Signs you're underfueling

In this episode of The Endurance Lab Podcast, I’m joined by Alex Larson, a registered dietitian and endurance sports nutrition coach who has spent more than 15 years helping runners, cyclists, and triathletes fuel in a way that actually works in real life.

Alex works with everyday endurance athletes juggling training, careers, families, and long-term health goals. In this conversation, we break down how midlife runners can improve body composition, preserve lean muscle, and support metabolic health without sacrificing performance or falling into RED-S or chronic fatigue.

📚 Alex Larson Resources:https://alexlarsonnutrition.com/

We explore two key runner profiles throughout the episode:

• Midlife runners new to the sport, running for fat loss, health, and metabolic function

• Seasoned masters runners chasing new PRs while staying healthy and durable

In this episode, we discuss:

• How to lose body fat while still fueling training properly

• Why underfueling workouts backfires for performance, recovery, and long-term health

• Protein needs for runners in their 40s, 50s, and beyond

• Whether fasted training actually improves fat loss or metabolic flexibility

• How to structure nutrition across a full day to support training and energy

• High-carb fueling vs low-carb approaches for masters athletes

• Exogenous ketones, insulin response, and why they often do more harm than good

• How to fuel runs by duration and intensity

• Carb loading strategies that actually work

• Glucose-to-fructose ratios in gels and why they matter for gut comfort

• Cost-effective fueling alternatives to expensive gels

• How to recognize early signs of underfueling before injuries and burnout appear

This is a practical, evidence-based conversation designed to help midlife runners make better nutrition decisions so they can train harder, recover faster, and stay healthy for years to come. If you want to get leaner, stay lean, and perform better without compromising your health, this episode is for you.

Time Stamps

0:00 Intro

3:56 How to fuel training and still lose fat

8:10 How to improve metabolic health

17:42 Consequences of underfueling during training

20:38 Fasted training

24:56 Underfueling warning signs

28:01 High carb vs high fat

31:34 Exogenous ketones

35:28 Racing weight

37:44 Carb loading strategy

41:56 Glucose to fructose ratio

50:06 Cheaper alternatives to sports gels

52:54 How to fuel training runs

🎧 About The Endurance Lab PodcastFrom January 2026, I’m releasing 3 episodes per month - thoughtful, evidence-based conversations on training, performance, nutrition, recovery, and longevity for runners over 40. If there’s a topic you want me to explore (or a guest you’d love to hear from), drop it in the comments — I read every single one.

🤝 Work with me

Coaching: https://www.limitlesscoaching.run/one-on-one-coaching

📌 DisclaimerThis content is for educational purposes only and is not medical advice.