The Impact of Long-Term Vegetarian Diets on Endurance Performance: An Analysis of Potential B12 and Iron Deficiencies

This article is based on peer-reviewed research from international sports science journals, providing an in-depth analysis of the impact of “plant-based diets for athletes” on sports performance. It also incorporates Taiwan’s local cycling and race scenarios to offer actionable training nutrition recommendations.

Plant-based diets are increasingly popular in the endurance community. Research shows they are not detrimental—and may even be beneficial—to performance, but potential deficiencies in B12, iron, zinc, and Omega-3 must be carefully managed.

In Taiwan’s endurance sports community—whether it’s the climbing enthusiasts heading up Wuling, the long-distance riders traversing the East Rift Valley, or participants in Sun Moon Lake circumnavigation, Taroko Marathon, or 226km Ironman triathlons—the topic of “plant-based diets for athletes” matters because it directly determines whether you can maintain your pace in the latter stages of a race, avoid cramping and hitting the wall, and recover effectively between consecutive training days. Many amateur athletes pour all their effort into power training and equipment upgrades while overlooking nutrition—this “free margin for improvement.” In fact, when training volume and equipment are comparable, the quality of nutritional strategy is often the key variable separating finishers from DNFs, and personal bests from blow-ups. This article will guide you through the complete context—from cellular molecular mechanisms and randomized controlled trial evidence to dose-response curves and practical application—debunking long-circulated myths and putting your fueling strategy on a truly scientific foundation.

Academic Research Review

Regarding the scientific exploration of “plant-based diets for athletes,” top international journals have accumulated rich and rigorous evidence. Below are several representative studies selected for their value in methodological design, sample populations, and strength of conclusions, which together build our current understanding of this topic:

1. Lynch HM et al. (2018, Nutrients) reviewed that plant-based diets have no overall negative impact on sports performance.

2. Craddock JC et al. (2016, IJSNEM) reviewed nutritional considerations for vegetarian athletes.

3. Rogerson D (2017, JISSN) provided a nutritional guide for vegan athletes.

4. Barnard ND et al. (2019, Nutrients) explored plant-based diets and exercise recovery.

Looking across these studies, the scientific picture of “plant-based diets for athletes” is not a single, fixed conclusion but rather something continuously revised and deepened as research methods advance. Early studies mostly used laboratory-controlled time trials or exhaustion tests, while subsequent research gradually incorporated stable isotope tracing, muscle biopsies, functional magnetic resonance imaging (fMRI), and molecular biomarkers, allowing us to move from “observing phenomena” to “explaining mechanisms.” Notably, most high-quality studies employ randomized crossover designs, where each subject serves as both experimental and control, greatly reducing noise from individual differences. However, extrapolating research conclusions requires caution: the responses of well-trained subjects in the laboratory may not fully apply to general amateur athletes; the effects of a single acute intervention may not equate to long-term chronic adaptation. When reading the “effect sizes” and “statistical significance” of these studies, we must also distinguish between “statistically significant” and “practically meaningful”—a 1% improvement might determine medal placement in elite competition, but its significance is relatively limited for recreational riders.

Core Mechanisms

Plant-based diets are rich in carbohydrates, antioxidants, and fiber, which benefit endurance fueling and recovery. However, B12 exists only in animal foods, and its deficiency can cause anemia and neurological damage; plant-based iron (non-heme iron) has low absorption rates; zinc and long-chain Omega-3 (EPA/DHA) are also prone to insufficiency. Proper planning and necessary supplementation can avoid these risks.

To truly understand how “plant-based diets for athletes” affect sports performance, we must return to physiology at the cellular and systemic levels. Athletic performance results from the coordination of multiple systems: the cardiovascular system handles oxygen and fuel delivery, muscle cells handle energy conversion and mechanical contraction, the central nervous system regulates motor unit recruitment and fatigue perception, while the gut and liver form the hub of nutrient absorption and metabolism. The reason these mechanisms translate into measurable performance differences is precisely because they act on one (or multiple) critical links in this chain. The table below organizes the key action points of this topic across different physiological levels, helping you build a complete mechanistic picture:

| Level of Action | Key Mechanisms | Significance for Sports Performance |

|—|—|—|

| Cellular/Molecular | Affects mitochondrial efficiency, enzyme activity, and signal transduction | Determines the efficiency of energy conversion and the direction of adaptation |

| Muscle Tissue | Regulates substrate utilization, buffering capacity, and contractile function | Affects sustainable power output and the onset of fatigue |

| Systemic Integration | Alters blood flow distribution, thermoregulation, and hormonal environment | Determines stability and safety during prolonged exercise |

| Central Nervous System | Regulates fatigue perception, drive, and motor unit recruitment | Affects “how tired it feels” and the ability to push through |

Two dimensions deserve special emphasis: “dose-response” and “temporal dynamics.” The same nutritional intervention, at different intake levels and different timing, can produce vastly different or even opposite effects—this is precisely why many popular recommendations are one-sided. Only by understanding the mechanisms can we judge “when to use it, how much to use, and when to take it,” rather than blindly following trends.

Furthermore, the limiting factors of athletic performance shift dynamically with exercise intensity and duration: in short, high-intensity efforts, limitations often come from the phosphagen system and the accumulation of glycolytic byproducts; in multi-hour endurance events, limitations shift toward the combined effects of glycogen depletion, rising core temperature, fluid and electrolyte imbalance, and central fatigue. “Plant-based diets for athletes” deserves in-depth exploration precisely because it can specifically influence some of these limiting factors. This also reminds us that no nutritional strategy can be evaluated in isolation from the “exercise context”—a fueling rhythm suitable for a 40-minute criterium may not apply to a 6-hour climbing epic; and vice versa. The more thoroughly you understand the mechanisms, the more flexibly you can adjust across different race formats, rather than rigidly adhering to a fixed formula. This ability to “adjust according to context” is precisely the dividing line between amateur athletes and those who truly understand sports science.

Dose-Response Relationships

In sports nutrition, “the dose determines both the toxicity and the benefit.” Too low a dose fails to reach the physiological threshold and is futile; too high a dose may trigger side effects, gastrointestinal distress, or even interfere with training adaptations. The table below organizes the dose-response relationships for “plant-based diets for athletes” and serves as the most important quantitative reference when developing a personal fueling plan:

| Dose / Condition | Effect Description |

|—|—|

| B12 | Supplementation is mandatory |

| Iron | Pair with Vitamin C to enhance absorption |

| Zinc/Omega-3 | Pay attention to intake |

| Protein | Combine multiple sources + increase amount |

As seen in the table above, benefits often follow an “inverted U-shaped” or “threshold-plateau” curve: effects increase with dose until an effective threshold is reached, but beyond a certain plateau point, there are not only no additional benefits, but marginal costs (side effects, gastrointestinal burden, financial expense) rise sharply. This means “finding your own optimal dose” matters far more than “eating as much as possible.” It is recommended to progressively test different doses during training (not on race day), recording subjective feelings, gastrointestinal responses, and power data to build your own dose profile. Remember: the laboratory average is a starting point, not the endpoint; everyone’s body weight, metabolic rate, gut tolerance, and genetic background will cause individualized shifts in the optimal dose.

Differences Across Populations

The benefits of “plant-based diets for athletes” are not equal for everyone. Age, sex, training status, body composition, and genetic background all significantly modulate individual response magnitude. Ignoring these differences and applying a one-size-fits-all recommendation is one of the most common mistakes in sports nutrition.

| Population Dimension | Response Characteristics | Practical Recommendations |

|—|—|—|

| Beginners vs. Advanced | Advanced athletes have more mature physiological adaptations; responses are often more stable but with smaller marginal benefits | Beginners should start conservatively with low doses and build tolerance first |

| Male vs. Female | Differences in body weight, hormonal cycles, and sweat composition affect dosage and requirements | Females should individualize by body weight and pay attention to iron and energy availability |

| Young vs. Older | Older individuals often have reduced absorption efficiency and anabolic resistance | Older individuals may need higher doses or better timing |

| Body Size Differences | Body weight directly affects absolute amounts calculated per mg/kg or g/kg | Always convert to a dose corresponding to individual body weight; avoid copying general rules |

When interpreting “individual differences,” one must also be wary of a common statistical trap: studies mostly report “group average responses,” but beneath the average often lies enormous individual variability. In the same intervention, some may be strong responders, some non-responders, and some even negative responders. This is why even when a study shows “average effectiveness,” you still need to confirm through your own experimentation which category you fall into. A recommended approach is to conduct personalized A/B testing: in two training sessions with as similar conditions as possible, adopt and then not adopt the strategy respectively, compare power, heart rate, and subjective feelings, and repeat several times before drawing conclusions. This empirical spirit of “using yourself as the sample” is the essential path from group science to personal prescription.

Taking Taiwan’s common amateur endurance population as an example, many are masters athletes over 35 who train in their spare time around work. This group simultaneously faces declining recovery rates, insufficient sleep, and time pressure, so the “return on investment” of nutritional strategies is often higher than for young elites—meaning correct nutritional interventions can yield relatively greater room for improvement. Female athletes need to pay special attention to the effects of the menstrual cycle on metabolism and requirements, as well as whether energy availability is sufficient, avoiding falling into the low energy availability (LEA) trap while pursuing lighter body weight. After understanding population differences, you will realize: truly professional nutritional advice is always an individualized prescription that “varies by person,” not a one-size-fits-all slogan.

Practical Training Application

Theory must ultimately be implemented in training plans and on the race course. Below is a practical framework for translating “plant-based diets for athletes” into concrete training and race operations:

• Pre-race testing principle: All nutritional strategies must be rehearsed in training first; “never try anything new on race day” is an iron rule. Gastrointestinal tolerance to new fueling products takes time to build.

• Periodization mindset: Align nutritional strategies with the training cycle—the base phase can focus on adaptation-oriented strategies, while the pre-season shifts to performance-oriented fueling optimization.

• Progressive introduction: Start with low doses and low frequency, adjust gradually based on body responses, and build a personalized dose and timing profile.

• Data tracking: Combine power meter data, heart rate, subjective fatigue (RPE), and gastrointestinal comfort records to objectively evaluate whether an intervention is truly effective.

• Holistic context: Nutrition is one component of training, sleep, recovery, and psychology; no single supplement can compensate for sleep deprivation or flawed training design.

Taking a one-week training schedule as an example, it is recommended to rehearse different fueling scenarios during the week’s key high-intensity sessions (such as threshold intervals or repeated climbs) and the weekend’s long-distance rides: high-intensity days focus on rapid energy supply and central nervous system activation, while long-distance days focus on sustained fueling, gastrointestinal tolerance, and recovery. Through repeated rehearsal, your body can execute the optimal fueling rhythm “automatically” on race day, freeing mental resources for pacing and tactical decisions. Remember, the goal of a nutritional strategy is not theoretical perfection, but stable reliability under the fatigue, heat, and pressure of a real race course.

The most common mistake many people make when executing a nutrition plan is “being serious only on race day and eating casually during regular training.” This is precisely putting the cart before the horse: regular training is the best laboratory for building gut tolerance, testing doses, and cultivating fueling rhythm. If you hope to execute an 80g/hour carbohydrate fueling plan on race day, you must rehearse it repeatedly in training until your body becomes accustomed to it; if you want to rely on a certain supplement, you must confirm in training that it is genuinely effective for you and free of side effects. It is recommended to integrate a nutrition log with your training log, recording fueling content, intake timing, gastrointestinal responses, and performance data for each key session. After weeks to months of accumulation, the value of this personalized database will far exceed any generic nutrition guide. Additionally, do not overlook the often-underestimated “post-training recovery fueling” component—the quality of recovery between consecutive training days often determines whether you can steadily accumulate training volume without injury, and training volume is the most fundamental engine of long-term progress. Treat nutrition as an integral part of training, not a last-minute accessory before races, and your progress curve will look noticeably different.

Local Application in Taiwan

Taiwan’s unique climate, terrain, and race culture add localized considerations to the application of “plant-based diets for athletes.” Taiwan’s summer heat and humidity often push the perceived temperature above 35°C, with sweat rates and fluid/electrolyte losses far exceeding the research contexts of temperate countries. This means hydration and fueling recommendations from foreign literature often need to be “adjusted upward.” In events like the Wuling climb, which ascends from sea level to 3,275 meters, the appetite suppression, cold temperatures, and prolonged exercise at high altitude pose a severe test for energy planning.

Regarding local fueling options, Taiwan’s abundant bananas, sweet potatoes, pineapples, sports drinks, and convenience store ready-to-eat foods can all be incorporated into fueling strategies; the extremely high density of convenience stores also makes mid-ride refueling on long distances relatively easy. It is recommended that Taiwanese riders planning classic routes such as Sun Moon Lake, Wuling, Beiyi, Buyanting, or the East Coast Crossing inventory fueling points along the way in advance, and strengthen sodium and fluid intake given Taiwan’s hot and humid environment. Athletes in the Taroko Marathon, Taipei Marathon, and various local triathlons should equally incorporate the above local climatic factors into their personalized nutrition plans to perform at their best under subtropical conditions.

Debunking Common Myths

Myth: The myth is that “a plant-based diet definitely means protein deficiency and poor performance.” In fact, a well-planned plant-based diet can support endurance performance; what truly requires attention is B12, iron, and Omega-3.

These myths spread widely often because they “sound reasonable,” are easy to pass along by word of mouth, or are amplified by marketing rhetoric. Yet the value of science lies in testing intuition with rigorous evidence: many seemingly obvious notions fail to hold up under scrutiny in randomized controlled trials. Sports nutrition is especially rife with oversimplified “panacea” style marketing that compresses complex dosing, timing, and individual differences into a slogan. The next time you hear a categorical nutritional claim, it’s worth asking: “What is the level of evidence for this claim? Who is the target population? Are the dose and timing clearly specified?” Cultivating this evidence-based critical thinking is more valuable than memorizing any single conclusion, and it is a key step for amateur athletes moving toward scientific training.

Conclusion

“Plant-based diets for athletes” is a topic in sports nutrition with both theoretical depth and practical value. From the academic evidence reviewed in this article, its benefits are real, but it is by no means an unconditional panacea—the key lies in correct dosing, appropriate timing, individualized adjustment, and synergy with overall training, recovery, and sleep. For endurance enthusiasts in Taiwan, while mastering the scientific principles, it is even more important to combine local climate, terrain, and race characteristics to transform general rules into a personalized prescription that suits you. May every rider sweating on Wuling, in the Rift Valley, or on the island-circumnavigation route break through their limits through science-based nutritional strategies and enjoy the pure joy of sport. Next time you step onto the race course, remember—your fuel bottle holds not just water and sugar, but an entire validated body of sports science.

Related Reading

• A Survey of Taiwanese Professional Cyclists’ Dietary Habits: Energy Intake and Macronutrient Analysis
• The Application of Personalized Nutrition in Sports: Precision Diets Based on Genomics and Gut Microbiota
• Prevalence of Vitamin D Deficiency Among Indoor Trainers in Taiwan and Supplementation Recommendations
• Nutritional Planning for Vegetarian/Vegan Endurance Athletes: Easily Overlooked Key Nutrients