Combining These Two Types of Sugars Will Fuel Your Performance While Lowering Risk of GI Issues
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Troubling headlines about sugar tend to fill the media: Sugar causes diabetes. Sugar causes cancer. Sugar causes obesity. In an attempt to limit the detrimental health effects of too much of the sweet stuff, the Dietary Guidelines for Americans advise that we limit added sugars in the diet to less than 10 percent of total calories. (For a 2,000 calorie per day diet, that translates to 200 calories of added sugar daily, or about 12 teaspoons.)
However, sugars tend to get a “good” label when it comes to athletes, as sports nutrition products boast a high sugar content to fuel performance. The reason: For a few decades now, it has been known that sugar intake during endurance exercise, like cycling, can improve performance by helping delay fatigue.
If you want to go fast for long, you need carbs on board to quickly fuel your working muscles, which is why sugar intake recommendations for the general population don’t necessarily apply to athletes—at least not all the time. Research also demonstrates that not all types of sugars are equal when it comes to powering rides.
Enter: glucose and fructose, two sugars that have become the darlings of sports nutrition research. These forms of simple carbs have been proven as assets when you want to go the distance and not limp across the finish line. And it turns out, this is especially the case when you team them up during a long workout.
Here’s everything you need to know about glucose and fructose, and how to make the most of them for riding results you’ll want to brag about.
Understanding Glucose and Fructose
The most common carbohydrate in the body is glucose, which is considered a monosaccharide (a.k.a. a simple carbohydrate). In certain body tissues—including the muscle and liver—glucose is stored as glycogen.
Fructose is another type of sugar known as a monosaccharide, with the same chemical formula as glucose: C6H12O6. A different molecular structure, however, makes fructose (also known as “fruit sugar” as it naturally occurs in fruit) taste significantly sweeter than glucose, but both glucose and fructose provide 4 calories per gram.
If we link two glucose molecules, it forms a disaccharide known as maltose. If we combine 50 percent glucose and 50 percent fructose, we get the disaccharide sucrose, which is a very common form of sugar in our diet known as table sugar. When glucose and galactose, the third type of monosaccharide, are combined it forms lactose, the disaccharide we find in milk. And when you combine several monosaccharides you get what is called polysaccharides a.k.a. complex carbs.
Let’s review where you can find these sugars:
Fructose = fruit sugar
Glucose = corn syrup, honey, and some dried fruits, like dates and apricots
Maltose (glucose and glucose) = molasses
Sucrose (glucose and fructose) = table sugar
Lactose (glucose and galactose) = dairy
Our bodies process each of these sugars differently, so when we consider what foods will help us hold onto a steady state of energy during a long ride and what might upset our stomachs, we need to consider the rate at which we burn calories that come from different sugars. Too much lactose, and many of us experience gas and bloating, for example.
How Glucose and Fructose Fuel Your Rides
Glucose is the only form of carbohydrate that your muscle cells use for energy generation. The mitochondria in your cells use this simple sugar to produce adenosine triphosphate (ATP), the energy source for muscular contraction.
Fructose, whether from fruit or as an ingredient in a sports drink or gel, gets metabolized by the liver and converted into glucose so your body can use it for energy.
Glucose, in contrast, gets released into the bloodstream and then can bypass the liver and go directly to working muscles. This is one of the reasons that fructose is a bit slower as an energy source than glucose, as there is an extra step before it can be used as a fuel. This also applies to galactose, which also gets metabolized in the liver and requires three steps before being released as glucose—it has the slowest oxidation rates.
Because glucose is much quicker to get to your muscles for energy-generating purposes than fructose, many athletes consider this the preferential type of carb to consume when exercising. But the best type really depends on the length of your ride—and a little bit on your personal biology.
Why It’s Helpful to Consume Different Types of Sugars
Athletes attempting to maximize their carbohydrate utilization and minimize GI distress should consume sports nutrition products or food items with multiple sources of carbohydrates, Kim Schwabenbauer, Ph.D., R.D., C.S.S.D., former professional triathlete and board-certified specialist in sports nutrition tells Bicycling.
When you take in products like sports drinks that contain only glucose, research suggests you can absorb and utilize about one gram of sugar per minute (60 grams per hour), compared to 1.7 grams per minute or higher when you take in nutrition that contains both glucose and fructose.
If you’re doing a shorter, less intense ride, consuming just glucose at that lower rate will likely sufficiently fuel your workout. But when you need to ramp up your carb intake, like when following a high-carb fueling protocol for more demanding rides, having the higher uptake rates that come with pairing together glucose and fructose will both give you the energy you need and help you sidestep stomach discomfort.
This is because the body’s two main sugar transporters, SGLT1 and GLUT5, can only handle about 40 to 60 grams of carbohydrate per hour. So even if you continue to ingest a greater amount of a single sugar, you are not necessarily using it efficiently, rather you are increasing your risk of gastrointestinal distress.
In fact, one study in the Journal of Applied Physiology found that carbohydrate oxidation (or the breakdown of glucose to generate energy) was 55 percent higher during a 120-minute ride when participants consumed a mix of glucose and fructose, compared to just glucose. These carb-burning results have been echoed in other research, too.
It’s worth noting that consuming too much fructose in isolation, 30 grams per hour or higher, can lead to GI woes like bloating and diarrhea, so you don’t want to just eat apples or bananas on a multi-hour ride. It seems when you consume glucose in isolation, however, most people can tolerate at least 60 grams per hour. Interestingly, in combination with glucose, the fructose-related GI problems tend to subside, and fructose becomes more tolerable at higher intake levels.
As for the proven performance benefits of taking in multiple forms of sugar, a research review published in Sports Medicine determined that pairing up glucose and fructose to fuel rides that last at least 2.5 hours, can improve power output when carbohydrate intake is at least 1.3 grams per minute (78 grams per hour). Even more performance benefit was shown with intakes of 1.7 grams per minute (102 grams per hour) or higher.
A separate investigation in the Journal of Strength and Conditioning Research found that perceived effort was lower in participants when consuming glucose and fructose, as opposed to just glucose, during an endurance cycling test.
Generally, experts recommend consuming a ratio of 2:1 glucose to fructose, which means 60 grams per hour of glucose and 30 grams per hour of fructose, if you’re aiming to take in a total of 90 grams of carbs per hour of activity. But this is not a magic ratio, and most individuals will need to test out what works best for them. For some, Schwabenbauer says a 1:0.8 ratio may bring about more favorable results.
When figuring out when and how much to eat during your next ride, here’s a quick guide from Schwabenbauer:
If you’re riding for less than an hour, you likely don’t need to take in any extra carbs to fuel performance.
For rides lasting longer than an hour and up to 2.5 hours, go for 30 to 60 grams of carbs every 60 minutes.
For rides lasting longer than 2.5 hours, aim for 60 to 90 grams of carbs every hour.
Where to Get Your Glucose and Fructose
Many sports nutrition products including drinks, gels, and chews on the market combine forms of glucose and fructose to increase carbohydrate oxidation and avoid the absorption-rate limiting effect.
If you are looking to consume both glucose and fructose during a ride you can choose products that list any of these combinations on the ingredient list:
Glucose and fructose
Maltodextrin and fructose
Glucose and sucrose (sugar)
Dextrin and fructose
Dextrose and fructose
Sugar and glucose syrup
Tapioca syrup and maltodextrin
Research suggests that there is no advantage to getting your glucose and fructose from one of these compared to another—all can be used to go big on carbs and increase burn rates.
Unfortunately, manufacturers of sports nutrition products don’t always list the quantities or ratios of ingredients on packaging. So it can be a challenge to know how much glucose and fructose you are getting and in what ratio. Sometimes fructose is used only in small quantities to improve taste, but not enough to have any physiological effects. You may have to search the brand's website or even contact them directly to find out what levels of these sugars are in the product you are using.
It’s possible to also get some of your glucose and fructose during a ride from liquid sweeteners, including maple syrup and honey. A tablespoon of maple syrup has 13 grams of carbs with 87 percent from sucrose, which is a 1-to-1 combo of glucose and fructose. A tablespoon of honey delivers 17 grams of carbs with a near 1-to-1 ratio of glucose and fructose. Some riders have been known to dump a bunch of maple syrup or honey in a gel flask as an alternative to packaged gels.
There is also the potential for getting some of your performance sugars from dried fruits. For example, one date supplies about 5 grams of carbs which mainly come from sucrose, glucose, and fructose. But some people find the amount of fructose found in various dried fruits, and perhaps the fiber as well, can cause stomach issues during a workout, so you’ll want to test out how dried fruits settle for you before going big on a ride.
“Whole food sources of carbohydrates can work for athletes as long as they recognize there may not be the same exactness in the ratios when comparing these to sports nutrition products and some trial and error in terms of serving sizes to achieve the optimal amounts may be necessary,” says Schwabenbauer.
Why Glucose and Fructose Is Beneficial After a Ride, Too
Following a solid ride, you are faced with a second metabolic challenge and that is to properly restore muscle and liver energy or glycogen stores. This is more pressing for athletes involved in repeated strenuous activity, such as multi-day cycling events.
Some studies suggest that overall post-exercise glycogen synthesis can occur faster and be more complete and with less gut discomfort after co-ingestion of fructose and glucose instead of just relying on one sugar source.
One investigation in the International Journal of Sports Nutrition and Exercise Metabolism found that post-exercise glucose-fructose ingestion following a glycogen-depleting ride resulted in improved performance in a next-day workout, compared to when the same number of carbs were consumed from just glucose. This might be because liver glycogen replenishment was greater with the sugar duo and, like muscle glycogen, liver glycogen availability may also be important for the capacity to perform prolonged exercise.
After a workout when quick recovery is paramount (like when there is another competition or hard training session several hours later), you can use sugars to replenish glycogen quickly.
Those wishing to optimize post-exercise carbohydrate storage can consider aiming for 1.0 to 1.2 grams of fructose-containing carbohydrates, like sports drinks and dried fruit, per kilogram body mass per hour for the first four hours of recovery. If you have more time (more than 24 hours) between workouts, however, it’s likely possible to use other carbohydrate sources like grains, fruits, and starchy vegetables consumed in enough quantities to get what you need to adequately replenish your energy stores.
The Bottom Line on Your Sources of Carbs
It’s fairly clear that when the quality of training and racing is important, fueling with sugars is a good option. “Consuming multiple carbohydrate types during exercise allows for maximum carbohydrate oxidation, lessens the chance of GI upset and can enhance endurance performance by reducing fatigue,” says Schwabenbauer.
Keep in mind, though, there are different carbohydrate needs for different durations of exercise as well as for different workout goals. If you prefer to simply hop on the saddle and go out for a couple of hours, cruising around at a casual pace without worrying about nailing an average speed or the watts you are holding, the need to pound back multi-sugar gels is hardly a game changer. But if you’re looking to compete at a race or take your personal performance to the next level, paying closer attention to the specific carbs you eat can give you the edge you need.
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