Written by: Matt Fitzgerald
You’re at your local running specialty shop, trying to choose between two
sports drinks. One contains complex carbohydrates and not much sugar, which, according to the packaging, provides “sustained energy” during exercise. The other sports drink contains a lot more sugar and says nothing about sustained energy. Which sports drink should you buy?
The answer might surprise you. The sports drink with more sugar and no promises of sustained energy will have a significantly greater positive effect on your running performance than the other product. Now, if you were choosing a sports drink for everyday nutrition—perhaps to consume as a snack, while sitting at your desk at work—the product with complex
carbs and little sugar would be the better choice. But the rules of nutrition and the realities of metabolism are completely different during exercise than at rest.
A surprisingly large number of sports drinks and other sports nutrition products are formulated and marketed under the false assumption that the rules of everyday nutrition also apply to exercise nutrition, and all too many runners fall for this marketing. Underneath the false assumption that the rules don’t change at the start of exercise are several specific errors concerning exercise metabolism. Following are three important facts that are masked by these errors.
1. It’s not how long an energy source lasts that matters. It’s how fast it gets to your muscles.
All ingested carbohydrates are broken down to glucose before they enter the bloodstream. Some carbohydrates are absorbed and metabolized relatively slowly. Consequently, they make energy available to the muscles, brain, and other organs and tissues at a relatively low rate for a relatively long period of time. Other
carbs are absorbed and metabolized very quickly. They make energy available to the muscles, etc. at a relatively high rate for a relatively short period of time.
The important thing to understand here is that a carbohydrate can only provide “sustained energy” by providing energy slowly. Sustained energy equals slow energy. Now, slow energy is fine when you’re sitting at your computer and your muscles are using and demanding little energy. But when you start running, your muscles’ rate of energy consumption may increase as much as twenty-fold. Suddenly, slow energy means not enough energy.
During intense exercise, the muscles burn carbohydrate faster that you can possibly absorb fresh carbs from any kind of sports drink. No matter what you do, there’s an ever-increasing deficit. You must minimize this deficit to maximize performance. The two things you can do to minimize your carbohydrate deficit during exercise are 1) to consume as much carbohydrate as your GI system can tolerate and 2) to consume the fastest (that is, the most rapidly absorbed) types of carbohydrate. It’s important to understand that there is no difference between slow, complex carbs and fast, simple sugars in terms of the total amount of energy each provides. Your stomach can’t tolerate any more complex carbs during running than it can simple sugars. The only difference between the two types of carbs is how quickly they get to your muscles from your stomach. Consuming slow, complex carbohydrates instead of fast, simple sugars will only compound your carbohydrate deficit. Your muscles are crying out for fuel. Whereas simple sugars rush quickly to the muscles’ aid, complex carbs sit around in your stomach and/or liver, taking their sweet time.
Imagine you were in the market to buy a racecar and a certain racecar salesman told you, “The great thing about this here racecar is that it really makes fuel last. It does this by only providing enough fuel to the engine to go 20 miles per hour. Even when you press on the accelerator and try to go 150 miles per hour, the rate of fuel supply to the engine doesn’t change, so the fuel really lasts.” Of course, you’re going to look at this salesman like he’s crazy because what he’s just told you is that his racecar cannot ever go faster than 20 miles per hour.
As crazy as this illustration seems, it represents exactly the same logic that makers of sports drinks touting their sustained (i.e. slow) energy supply are feeding you.
2. Exercise fatigue is not caused by blood sugar crashes.
In boasting of their complex carbohydrate formulas and sustained energy provision, the makers of certain sports drinks and other sports nutrition products never fail to mention that their products spare you from the “insulin spikes” and “blood sugar crashes” that high-sugar sports drinks cause. This argument is based on total ignorance of how insulin and blood glucose are regulated during exercise.
During exercise, the body enters a physiological stress state where blood glucose levels are very tightly controlled. Research has shown that “reactive hypoglycemia” simply does not occur during exercise. The same sugars that, when consumed at rest, cause a quick spike of blood glucose, followed by a quick spike of insulin, followed by a blood sugar crash, cause only a moderate, sustained elevation in blood glucose and insulin during exercise.
The only circumstance in which hypoglycemia does occur during exercise is when a person starts exercise in a fasted state, consumes no carbohydrate during exercise, and continues until the liver runs out of glycogen with which to replenish the blood glucose supply.
3. It’s not the carbs you get from you sports drink that need to last. It’s the carbs already in your muscles.
One of the most dangerously misleading ideas hidden in the notion that sources of “sustained energy” are preferable during exercise is the idea that bonking occurs when the supply of
carbs you’ve consumed in your sports drink run out. Basically, the argument goes like this: If you drink a sports drink containing fast, simple sugars, these sugars will race through your body and be used up in a hurry, and when they’re used up, you bonk.
But that’s not what happens at all. In prolonged exercise, bonking typically occurs when the supply of glycogen in the working muscles is depleted. In other words, glycogen in the working muscles is your limiting energy source. When it’s gone, you bonk. Therefore, the longer you can make your muscle glycogen stores last, the longer you will go before you bonk. So you want to spare muscle glycogen in any way you can—except by slowing down (which is a very effective way of sparing glycogen but not exactly helpful for performance).
Now, which do you think does a better job of sparing muscle glycogen: a sports drink containing slow, complex carbs, or one containing fast, simple sugars? Clearly, the latter. Here’s why: Let’s suppose that your working muscles must burn 100 grams of carbohydrate per hour to sustain a given pace. Your sustained-energy sports drink supplies carbs at a rate of 45 grams per hour. Your sugary sports drink provides carbs at a rate of 60 grams per hour. Both drinks leave a balance that your muscles have to get from another source—namely, its own muscle glycogen supply. But the sustained-energy sports drink leaves a much larger balance (55 grams per hour versus 40 grams). Therefore it does a much worse job of sparing glycogen and hastens glycogen depletion and bonking compared to the sugary sports drink.
A Case in Point
One thing you’ll notice if you pay attention is that the makers of sustained-energy sports drinks love to talk about the physiological reasons for the superiority of their products but never point to studies that simply compare the effects of their products to the effects of simple sugar-based sports drinks on performance. And there’s a reason for this, which I will reveal by example.
A number of years ago there existed a sports drink called GPush. Like many sports drinks that came along before it and many other that came along after it, GPush was touted as superior to other sports drinks because it was formulated to provide sustained energy. GPush contained a carbohydrate called galactose, which is technically a simple sugar but is a vey low-glycemic (i.e. slow) sugar because it has to be processed by the liver before entering the bloodstream, unlike other sugars, such as sucrose, which is broken down to glucose in the stomach and intestine.
A few studies comparing galactose-based sports drinks and fast-sugar-based sports drinks were performed. Incredibly, even some exercise physiologists knew little enough about exercise metabolism to think that the slower formulation might enhance endurance more by providing sustained energy. In fact, it did exactly the opposite.
For example, a 2009 study by New Zealand researchers “tested the hypothesis that supplementation with galactose before and during endurance exercise would spare carbohydrate (CHO), optimize fat utilization and improve performance compared with a typical sports drink formulation.”
A galactose-only formulation was compared to a 50 percent galactose/50 percent glucose formulation and an 80 percent glucose/20 percent fructose formulation (with all three formulations containing the same total amount of carbohydrate) in a stationary cycling workout. The galactose-only formulation did everything it was supposed to do physiologically. When subjects used it their insulin levels were lower and they burned more fat. But they also performed worse—much worse. Average power output was significantly higher when the subjects drank the fast-sugar
sports drinks than they did when they consumed the sustained-energy sports drink.
