Effects of vegetarian diets on sports

In a recent review published in Nutrients Journalresearchers looked at the effects of vegetarian and omnivorous diets on athletic performance.

Lesson: The Relationship Between Vegetarian Diet and Sports Performance: A Systematic Review. Image Credit: ME Image/Shutterstock.com


Saul Ñiguez and Novak Djokovic are famous soccer and tennis players who have adopted a vegetarian diet. Even among vegetarians, different groups, for example, vegetarians, ovolactovegetarians, and vegans, can vary in terms of calories and fiber, like omnivorous diets.

The American Dietetic Association has confirmed that a plant-based diet supports health and disease prevention. However, the possibility of nutritional deficiencies, especially of vitamin B12, zinc, iron, calcium, omega-3 fatty acids, and protein, remains.

Athletes need a healthy and nutritious diet that supports their performance and overall health. For example, they need more non-heme iron (which is very important) because iron releases oxygen to the muscles, especially when used with supplements, such as vitamin C and citric acid.

In addition, their diet should provide enough calories for sports, calculating their total energy based on the sport they play, their metabolism, and the energy of the food.

They may also need additional vitamin D, which is directly related to muscle and bone function, and vitamin B12, which is important for the immune system to function.

For those who exercise, eating protein through beans, grains, nuts, whole grains and oils is also highly recommended.

Overall, vegetarian athletes need a well-planned diet with the right combination of nutrients to achieve peak performance. Therefore, it would be interesting to know how sports evolve as a food service.

About this study

First, the researchers conducted a detailed search of the Web Of Science, PubMed, Cochrane, and Dialnet articles using the keywords “vegetarian diet”, “vegetarian diet”, “work”, “sports”, and “exercise”.

The initial search returned 933 studies, of which 903 remained after duplicates were removed. The development of this research left 141 clinical trials and clinical trials (RCTs) published in English and Spanish.

These studies were published from 2013 to 2023 and described the relationship between diet and exercise using a placebo or a control group. In addition, they included cytokine analysis in women of working age who underwent physiotherapeutic intervention.

Next, they critically reviewed the themes and summaries of the six studies that met the inclusion criteria. They evaluated the six studies using the PEDro scale. It is an 11-item number derived from the Delphi series, where the maximum number is 10 points, and the minimum is zero.

The PEDro scale allowed them to assess the practices, outcomes, and design of the included studies, the source of the studies, and whether they were randomized, blinded, or hidden. Grades 9-10, 6-8, and 5 were excellent, good, and good, respectively.

In addition, systematic reviews and meta-analyses followed the Cochrane Handbook 5.1.0 to assess the risk of bias.


In the six studies analyzed in the systematic review, 3,363 people participated, of which 1,921 were women and 1,442 were men. Of the female runners, 543, 652, and 726 were vegetarians, vegans, and omnivores, respectively. Similarly, 305, 352, and 785 of the 1,442 male athletes were vegetarians, vegans, and omnivores, respectively.

Five of the six studies assigned a group of athletes who ate a vegetarian or vegan diet, while the control group consisted of athletes who ate a omnivorous diet. A sixth study compared subjects based on diet and exercise, including 10 km, half, and full marathons. In addition, on the PEDro technical scale, five subjects were good and one was fair.

Analyzing the performance of runners in different endurance tests as a function of food revealed that in races of less than 21 km, male and female runners on a vegetarian diet performed significantly higher in endurance tests (14% and 10%, respectively); while in the half marathon, 32% of male vegetarians and 43% of female non-vegetarians tried harder.

In fact, 60% of male and 37% of female runners on the nivorous diet completed the highest performance test in a marathon or ultra-marathon.

The health of women who ran half marathons was the best, followed by marathon or marathon runners. However, among male runners, fitness decreases as distance increases.

A vegetarian diet protects athletes from degenerative and inflammatory diseases and improves their body shape, which is directly related to exercise.

The three measures of body composition are body weight, lean mass, and fat mass. Vegetarians had 11% more body weight than omnivores, while lactovegetarians, who eat milk, instead, had 7.3% less body weight compared to omnivores.

Vegetarians were 11.1% who may have a “normal weight” according to the World Health Organization (WHO), i.e. having a body mass index (BMI) between 18.5 and 25 kg/m2.

Also, their lean muscle mass was 7% lower than the omnivorous runners. Interestingly, fat mass varies with the sex of the athletes; therefore, while female omnivorous athletes had 1.4% more fat according to their body weight, men did not show such a difference.

Also, the results show that athletes who follow an omnivorous diet report better mental and social skills; however, the difference was small.

Regarding physical activity, the survey showed that vegetarians had more nutrition and physical activity than omnivores (55% vs. 32%).

In addition, vegetarian athletes performed significantly better in endurance sports, as measured by maximal oxygen consumption (VO2máx) in an incremental ergometer test performed at a moderate intensity.

For strength training, such as shoulder exercises and quadriceps extension, the 1 RM approach did not show significant differences in vegetarian athletes compared to omnivores.

However, ovolactovegetarian athletes showed a 21 W improvement in muscle power in a one-hour test at 60% maximum HR.

Macronutrient oxidation is another important sports indicator. Vegetarian athletes and omnivores oxidized fat and protein at similar rates; however, carbohydrates at different rates.

Also, vegetarian athletes consumed more food than omnivores (343 g vs. 322g). As expected, daily caloric intake was lowest for carnivores and highest for omnivores (2383 kcal and 2985 kcal, respectively).

In addition, this analysis showed that the protein and fat intake of vegetarian athletes is low. Therefore, they need to eat soy, almond milk, flax seeds for protein, and tahini, soy, and olive oil to meet the fat requirement.

Proteins, especially iron (Fe) and calcium (Ca), are also important for athletes. A research study showed that among endurance athletes, iron intake was higher for vegetarians than for omnivores (19.4mg vs. 15.4 mg), which is a significant difference.

Likewise, calcium intake was higher for vegetarians than for omnivore athletes, with a daily difference of 266 mg.

The end

Athletes on a vegetarian diet performed better in a variety of sports, such as better ventilation and more energy; however, they did not perform well on energy-related parameters compared to athletes on the omnivorous diet.

Although the vegetarian and meat-loving athletes ate more carbohydrates, less protein, and saturated fat, they, especially the vegetarian women, showed increased body fat.

More research is needed to determine whether vegetarian athletes can perform better in sports.

However, all athletes should stick to a diet that meets their nutritional needs based on their sport and the season of the game.

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