Nutrients
Interest for Vegetarian and Vegan Athletes
The process of providing the best nutrition for athletes is complex and challenging. Various factors such as athlete type, level, priorities, and personal characteristics continuously change what is considered optimal nutrition. Adapting to these changes requires considering a wide range of foods. However, one challenge is accommodating the food preferences or dietary choices of athletes. Limiting the consumption of animal-derived foods, to some extent, is becoming more important, and these limitations can be influenced by various factors such as cultural, religious, and personal beliefs.
Veganism has gained interest in the field of sports nutrition due to its extreme form of dietary restriction. Adopting a vegan diet requires eliminating all animal-based products, including meat, poultry, dairy, seafood, eggs, honey, gelatin, and rennet. This type of diet, also known as a “plant-based” diet, is growing in popularity, especially in Western cultures. People are drawn to veganism for perceived health benefits, ethical beliefs, environmental concerns, social factors, and sensory disgust. While the prevalence of veganism among athletes has not been thoroughly quantified, it is reasonable to assume that it will follow the trend seen in the general population. Athletes are particularly interested in veganism, in addition to the reasons mentioned above, as anecdotal reports suggest that it may provide training and performance advantages. This interest may be fueled by the visibility and marketability of elite athletes who follow vegan diets and claim athletic benefits. The popularity of documentaries like “The Game Changers” further contributes to the discussion and potential adoption of plant-based diets in conjunction with training. However, despite the rising popularity, there is a lack of strong empirical reviews evaluating the impact of a vegan diet on training adaptation and performance outcomes. This is due to the wide range of variables that would need to be considered, such as the specific endpoint being assessed (performance, adaptation, recovery), the measures used to assess that endpoint (e.g., time trial, strength gains, glycogen resynthesis), and the type of athlete (endurance, power, team sport). Additionally, each endpoint, measure, and type of athlete may be affected differently by a vegan diet. Therefore, it is challenging to draw definitive and quantitative conclusions about the effects of a vegan diet on an athlete’s lifestyle.
Vegan Sports Nutrition; Defining Deficiency Compared with Suboptimal
When discussing the advantages or disadvantages of vegan nutrition in sports, it is important to differentiate between nutritional deficiencies and suboptimal intakes. A nutritional deficiency pertains to the minimum amount of a nutrient needed for basic function or health in the general population. Government authorities establish their recommended daily intakes (RDIs) based on this value. While this is crucial for public health, sports nutrition is often more concerned with achieving ‘optimal’ levels rather than preventing deficiencies. In this context, ‘optimal’ refers to nutrient intake that maximizes athletic performance. This requires more precise attention to diet compared to the general population and a case-by-case approach rather than following standardized guidelines (which do not exist for sports nutrition, outside of the scientific community). While this review will touch on potential nutrient deficiencies, the focus will be on how adopting vegan practices can impact optimal nutrition. Consequently, we define optimal nutrition within sports and exercise as dietary approaches that enhance performance, encompassing aspects such as performance nutrition, adaptation, and recovery.
Restricting available foods for an athlete’s diet may initially seem unfavourable, as it limits the options for obtaining necessary nutrients. Therefore, it is important to examine the key macronutrients and micronutrients found in animal-derived foods that could negatively affect an athlete’s performance, recovery, or adaptation when eliminated or reduced. Additionally, we must determine if these issues can be resolved or improved through a well-designed vegan diet. The authors recognize that following a vegan diet may result in an increased intake of beneficial nutrients like nitrate and polyphenols, which have been shown to enhance athletic performance when supplemented. However, this review mainly focuses on addressing the potential considerations and challenges for vegan athlete striving to optimize their sports nutrition.
Energy Intake
The foundation of most sports nutrition is arguably based on energy requirements. These energy requirements can vary significantly depending on factors such as the specific sport, body size and composition, sex, training type, season, and stage. Failing to reach energy balance or experiencing prolonged low energy availability can lead to an increased risk of injury, illness, overtraining syndrome, and undesired weight loss, which can impair training adaptation and performance. While many athletes do not face issues with maintaining energy balance, it can be a concern for larger athletes or those involved in high-volume/intensity training. This may be due to limited time, difficulty consuming large amounts of food, frequent travel, or limited access to food. On the other hand, consideration must also be given to athletes who are limiting their energy intake, which is often the case for those involved in weight-restriction sports or during periods of reduced activity such as the off-season or during injury.
In the omnivorous diet, animal-derived foods make up a significant portion of energy intake. For example, in the diet provided for a strength athlete, 43% of the total energy comes from animal sources. On the other hand, a vegan diet is higher in fruits and vegetables, which are generally less energy-dense. These plant-based foods, which are also rich in fibre, promote a feeling of fullness. While they can be helpful for weight loss and reducing calorie intake, low-energy-density foods that cause early satiety could pose a challenge for athletes trying to meet high-energy goals. Additionally, consuming fibre-rich foods may lead to gastrointestinal stress during and after exercise. Although there is no comprehensive assessment regarding athletes’ spontaneous energy intake when animal-based products are excluded from the diet, a recent systematic review found that the general population following a vegan diet consumes fewer calories compared to those following omnivorous/vegetarian diets. Nevertheless, when looking at various studies, the energy intake of vegans was on average only 5% lower than that of omnivores, which is likely insignificant considering that vegans often have a lower body mass. Therefore, athletes interested in adopting a vegan diet can do so without compromising energy balance, although they should take into account this factor, especially when facing high energy demands.
Micronutrients
Protein
According to the Institute of Medicine, vegetarian/vegan athletes do not require higher protein intake compared to their meat-eating counterparts, unless they primarily rely on hard-to-digest sources like legumes and cereal grains, rather than soy protein.
For an ideal vegetarian or vegan athlete, it is recommended to consume a range of plant-based protein sources such as soy products, legumes, nuts, seeds, cereal grains, eggs, dairy products (for vegetarians), meat substitutes, and certain vegetables. This variety is crucial because plant-based proteins generally lack all the essential amino acids that are necessary in our diet. By consuming different sources of plant-based protein throughout the day, the athlete can ensure they are obtaining all the essential amino acids. Previously, it was believed that proteins needed to be complemented with different amino acid profiles at the same meal, but now researchers believe that consuming various sources throughout the day is sufficient.
To guarantee sufficient lysine intake, which is an essential amino acid, athletes who do not consume dairy and eggs should make sure to include legumes and/or soy products in their diet. Additionally, it is crucial to obtain enough leucine after a workout, as it is the branched-chain amino acid (BCAA) closely linked to muscle adaptation. While whey protein is an excellent source of leucine, soy and other legumes also provide high levels of this BCAA.
The current recommended daily allowances (RDAs) for protein intake in the general population in the UK and US are 0.75 to 0.8 grams per kilogram of body mass per day. However, it is widely agreed among scientists that athletes of all types require higher protein intake to optimize training adaptations, recovery, and performance. Depending on the volume of their training, endurance athletes are advised to consume about 1.2 to 1.6 grams of protein per kilogram of body mass per day to support recovery, promote training adaptations, and account for the increased amino acid oxidation rates during exercise. Recent meta-analyses have shown that resistance training athletes at all levels require at least 1.6 grams of protein per kilogram of body mass per day to maximize increases in muscle mass and strength resulting from training. Additionally, many athletes participate in both endurance and resistance training, which may further increase their protein requirements. In fact, a recent review suggests that protein intakes of 1.7 to 2.2 grams per kilogram of body mass per day are needed to support lean mass adaptation during concurrent exercise training. It is important to note that these guidelines have been established based on data from omnivorous individuals, and the adequacy of protein consumption among vegan athletes, as well as their ability to meet the recommended intake, has rarely been considered. This is significant because it has the potential to change the dietary protein guidelines specifically for vegan athletes.
Animal-based food sources, like meat and dairy products, are usually high in protein and make up a significant portion of protein consumption in the general population. On the other hand, plant-based protein sources generally contain a lower proportion of protein, which means that larger amounts of plant-based food need to be consumed to get an equivalent serving of protein.
The term ‘protein quality’ is challenging to define concisely and is discussed in more detail elsewhere. In short, it encompasses the amino acid composition, digestibility, and subsequent bioavailability of amino acids in a protein source, as well as the metabolic fate of those amino acids. These factors are influenced by the specific protein source, whether it is consumed as isolated protein or as part of a protein-rich whole food, and whether it is consumed alongside other foods. However, the quality of a protein source has consistently been shown to have a significant impact on the post-exercise muscle protein synthesis (MPS) response. For example, milk, egg, and meat-based proteins all stimulate strong post-exercise MPS responses. This is due to their high content of essential amino acids (EAAs), especially leucine, the absence of notable amino acid deficiencies, rapid digestibility, and a high level of digestibility/absorbability, which ensures availability in the circulation (referred to as ‘bioavailability’). To illustrate these concepts, Gorissen et al. collected multiple studies using intrinsically labelled milk proteins and found that approximately 65%, 57%, and 45% of the protein from milk, whey, and casein, respectively, becomes available in the circulation over at least 5 hours after consuming it. Similarly, van Vliet et al. demonstrated that approximately 67% of the protein from intrinsically labelled egg protein becomes available within a 5-hour postprandial window. Additionally, Pennings et al. observed approximately 61% and 49% availability of amino acids from minced beef and beef steak, respectively, over a 6-hour postprandial period. Much of our knowledge about optimal protein nutrition, such as dosage, timing, and daily distribution, is based on data obtained from studies using these animal-based protein sources.
There is a lack of in vivo data on the post-exercise MPS responses of non-animal-derived proteins. However, it is widely believed that non-animal proteins are not as effective as animal proteins in stimulating post-exercise MPS rates. This is thought to be due to a few factors. The presence of nonprotein constituents and antinutritional factors slows down the digestion and absorption of protein, resulting in a lower availability of ingested amino acids in the circulation after a meal. However, the lower digestibility of non-animal-derived protein is believed to be caused by their food matrix rather than the protein itself, as protein isolates produced through purification have similar digestibility to animal proteins. Additionally, plant sources often have lower levels of essential amino acids, such as leucine, methionine, and lysine, which may limit MPS at the molecular signalling or substrate availability levels.
The studies mentioned support the idea that animal-based protein sources have a stronger effect on muscle protein synthesis (MPS) compared to wheat or soy protein. For instance, Wilkinson et al. found that 18 g of soy protein stimulates MPS to a lesser extent than an equal amount of milk protein. Another study showed that casein, a type of milk protein, increased MPS more than wheat protein in older men. However, some studies contradict this narrative. For example, soy and whey protein had equivalent effects on MPS in young men who participated in concurrent training. Additionally, milk and wheat protein had similar effects on MPS in young men. Our recent study showed that mycoprotein, a protein-rich food from fungi, stimulated MPS more than milk protein when the two were consumed in equal amounts of leucine. This suggests that nonanimal protein sources are not necessarily less anabolic than animal-based sources, but it depends on the specific case. It is becoming clear that differences between animal- and plant-based sources are not significant when higher doses of protein (about 30 g) are consumed, although there are exceptions. Therefore, while 20 g may be considered optimal for animal-based proteins, a higher dose may be needed for some nonanimal proteins. More research is needed to determine the best sources and doses of protein for maximizing muscle response to exercise. It is also important to find ways to optimize the efficiency of suboptimal protein sources, as simply consuming more may not always be feasible or advisable.
To prevent EAA deficiencies, it is recommended to combine different plant-based protein sources. For instance, brown rice, which lacks lysine but is high in methionine, can be combined with pea, which is low in methionine but high in lysine. This combination would create a more comprehensive EAA profile. A few studies have supported this blending technique by showing that a blend of plant and animal protein or exclusively plant-based protein can stimulate the same MPS response as animal-based protein. However, it is worth noting that all the studies involving plant protein blends used a minimum of 30g of protein, so the potential EAA deficiencies corrected by the blending may already be accounted for by the large amount of protein consumed.
One suggested approach to enhance the anabolic capacity of plant proteins is by enriching a specific protein with amino acids. Leucine is considered the crucial amino acid for initiating the molecular signalling cascade that supports the increase in MPS after eating. Plant proteins often have a low leucine content, and it is believed that adding more leucine could enhance their postprandial anabolic response. Some studies have shown that leucine fortification can enhance the MPS response to suboptimal doses of animal protein, but this effect is not consistently observed. However, current evidence suggests that fortifying non-animal-derived protein sources with leucine or branch-chain amino acids does not offer any advantages, indicating that other amino acids may be limiting factors for the MPS response. On the other hand, fortifying with lysine is an effective method for supporting growth and lean mass accumulation. A single study has examined a lysine-enriched plant-based protein blend and found it to be on par with chicken protein in terms of its ability to increase MPS in humans. This study used a relatively high dose of protein (≥30 g) and did not include a control group without lysine enrichment. Clearly, more research is needed to determine whether amino acid fortification is an effective or necessary strategy for enhancing the anabolic potential of plant proteins.
When considering the lower quality of certain non-animal proteins, the main question is how much protein intake is needed and whether choosing higher-quality sources or using blends and fortification can help address this in a vegan diet. Further research is needed in applied nutrition to determine, for instance, the relationship between protein dosage and muscle protein synthesis response for different proteins. Additionally, it is important to investigate the role of the entire food matrix (both plant and animal components), as well as ecologically valid and diverse exercise approaches, to understand how these factors can ultimately affect phenotypic changes over different periods in both animal and non-animal diets.
Fat
The recommended fat intake range for athletes is 20-35% of total calories. If less than 20% fat is consumed, it can have negative effects such as impairing endurance performance, interfering with the female menstrual cycle, and impacting lipid profiles. Vegetarian and vegan diets tend to be rich in omega-6 fatty acids but may lack omega-3 fatty acids. Since omega-3s, especially DHA and EPA, are important for reducing inflammation and promoting brain health, it is crucial to include plant-based sources in the diet. Sources of plant-based omega-3s include walnuts, flax, chia seeds, walnut oil, and hemp oil. Although ALA, the form of omega-3 found in these sources, can be converted to DHA and EPA in the body, the conversion rates are typically low. On the other hand, microalgae supplements are high in DHA and have better absorption compared to other plant-based sources. Pregnant athletes, individuals with chronic inflammatory injuries, or those with cardiovascular disease should especially consider incorporating a microalgae supplement into their diet.
Calcium and Vitamin D
Athletes who avoid consuming dairy products must ensure they receive sufficient calcium and vitamin D to support their bone health. There are plenty of plant-based options for calcium, such as tofu, fortified orange juice, soy, almond and rice milk, broccoli, Chinese cabbage, kale, collard/mustard/turnip greens, almonds, tahini, texturized vegetable protein, and certain legumes. In terms of vitamin D, plant-based sources include some soy and rice milk, orange juices, cereals, and sun-dried mushrooms. Additionally, the body can produce vitamin D with brief periods of sun exposure. Athletes who consistently use sunscreen or reside in colder regions should check their vitamin D levels and consider supplements if needed. Insufficient vitamin D can lead to fatigue and weakened bone health.
Iron
To meet their iron needs, vegetarian and vegan athletes require higher amounts of iron due to the lower absorption rates of plant-based iron (known as non-heme iron). It is estimated that only 2 to 20% of non-heme iron is absorbed, whereas heme iron found in animal products has an absorption rate of 15 to 35%. Therefore, vegetarian and vegan athletes need 1.8 times the amount of iron compared to meat-eating athletes. Additionally, non-heme iron is more susceptible to inhibitors of absorption like calcium and polyphenolics present in coffee, tea, and cocoa. Since iron plays a crucial role in athletic performance, I advise vegetarian and vegan athletes to regularly test their iron and ferritin levels.
Zinc
Due to the lower bio-availability of zinc in plant foods compared to animal products, vegetarian and vegan athletes need to make sure they meet the recommended dietary allowance (RDA) for zinc. Legumes, nuts and seeds, whole-grain products, fortified cereals, soy products, hard cheeses, and meat analogues are examples of plant-based sources of zinc that can be consumed.
Iodine
Recent research has indicated that vegetarian and vegan athletes have a higher likelihood of experiencing iodine deficiency. This can be attributed to the reduced utilization of iodized salt in plant-based foods, as well as the cultivation of plants in iodine-deficient soil and the limited or nonexistent intake of seafood and bovine milk. Therefore, it is recommended for vegetarian and vegan athletes to guarantee the consumption of ½ teaspoon of iodized salt daily.
Vitamin B12 and Riboflavin
Riboflavin is essential for converting energy from food and maintaining normal vision. Vitamin B12 plays a crucial role in cell production and a healthy nervous system. Vegan athletes who do not consume eggs or dairy are susceptible to deficiencies in both Riboflavin and Vitamin B12. To ensure sufficient B12 intake, vegan athletes should consider taking supplements or consuming B12-fortified foods such as nutritional yeast, cereals, and certain types of soy and rice milk. Athletes need to meet the recommended daily intake of Riboflavin, which can be obtained from plant sources such as fortified bread and cereals, legumes, tofu, nuts, seeds, tahini, bananas, asparagus, figs, leafy greens, avocado, and most types of seaweed. If athletes are unable to meet their Riboflavin needs through dietary sources, a supplement is advisable.
Summary, Conclusions, and Future Directions
The vegan diet is becoming more popular in the general population, especially in Western cultures. As elite performers continue to embrace and promote veganism, it is expected that athletes will also be interested in this dietary choice. It is important to evaluate whether athletes can follow a vegan diet without affecting their performance, adaptation, or recovery. So far, there is limited research comparing vegan and omnivorous diets in athletes and their effects on adaptation and performance. This lack of evidence makes it challenging to draw definite conclusions about the overall consequences of adopting a vegan diet. Therefore, we must rely on data that examines the dietary intake of vegans, primarily in the general population, to understand how shifts in energy and nutrient intake might impact athletes.
Although there is no evidence suggesting that a vegan diet provides athletic benefits, it is possible to follow a vegan diet without hindering performance or adaptation. The fact that many elite athletes adhere to a vegan diet while competing at a high level is proof that it can support elite athletes, although this likely requires careful planning and application beyond what is needed with an omnivorous diet. While overall energy intake does not seem to be significantly compromised on a vegan diet, there is a change in the composition of macronutrients. Although total carbohydrate and fat intake are not a concern, athletes may have less flexibility in manipulating their macronutrient intake, such as following a low carbohydrate diet, due to the high carbohydrate content of plant-based sources. More attention needs to be given to the quantity and quality of protein consumed, as it appears that insufficient intake from non-animal sources can negatively affect muscle protein turnover and adaptation. While it is possible to meet the higher protein requirements with a vegan diet, it is important to ensure that the athlete consumes enough high-quality protein. Further research is needed to determine the optimal doses, sources, and supplementation strategies for non-animal-derived protein sources to maximize adaptation. The vegan diet lacks ergogenic compounds like creatine, carnitine, and carnosine, resulting in lower concentrations in the bloodstream and muscles. Although limited data is suggesting that these lower concentrations may affect performance and adaptation, it may be worth considering supplementation with these popular ergogenic aids for athletes, especially vegans. Lastly, athletes may be at a higher risk of specific micronutrient deficiencies, which can be worsened by a vegan diet. Therefore, it is important to regularly monitor micronutrient status and address any deficiencies through diet or supplementation if necessary.
In Conclusion
Some athletes have been able to switch to a vegan or vegetarian diet with success. Brendan Brazier, who is a professional triathlete and endurance runner from Canada, is particularly well-known as a vegan triathlete. Brazier is the author of a book called The Thrive Diet and has earned the title of Canadian 50km Ultramarathon Champion twice. Additionally, other notable athletes follow a vegetarian or vegan diet, such as Laura Philipp, a professional Ironman 70.3 athlete, Bart Yasso, a prominent figure in running, and Scott Jurek, an ultra-endurance runner.
By following a carefully planned plant-based diet and seeking guidance from experts, vegetarian or vegan athletes can achieve significant success in their training and racing without compromising their health.
