Introduction

The popularity of vegetarian diets has been fuelled by the success stories of athletes who are world champions and also vegetarians - Dave Scott (vegan and five-time winner of the Hawaiian Ironman Triathlon), Martina Navratilova (tennis), and Edwin Moses (Olympic hurdling champion). Vegetarian diets have experienced an increase in popularity. Moreover, they have been associated with a number of health benefits including: lower risk of death from heart disease, lower low-density lipoprotein (LDL) cholesterol levels, lower blood pressure, lower rates of type 2 diabetes, lower body mass index, and lower rates of certain cancers (4, 10, 12). Accordingly, there has been tremendous interest in these diets for athletes and other active individuals and their effects on overall health. In particular, their effects on performance are of great importance to athletes, this article will focus on dietary considerations for the vegetarian athlete and the effects of these diets and lifestyles on performance.

Vegetarians do not eat any animals. This includes pigs, chickens, cows, sea animals, and every other animal but they tend to consume dairy products and eggs. Typically, vegetarian diets are broken into three or more groups (Table 1) including lacto-ovo vegetarians (whose diets include eating dairy products and eggs), lacto vegetarians (who eat dairy, but avoid eggs), and vegan vegetarians (those who avoid animal products altogether). In addition to not consuming any animal flesh, a vegan (strict vegetarian) also does not eat dairy products, eggs, or any other product derived from an animal. Vegans may also avoid using products that have been tested on animals or made from animal skins. A vegan diet typically minimizes food allergies or intolerance since it eliminates the most common allergens like shellfish, eggs and dairy.

Vegetarians, Exercise, and Performance

It is the position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine that physical activity, athletic performance, and recovery from exercise are enhanced by optimal nutrition (10). Athletes can follow a vegetarian diet with a goal of obtaining health and performance benefits. In general, the plant-based foods such as vegetables, fruits, and grains are high in carbohydrates, and they can serve as a primary source of energy for endurance athletes. Vegetarian or semi-vegetarian eating patterns are more common among endurance athletes, such as distance runners and triathletes (11). The quality of vegetarian diets to meet nutritional needs and support peak performance among athletes continues to be questioned. Appropriately planned vegetarian diets can provide sufficient energy and an appropriate range of carbohydrate, fat and protein intakes to support performance and health.

The acceptable macronutrient distribution ranges for carbohydrate, fat and protein of 45-65%, 20-35% and 10-35% of energy, respectively, are appropriate for vegetarian and non-vegetarian athletes alike, especially those who perform endurance events. Vegetarian athletes can meet their protein needs from predominantly or exclusively plant-based sources when a variety of these foods are consumed daily and energy intake is adequate. Muscle creatine stores are lower in vegetarians than non-vegetarians. Creatine supplementation provides ergogenic responses in both vegetarian and non-vegetarian athletes, with limited data supporting greater ergogenic effects on lean body mass accretion and work performance for vegetarians. The potential adverse effect of a vegetarian diet on iron status is based on the bioavailability of iron from plant foods rather than the amount of total iron present in the diet. Vegetarian and non-vegetarian athletes alike must consume sufficient iron to prevent deficiency, which will adversely affect performance. Other nutrients of concern for vegetarian athletes include zinc, vitamin B12 (cyanocobalamin), vitamin D (cholecalciferol) and calcium. The main sources of these nutrients are animal products; however, they can be found in many food sources suitable for vegetarians, including fortified soy milk and whole grain cereals.

Oxidative stress is a natural physiological process that describes an imbalance between free radical production and the ability of the body's antioxidant defense system to neutralize free radicals. Free radicals can be beneficial as they may promote wound healing and contribute to a healthy immune response. However, free radicals can have a detrimental impact when they interfere with the regulation of cell turnover in the body and thus play a role in the promotion of some cancers and conditions such as cardiovascular disease. Vegetarians have higher antioxidant status for vitamin C (ascorbic acid), vitamin E (tocopherol), and beta-carotene than omnivores, which might help reduce exercise-induced oxidative stress. Research is needed comparing antioxidant defenses vegetarian and non-vegetarian athletes reduce; however, it is possible that the consumption of antioxidant-rich foods by vegetarians can reduce exercise-induced oxidative stress.

The currently available evidence supports neither a beneficial nor a detrimental effect of a vegetarian diet on physical performance capacity, especially when carbohydrate intake is taken into consideration. In fact, a recent case report outlines the performance and physiologic characteristics of a vegan triathlete and shows virtually no different to a control group of 10 triathletes consuming a mixed diet (1). Concerns have been raised that an emphasis on plant foods to enhance carbohydrate intake and optimize body glycogen stores may lead to increases in dietary fiber and phytic acid intake to concentrations that reduce the bioavailability of several nutrients, including zinc, iron, and some other trace minerals. There is no convincing evidence, however, that vegetarian athletes suffer impaired nutrient status from the interactive effect of their heavy exertion and plant-food based dietary practices to the extent that performance, health, or both are impaired. Although there has been some concern about protein intake for vegetarian athletes, data indicate that all essential and nonessential amino acids can be supplied by plant food sources alone as long as a variety of foods is consumed and the energy intake is adequate (see section below for details). There has been some concern that vegetarian female athletes are at increased risk for menstrual dysfunction, but evidence suggests that low energy intake, not dietary quality, is the major cause. Furthermore, there is no concrete evidence that a vegetarian diet per se, is associated with any change in aerobic endurance performance.

Vegetarian diets, if very high in fiber and bulk, are associated with low energy intakes because fiber satisfies hunger. Vegetarian athletes, particularly children and adolescents, may have difficulty meeting the daily energy requirements to support general growth along with the added demands of training. Legumes, whole grain cereals and grains, soybeans and many vegetables and fruits are high-fiber, relatively low-fat foods. For the vegan athlete, incorporating energy dense foods such as nuts, tofu, tempeh, textured vegetable protein and commercially prepared meat analogues helps increase energy density of the diet. For lacto-ovo vegetarians, the addition of cheese, yogurt and custard further removes bulk from the diet and makes if easier for athletes to maintain energy balance, particularly during periods of intense training or competition.

Dietary Considerations for the Vegetarian Athlete

The Academy of Nutrition and Dietetics has identified several key nutrients for vegetarians including protein, iron, zinc, calcium, and vitamin B12 (4).

Protein: Protein recommendations for vegetarian athletes are slightly higher due to the decreased digestibility of plant foods. Meat, dairy, and eggs are 94 to 97 percent digestible, but grains and beans are only about 85 percent digestible. Therefore, an increase in protein intake of about 10 percent is advisable for athletes. In general, vegetarian athletes do not have to depend on protein supplements or special foods. Lacto-ovo vegetarians can easily derive adequate protein from dairy products and eggs. Plant proteins such as sesame seeds, sunflower seeds, tofu, and pumpkin seeds are rich sources of branched chain amino acids (BCAA) that aid in reducing exercise-induced muscle damage and promote muscle protein synthesis (9).

Exercise-induced muscle damage is commonly experienced after physical activity, and different studies showed that the amount of protein consumed seems to affect its magnitude. In this regard, some concern has been raised about vegetarian athletes and at least one case report has noted an association between intense physical activity and the occurrence of rhabdomyolysis in a vegetarian athlete (2). A moderated introduction of a planned amount of protein in the diet allowed the athlete to carry on with his sporting activity fully without any further muscle problems. A vegetarian diet per se is not associated with detrimental effects in athletes, but an optimal protein intake should be achieved through careful planning with an emphasis on protein-rich plant foods.

Iron: The vegetarian athlete who restricts meat intake may have an altered iron status when compared to nonvegetarian athletes even with similar amounts of dietary iron intake. Although some studies have cited decreased iron stores in vegetarians, none have demonstrated increased rates of iron deficiency anemia or decreased haemoglobin (Hb) concentrations. A recent study in dogs consuming a meat-free diet resulted in no evidence for anemia or decreased performance over 10 weeks of competitive racing (3). On the contrary, erythrocyte counts and Hb values increased significantly over time (P < 0.01) in both groups of dogs, one fed a commercial diet for active dogs and the other a soybean, meat-free diet. Vegetarian athletes can increase their iron consumption by including more fortified/enriched cereals and grains, green leafy vegetables, tofu, lentils, nuts, seeds, and dried fruits.

Zinc: Zinc is essential for optimal immune function and supports enzyme reactions related to gene expression. The bioavailability of zinc from vegetarian diets may be less than that of nonvegetarian diets. In particular, plants rich in zinc such as legumes, whole grains, nuts, and seeds are also high in phytic acid, an inhibitor of zinc bioavailability. Therefore, zinc supplementation may be a wise choice particularly for vegan athletes. A recent study supports this notion where a high prevalence of zinc deficiency was noted in vegetarian athletes(5).

Calcium: Calcium is important to meet optimal bone mineral accretion. It is well known that many adolescents do not meet the recommended adequate intake level of 1000mg/day. Nuts and seeds are rich in calcium. Calcium-rich plant foods include watercress, bok choy, kale, tofu, unhulled sesame seeds, chia seeds, kidney beans, and almonds. Vegan athletes can meet their calcium needs by incorporating calcium-fortified food sources like orange juice, soy mild, tofu, and soy yogurt. A lacto-ovo vegetarian athlete can easily meet daily calcium requirements by incorporating 8 fluid ounces of milk, 8 ounces of yogurt, and 1.5 ounces of cheese twice a day. One cup of calcium-fortified orange juice and 1 cup of almonds provide the same amount of calcium (300 mg) as does 1 cup of milk.

Vitamin B12: Vitamin B12 is essential for proper nervous system function and DNA synthesis, especially in red blood cells. The richest sources of B12 are animal products, milk, eggs, and fortified foods. Vitamin B12 is not found in plant-based food products, including fermented soy products. A vegan athlete can incorporate fortified soy products such as soy milk, tofu, and soy yogurt to meet the B12 recommendations. Milk, milk products, and eggs provide sufficient B12 for lacto-ovo vegetarians. Despite the food sources that can provide sufficient B12, it is becoming more common to supplement at a minimum of 6 µg.d-1.

Conclusions

Vegetarian diets are associated with several health benefits, but whether a vegetarian or vegan diet is beneficial for athletic performance has not yet been defined. Based on the available evidence that diets high in unrefined plant foods are associated with beneficial effects on overall health, lifespan, immune function, and cardiovascular health, such diets likely would promote improved athletic performance as well.

The quality of vegetarian diets to meet nutritional needs and support peak performance among athletes continues to be questioned. Appropriately planned vegetarian diets can provide sufficient energy and an appropriate range of carbohydrate, fat and protein intakes to support performance and health. The acceptable macronutrient distribution ranges for carbohydrate, fat and protein of 45-65%, 20-35% and 10-35% of energy, respectively, are appropriate for vegetarian and non-vegetarian athletes alike, especially those who perform endurance events. Vegetarian athletes can meet their protein needs from predominantly or exclusively plant-based sources when a variety of these foods are consumed daily and energy intake is adequate. Muscle creatine stores are lower in vegetarians than non-vegetarians. The performance enhancing effects of creatine supplementation are greatest when initial creatine stores are low. Given this, you would suspect that the performance benefits of creatine supplementation in vegetarians with low creatine muscle stores would be more pronounced than athletes who eat meat. Although this sounds reasonable in theory, research conducted to date is inconclusive with regards to this issue.

Vegetarian and non-vegetarian athletes alike must consume sufficient iron to prevent deficiency, which will adversely affect performance. Other nutrients of concern for vegetarian athletes include zinc, vitamin B12 (cyanocobalamin), vitamin D (cholecalciferol) and calcium. The main sources of these nutrients are animal products; however, they can be found in many food sources suitable for vegetarians, including fortified soy milk and whole grain cereals. Vegetarians have higher antioxidant status for vitamin C (ascorbic acid), vitamin E (tocopherol), and beta-carotene than omnivores, which might help reduce exercise-induced oxidative stress. Research is needed comparing antioxidant defenses in vegetarian and non-vegetarian athletes.

References

1. Baguet A et al. Effects of sprint training combined with vegetarian or mixed diet on muscle carnosine content and buffering capacity. Eur J Appl Physiol. 2011: 111(10): 2571-2580.

2. Borrione P et al. Rhabdomyolysis in a young vegetarian athlete. Arch J Phy Med Rehab. 2009: 88(11): 951-954.

3. Brown WY et al. An experimental meat-free diet maintained haematological characteristics in sprint-racing dogs. Br J Nut. 2009: 102(9): 1318-1323.

4. Craig WJ, Mangels AR. American Dietetic Association. Position of the American Dietetic Association: vegetarian diets. J Am Diet Assoc. 2009: 109(7): 1266-1282.

5. De Bortoli MC, Cozzolino SM. Zinc and selenium nutritional status in vegetarians. Biol Trace Eelm Res. 2009: 127(3): 228-233.

6. Hietavala EM et al. Low-protein vegetarian diet does not have a short-term effect on blood acid-base status but raises oxygen consumption during submaximal cycling. J Int Soc Sports Nutr. 2012: 9(1):50.

7. Leischik R, Spelsberg N. Vegan Triple-Ironman. Case Rep Cardiol. 2014; 2014: 317246.

8. Nieman DC. Physical fitness and vegetarian diets: is there a relation? Am J Clin Nut. 1999: Sep;70(3 Suppl):570S-575S.

9. Negro M et al. Branched-chain amino acid supplementation does not enhance athletic performance but affects muscle recovery and the immune system. J Sports Med Phys Fitness. 2008: 48(3): 347-351.

10. Rodriguez NR et al. American College of Sports Medicine position stand. Nutrition and athletic performance. Med Sci Sports Exer. 2009. 41(3): 709-731.

11. Williams, PT. Interactive effects of exercise, alcohol, and vegetarian diet on coronary artery disease risk factors in 9242 runners. Am J Clin Nutr. 1997: 66: 1197-1206.

12. Yokoyama Y et al. Vegetarian Diets and Blood Pressure A Meta-analysis. JAMA Intern Med. 2014: 17494): 577-587.

Table 1. Types of Vegetarian Diets
Type Foods Included Foods Excluded
Lacto-ovo vegetarian Grains, vegetables, fruits, legumes, seeds, nuts, dairy products and eggs Meat, fish, poultry
Lacto vegetarian Grains, vegetables, fruits, legumes, seeds, nuts, and dairy products Meat, fish, poultry, and eggs
Vegan Grains, vegetables, fruits, legumes, seeds, and nuts Meat, fish, poultry, eggs, and dairy