On two separate occasions, the cyclists pedaled for 3 hours at moderate intensity, while consuming a drink with 102 grams (just over 400 calories) of pure glucose per hour in one trial and the same amount of sucrose in the other. The performances were then compared.
The result? The athletes found the cycling task subjectively easier when consuming the sucrose drink, and they also found it more comfortable on the GI Tract (stomach).
To understand why these cyclists found the task easier when consuming sucrose, all you need to know is that while both glucose and sucrose are sugars and sources of energy for exercising muscles, sucrose is actually a double sugar molecule - and in the gut, the sucrose is split into separate glucose and fructose molecules.
This is an important distinction to understand. The body has multiple transports by which it absorbs liquids and fuels during exercise to allow athletes to continue performing optimally over time. One transporter is the lactate transporter; another is the glucose transporter; a third is the fructose transporter; and the last one is the water transporter. When you just consume glucose, you are over-taxing that one sugar transporter which can lead to stomach upset. Certainly, it leads to a stark slowdown in absorption. Meaning, when you need the fuel, it’s not readily available so you leach more muscle glycogen than you otherwise could. And, as you (hopefully) know, when muscle glycogen is tapped out, so too does your performance decline. You bonk. You’re scraping the bottom of the barrel. Stick a fork in you, you’re done.
Sucrose provides a distinct advantage over glucose because the two different sugars that make up sucrose are absorbed by two different transporters into the muscles. In other words, when sucrose is consumed, instead of only 1 way, there are now 2 ways for energy to reach the working muscles.
Should I throw away my sports drink? "Wow - that's amazing!" I hear you say. "Time to throw away my sports drink and replace it with some spoonfuls of table sugar."
Except it's not so amazing, really. Bear in mind if you decided to do this – using table sugar (sucrose) as your fuel source – that adding a spoonful of table sugar to a glass of water would provide you with just 4 grams of carbohydrate - when your muscles require 60-80g per hour during really hard exercise. Try drinking 20 glasses of sugar-flavored water in an hour and see how you feel.
Scientists have long known that a carbohydrate drink containing a simple mixture of glucose and fructose results in better energy uptake and use by exercising muscles compared to glucose only. Sports drinks manufacturers have been quick to catch on, too; many of the leading brands now offer glucose/fructose carbohydrate drinks - often branded as "2-to-1" drinks because research shows that two parts of glucose to one part of fructose is extremely effective at enhancing endurance performance.
As I contend above, relying on just glucose causes the double risk of relying too heavily on muscle glycogen stores and experiencing GI distress – both of which lead to sub-optimal performance. In simplest terms, the body is a machine and that which you ingest is simply fuel. If sucrose is a better option for performance fuel than glucose, it behooves athletes to worry less about how pure their sports drink is and focus more on the answer to the question of “what type of fuel is going to best set me up for training and racing success?”
I’m not suggesting you throw out the sports drink you currently use. What I am suggestion is that you take a look at its ingredients. If you find it lacking in the sugars, or if your GI Tract is typically left gurgling or upset during or after workouts, then experiment with other options to see if another works better for you or causes less GI distress.
Lastly, experiment with how strong or weak you mix your bottles. I find that half- to two-thirds strength tastes great in any weather conditions, never tastes too sweet and provides me with plenty of energy for most of my riding.