Cabohydrates and Endurance Sport

This winter has been the winter of a complete nutrition revamp for us (Heather and Trevor Wurtele – coauthors of all posts on the IMTT site).  Some race issues that were slowly becoming a trend (in a bad way) had to be changed.

This post is not about all the factors that affect your race nutrition, just the nutrition itself.  Specifically, the concentration and dilution of your carbohydrate intake.  Okay, we’ll mention a couple issues first.  Adequate training being the number one concern – if you haven’t done the work you will fall apart before the finish line, regardless of what you eat.  Issue number 2: Pacing.  Simply put, know your limits.  50% of the ‘nutrition’ issues in a race are actually pacing issues.  You’ve gone too hard on the bike in order to keep up with stronger cyclists, then blow up half way through the run.  There’s a reason why more men fall apart at the end of race than do women…and it’s not because woman are tougher, it’s because most are better at controlling their ego on the bike.

With respect to ACTUAL nutrition issues, here’s what we’ve found after talking to many ‘people in the know’.  First off, be wary of anything containing complex Fat or Protein (as opposed to nice, easy to digest, amino acids and cabohydrates) making their way into your stomach during the race.  Calories from those sources are very hard to breakdown efficiently and can cause some intestinal shut down once the intensity (on the run) picks up.  If your race intensity is low enough, you can most likely digest fat/protein properly without adverse affects to your performance.  So, if you plan on walking the entire marathon or half marathon, go for it! The other item  to consider (as if there were only two!) is how you dilute the carbohydrates you take in.  Most drink mixes out there give you a suggested serving like 1 scoop per 12 Oz.  TURNS OUT, there’s a reason for that!!! Wow.  On our First Endurance EFS drink for example, they say exactly that (1 scoop per 12 Oz), and because they’ve done their research they know that this the optimal dilution for our bodies to process those carbohydrates without leaching water from our cells – therefore keeping you hydrated and fueled properly over an endurance event.


If we look at that EFS drink label a bit further: 1 scoop has 24 grams of carbohydrate.  Convert the Oz. to ml (not sure why the United States must use both the metric and imperial system on their labels, seems kinda ridiculous) which gives you 355 ml.

Don’t lose focus yet, it’s worth knowing this stuff, trust us.

24 grams of carbohydrate divided by 355 ml gives you just under 7% solution.  That’s an optimal dilution for keeping yourself fueled without compromising hydration.  (Hydration is another post altogether. Here we’re dealing with carbohydrate dilution – how to best absorb your calories).  Another piece of the puzzle is that the human body can actually only absorb about 60 grams of carbohydrate per hour, but you can bump that number up close to 80-90 grams of carbohydrate per hour if you use a product with multiple types of carbohydrate (sugars – sucrose, dextrose) which have different receptors in your cells.

One more multiplication to keep in mind – carbohydrates have 4 calories per gram (fat has 9, protein has 4), so your upper hourly limit to carbohydrate intake, assuming optimum absorption, is ~360 calories (4 x 90).  If you take in that many calories, you need to take in about 1.25 liters of water in order to achieve that happy number for your stomach ~7% dilution.  7% isn’t a hard fast rule, but a good approximate.  If you are good at drinking water during races, you could lean towards 8% and assume that the water will dilute the carbohydrates you consume.  For a shorter,  higher intensity race you could even go closer to 9 or 10%.

So, what if you need more than ~360 calories per hour?  You can certainly take in more than 90 g of CHO per hour, but they’ll sit around waiting to be digested.  In the last hour of the bike, leaning towards an extra 25 grams of CHO may be fine, because you’ll almost certainly be consuming far less during the run.  You could also throw in small amounts of fat/protein from a bar (quarter bar per hour, as an example).  Another 50 calories per hour (5.5 grams of fat) is most likely not going to cause any stomach issues unless you’re redlining your heart rate for too long.  Play around in training, but really think about it. Look at labels and do some math, don’t just wing it and threaten your race, like we did in the past!