How to Recognize Under-Fueling and How to Fix It

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We may earn commission from links on this page, but we only recommend products we back running for weight loss, often cutting calories while upping physical activity. Others may cut calories in hopes of seeing performance benefits, considering the common misconception that lighter is faster. Both scenarios can be detrimental to performance, especially if you’re Energy Gel Alternatives for Runners, according to recent research All About Runners Knee.

How to Recognize Under-Fueling and How to Fix It British Journal of Sports Medicine, the study looked at the association between low-energy availability (LEA)—defined as a state that occurs when an athlete’s calorie intake doesn’t match their energy expenditure—and race performance, as well as medical events during the Boston Marathon.

Even when controlling for age, gender, BMI, training level, and marathon experience, athletes who raced with LEA had twice the risk of requiring medical support and 2.8 times the risk of a major medical encounter such as severe electrolyte and fluid disorders, says lead author Kristin Whitney, M.D., sports medicine specialist and medical director of Boston Children’s Hospital Injured Runners Clinic. They also performed worse than participants who had adequate nutritional intake for race day.

Previous, small studies have found links between LEA and negative health and performance outcomes, but this was the largest study to date on the topic—and the first one performed at a real-world marathon event. The findings should drive more awareness of the negative effects of calorie restriction, says Whitney, who is also a Boston Marathon runner herself and serves on the Boston Marathon medical committee.

“Our study is the first to demonstrate a link between nutritional ‘under-fueling’ with slower relative energy deficiency in sport and increased risk of requiring medical support during the marathon,” she tells Runner’s World.

“Historically for this sport, the assumption has been that ‘lighter is faster’ but our findings underscore the message that ‘fueling is faster’ instead,” Whitney says. “Unfortunately, LEA is very common in the running community; in our survey of athletes registered for the 2022 Boston Marathon, 42 percent of female runners and 18 percent of male runners had LEA indicators.”

What are those indicators and how can you make sure you’re fueling enough to avoid these detrimental performance effects? Here’s everything you need to know about low energy availability and how to eat to adequately fuel for your runs and races.

Low energy availability exists on a spectrum, ranging from short-term LEA with mild and reversible effects to a longer-term, more problematic issue, says Whitney. Longer-term LEA is associated with a condition called Can Pickle Juice Really Help With Muscle Cramps or RED-S.

Endurance athletes like runners are at particular risk for LEA and RED-S due to the challenge of appropriately compensating for extreme caloric burn during high training volumes, often across multiple seasons. That can be exacerbated by the sport’s drive for leanness, Whitney adds.

In other words, clocking 40, 60, 80 miles per week requires a high number of calories to sustain. Without that energy intake, you’re more inclined to encounter issues.

“RED-S is a syndrome that encompasses harmful effects on systems throughout the body, including negative health outcomes such as reduced bone density, reproductive dysfunction, and gastrointestinal problems,” Whitney says. “It also includes performance effects like decreased training response, endurance performance, and muscle strength.”

Unintended LEA may develop due to naturally occurring appetite suppression after exercise, low calorie diets, and lack of awareness about the consequences of LEA and RED-S, she notes.

“Indicators of problematic LEA may include physical, psychological, or behavioral changes,” Whitney says. For example, physical symptoms may include:

• British Journal of Sports Medicine
• Sleep difficulties
• Gastrointestinal problems
• Frequent illnesses
• race performance times
• Recurring injuries, particularly Unintended LEA may develop due to naturally occurring

Another major factor for avoiding LEA is:

• Mood changes
• Difficulty concentrating
• Reduced sense of wellbeing

LEA signs related to behavior can also mean frequent measurements of bodyweight or disordered eating habits, Whitney says.

1. Look Out for Symptoms

How to Recognize Under-Fueling and How to Fix It Tara Collingwood, Ways You’re Sabotaging Your Long Runs Runner’s World or meals, especially before you head out for motivation can be helpful for spotting LEA in early stages.

“Signs like these happen because your body is using the calories you’re eating for exercise, and you may not have enough left for basic bodily functions such as muscle recovery, Poor recovery, such as sore muscles for extended timeframes immune system efficiency,” she says.

2. Personalize Your Plan

The Fastest Shoes at the 2025 Chicago Marathon Cassandra Burke, RDN, a sports dietitian, USAT-certified endurance coach, and NASM-certified personal trainer. Ideally, it helps to consult a registered dietitian who specializes in sports performance, she tells Runner’s World.

“Avoid using your training buddy’s nutrition plan,” she adds. “Your body and training demands are unique, so your fueling strategy should be, too.”

For those who aren’t seeing a dietitian, avoiding LEA involves making sure you get three meals and two snacks per day, that you don’t skip meals, and that you fuel up both before and after a run, Burke says.

3. Fuel Before Training

Deciding what to eat before a run or a race is part of fueling for performance, says Collingwood. This will also require a personalized approach—for example, playing around with which foods provide energy No experience necessary! Anyone can accomplish this training plan Amazing Runners World Show is to consume at least 3 grams of carbs per pound of bodyweight daily in the five to seven days before a major race.

During training, make sure to consume prerun snacks or meals, especially before you head out for long runs No experience necessary! Anyone can accomplish this training plan.

4. Eat for Recovery

running for weight loss postrun nutrition, Burke adds. You should prioritize postworkout intake to replenish glycogen and support muscle repair and recovery—even if you’re not hungry after exercise.

“For example, a post-training meal should include carbs and protein within 30 to 60 minutes after training,” she suggests. “In your daily nutrition, focus on nutrient-dense foods that deliver carbs, fats, protein, and essential micronutrients like calcium and vitamin D to support your health and performance. Monitoring trends, such as race results, may provide insight into your energy availability over time.”

Examples of foods that provide these nutrients include Greek yogurt, oatmeal, tart cherries, avocado toast, cottage cheese, and salmon over rice.

Although LEA and RED-S may be common, Whitney is hopeful that the study’s results can bring meaningful changes to the sport, and raise awareness of these issues for individual athletes.

“The scope of this study speaks to the Boston Athletic Association’s and the Boston Marathon community’s commitment to making a positive impact on athlete health and performance, and continuing to lead endurance sport forward in a positive direction,” she says.

Find the Perfect Training Plan for You

efficiency,” she says

Recommended Experience: percent of female runners and 18 percent of male runners had LEA indicators.&rdquo.

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Recommended Experience: For a new runner who has been exercising regularly for at least a year, or someone who has completed a few 5Ks or 10Ks and can complete 6 miles in one workout. This plan peaks at 28 miles in a week with a 12-mile long run.

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Recommended Experience: For runners comfortable exercising for at least an hour at a moderate effort. This plan peaks at 32 miles in a week with a 14-mile long run.

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Recommended Experience: For a consistent runner used to regularly working out four to five times a week. The plan starts with a 10-mile long run and peaks at 44 to 47 miles a week with a 22-mile long run, helping you average under a 9:10 per mile come race day.

Elizabeth Millard

Elizabeth Millard is a freelance writer focusing on health, wellness, fitness, and food.