On the Fuelixir Blog we are passionate about providing evidenced-based sports nutrition information to our readers. Sometimes it can be overwhelming to read through scientific research and studies about sports nutrition. So here we try to make things simple. We read the articles, condense the information, and provide you with a nice short and sweet blog post with key points that you can takeaway and implement in your training. This week we look into fueling with carbohydrates during your workouts and find out that there may be such thing as too much.
Carbohydrates have been well researched in academia, and the performance benefits attained by ingesting carbohydrate during training and racing are widely recognized. The underlying benefit of carbohydrate ingestion during exercise, especially longer endurance type exercise, is primarily related to the fact that your body’s internal energy stores become lower (and eventually run out) as the duration of exercise goes on. So ingesting carbohydrate during exercise counters this fate, and allows you to continue to exercise. Given this one might think that the more carbohydrate you eat during exercise the better…wrong! Consume too much carbohydrate during exercise, and you risk having it accumulate in your gut. This can impair your performance by causing GI issues, ultimately slowing you down.
There is actually a maximum rate at which your body can utilize (or “oxidize”) carbohydrate for energy. This was originally thought to be 1 gram per minute, or about 60 grams per hour. That would equate to about 2 bars or 2-3 energy gels. However, recent research has found this maximum rate to actually be significantly higher, around 1.5 grams per minute at least. That’s about 3 bars or 4 gels! We don’t want to delve too much into the science here, but in brief what’s happening here is that that amount of carbohydrate your body uses during exercise is limited by the absorption of the carbohydrate in your intestine. The reason 1 gram per minute was thought to be the maximum rate was because rate of use of different sugars was not looked into.
If you ingest only glucose (a very common form of carbohydrate found in many energy drinks and gels), the oxidation rate will in fact be around 1 gram per minute. This is because of a “transporter” called SGLT1 that transports glucose across the membrane of the small intestine so it can be subsequently used for energy. SGLT1 can only handle a certain amount of glucose, hence the limit of 1 gram per minute. But if you ingest other forms of carbohydrate, for example fructose, there are other transporters that handle the absorption processes. With regards to fructose, GLUT5 is the transporter in play. So what this essentially means is that you can achieve higher rates of carbohydrate utilization if you consume different forms of carbohydrate!
But before you go out on your next bike ride or run there are some important factors to consider before you start chowing down 3 bars for every hour you are working out! The amount of carbohydrate to ingest while working out is heavily dependent on both the intensity and duration of the workout. For light workouts less than 90 minutes in duration, you likely do not need to consume any carbohydrate, especially if you’ve had a sufficient meal 3-4 hours before your workout. For moderate intensity workouts about 2-3 hours in length, you may gain a benefit from ingesting some carbohydrate, but something like 30-45g per hour (a gel or a bar) would likely be sufficient. Cases where more than 60g per hour would be beneficial would be for ultra-endurance efforts of 3 hours or more at a moderate to high intensity.
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