The three keys to fueling your marathon

The fall marathon season is almost upon us! With only a few weeks to go for many of you, it’s time to taper, to let the body recover and to get ready for battle. At this point it’s difficult to make any significant fitness gains, so dial back on that running. It is, however, quite easy to do a number of different things that can sabotage your performance. One of these detrimental decisions is not managing your race day nutrition properly.

Usually I present novel research studies in this column, but today I am going to give you a breakdown/reminder of what to do during your race to optimize performance. It is important to make a nutrition plan and stick to it. Going by hunger or the desire to consume food will leave most runners not consuming enough and therefore not running to the full potential of their current level of fitness.

When it comes to the research there is a lot in sports nutrition that we do not know (i.e. when exactly is beet juice helpful, if at all), and these areas need more time for definite guidelines to be established. Fortunately there is a lot that we do know for sure, and have been proven to make any runner faster. Here are the three most important nutrition rules to following during your marathon:

  1. energytitleCarbohydrate Intake During:

As most runners know, carbs are the fuel that we use to run. Glycogen is glucose stored in chains within our muscles.   This glycogen is typically depleted in ~2 hours of running, but our performance drops even sooner as our body recognizes this plummeting resource.

Fortunately, we can slow the loss of glycogen by taking in carbs as we run. The best carbohydrate to ingest during the race is the one that is absorbed most efficiently: glucose. The more readily the carbohydrate is absorbed means the less time it spends in our GI system, which therefore results in a decreased probability of GI distress. So, for one time in your life, it’s 100% better to go for glucose!

I have seen many health-conscious runners who have concerns about the insulin spike that takes place when ingesting sugar. That is why foods with a lower glycemic index are normally better options for us; they enter the bloodstream more gradually, and that acute insulin spike is avoided. The beautiful thing about running is that it depresses this spike. As we tackle marathons, we utilize every gram of glucose that hits our blood, so the need to store it never arises, and insulin does not skyrocket!

The amount you ingest during the race is very important. The gold standard is 60g/h. Most gels have just under 30g of carbs, so 1 gel every 30 minutes is a great strategy. It is important to actually take a gel every 30 minutes since the maximum ability of our GI tract to absorb glucose is about 60g/h. So, if you do nothing for the first 90 minutes, and then try to dump 90g of carbs into your stomach, it will be too late to catch up. Even though you will need 90g, only 60g will actually be absorbed over the next hour. So timed, staggered feeding is very important.

  1. Water-for-runnersWater During

Unlike the consumption of carbs, which have a consistent plan no matter what, hydration depends on race conditions and your personal sweat rate. Everybody is different, and everybody will sweat more the hotter the race is. A general rule of thumb is to make sure you do not exceed 3% loss of body weight throughout a run. So if a runner weighs 150lbs, that athlete can afford to lose up to 4.5 lbs throughout the race without seeing a significant drop in performance.

The best thing you can do is to have a general idea of your sweat rate under various conditions. I recommend weighing yourself before and after a variety of runs in the weeks leading up to your big race. Have an idea of how much weight you lose an hour at a range of temperatures with your current hydration strategy. If it seems like you might lose more than 3% over the course of your anticipated marathon finish time, add more fluid. A good starting point for most runners is 5-8 ounces every 15 minutes. I wish there was a more definite answer, but personal sweat rate is so variable (usually 1-2L/hour, up to 4L/hour for some!) that weighing yourself is the only way to ensure you are taking in an appropriate amount of fluid.

  1. Sodium During

Sodium is the main extracellular electrolyte found in our bodies. As a result, it is the only electrolyte we lose to any significant degree as we run. It might be a different story in ultras, but throughout your marathon you should only worry about sodium. Generally speaking, if you are fueling with gels or with a sports drink, your sodium requirements will be taken care of. Runners should aim to maintain 1g for every 1L of fluid ingested.

Don’t Worry About…

In terms of fuel during your marathon, the above three items are all you should worry about. There are several things runners are sometimes concerned with, but don’t need to be. Here are a few common ones to forget about:

Do not ingest protein, fibre or dairy products during your race. All of these things are not absorbed easily if at all, and are not efficiently used as fuel sources in the moment. Not only does your body like to use carbs more, but these types of food will sit in your GI system longer before being absorbed with some components not being absorbed at all. This makes for more GI issues. Carbohydrates are all you need in the moment to fuel your 42.2!

Potassium is another one that I get asked about frequently. Potassium is the main electrolyte within cells, and thus is not lost nearly as much in sweat as sodium. It is easily replenished via the regular consumption of fruits and vegetables in a normal healthy diet, and is not needed for acute maintenance in performance.

Take Home

Keep your plan simple and methodical during race day. Don’t listen to your hunger or thirst, don’t stress about non-important components of nutrition, and make sure you absolutely master the following 3 keys:

  • Make sure to ingest 30g of glucose every 30 minutes, and do not fall behind.
  • Plan a custom hydration strategy that allows for no more than 3% body weight loss.
  • Ingest 1g of sodium for every 1L of fluid you take in.

If you do these things without fail, you will ensure that fueling during the race is not a limiting factor in your performance.

Want more details along with some of the references supporting these strategies? Here is a great place to start– a full-text review article by a leading researcher in the field, Asker Jeukendrup. His review goes into much more depth and includes an outstanding reference list.

Enjoy your glucose, and good luck on race day!

Dr. Sean Delanghe, BSc. (Hons), DC is a chiropractorcoach, and a regular contributor to the RunWaterloo blog.