A new Frontiers in Nutrition study (2025) is the first to directly compare EPA-rich vs DHA-rich omega-3 supplementation in trained endurance athletes. Result: both forms lower submaximal heart rate — but only EPA raises the respiratory exchange ratio. Here's what that means for your training.
Key Takeaways
- 6-week RCT in trained male endurance athletes (Frontiers in Nutrition 2025)
- Both EPA and DHA: lower submaximal heart rate and perceived exertion
- Only EPA: increases respiratory exchange ratio during exercise
- Omega-3 + resistance training: IL-6 reduced 27-41%, antioxidant capacity up 15%, malondialdehyde down 33%
- Recommendation: 2-3g combined EPA+DHA/day for active athletes
What the study tested
For 6 weeks, two groups of trained male endurance athletes received either an EPA-rich or DHA-rich supplement at equivalent doses. The researchers measured several submaximal exercise parameters on a treadmill. This is the first study to rigorously separate the effects of the two omega-3 forms in endurance athletes — most previous work used standardized EPA+DHA blends.
What both forms share
Both supplements significantly reduced heart rate during submaximal exercise, and perceived exertion (RPE) at the same intensity. Practically: at the same cycling power or running pace, athletes had a lower heart rate and felt less effort. This is exercise economy improvement — doing more with less.
What's unique to EPA
EPA's specific effect: an increase in the respiratory exchange ratio (RER) during exercise. RER is the ratio of CO2 exhaled to O2 consumed — it signals what proportion of fat vs carbohydrate the body is burning as fuel. A higher RER suggests greater carbohydrate contribution to energy metabolism during effort. The interpretation of this effect is still debated among researchers — it may reflect enhanced ability to utilize carbohydrate substrates at specific intensities.
The limits of the research
The broader omega-3 and performance research body remains mixed. A recent review concluded that the impact on exercise physiology is inconsistent across studies. The most robust, reproducible benefits are on recovery and adaptation: reduced post-training inflammation, improved antioxidant capacity, less delayed onset muscle soreness. Direct competition performance effects are harder to isolate. In practice, athletes who supplement with omega-3 do so primarily for recovery — and the data there is solid.