At a recent running camp in the trail-lined backcountry, runners had the opportunity to connect with Erin Sparrold. While Sparrold was volunteering as a camp counselor, her primary career lies in sports nutrition: she is a veteran sports nutrition coach with over 25 years of industry experience.
Sparrold supports collegiate athletes across all disciplines at Lafayette University and works specifically with the wrestling program at Lehigh University. As a lifelong endurance athlete herself (a former competitive swimmer turned multi-sport athlete and half-Ironman triathlete), Sparrold brings a wealth of practical and clinical wisdom to endurance sports.
The core of her work revolves around one of the most pervasive yet misunderstood challenges in distance running today: underfueling, low energy availability, and how ignoring the body’s metabolic baseline can derail both athletic performance and long-term health.
What Is Underfueling? Understanding Low Energy Availability (LEA)
In sports science, underfueling isn’t just “feeling hungry.” It is defined clinically as Low Energy Availability (LEA).
“After accounting for all energy output in training, gym time, and conditioning, low energy availability measures how much energy resource is left over to run basic life processes: your heart, lungs, brain, and digestive system,” SpARROld explains.
When runners balance heavy training loads alongside busy careers and personal lives, nutritional intake frequently falls short. While short-term energy deficits are adaptable and even useful for targeted body composition adjustments, long-term LEA triggers a dangerous cascade of metabolic adaptations.
The Timeline of LEA and REDs
When an athlete stays in a severe energy deficit, the body stops adapting to training and shifts strictly into survival mode:
- Short-Term (A Few Days): Slight performance dips, delayed muscle recovery, poor sleep quality, and a noticeable drop in workout power output.
- Medium-Term (1 to 2 Weeks): Impaired immune function, frequent illness, and elevated injury rates. Without adequate calories and macronutrient building blocks, training stress simply accumulates without adapting into speed or strength.
- Long-Term (4 to 8 Weeks): Progression into Relative Energy Deficiency in Sport (REDs). This downshifts resting metabolic rate across every organ system. In female runners, suppressing the reproductive endocrine system leads to amenorrhea (loss of periods), low estrogen, and severe bone density loss, resulting in stress fractures and reactions.
Weight-Scale Delusions: Can You Underfuel Without Losing Weight?
One of the biggest misconceptions in endurance sports is that underfueling always manifests as dramatic weight loss. According to Sparrold, that is simply not true.
Because long-term LEA downshifts resting metabolic rate (RMR), the body conserves energy by burning fewer calories at rest. An athlete can maintain a stable body weight on the scale while simultaneously suffering from active REDs, suppressed hormone levels, and compromised bone density.
Macro Baseline: Dialing In Daily Fueling
Calculating baseline nutritional needs does not require an elite laboratory setup. While wearable technology (such as Garmin, WHOOP, Apple Watch, or Fitbit) has a margin of error, it provides a functional baseline for daily energy expenditure.
When setting up daily macronutrient requirements, Sparrold recommends treating carbohydrates as a variable “fuel dial” while keeping protein and fat relatively stable:
- Protein: Target approximately 2.0 to 2.2 grams per kilogram of body weight (roughly 1.0 gram per pound of body weight). This preserves lean muscle mass and repairs structural tissue damage.
- Healthy Fats: Target a minimum of 1.0 gram per kilogram of body weight. This maintains endocrine system balance, joint health, and essential hormone production.
- Carbohydrates: Flexible fuel dial starting around 4.0 to 6.0 grams per kilogram of body weight (roughly 2.0 grams per pound) for endurance athletes, scaling up to 10.0+ grams per kilogram per day for high-volume efforts.
“Carbohydrates are the primary variable,” notes SpARROld. “On light or rest days, you dial it back. On big training days, you dial it up. Some of my high-volume endurance athletes dial up to 10 grams of carbohydrate per kilogram per day to support their output.”
Lifelong Longevity vs. Staying Small
For many adult runners, exercise is often framed around aesthetics or weight management. However, chronic deficits carry heavy consequences later in life.
Chronic Energy Deficits → Suppressed Hormones → Bone Density Depletion → High Fracture & Osteoporosis Risk
Building structural strength and bone density in early and middle adulthood dictates mobility and health span in later decades. Prioritizing strength training alongside whole-food nutrition ensures that training stress builds structural resilience rather than robbing density from bones and muscle.
Whole Foods First: Practical Nutrition Rules
When structuring a daily plate, Sparrold emphasizes minimal processing and high nutrient density:
- Embrace Single-Ingredient Foods: Focus on whole foods that undergo minimal steps from harvest to plate.
- Eat the Rainbow: Fill plates with vibrant fruits and vegetables. Each distinct color delivers unique polyphenols, antioxidants, and micronutrients essential for cellular repair.
- Quality Carbohydrate Sources: Prioritize potatoes, sweet potatoes, and fiber-rich legumes (beans, lentils) that provide stable energy alongside crucial minerals.
- Bioavailable Micronutrients: Ensure adequate intake of iron-rich protein sources (such as red meat, fish, eggs, and yogurt) to protect against anemia and chronic fatigue.
Connect with Erin Sparrold
For athletes looking to optimize performance fueling or address chronic recovery issues, Sparrold is currently accepting new clients:
- Website: esperformancenutrition.com
- Instagram: @ErinSparrold
