Two diets, one finish line
Endurance training is known to have a large impact on the cardiovascular system: larger heart chambers, stronger stroke volume, more flexible arteries, better oxygen delivery. What's less clear is whether this impact is the same in athletes who fuel their training with a plant-based diet versus those who fuel it with animal products. Any difference that does show up is interesting for two reasons: it tells us something about how the body adapts to sustained training, and the specific metrics involved — arterial stiffness, diastolic filling, iron stores — are also the metrics that predict long-term cardiovascular health in the general population.
A group led by Glenn Jo and colleagues, publishing in Bioinformation, took a look at this question by comparing 80 competitive endurance athletes aged 18–35 who had been on either a vegan or an omnivorous diet for at least two years [1]. Each group had 40 athletes, matched for age, sex ratio, training history, and weekly training hours — so the comparison comes down to the diet, not the training.
The athletes were put through a fairly comprehensive battery. Echocardiography — ultrasound imaging of the heart — measured how forcefully the heart contracts (left ventricular ejection fraction) and how well it relaxes and fills between beats (the E/A and E/e' ratios, explained below). Pulse wave velocity, a measure of how quickly a pressure pulse travels down the arteries, quantified arterial stiffness: stiffer vessels move the wave faster. A graded treadmill test with gas exchange analysis determined VO₂ max, the standard marker of aerobic capacity. And fasting blood samples captured hemoglobin and ferritin, indexing oxygen-carrying capacity and iron stores.
Inside the heart and arteries
Raw pumping power was indistinguishable. Both groups had left ventricular ejection fractions around 63%, well within the range expected for well-trained athletes. Neither diet blunts the heart's ability to contract and push blood out.
The difference emerged in how well the heart relaxed between beats, and how flexible the arteries leading away from it were. Two echocardiography numbers capture this. The E/A ratio compares the speed of blood entering the heart during the two phases of diastole — the early, passive phase and the late "kick" from atrial contraction. A higher E/A ratio means more of the filling happens passively, which is the sign of a relaxed, compliant ventricle. The E/e' ratio estimates the pressure inside the left ventricle as it fills; a lower E/e' means lower filling pressures, which is better. Vegan athletes scored better on both (E/A 1.7 vs. 1.5; E/e' 7.8 vs. 8.5).
They also had more flexible arteries. Pulse wave velocity was lower in the vegan group (6.4 vs. 7.0 m/s, p=0.001), a substantial difference in a metric that predicts cardiovascular risk across a lifetime.
Worth noting: this vascular advantage may be specific to trained athletes. A 2022 study by Macarena Ramos Gonzalez and colleagues compared young healthy vegetarians and omnivores who were not competitive athletes and found no significant difference in pulse wave velocity between them (5.3 vs. 5.6 m/s, p=0.17) [2]. Two readings of this are plausible. Either chronic endurance training amplifies a small dietary effect into a detectable one, or endurance athletes who stick with a vegan diet differ from their omnivorous peers in other ways the Jo study didn't capture — training style, body composition, or broader lifestyle. The current study cannot distinguish between these, but the finding holds up regardless: among these particular athletes, the vegan group had measurably more compliant arteries and better diastolic filling.
Iron, oxygen, and performance
The trade-off ran the other way in the blood work. Omnivorous athletes had significantly higher hemoglobin (14.2 vs. 13.6 g/dL, p=0.01) and ferritin (78.3 vs. 65.2 ng/mL, p=0.02). Hemoglobin carries oxygen in red blood cells; ferritin reflects the body's iron stores. The explanation is straightforward: iron in animal foods is bound to the heme ring of myoglobin and hemoglobin (heme iron) and is absorbed relatively efficiently — roughly 15–35% of what's eaten. Iron in plants (non-heme iron) is absorbed at 2–20%, depending on what else is in the meal. Endurance training compounds the challenge by increasing iron losses through sweat, gastrointestinal effects, and the foot-strike hemolysis that comes with repeated impact.
The natural next question is whether all that extra iron translated into better aerobic performance. In this study, it didn't clearly do so. VO₂ max was numerically higher in the omnivore group (64.7 vs. 62.1 ml/kg/min), but the difference was not statistically significant (p=0.09) — a trend in the omnivores' favor that a larger sample might yet confirm. As the data stand, the hematological edge didn't produce a measurable performance edge in the lab, which cuts against the assumption that better iron status automatically means better endurance output.
The practical implication is still real. Vegan endurance athletes are a recognized higher-risk group for iron deficiency, and screening ferritin periodically is standard sports-medicine practice [3]. But the tidy narrative that plant-based athletes pay a performance tax because they can't keep their iron up — that narrative is not what the data show here.
The take-home
The interesting finding isn't which diet wins. It's that the two paths to elite endurance adaptation diverge in predictable ways, and neither path is obviously worse. Vegan athletes in this sample came out ahead on two metrics — diastolic filling and arterial compliance — that matter not just for athletic performance but for cardiovascular risk across a lifetime. Omnivorous athletes came out ahead on iron status, but without a measurable performance dividend at this training level. Both groups reached comparable aerobic capacity through different physiological routes.
For an endurance athlete choosing a dietary pattern, the paper doesn't push in either direction. It suggests that what to monitor matters more than which diet to pick: a ferritin test every few months if you're vegan, an honest look at what else is in the diet (saturated fat, plant intake, fiber) if you're omnivorous. The usual caveats apply — this is a single cross-sectional study of 80 athletes in a modest journal, so the pattern needs replication with a larger sample to fully confirm. But the direction of the findings lines up with the broader literature on plant-based diets and cardiovascular health, and it reframes the endurance-nutrition debate in a more useful way. The finish line is the same. What's happening inside the athletes who reach it is where the interesting story lives.
References
- Jo G, Tamrakar S, Sharma S, Koppolu S, Goldy EE, Kumar SIS. "Comparative cross-sectional study of vegan and omnivorous diets and their impact on cardiac function among endurance athletes", Bioinformation 21 (2025) 4350–4354. https://pubmed.ncbi.nlm.nih.gov/41907986/
- Ramos Gonzalez M, Zuelch ML, Smiljanec K, et al. "Arterial stiffness and endothelial function are comparable in young healthy vegetarians and omnivores", Nutrition Research (2022). https://pubmed.ncbi.nlm.nih.gov/36054948/
- Peeling P, Dawson B, Goodman C, Landers G, Trinder D. "Athletic induced iron deficiency: new insights into the role of inflammation, cytokines and hormones", Int J Sport Nutr Exerc Metab 17 (2007) 221–231. https://pubmed.ncbi.nlm.nih.gov/17693684/