We’ve known for a long time that carbohydrates are an essential fuel for exercise, especially endurance activities. Consuming carbs during exercise lasting longer than two hours is needed to prevent hypoglycemia (low blood sugar) and increase endurance capacity. (For more on this, see Carbohydrates—Why You Need Them).
In the past, guidelines were usually stated in terms of the amount of carbohydrates you should consume, expressed as grams per hour. For example, the American College of Sport Medicine (ACSM) recommends carbohydrate intake of 30—60 grams per hour. (The guidelines are usually stated in terms of the athlete’s body weight, e.g., grams per kilogram of body weight per hour). The problem with this recommendation is that it represents a wide range—and is independent of type, duration, or intensity of your activity, or training level.
But recent research1 has led to significant changes in our understanding of the role of carbohydrate consumption during exercise and its effect upon performance. And with that information, you can now tailor your intake of carbs to your specific training plan and activities.
According to recent studies, it is important to take into account the duration and intensity of your activity, and the types of carbohydrate you consume. And surprisingly, the resulting guidelines generally disregard body weight and training status. What we now know is summarized in the following table.
Single or multiple
Single or multiple
Single or multiple
Let’s work through the details—they may surprise you.
If you’re exercising for less than an hour, you don’t need much. Even for exercise at a moderate level of intensity (see Target Heart Rate Zones), 20 grams of carbohydrate is probably sufficient.
But here’s the shocker: You don’t have to eat your carbs. Research shows that just rinsing your mouth with a carbohydrate drink results in performance improvements. For exercise lasting less than an hour, there is no real advantage in actually consuming carbohydrates. Simply tasting them (independent of how they taste) is enough to enhance your performance. [Note: If your source of carbs is a drink (like Hammer HEED), you will still need to drink to remain hydrated.]
Ready for the next shocker? The fastest you can make use of carbohydrates (your oxidation rate) is about 0.8-1.0 g/min, or 30-60 g/hour—no matter how much you consume. The limiting factor is absorption from the your intestine—which, by the way, doesn’t depend at all on how big or small you are (so why are the ACSM guidelines expressed as "per kilogram of body weight"). That’s the fastest your body can make use of glucose.
Now wait for it. There’s a way around the 30-60 g/hour limit, and using it can make a big difference in your performance.
If you consume two types of carbohydrates, you can increase your oxidation rate by as much as 75%. For example, combining glucose and fructose, or maltodextrin and fructose, allows you to take in and use as much as 90g/hour!
What’s the big deal? For activities lasting more than three hours, how about delayed fatigue, improved performance, being able to maintain a high cycling cadence even after 5 hours, or finishing a marathon faster. And if you combine specifically maltodextrin with fructose sources of carbohydrates, you are likely to experience a decrease in gastrointestinal discomfort. Not bad, huh?
By the way, this trick works whether you take your carbs in liquid (e.g., Hammer HEED), semi-solid (e.g., Hammer Montana Huckleberry, Raspberry or Orange, or GU Mandarin Orange, Expresso Love, Blueberry Pomegranate, or Jet Blackberry gels), or solid (Clif Bars, Larabars) form. [Note: for the best results, look for low-fat, low-fiber, low-protein energy bars.] And research indicates that it works for all endurance activities: cycling, running, triathlons, swimming, cross-country skiing—you get the idea. Even in team sports, high carbohydrate consumption may improve time to fatigue, especially near the end of a game.
The higher your training or exercise intensity, the more your muscles become dependent upon carbs as an energy source. So for levels intensity Light and above (see Target Heart Rate Zones), the new guidelines apply. Anything less, adjust your carb intake downward.
As much as exercise intensity matters, body weight doesn’t. Recent research shows no correlation between body weight or muscle mass and your oxidation rate. There are, of course, some differences from person to person; but they are simply not significant.
Also, fitness level doesn't seem to matter. The research indicates that the results of higher, multiple source carbohydrate consumption applies equally to people who regularly exercise at light-to-moderate vs. high level intensity. On the other hand, you won't get these results if you're sedentary (in which case, we need to talk).
The more carbohydrates you can absorb, the more you’ll experience performance improvement. So its interesting to note the you may be able to increase your gut's absorptive capacity. At this point, the evidence is anecdotal. But according to many sports nutritionists, its worth trying to slowly increase your carbohydrate intake during training.
So rinse, drink, slurp or chew—take your carbs. Lots of them and multiple types.
1. Jeukendrup, Asker. "A Step Towards Personalized Sports Nutrition: Carbohydrate Intake During Exercise." Sports Medicine (Auckland, N.z.)44.Suppl 1 (2014): 25–33. PMC. Web. 30 Aug. 2016.