trying to run your car without gas.

So what is bad about sugar? Consuming a high glycemic highly refined food when you are hungry causes a sugar high, strong insulin response, then a sugar crash. This ultimately can lead to insulin resistance and diabetes. This also causes consumers to eat more because with each sugar crash they crave more food. However, during exercise our physiology is different. While at rest your insulin works efficiently to bring high circulating glucose down. While exercising, the body wants the high circulating blood glucose to be driven to the working muscles as fuel. Hence, insulin is blunted while exercising, so eating a high glycemic food does NOT result in a sugar crash like it would at rest. TIP: Adding a low glycemic nutrient like protein or fat or even another low glycemic carbohydrate can lower its glycemic index and would therefore reduce the unwanted sugar high/low cycle.

Example#1: taking a couple handfuls of Rice Chex (GI=89), a short time later you feel emptiness (due to the sugar crash) and repeat the cycle. This leads to numerous health problems like insulin resistance, diabetes and weight gain. Let’s be clear here that it is not sugar that is the culprit but a high glycemic choice while at rest**. Now if you added some protein or fat to that snack choice, like nuts or an avocado, you have effectively reduced the glycemic index and will not get the sugar high/sugar crash result.

Example #2: You choose to have a piece of gluten free wheat bread (GI=90). Sugar high, sugar crash…repeat. Most don’t associate gluten free bread as being a bad choice but then again most don’t clearly understand the implications of glycemic index. Add a bit of peanut butter to the bread which is primarily protein and fat and you have reduced the glycemic index and hence stabilized blood sugar.

In these examples you can clearly see that it’s not the sugar that is the culprit in bad health but the high glycemic choice. In both examples you can consume the same amount of sugar, yet #2 is low glycemic and will therefore stabilize blood sugar.

#4 Misconception: Since I am doing a long race, I should consume slow burning carbohydrates

In the opening paragraph we stated that clinical data on the general population does not extrapolate to endurance athletes. From the misconception #3 you should have learned that high glycemic foods result in a sugar high and sugar crash. This is true in all situations EXCEPT when you are exercising and immediately following. Many athletes have taken what they learn from the media and have concerned themselves with consuming sugar and hence opted for a more sustained energy flow coming from maltodextrin (a complex carbohydrate). Their reasoning of WHY they chose maltodextrin is wrong on three counts.

1) As stated above, when you are exercising your insulin is blunted. Meaning, that when you are exercising and you consume a high glycemic food, you do not get a strong insulin response and hence you do not get a sugar crash. Your body is very smart and it clearly understands that when you are exercising you want to use the food or drink you consume to fuel your muscles. If insulin kicked in, the food or fuel you consumed would not get to the working muscle.

2) Athletes tend to choose maltodextrin, which is a good choice, but do so for the wrong reasons. As you learned from misconception #1 maltodextrin is actually high glycemic not low glycemic. Hence maltodextrin is a good choice because it is fast absorbing, not because it’s slow absorbing.

3) Looking for that low glycemic, slow sustained energy will actually cause you to bonk prematurely. Some even consider using some fat because they are going long. Understand that we all have about two hours of stored glycogen. Once this runs out, we bonk. If you consume a slow absorbing/low glycemic food while exercising you are forcing your body to rely on its stored glycogen. The entire goal of fueling for long endurance racing is to spare your muscle glycogen. In other words, do what you can to hold on to that stored glycogen. The best way to accomplish this, outside of appropriate pace and training, is to consume primarily fast absorbing carbohydrates to fuel your exercise. This will allow you to immediately use what you consume for the working muscle, so you can spare your stored muscle glycogen.

The act of consuming slow nutrients can also cause gastric distress. Consider that slow absorbing nutrients spend a lot of time in the digestive system. Doing this while exercising simply backs up the digestive system and does not allow for those fast nutrients to get absorbed. Often athletes cannot understand why they bonked when they consumed a large amount of calories. The simple answer is that they likely consumed slow calories that did not absorb before their glycogen ran out and often you feel this through considerable stomach discomfort.

*Glycemic index is the measure of your blood sugar response following the consumption of food. High glycemic foods result in a sugar high. Low glycemic foods are absorbed more slowly and result in a steady blood sugar response. Adding fat, protein or fiber to any food effectively reduces its glycemic index. Though there are two scales used, the more common scale measures glycemic index from 0 to 100.
**While at rest your insulin works efficiently to bring high circulating glucose down. While exercising the body wants the high circulating blood glucose to be driven to the working muscles as fuel. Hence, while exercising, insulin is blunted and therefore eating high glycemic food does NOT result in a sugar crash.
Resent research has proved that during exercise carbohydrates can be absorbed concurrently in multiple channels. Consuming several carbohydrate sources will allow the endurance athlete to better absorb the fuel needed to sustain endurance activity.

Nutritional Information for First Endurance EFS (Electrolyte Fuel System) can be found HERE.

EFS Drink Mix





Nutritional Information for First Endurance Ultragen Recovery Drink can be found HERE

ULTRAGEN Recovery Drink Mix

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