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Sugar Breakdown

In the simplest terms, sugar is a carbohydrate. Carbohydrate molecules (CHO) are composed of carbon, hydrogen, and oxygen in a 1:2:1 ratio. Carbohydrates come in many forms: simple sugars (glucose, fructose, and galactose, as well as maltose, lactose, and sucrose) and complex sugars (glycogen, maltodextrin, starches, and fiber). When we consume carbohydrates, our body breaks them down into simple sugars, which are absorbed into the bloodstream and used for energy.

Glucose is our primary source of energy and is used/consumed by almost every cell in the body. Of the other two forms of simple sugars, fructose is metabolized primarily in the liver, while galactose is converted to glucose and used for energy. This is especially important in long-distance endurance events (such as Ironman, stage races, and ultramarathons) that require higher levels of carbohydrate consumption.

Ultramarathon runners and cyclists require carbohydrates for energy. These "sugars" help us maintain energy and performance throughout training and racing. During exercise, the body primarily uses glucose as its primary fuel source. An article published in the Journal of Sports Sciences states: "Muscle glycogen and blood glucose are the most important substrates for contracting muscle. Fatigue during prolonged exercise is often associated with muscle glycogen depletion and reduced blood glucose concentrations."

Recent research indicates that the optimal amount of carbohydrate to consume during these events for maximum performance is 90-120g CHO/hour. The challenge lies in how and what to consume to achieve this high level of carbohydrate intake, especially while running. Intestinal absorption may be the limiting factor, which has led to the development of products such as hydrogels and powder formulations that use Clustered Dextrin. Before delving into these, let's review what happens in the gut during endurance events.

It's a Gut Issue

An athlete's gut undergoes significant changes during longer-distance endurance events due to the physical demands of the activity. As the body works to supply the muscles with the energy needed to continue swimming, cycling, and running, blood flow is redirected away from the digestive system, leading to decreased digestive function.

These demands on the system can result in less desirable GI symptoms: nausea, abdominal cramps, vomiting, and diarrhea. While the exact causes are not fully understood, it is believed to be a combination of factors, including dehydration, "nutrition" intake, decreased blood flow to the gut, changes in hormone levels, and increased stress on the gut due to all the jolting.

Good news: the gut is extremely adaptable, allowing athletes to manipulate the amount, timing, and type of fuel consumed. Gut training involves challenging the gut with a high carbohydrate content and volume and testing different types of carbohydrates. This gut training has been shown to improve carbohydrate malabsorption, improve blood glucose availability, and substantially reduce intestinal discomfort, which translates into better endurance performance.

The Different Types of Sugars Used in Fuels

So what options do athletes have to meet these higher carbohydrate recommendations? We present multiple transportable carbohydrates, hydrogels, and superfuels. According to the research, "Among nutritional factors, a high intake of carbohydrates and hyperosmolar solutions increases GI problems. Several nutritional manipulations have been proposed to minimize GI symptoms, including the use of multiple transportable carbohydrates. This type of CHO intake increases oxidation rates and may prevent carbohydrate accumulation in the intestine."

Traditional Gels

Traditional gels, such as Precision Hydration/GU/Clif, use a combination of maltodextrin and fructose or sucrose. These are examples of multiple transportable carbohydrates and are highly effective in allowing athletes to achieve the desired 90-120 g/hour with minimal GI discomfort.

We know that dosing carbohydrate nutrition during exercise allows up to a maximum of ~60 g/h of glucose/maltodextrin to be absorbed and used for oxidation. However, adding fructose to this glucose dose allows for higher rates of carbohydrate ingestion, absorption, and oxidation because fructose uses a different transport protein to move from the intestine to the bloodstream. In other words, by ingesting glucose and fructose together, we can absorb carbohydrates at rates that exceed the absorption limit for glucose alone.

Modern Hydrogels and Gastric Emptying

Carbohydrate hydrogels are regular sports drinks containing carbohydrates with added pectin and sodium alginate. Pectin and sodium alginate form a gel-like mixture when in contact with the high acidity of the stomach. This gel-like mixture allows for faster passage through the stomach into the intestine—called "gastric emptying"—and accelerates the rate at which ingested carbohydrate is available for absorption from the intestine and use as a fuel source by working muscles.

The big question with any new "engineered" product is "does it work?" Previous studies (2020) on the gastrointestinal and metabolic effects of carbohydrate hydrogels were inconclusive, and research demonstrated no positive effects on exogenous carbohydrate availability or gastrointestinal symptoms during exercise. However, current research supports the use of hydrogels. "Ingestion of glucose and fructose in hydrogel form during running benefited endurance performance, exogenous CHO oxidation, and GI symptoms compared to a standard CHO solution."

In January 2022, a study published in Medicine & Science in Sports & Exercise compared the consumption of 90 g/hr of glucose and fructose in a 2:1 ratio as a hydrogel or a standard carbohydrate product (or a placebo drink without carbohydrates) during 120 minutes of steady-state running at 70% VO2max, followed by a 5 km time trial. "Ingestion of glucose and fructose in hydrogel form during running benefited endurance performance, exogenous CHO oxidation, and GI symptoms compared to a standard CHO solution."

Carbohydrate consumption improved performance compared to placebo, and hydrogel consumption was shown to improve performance compared to a standard carbohydrate drink by ~2.1%. From a metabolic perspective, exogenous carbohydrate oxidation rates were higher with the hydrogel. However, it is important to note that absolute rates of liver and muscle glycogen oxidation were similar under the standard hydrogel and carbohydrate conditions. It is also important to note that gastrointestinal discomfort was worse with the standard carbohydrate compared to the hydrogel.

Another study on hydrogels analyzed participants ingesting 70 g/hr of maltodextrin and fructose as a standard carbohydrate solution or hydrogel, a massive 180 g/hr of maltodextrin and fructose as a hydrogel, or water during 105 minutes of running at 70% VO2max. Focusing on the 70 g/hr data, hydrogel ingestion did not increase exogenous carbohydrate oxidation or impact reports of gastrointestinal symptoms during exercise.

Combining these data with those from the previous study supports the claim that hydrogels are most likely to be useful in challenging scenarios where the carbohydrate dose ingested during exercise is notably high (>90 g/hr). Maurten is an example of a hydrogel. They claim that their "biopolymer matrix," with a 0.8:1 ratio of fructose to glucose, allows an athlete to consume up to 100 g of carbohydrates per hour.

Corn Starches or Clustered Dextrins

Finally, we have highly branched clustered dextrin (HBCD), a type of carbohydrate derived from cornstarch. Due to its high molecular weight and low osmolality, HBCD is believed to provide an ergogenic advantage over other carbohydrate sources through faster gastric emptying and absorption. In theory, faster gastric emptying means "easier to digest," reducing the risk of GI discomfort.

HBCD also provides sustained energy release due to its slow breakdown over a prolonged period in the body. Much of this is explained by the large size of clustered dextrin. A single molecule contains between 60 and 70 glucose units, with an average molecular weight of 10.548 grams per mole, with a dextrose equivalent of 1.7.

In contrast, a long-chain amylose starch like maltodextrin contains only 3 to 20 glucose units, with an average molecular weight of 2,000 grams per mole, and a dextrose equivalent of 8 to 10. Skratch Labs (Super-High Carb Sport Drink Mix) is an example of a HBCD. They claim their "Super-High Carb Sport Drink Mix" is an extremely flexible fuel (and hydration) source that can be used at lower or higher concentrations depending on workload and caloric needs.

What is the Conclusion?

In short, athletes have many options when it comes to carbohydrate fueling during long-distance endurance events. Multiple transportable carbohydrates, hydrogels, and superfuels each have unique formulations, benefits, and palatability. Whether you're trying to increase carbohydrate intake during training and racing or need to alleviate GI issues, any of these options, alone or in combination, should do the trick.

Main Conclusions:

In short, athletes have many options when it comes to carbohydrate fueling during long-distance endurance events. Multiple transportable carbohydrates, hydrogels, and superfuels each have unique formulations, benefits, and palatability. Whether you're trying to increase carbohydrate intake during training and racing or need to alleviate GI issues, any of these options, alone or in combination, should do the trick.

• Various products (hydrogels, superfuels, glucose-fructose gel combinations) can provide the carbohydrates needed for performance while reducing the negative GI symptoms experienced by endurance athletes.

• Regardless of the product you choose, the gut is trainable and should be tested/pushed to increase tolerance and effectiveness.

• Hydrogels and superfuels (Clustered Dextrins) have solid research supporting their use in alleviating GI symptoms, which may or may not improve performance. The important thing is that each athlete practices race-day nutrition well in advance of the big day to find the right combination that works for them.