Gastric Emptying Rate in Ultramarathons: The Relationship Between Intensity and Food Form on Supplement Absorption

Introduction

The moment you swallow an energy gel does not mean the energy is already available for your muscles. Food must first pass through the stomach and enter the small intestine before it can be absorbed into the bloodstream. The “gastric emptying rate”—the speed at which food moves from the stomach into the small intestine—is a key factor determining fueling efficiency. In endurance events like ultramarathons, changes in gastric emptying rate directly affect the timing and effectiveness of supplement absorption.

1. Basic Physiology of Gastric Emptying

Gastric emptying is regulated by the following factors:

• Pyloric sphincter: Controls the rate at which chyme enters the duodenum
• Neuroendocrine signals: Including hormones such as glucagon and CCK
• Gastrointestinal reflex: When the intestines are full, signals are sent to the stomach to slow down

At rest, liquid gastric emptying takes approximately 30–60 minutes, while solid food takes 2–4 hours.

2. The Effect of Exercise Intensity on Gastric Emptying

This is the most underestimated piece of knowledge in ultramarathon fueling:

Conclusion: The pace of an ultramarathon (typically 60–70% VO2max) has a relatively mild effect on gastric emptying. The main problems arise during sudden accelerations or uphill surges.

3. The Effect of Food Form on Gastric Emptying Rate

Liquid vs. Solid vs. Semi-Solid

4. Other Factors Affecting Gastric Emptying

The Key Influence of Osmolality

When hypertonic fluids (sugar concentration >10%) enter the duodenum, the intestine automatically slows its absorption rate to protect the intestinal mucosa. This is why overly concentrated energy drinks or drinking energy gels directly (without water) can feel like they are “stuck in the stomach.”

Practical advice: Energy gels must be consumed with 200mL of plain water. Only after dilution can the osmolality be rapidly absorbed by the intestines.

The Effect of Temperature

Cold drinks (4°C) empty from the stomach slightly faster than warm drinks, but the difference is small (approximately 5–10%). In Taiwan’s summer ultramarathons, the cooling effect of ice water is actually more important.

Emotions and Stress

Negative emotions such as anxiety and fear slow gastric emptying through the autonomic nervous system. This is also why you often feel a “bloated stomach” when nervous before a race.

5. Designing Supplement Timing Based on Gastric Emptying

Work backward from gastric emptying time to plan supplement timing:

• Need energy in 30 minutes: Consume liquid carbohydrates now (sports drink)
• Need energy in 60 minutes: Consume an energy gel now (with water)
• Need energy in 90–120 minutes: Consume a banana or white rice now

6. Practical Recommendations

• Avoid solid food before and after uphill surges; wait until you return to a steady pace before eating
• If you feel “fuel stuck in your stomach,” slow down, drink plain water, and wait for gastric emptying
• Test different supplement forms and timings during training to find your personal optimal setup

Conclusion

Understanding the gastric emptying mechanism allows you to solve many fueling mysteries: Why do you sometimes fuel up but feel nothing? Why does the same food sometimes go smoothly and other times cause discomfort? Designing supplement timing around gastric emptying rate is the key upgrade from “spraying and praying” to “precision fueling.”

Related Reading

• Ultramarathon Fueling Strategies: Energy and Electrolyte Rhythm from 50K to 100K
• Ultramarathon Gut Training: How to Train Your Intestines to Accept Solid Food During Training
• Ultramarathon Gut Training: Keeping Your Digestive System Able to Process Solid Food at High Intensity
• Complete 100K Ultramarathon Fueling Plan: The Science of Hourly Calories, Sodium, and Solid-Liquid Switching