Common Nutritional Mistakes Marathoners Make

By Kim Mueller, MS, RD, CSSD

As many marathoners have discovered, you don’t have to be a rookie to falter on the nutrition front.  In fact, many find nutrition to be the hardest aspect of marathon performance to perfect. Below I cover some of the more common mistakes I currently see and the quick fixes to ensure a successful marathon journey.

The concept of “training low, racing high”, which refers to the act of avoiding use of carbohydrate in and around training and then introducing carbohydrates on race day, has become quite trendy in the endurance sporting arena and, with good reason. A large handful of studies over the past decade have found strategic implementation helps to enhance an athlete’s utilization of fat as a fuel, thereby sparing limited carbohydrate stores and paving the way for enhanced endurance performance. On the downside, however, there is also evidence that poor execution can lead to a plethora of performance-crushing problems, including reduced endurance, poor recovery times, and an increased number of nagging injuries and illnesses. Therefore, understanding how to best engage the benefits while minimizing side effects and performance detriments is key.

Some of the most memorable, though not pretty, images of marathoners are of athletes staggering towards the finish line and ultimately being treated for fluid and electrolyte imbalances.  To avoid being the subject of such an image, it is important to determine sweat rate in a variety of different conditions (hot versus cold, humid versus dry, etc) as well as understand personal tolerance to fluids (how much can you absorb) so an appropriate hydration plan can be drawn up for race day.  Knowing how to adjust effort when Mother Nature deals not-so-ideal race conditions like heat and humidity take effect as most athletes will find their sweat output far exceeds ability to absorb in such conditions and thus failure to reduce heat generated by exertion pretty much guarantees a trip to the medical tent or ER.

Quick fix: Consider investing in a digital scale and journal to help monitor sweat rate and hydration throughout training and ultimately create a hydration plan for race day. Within the journal, make note of the workout (those closest to target race pace most relevant) and Mother Nature’s mood (was she hot, cold, etc.). In addition, log data from the sweat test, which entails measuring pre- and post-workout weight as well monitoring fluid intake and urine loss during the workout. Each pound lost is equivalent to approximately 1 pint of fluid and 200-500 mg of sodium. Voiding a significant volume of urine, a urine color that is consistently clear, sloshy gut, weight gain, nausea and vomiting are all signs that fluids are not being absorbed. Be aware that not many can tolerate more than a liter of fluid per hour. In order to protect against performance and health declines associated with dehydration, post-workout weight should stay within 2-3% of pre-workout weight.

If I received a dollar for the number of times I have heard “but my nutrition worked in training” after describing a dreaded cocktail of gastrointestinal problems experienced on race day, I’d be a millionaire.  Because heart rate and oxygen consumption by muscles tends to be higher on race day (thus less available for digestion), it is important to train the gut on the nutrition front, including planned pre- and race day fuel, at target race day intensity.  

There is no doubt that finding the ideal “race weight” is a tricky science. Proper execution of a fat loss program can most certainly aid running performance. However, cutting the wrong corners or being overzealous with restriction can lead one to be defeated and/or injured at the same weight.  Finding a sweet balance between energy intake from food and output from training, therefore, is key.