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.

“Training low” too often

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.

Quick fix: Right off the bat, it is important to note that the act of “training low” is proven ineffective for high-intensity training and thus is only recommended as a potential performance tool for aerobic-focused training and racing. To garnish the benefits of training low, approximately once a month, an athlete may complete an aerobic long run (up to 2 hours or 14 miles) without taking in carbohydrate fuel during the workout. In addition, once a week, an athlete may complete an aerobic-focused workout in the morning after an overnight fast OR complete 2 workouts in a day without replenishing carbohydrate between efforts.  An extra day of recovery should be penciled in after any “low” session.

Not nailing down a hydration plan before race day

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.

Failure to train gut at race pace

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.  

Quick fix: At least once a month before a key training session or at a “B” race, complete a race simulation where everything from carbo-loading, timing and execution of pre-race fueling, and fueling and hydration on run are practiced at target race pace/heart rate.

Skimping on performance-focused fuel in attempt to lose a few pounds

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.

Quick fix: Calorie restriction should be avoided on key training days and weekly calorie deficit should not exceed 3500 calories (500 daily) while in marathon training mode. Unless purposeful, such as during a “training low” session, it is not recommended to skip pre-, during, and post-workout fuel demands. Significant weight loss (>10% body weight) is best achieved in the off-season.

Kimberly Mueller, MS, RD, CSSD is a Registered Dietitian, Board Certified Specialist in Sports Dietetics, author of The Athlete’s Guide to Sports Supplements (Human Kinetics, 2013) and elite runner who enjoys helping others fine tune their nutrition as means to achieve a variety of health and performance-related goals with her company, Fuel Factor (www.Fuel-Factor.com). Contact her at kim@Fuel-Factor.com.