Vegan diets support high-level training, but risks of muscle loss

By Dr. Liji Thomas, MDReviewed by Lauren HardakerJul 22 2025

Thinking of kicking meat off your plate? A new study shows that vegan diets keep soccer players running strong but warns that maintaining muscle requires smart planning.

Study: The Effect of an 8-Week Vegan Diet on the Nutritional Status and Performance of Semi-Professional Soccer Players—Results of the VegInSoc Study. Image credit: Prostock-studio/Shutterstock.com

With rising awareness of the environmental cost of omnivorous diets, people worldwide are considering the potential benefits of plant-based diets. Athletes form a special group with their unique need for energy and protein to sustain the high metabolic cost of training and performance. A new study recently published in Nutrients explored how a vegan diet impacted performance in semi-professional soccer players.

Introduction

Proper diet attention is crucial in sports science, but it includes more than just the type of nutrients or their amount. The relative proportion, energy contribution by each, and the type and quality of the food are all essential aspects.

Plant-based diets are not just more sustainable. They reduce cardiovascular risk and oxidative stress while reducing the pro-inflammatory burden. Additionally, they can enhance mitochondrial function and regulate energy and endurance-linked pathways. Thus, they promote muscle recovery and adaptation to rigorous training.

However, there is little large-scale data on whether vegan diets and supplements can support the demands of athletic training, especially at elite levels. The risk of deficiencies, whether macronutrients like protein and omega-3 fatty acids, or micronutrients including vitamin B12 and essential minerals like iron, calcium, zinc, and iodine, remains unclear. These are key to muscle repair, energy cycling, immune function, and tissue oxygen availability.

Semi-professional athletes undergo regular training and have regularly scheduled matches, though they are not full-time athletes competing nationally or internationally. Soccer is a demanding sport that needs strength, endurance, and agility. Thus, the current study chose semi-professional soccer players to test the effect of a vegan diet on their performance, using a controlled, non-randomized, longitudinal pilot design that compared two self-selected groups rather than randomized assignment.

About the study

This small, non-randomized, controlled interventional study compared a self-selected vegan group to a control omnivorous group over eight weeks during the soccer season.

The original study enrolled 16 participants from the SV Babelsberg 03 sports club in Potsdam, Germany. However, due to protocol deviations and incomplete data, the final analysis included 9 participants in the vegan group and 6 in the control group for most main results. At baseline, they had similar body composition and dietary supplement intake and were comparable in age and education.

Both groups trained for 60-90 minutes almost every day during the season and had 38 to 40 game days when they had more intensive exercise.

Results

This is the first study to examine the effects of a vegan diet on the nutritional and dietary status of semi-professional soccer players and their exercise performance using this specific design. The study highlights that no nutritional guidelines are designed specifically for vegan athletes. However, general recommendations such as the Union of European Football Association (UEFA) “food first principle” apply to all athletes.

Macronutrient intake

The comparison showed both groups' inadequate energy and carbohydrate intake, given their high activity levels. The vegan group ate more legumes, nuts, plant milks, and meat alternatives. They had more vegetables, fruits, and grains throughout the study.

Carbohydrate intake was consistently higher in the vegan group, indicating that vegan diets can provide enough carbohydrates with proper planning. Both groups increased energy and fat intake over time. Both ate more convenience foods, but the actual increase was higher in the vegan group than in controls, although confidence intervals overlapped.

Fat intake in both groups exceeded the recommended 30% but remained within the “safe” 42%. Vegans consumed energy as 46% of their dietary intake, vs 38% in the control group.  In contrast, protein intake remained lower than recommended for athletes in the vegan group over the whole study period. Both groups failed to meet recommended energy and carbohydrate intakes for their training levels, and the vegan group in particular did not meet the protein recommendations.

Micronutrient intake

During this period, vegans consumed higher vitamins A, E, and K and folic acid and B12, probably because of supplement intake. The vegan group used more vitamin B12 supplements, while the control group took more calcium, iodine, and vitamin C supplements. Deficiencies of vitamin D or ferritin were not noted in either group. Most blood biochemical markers remained within normal ranges in both groups throughout the study period, except for a rise in triglycerides in the control group.

Notably, “the Union of European Football Associations (UEFA) expert group strongly recommends the 'food first principle' as the foundation of dietary strategies, rather than reliance on supplements.

Body composition

Vegans had reduced total and low-density lipoprotein (LDL) cholesterol. Lean mass was reduced by 2 kg only in the vegan group. Fat-free mass did not change in either group. This indicates the need for personalized dietary plans to prevent muscle protein loss and encourage its synthesis in vegan athletes, especially as this short-term intervention led to loss of lean mass in the vegan group.

Exercise performance

The resting heart rate was initially higher in vegans but decreased by 15 bpm at the end of the study. It reduced significantly in both groups, decreasing by 6 bpm vs 3.6 bpm for vegans and controls, respectively. This indicates proper training adaptations to exercise.

The individual anaerobic threshold (IAT) measures the maximum level of exercise that can be performed without resorting to anaerobic metabolism, without the rapid accumulation of lactate, indicating muscular fatigue. The IAT was assessed using incrementally increasing exercise on the treadmill.

Participants were asked to begin running on the treadmill at an initial speed of 6 km/h, increasing by 2 km/h every three minutes, until the subject felt too exhausted to continue despite verbal motivation. Lactate levels reduced slightly and comparably between the groups. However, maximum lactate values were higher in the vegan group.

The maximum running velocity was higher at all points in the vegan group, and time to exhaustion increased for both groups after the intervention, but the specific increase was less than two minutes; the vegan group increased maximum treadmill running speed by approximately 0.87 km/h, indicating similar training-related improvements. Increased time to exhaustion, higher maximum running velocity, and higher carbohydrate intake could explain the higher lactate.

The relative VO2_max, which indicates athletic training adaptation, was initially comparable in both groups but increased after the intervention in the vegan compared to the control group. However, the increase in relative VO2_max for the vegan group was primarily due to weight loss, rather than an actual increase in absolute aerobic capacity. Absolute VO2_max values did not change significantly in the vegan or control groups over the study period.

Conclusions

A short period on the vegan diet was consistent with sustained athletic performance and improvements associated with training. The performance improvements were observed in both groups and are likely attributable primarily to training, with no evidence that a vegan diet impairs athletic progress in the short term. “A short-term vegan diet may be suitable for semi-professional soccer players.”

However, it is essential to note that this study was a small, non-randomized pilot with self-selected groups and limited generalizability; larger randomized studies are needed to confirm these findings.

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