Everyday Ultra

Nutrition for Ultrarunners: The Science, Myths, and Strategies That Actually Work with Claire Shorenstein

Nov 25, 2025
Guest
Claire Shorenstein
In this engaging discussion, Claire Shorenstein, a Board-certified sports dietitian and endurance athlete, unveils the science behind ultrarunning nutrition. She tackles common GI issues and their triggers, offering strategies to prevent them. Claire demystifies sodium’s role, emphasizing personalized hydration plans. She debates high-carb fueling trends and stresses the importance of daily nutrition. With practical tips for busy athletes, she highlights the need for meal prep and compassionate planning. Tune in for actionable insights that can elevate any ultrarunner's performance!
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ADVICE

Use Mixed Sugars, Limit Excess Fructose

  • Use mixed sugars (glucose/maltodextrin + fructose) to access different intestinal transporters and increase carb absorption.
  • Avoid excessive fructose alone because it commonly causes GI upset.
ADVICE

Run A Sweat Test To Guide Sodium Needs

  • Do a simple sweat (pre/post weight) test in different conditions to estimate volume losses and guide fueling.
  • Aim to replace ~60–90% of sweat losses; sodium becomes important as total fluid turnover rises.
INSIGHT

Sodium's Role Is To Support Fluid Balance

  • Sodium matters mainly because it helps maintain fluid balance when you drink large volumes during long efforts.
  • Sodium alone won't boost performance unless it enables better fluid intake.
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