Research on Carbohydrate Concentration, Sugar Combination and Impact on Marathon Performance
Since Gatorade was first introduced in 1965 by a University of Florida medical team, researchers have sought to understand a sports drink’s effects on athletic performance.
Gatorade, and the later developed competing sports drinks, were designed to give athletes a convenient way to replace the fluids and electrolytes lost in perspiration and the carbohydrates burned in intensive exercise.
A flavorful and refreshing beverage available on the athletic field seemed to be the best solution – thus, Gatorade was born.
Over the years, the athletic field has extended to the running course where the utilization of fluid stations at long distance events and the development of water bottles, fuel belts and CamelBaks have solidified the beverages’ role as a runner’s mainstay.
It is now easy to access sports drinks while out on a run, but the availability of so many varieties can be overwhelming and leave us wondering which to use and when and how to use them. Hopefully this article will provide clarity.
How to select a sports drink
When developing a sports drink, manufacturers aspire to create a readily and quickly absorbable product that will tread lightly on the body’s digestion while running.
The term “gastric emptying” refers to how quickly a drink leaves your stomach so that the fluids and carbohydrates can be absorbed into the bloodstream. The fluid (water) in a sports drink helps maintain a stable blood volume and offset sweat losses. The carbohydrates (sugars) help maintain stable blood glucose levels as well as provide energy to the working muscles. Gastric emptying of a sports drink, and thus how quickly these processes are able to happen, is determined by the concentration of the solution and the volume ingested.
Research has shown that the most efficient and effective sports drinks have a carbohydrate concentration of 6 – 8 percent and absorb into the bloodstream quickly, at about the rate of plain water.
In comparison, the 10 to 12 percent carbohydrate concentration in soft drinks and fruit juices slows the stomach emptying and increases the cramping and other GI disturbance risks.
Fluid volume also determines how quickly your stomach will empty as the more distended your stomach becomes, the more quickly liquids will empty from your stomach.
Dehydration, on the other hand, slows down the rate of gastric emptying which is why it is important to drink early on and prevent dehydration. We will discuss fluid volume more in a bit.
Does the sugar type make a difference?
The fluids in an optimally formulated sports drink are absorbed just the same as water; however, the precise carbohydrate content in each has a greater variation range and is absorbed in the body via different mechanisms.
The most common carbohydrate forms are glucose and fructose (monosaccharides), sucrose (disaccharide formed from glucose + fructose), and maltodextrin (a polysaccharide also referred to as glucose polymers).
Early research on sports drinks concluded that the maximum amount of a single form of carbohydrate that could be absorbed during exercise was about 1 gram per minute. Once the glucose transporters are saturated, the body cannot absorb any additional sugar in the form of glucose no matter how much is given.
Recent research has since shown that the body can increase CHO absorption to 1.5 grams of glucose per minute when multiple carbohydrate forms are combined.
This is because the different sugars use different transport mechanisms to pass through the intestinal wall. Fructose uses a different intestinal transporter so the body can continue to absorb sugars via that mechanism after the glucose transporters are saturated. The result is more carbohydrate being available as fuel and less sitting in the stomach and potentially causing cramping or other GI problems.
The research on absorption and sugar combinations
Dr. Jeukendrup at the University of Birmingham School of Sport and Exercise Sciences has conducted a great deal of research on sports drinks and carbohydrate absorption and oxidation rates.
In 2008, eight trained male cyclists participated in a randomized crossover study in which they consumed either water, a glucose-only beverage, or a 2:1 ratio glucose and fructose beverage.
The beverages were ingested before exercise, at 15 minute intervals during two hours of steady state cycling, and at three separate intervals during a time trial immediately following the steady state ride.
Results showed that ingesting a 2:1 ratio glucose and fructose beverage improved time performance by 8 percent compared with just glucose and an 18 percent improvement compared with just water.
Results from cycling studies of this nature can generally be applied to running as well, since in later studies when measured during both cycling and running at a moderate intensity, absorption rates were similar. (Pfeiffer et al. 2011).
Researchers concluded that a mixed carbohydrate beverage that includes fructose, increases absorption and subsequent oxidation of carbohydrate.
Jeukendrup has researched additional sugar combinations that include fructose (glucose + fructose, maltodextrin + fructose, and a mixture of glucose, fructose, and sucrose) and has seen similar absorption and oxidation rates.
The following is a list of common brands of sports drinks and the sugars they contain:
- Accelerade — Ingredients: Sucrose, fructose, maltodextrin; 8 percent carbohydrates
- Cytomax — Ingredients: Fructose, maltodextrin, polyactate, glucose; 8 percent carbohydrates
- EFS– Ingredients: Complex carbohydrates, sucrose, dextrose; 8 percent carbohydrates
- Gatorade — Ingredients: Sucrose, glucose; 6 percent carbohydrates
- GU Electrolyte Brew – Ingredients: Maltodextrin, fructose; 5 percent carbohydrates
- HEED – Ingredients: Maltodextrin; 5 percent carbohydrates
- Power Ade – Ingredients: Fructose, sucrose; 6 percent carbohydrates
- PowerBar Endurance Sports Drink – Ingredients: Maltodextrin, dextrose, fructose; 7 percent carbohydrates
When to use sports drinks
While the studies mentioned above suggest that ingesting a sports drink during training may enhance performance, a sports drink is appropriate only for a particular workout length and intensity.
In 2010, Rollo and Williams determined that ingesting a 6.4 percent carbohydrate-electrolyte solution at 15 minute intervals during a one-hour run did improve performance or reduce perceived exertion compared with a placebo. The high-carbohydrate meal participants consumed three hours before the run likely provided all of the carbohydrates needed to complete the one-hour test.
However, consuming sports drinks during longer workouts can help maintain blood glucose and deliver additional fuel to working muscles in order to delay fatigue and improve your end-of-workout performance.
The general rule is using sports drinks for steady state endurance runs lasting longer than 90 minutes or high-intensity workouts lasting about 60 minutes.
The following guidelines provided by Monique Ryan in her book Sports Nutrition for Endurance Athletes, 3rd edition can be useful when determining whether or not you should bring a sports drink along with you on your next run.
Under 45 minutes: probably not needed
You may consider bringing along a sports drink if the workout is very high intensity or you have multiple training sessions that day
45-70 minutes: up to 30 g of carbohydrate per hour
If you have an early morning workout and haven’t had breakfast, or your workout is several hours after your last meal, carbohydrates provided by a sports drink may be beneficial if consumed during the workout
1-2.5 hours: 30-60 g of carbohydrate per hour
Uses these runs to practice and refine your fueling plan to meet your hydration needs while minimizing GI discomfort. Start drinking early and drink at regular intervals of 15-20 minutes.
More than 2.5 hours: 80 – 90 g of carbohydrates per hour
Products that provide multiple sources of carbohydrate are required to absorb a high rate of carbohydrate. Additional products like gels, bars, or gummies may be needed to meet carbohydrate needs.
- When you consume a sports drink, aim for regular intervals of 15-20 minutes and at least 20 ounces (2.5 cups) for each hour of the workout. Keep in mind that you don’t have to drink the entire amount at once.
- One big gulp is about 1 ounce of fluid, so try taking 4 big gulps at every drinking interval and you should be set.
- Sports drinks providing at least two sources of carbohydrate may have an advantage over those with just one
- Individual stomachs will react differently to the sugars contained in different sports drinks so it is important to experiment and determine what works best for you
- Cool fluids empty from your stomach more quickly that warm fluids so try to find creative ways for keeping your fluids cool on the run
- Sports drinks are not health drinks- they contain a high amount of sugar just like soft drinks and sweets so they should be saved only for long or intense workouts that demand carbohydrate replenishment