Fuel to be faster: Studying the effects of low energy availability at the Boston Marathon

Like many sports medicine specialists, Kristin Whitney, MD, MA, suspected that many of the issues she treats in runners — bone stress injuries, anemia, decreased response to training, and reduced endurance to name a few — stemmed from insufficient nutrition.

Low energy availability, a state that occurs when an athlete’s energy intake doesn’t match their energy expenditure, is pervasive in the running community, says Whitney, director of Boston Children’s Injured Runners Clinic. Unfortunately, common assumptions in sports culture, such as “lighter is faster,” drive many runners to restrict calories, no matter how hard they’re training. Others unintentionally develop low energy availability due to lack of knowledge of nutrition and the fueling demands of endurance sports.

In its extreme form, low energy availability leads to relative energy deficiency in sport (REDs), a syndrome known to harm systems throughout the body, including bone health, reproductive health, cardiovascular health, and mental health.

But what about athletic performance? Is lighter indeed faster? Or is it possible that under-fueling could undermine an athlete’s ability to reach their goals?

A recently published study of more than 1,000 runners who competed in the 2022 Boston Marathon provides answers. Conducted by Whitney, Kathryn Ackerman, MD, MPH, of the Wu Tsai Female Athlete Program at Boston Children’s, and an international team of sports medicine and nutrition specialists, the study is the largest of its kind hosted at a marathon to date. And it has important implications for providers, athletes, and coaches. 

Low energy availability and marathon outcomes

Each year, about 30,000 athletes from around the world compete in the Boston Marathon. In 2022, 1,030 volunteers with Boston Marathon entries completed an electronic survey that assessed their marathon experience, training, medical history, and indicators of low energy availability. 

Study participants ranged from first-time marathoners to elite competitors. Forty two percent of female runners and 18 percent of male runners had self-reported indicators of low energy availability.

Using data from runners’ wearable timing chips, researchers found that runners with indicators of low energy availability had significantly worse race outcomes, even when matched with runners of similar BMI, sex, marathon experience, and training.

“Runners with signs of chronic underfueling had much slower times on race day,” says Whitney. They also required medical attention twice as often, with 22 percent of those medical encounters resulting in withdrawal from the event.

Raising awareness could boost runners’ performance

Although eating disorders and disordered eating are pervasive in the running community, more than half of the athletes with low energy availability did not have these behaviors.

“Under-fueling is often unintentional,” explains Whitney. In some cases, athletes simply don’t realize how many calories or what type of nutrients they need to meet the energy demands of their training. And endurance training often suppresses appetite, so eating only when hungry can lead to unknowingly under-fueling. 

The study also found no significant difference in BMI between athletes with low energy availability and their better-fueled counterparts, a fact that Whitney hopes will alert providers to the need to screen athletes with symptoms of low energy availability, regardless of their body type. 

“It’s important to know that low energy availability and REDs have more to do with an athlete’s feeding behaviors than their BMI, calculated by weight and height, or how they look,” she says.

Low energy availability and REDs have more to do with an athlete’s feeding behaviors than their BMI, calculated by weight and height, or how they look.”

Kristin Whitney, MD, MA

Given the size of the study and the results demonstrated among real-world athletes at the Boston Marathon, Whitney hopes the results will help chip away at myths that perpetuate unhealthy eating behaviors. To that end, the researchers hope to partner with the Boston Marathon and other race organizations to raise awareness of nutrition strategies to help athletes stay healthy and avoid under-fueling.

A shared commitment to athlete health and performance

Boston Children’s long-standing relationship with the Boston Marathon helped inspire this study. Each year for the past 50 years, clinicians from Boston Children’s Sports Medicine Division have staffed the medical tent at the Boston Marathon finish line, and in 2022, the Boston Athletic Association, which hosts the marathon, helped make the study possible. 

“The scope of this study really speaks to the Boston Athletic Association and entire Boston Marathon community’s commitment to supporting athlete health and performance and continuing to lead endurance sport forward in a positive direction,” says Whitney. As more runners become aware of the true nutritional demands of marathon training, she hopes more will be able to run past the medical tents at their goal pace without needing medical care.

Learn more about the Injured Runners Clinic, Wu Tsai Female Athlete Program, and Sports Medicine Division.