An Analysis of How Athletes at All Levels of Competition Can Meet Their Energy and Nutrition Needs on a Vegetarian or Vegan Diet
This short literature review will broadly discuss how the vegetarian and vegan diet impacts the ability of an athlete to meet their energy and macronutrient requirements, with a small section on micronutrient requirements.
Northern Ireland (NI) is lagging behind the rest of the United Kingdom (UK) in terms of vegetarianism. In 2016, only one percent of the population were completely vegetarian, in comparison to four percent and three percent of England and Wales, respectively (Food Standards Agency, 2016). Though underwhelming, this discrepancy shows the growth potential of vegetarianism and therefore the impact of these diets must be discussed.
The terms vegetarianism and veganism are commonly used interchangeably, however there are distinct differences between each of these. Melina et al. (2016) identified six common vegetarian and vegan diets, each with their own dietary restrictions. However, all of these diets have the common theme that it excludes flesh foods. Vegetarians can choose whether to include egg or dairy products in their diet, classifying them in a certain vegetarian diet. Vegans, however, do not eat egg, nor dairy, and may even opt to exclude products made by animals or insects such as honey. A more radical vegan is one that primarily eats raw foods such as vegetables, fruits, and nuts.
The purpose of this literature review is to discover the impact of a vegetarian or vegan diet on performance, by discussing its impact on an athlete, from beginner to elite. Recommendations will then be made as of how energy and nutrition needs can be met on such diet. The benefits and limitations of the diets will be discussed based on their ability to meet energy, macronutrient, and micronutrient needs.
Predictors of performance vary based on the sport. It is a complex mix between physiological and psychological factors, and nutrition can have a significant effect on an athlete’s performance at all levels of competition (Kraemer et al., 2016). Energy, macronutrient, and micronutrient consumption can be greatly affected by a restricted diet. A vegetarian or vegan diet can greatly limit the potential to achieve adequate nutrition, however it is very possible to successfully implement a meat-free diet, and the benefits of an adequate vegetarian diet may be substantial for both health and performance.
Energy requirements differ greatly between different athletes, depending on their level of training, the sport they participate in, their weight and their gender. According to Dunford (2010), the lowest energy expending athlete would be female baseball, softball and golf players, who train at a moderate intensity three to five days a week. In this case, the athlete would need an estimated 35kcal/kg of body weight. In contrast, an elite male runner, distance cyclist or triathlete requires almost double that, at a minimum of 60kcal/kg of bodyweight. These runners would average 15 miles of each day, which expends vast amounts of energy.
A male elite runner who weighs 75kg would require 4,500kcals per day; this is almost twice the dietary reference value for males aged 19-64 (Public Health England, 2016). This raises the question whether a vegetarian diet can meet energy demands of athletes.
Energy Balance on a Vegetarian Diet
There are two primary macronutrients that provide energy: fats and carbohydrates, which have an energy density of 9kcal/g and 3.75kcal/g, respectively (Webb, 2020). Each have their own purposes acutely, though chronically, these macronutrients both contribute to overall energy balance.
The main issue of a vegetarian, and especially the more limiting vegan diet, is that it may not have the ability to meet the large energy requirements of athletes. Because plant foods are generally low in calories, it means that a vegetarian athlete will have to attempt to eat large volumes of food to achieve an energy balance (Williams, 2010). This is worsened by the high fibre content of the diet (Cox, 2001). Fibre increased the volume of food, which can increase the feeling of satiety. In fact, fibre can decrease energy intake by one hundred to two hundred kilocalories per day (Jeukendrup and Gleeson, 2010). However, the consequence of this can be viewed differently based on the needs of the athlete.
Athletes who want to lose weight to meet a weight classification, such as boxers and rowers, may find a vegetarian diet advantageous, as it makes it more difficult to overconsume. On the other hand, the majority of athletes are looking to maintain their body mass, or grow their lean body mass. In effect, a diet that makes it difficult to consume enough calories to meet or exceed energy balance may be detrimental to their performance.
Nevertheless, many vegetarian and vegan foods are energy dense, and can meet these calorie needs. In fact, Cox (2001) refers to an article in Runners World by Pritikin (1987) which defends the ability of a vegetarian diet to meet the calorie requirements of an athlete. Vegetarian diets can still be high in carbohydrate rich food such as baked potatoes. A medium baked potato is about 200 calories (Insel et al., 2019). Therefore, energy balance is not a major issue on the vegetarian or vegan diet.
Macronutrients are essential nutrients that are needed in quantities greater than two grams (Williams, 2010). The three macronutrients are protein, carbohydrates and fats, each having their own important role for the body, and its ability to perform (Brouns, 2002). This section will assess the importance of each of these nutrients for health and performance and how a vegetarian or vegan diet may limit the quantity or quality of each of these macronutrients.
Proteins are compounds composed of carbon, hydrogen, oxygen and nitrogen. In addition to this, they may contain other trace minerals such as iron, sulphur and phosphate. Proteins in the body are made up of a selection of 20 amino acids, bonded by peptide bonds to form chains which can contain thousands of amino acids. The chain is then folded into a three-dimensional shape (Waugh and Grant, 2018).
Proteins are responsible for the structural components of the body; such as muscle tissue. They also form cell membranes and enzymes and are found within the blood and immune factors (Insel et al., 2019). In addition to this, proteins can be used for energy, providing around 4kcal per gram of energy. However, this only occurs in the latter stages of endurance events when glycogen stores have been exhausted, where it may contribute 10% to energy production, or during periods of semi- starvation (Bean, 2017).
Not all amino acids need to be consumed through ingestion. In fact, only nine of the twenty amino acids are essential, meaning that they cannot be synthesised in the body (Webb, 2020). Nevertheless, non-essential amino acids are still as important as essential amino acids in the body, and each amino acid must be in the correct quantities in the circulating plasma pool.
Homeostasis for the non-essential amino acids occurs through de novo synthesis, however this is not possible with the non-essential amino acids. In this case, the amino acids must be consumed from the diet or through the catabolism of functional proteins. for this reason, it is not only important to have a sufficient intake of all the essential amino acids to allow for functional protein synthesis, including muscle growth, but also to prevent the breakdown of tissue that would occur to compensate for amino acid deficiencies (Brouns, 2002). This would be detrimental to athletic performance due to the loss of muscle tissue.
Vegetarian and vegan diets are often comprised of incomplete proteins such as legumes and vegetables. They are defined as incomplete because they do not contain all the essential amino acids in the correct quantities, and their digestibility is no more than eighty-five percent. Complete proteins are generally from meat and dairy, however whole grains are also a source which is available to vegans (Austin and Seebohar, 2011).
Despite plant protein quality being lower in isolation, the consumption of more than one plant food can fulfil essential amino acid requirements. This is known as protein complementation, whereby several incomplete protein sources are eaten at one meal to supply all of the essential amino acids. This concept is important for a vegetarian or vegan to consider (Kenney et al., 2015). For example, combining pasta, which is deficient in lysine, with kidney beans, which are deficient in methionine and cysteine, a complete amino acid profile is created. The branched chain amino acids are the most important to an athlete, as they best support recovery after training (Rodgerson, 2017). Quinoa and soybeans are two complete proteins for vegans (Insel et al., 2019).
In addition to the protein quality of plant protein being inferior, the quantity of protein in plants foods is frequently less than that of animal foods. Edelstein and Sharlin (2009) suggest that a non-athlete requires 0.8g of protein per kilogram of body weight. This increases to 1.2 to 1.4g/kg and 1.6 to 1.7g/kg for endurance athletes and strength trained athlete, respectively. These protein requirements increase by 0.1g/kg at each level for vegetarians, due to the decrease in protein quality.
It is assumed that vegan diets are low in protein as if you take the animal products such as chicken, beef and milk out of a typical diet, the major sources of protein are lost. These sources contain 27g, 25g and 8g of protein per serving. In contrast, the food that usually compliment these foods such as whole wheat bread, brown rice and pasta are low in protein, with 3g to 3.5g of protein per serving. In addition to this, fruits and vegetables such as apples, bananas, carrots and broccoli do not exceed 1.3g of protein per serving (Fink et al., 2009).
Nevertheless, vegetarians can still consume high protein foods such as eggs, milk and Greek yoghurt, that contains 7g, 8g and 15g of protein per serving, respectively. Although vegans cannot eat these foods, however, substitutes such as chickpeas, tofu and peanuts are also great sources of protein for their diet, containing 18g, 13g and 12g per serving, respectively (Bean, 2017).
Due to the high protein demands of athletes, it may be difficult to consume large amounts of vegetarian foods due to the fibre and volume. This opens up the possibility to consume protein supplements. Vegetarians may have the opportunity to consume whey and casein protein, if they are allowed to consume milk products. This is a great opportunity as whey protein is a high quality, fast absorbing protein that can increase recovery (Bean, 2015). In addition, Casein has been shown to increase protein synthesis by 22% in resistance-trained males when they consumed 40g before sleep (Res et al., 2012).
Those who cannot consume dairy, such as vegan, must find an alternative protein supplement. Fortunately, substitutes to milk protein are now common. For example, soy protein supplements have become one of the most popular for vegans. MyProtein’s soy protein isolate contains 27g of protein per serving (MyProtein, 2020). However, both Wilkinson et al. (2007) and Hartman et al. (2007) found that milk protein brought about greater muscle protein synthesis than soy protein.
For virtually all sports, the primary source of energy is from carbohydrates. Dunford (2010) recommends that athletes should consume at least five grams of carbohydrate per kilogram of bodyweight, and up to 7g/kg for athletes with rigorous daily training. Not meeting this requirement can result in a depletion of glycogen stores, which will inevitably reduce performance (Fink et al., 2009).
Acutely, when an athlete is in competition, the amount of carbohydrate required is greater as glycogen stores must be maximised prior to the event, and often carbohydrate must be consumed during the event as a source of energy. Hawley (2010) suggests that marathon runners should consume seven to ten grams of carbohydrate per kilogram of body weight for the two days before the event. Chronically, carbohydrate consumption does not have a pronounced impact on an athlete’s performance, and it is more greatly related to energy balance.
Carbohydrate is an essential fuel for athletes, as glucose is the only fuel that can be used in anaerobic glycolysis, and is the most effect fuel in aerobic glycolysis. Therefore, glucose availability can become a limiting factor for performance. Fortunately, sources of carbohydrate are generally vegetarian and vegan, including pastas, grains, breads, fruits and sugars. Therefore, vegetarians should not struggle to achieve appropriate levels of carbohydrates. Some exclusions occur for vegans, such as milk sugars and honey, however other sugars can supplement these (Williams, 2010).
Fats can cause issues for vegetarians, commonly due to the lack of oily fish in their diet. This is why some vegetarians, known as pescatarians, will still consume fish as part of their diet (Wisehart, 2019). Oily fish are a good source of essential fatty acids, including docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). According to Hinton (2011), these are important cardiovascular, emotional and cognitive health. Unfortunately, it is very difficult to access this from a vegetarian diet, although alpha-linolenic acid (ALA) is available in soy, walnuts, flax seed and canola oil. ALA, however, does not great significantly converted into DHA and EPA, and therefore it is recommended that vegetarians should take a microalgae-produced oil supplement, as they cannot take regular fish oil.
Although important for health, research into the benefits of these essential fatty acids for sport’s performance is non-conclusive. However, triglycerides have a large role as a fuel source for low intensity, long duration activities. Fat oxidation occurs during these events such as marathons and long distance cycling, as means to spare glycogen. This is advantageous as maintaining higher levels of glycogen can delay the onset of fatigue, improving performance (Williams, 2010).
In addition, the fatty acids that vegetarians generally consume in their diet are more likely to be unsaturated. Monounsaturated fats are found in canola oil, peanut oil, almond oil and avocados. Polyunsaturated fats exist in soybean and corn oil; all of which are food available to vegetarians. Vegetarians are also exposed to less saturated fat as these are generally found in animal products such as beef and pork, and vegan also are not exposed to the saturated fats in egg yolk, cream, butter and cheese. However, saturated fats are present in coconut oil, palm oil and baked goods. For this reason, vegetarians, and especially vegans, are exposed to a lower risk of coronary heart disease and stroke, due to the atherosclerosis that occurs with excessive saturated fatty acid and minimal unsaturated fatty acid intake (McArdle et al., 2017). This can be helpful to those athletes that train at a high intensity, as they may be at a higher risk of coronary heart disease (Dores et al., 2018).
Micronutrients are essential nutrients needed in quantities that are no more than two grams; namely vitamins and minerals (Williams, 2010). Those that may be deficient in vegetarians and vegans include some B vitamins, including B3, B6 and B12, Vitamin D and minerals including iron and calcium (Schüpbach et al., 2017; Melina et al., 2016).
B vitamins are essential for energy metabolism and blood cell production (Bowers and Fox, 1992). A deficiency in these vitamins could result in lower energy production, and a lack of oxygen transport due to a lower erythrocyte count, which can accelerate the onset of fatigue, reducing performance. Good vegetarian sources of B vitamins include whole grain cereals, nuts and beans. Vegetarians should consume a B12 supplement since it is only available from meat sources (Jeukendrup and Gleeson, 2010).
A deficiency in iron can also decrease erythrocyte count, as iron is a key component to the production of haemoglobin. Wolinksy and Hickson (1994) found that those who do not eat red meats, such as vegetarians, are more likely to develop an iron deficiency. Good sources of iron for vegetarians include frozen peas, broccoli and spinach. However, the iron in plant foods are non-haem, which has a much lower bioavailability than haem iron (Webb, 2020).
Insel et al. (2019) explains that due to the lack of vitamin D and calcium in the diet, bone mineral density may decrease and a higher risk of stress fractures may occur. This is detrimental to performance as resting due to injury can lose the physiological adaptations to training, according to the principal of reversibility (Bowers and Fox, 1992). However, vegetarians can source calcium from beans, green leafy vegetables and cauliflower. Vitamin D can be found in carrots, green leafy vegetables, tomatoes and through sun exposure (Jeukendrup and Gleeson, 2010).
Conclusions and Recommendations
Vegetarian and Vegan diets have their limitations, and may make it more difficult for an athlete to achieve their nutritional requirements to reach their goals. However, it is certainly possible, and potentially advantageous to consume a vegetarian or vegan diet as an athlete, depending on the requirements of the sport and individual differences. Other research also indicates benefits to performance from vegetarian and vegan diets not discussed in this literature review. For example, a study by Beezhold et al. (2015) discovered that vegetarians have lower levels of stress and anxiety, which can benefit some sports people whose performance deteriorates from anxiety (Weinberg and Gould, 2016).
Further research should evaluate each nutrient in greater depth, to come to a strong conclusion about the impact of a vegetarian diet on sports performance. A comparative study between vegetarian and meat sources of these nutrients and how it would impact performance would be helpful in evaluating the use of a vegetarian or vegan diet for athletes.
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Suggested Harvard Reference:
Hagan, C. (2020) An analysis of how athletes at all levels of competition can meet their energy and nutrient needs on a vegetarian or vegan diet, unpublished BSc paper, The Queen's University of Belfast [Online]. Available at: https://cavanhagan.com/vegetarian-athlete-nutrition (Accessed: today's date)