Plant-Based Diets for Cardiovascular Safety and Performance in Endurance Sports

Studies suggest that endurance athletes are at higher-than-average risk for atherosclerosis and myocardial damage. The ability of plant-based regimens to reduce risk and affect performance was reviewed. The effect of plant-based diets on cardiovascular risk factors, particularly plasma lipid concentrations, body weight, and blood pressure, and, as part of a healthful lifestyle, reversing existing atherosclerotic lesions, may provide a substantial measure of cardiovascular protection. In addition, plant-based diets may offer performance advantages. They have consistently been shown to reduce body fat, leading to a leaner body composition. Because plants are typically high in carbohydrate, they foster effective glycogen storage. By reducing blood viscosity and improving arterial exibility and endothelial function, they may be expected to improve vascular ow and tissue oxygenation. Because many vegetables, fruits, and other plant-based foods are rich in antioxidants, they help reduce oxidative stress. Diets emphasizing plant foods have also been shown to reduce indicators of in ammation. These features of plant-based diets may present safety and performance advantages for endurance athletes. The purpose of this review was to explore the role of nutrition in providing cardioprotection, with a focus on plant-based diets previously shown to provide cardiac bene ts. Keywords:nutrition; exercise; athletic performance; vegan; vegetarian 1. Introduction: The Academy of Nutrition and Dietetics, Dietitians of Canada, and

These features of plant-based diets may present safety and performance advantages for endurance athletes. The purpose of this review was to explore the role of nutrition in providing cardioprotection, with a focus on plant-based diets previously shown to provide cardiac bene ts. Keywords:nutrition; exercise; athletic performance; vegan; vegetarian 1. Introduction: The Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine have determined that “the performance of, and recovery from, sporting activities are enhanced by well-chosen nutrition strategies” [1]. In this review, we examine physiological effects of plant-based diets that present potential safety and performance advantages in endurance sports. These include improvements in cardiovascular risk factors, improved blood ow, leaner body composition, reduced oxidative stress, reduced in ammation, and improved glycogen storage, among others. Several studies have shown that plant-based dietary patterns have particular bene ts for heart health. A low-fat, vegetarian diet, along with other healthful lifestyle changes, has been shown to reverse arterial plaque [2–4]. Compared with meat eaters, vegetarians are 32% less likely to develop coronary heart disease [5]. In this review, the terms “plant-based” and “vegan” will be used interchangeably to Nutrients2019,11, 130; doi:10.3390/nu11010130

Nutrients2019,11, 130 2 of 10 refer to a diet without animal-derived products. Variants of vegan diets, e.g., vegetarian diets that may include dairy products or eggs, will be identi ed when relevant. Arterial changes that contribute to atherosclerosis can begin early in life, even in utero [6]. By age 10 to 14 years, the majority of American children have fatty streaks in the left anterior descending coronary artery, and more than ve percent have more advanced coronary disease [7]. Autopsies of U.S. soldiers who died in the Korean War revealed severe coronary atherosclerosis (75% to 90% narrowing) in 6.4% at a mean age of 20.5 years [8]. A similar study of autopsies of soldiers who died in Operations Enduring Freedom and Iraqi Freedom/New Dawn between October 2001 and August 2011 showed that, at a mean age of 25.9 years, 8.5% had coronary atherosclerosis [9]. By age 20, approximately 10% of the population in developed countries have advanced atherosclerotic lesions in the abdominal aorta, reducing blood ow and contributing to disc degeneration and lower back pain [10]. Athletes are not immune to atherosclerosis or to cardiac events [11]. Surprisingly, endurance athletes may have more advanced atherosclerosis and more myocardial damage, compared with sedentary individuals, particularly as they age. In a 2017 study in the United Kingdom, coronary plaques were found in 44% of middle-aged and older endurance athletes engaged in cycling or running, compared with 22% of sedentary controls (p= 0.009) [12]. Similarly, a study of 50 men who had run at least 25 consecutive Twin Cities Marathons (Minneapolis, MN, USA) found the runners to have increased total plaque volume, calci ed plaque volume, and non-calci ed plaque volume, compared with 23 sedentary controls [13]. In a study of active German marathon runners 50 years of age, myocardial damage, as measured by magnetic resonance imaging, was found in 12% of active runners, compared with 4% of sedentary controls [14]. The degree of myocardial damage was predicted by the number of marathons run [15]. Sports-related sudden cardiac deaths are uncommon, but increase with age. In older athletes, these deaths are typically attributable

marathon runners 50 years of age, myocardial damage, as measured by magnetic resonance imaging, was found in 12% of active runners, compared with 4% of sedentary controls [14]. The degree of myocardial damage was predicted by the number of marathons run [15]. Sports-related sudden cardiac deaths are uncommon, but increase with age. In older athletes, these deaths are typically attributable to coronary artery disease (more than 80% of cases), with additional cases attributable to hypertrophic cardiomyopathy, arrhythmogenic right ventricular dysplasia, myocarditis, and valvular heart disease [16]. These studies show that well-trained athletes are at signi cant risk for atherosclerosis and myocardial damage. What they do not show is whether these changes are the consequences of athletic activity or of the foods often used to fuel it. To the extent that increased consumption of animal products supplies the energy for increased athletic activity, their saturated fat and cholesterol and relative absence of antioxidants and ber may contribute to atherosclerotic changes. Apart from increasing the risk of cardiac events, atherosclerosis may also narrow arteries to the legs, the brain, and other parts of the body, reducing blood ow and potentially impairing performance. While this is particularly evident in diagnosed peripheral artery disease [17], it may also be a factor, at least theoretically, for athletes with subclinical atherosclerotic disease. Plant-based diets address key contributors to atherosclerosis: dyslipidemia, elevated blood pressure, elevated body weight, and diabetes, each of which is brie y discussed in the following paragraphs. Regarding plasma lipids, dyslipidemia is a major contributor to arterial disease and is promoted by diets rich in saturated fat and, to a lesser degree, dietary cholesterol, as noted above. Dairy products and meat are the leading sources of saturated fat, and exclusion of these products predictably improves plasma lipid pro les [18], an effect that can be accentuated by the speci c inclusion of soluble ber (e.g., oats, barley, or beans), soy protein, almonds, and sterol-containing margarines. Combining these elements in a “portfolio” diet, University of Toronto researchers lowered low-density lipoprotein cholesterol levels by nearly 30 percent in four weeks [19]. Animal products are not the

improves plasma lipid pro les [18], an effect that can be accentuated by the speci c inclusion of soluble ber (e.g., oats, barley, or beans), soy protein, almonds, and sterol-containing margarines. Combining these elements in a “portfolio” diet, University of Toronto researchers lowered low-density lipoprotein cholesterol levels by nearly 30 percent in four weeks [19]. Animal products are not the only offenders. Trans fats also have harmful effects on plasma lipids and pose cardiovascular risks [20]. Regarding blood pressure, vegan and vegetarian diets reduce both systolic and diastolic blood pressure, which appears to be a consequence of reduced blood viscosity, increased blood potassium, and weight loss [21]. Lower blood pressure reduces the risk of atherosclerotic changes.

Nutrients2019,11, 130 3 of 10 Obesity is a risk factor for cardiovascular disease. Vegetarian, especially vegan, diets reduce body fat, even in the absence of intentional limitations on calories or portion sizes [22]. Regarding glycemic control, plant-based diets boost insulin sensitivity [23]. This is important for reducing the risk of type 2 diabetes and improving glycemic control in individuals with diabetes, which is a major contributor to atherosclerosis. Each of these factors is improved by plant-based diets. As part of an overall healthful lifestyle, a low-fat vegetarian diet has been shown to reverse coronary atherosclerosis, increasing blood ow and reducing the risk of coronary events [2]. Speci cally, the Lifestyle Heart Trial limited the use of animal products to egg whites and 1 cup of nonfat milk or yogurt daily. Because ow through a vessel is proportional to the fourth power of its radius, even small changes in the arterial diameter can lead to major changes in blood ow. 2. The Role of Diet in Athletic Performance Apart from their role in cardiovascular health, plant-based diets have other physiological effects that may offer performance advantages. These include a leaner body mass, ease of glycogen storage, improved tissue oxygenation, reduced oxidative stress, and reduced in ammation. 2.1. Leaner Body Mass As noted above, plant-based diets reduce body fat, an effect that not only reduces atherosclerotic risk but may also be directly bene cial for athletic performance. The reduction in body fat is mainly due to the low fat content and high ber content of these diets, traits that reduce the energy density of meals, with a corresponding reduction in energy intake. However, even without changes in body weight, transitioning to a meat-free diet can signi cantly reduce body fat as measured by skinfold thickness and waist:height ratio [24]. Plant-based diets also in uence postprandial energy expenditure. In a 2005 study, the use of a low-fat vegan diet for 14 weeks increased postprandial energy expenditure by 16% [23]. This effect may be due to changes in mitochondrial activity. The number and activity of mitochondria in muscle cells and other body tissues are

by skinfold thickness and waist:height ratio [24]. Plant-based diets also in uence postprandial energy expenditure. In a 2005 study, the use of a low-fat vegan diet for 14 weeks increased postprandial energy expenditure by 16% [23]. This effect may be due to changes in mitochondrial activity. The number and activity of mitochondria in muscle cells and other body tissues are not constant; rather, they change depending on the diet. In a study in which volunteers were fed a 50%-fat diet, mitochondrial biogenesis was signi cantly reduced within 3 days [25]. High-fat diets may also act on cellular metabolism indirectly through their effects on the gut microbiome. Gut bacteria produce endotoxins that can enter the bloodstream and, in turn, in uence cellular metabolism. High-fat diets appear to disrupt the intestinal barrier to the passage of endotoxins. In a 5-day experiment in human volunteers, a 55%-fat diet led to a marked increase in circulating endotoxins and, in turn, to a signi cant impairment of postprandial cellular glucose oxidation [26]. These ndings suggest that high-fat diets quickly disrupt cellular metabolism, reducing energy expenditure, while a low-fat, plant-based diet has the opposite effect, increasing postprandial energy expenditure. As we have seen, plant-based diets reduce body fat by reducing dietary energy density and increasing postprandial metabolism. However, there is also a greater metabolic cost of converting dietary carbohydrate to body fat, compared with converting dietary fat to body fat. As a result, low-fat diets are more effective than calorie-matched low-carbohydrate diets for reducing body fat. In a crossover trial including 19 overweight adults given two isocaloric diets for six days each, a low-fat diet resulted in a signi cantly greater loss of body fat ( 89 g of body fat per day) compared with a low-carbohydrate diet ( 53 g of body fat per day,p= 0.002) [27]. Eliminating excess body fat not only reduces atherosclerotic and metabolic risks, it also boosts endurance. Speci cally, reduced body fat is associated with increased submaximal and maximal aerobic capacity [28,29]. An athlete with a higher VO2 max relative to their body weight will have better endurance and will

low-carbohydrate diet ( 53 g of body fat per day,p= 0.002) [27]. Eliminating excess body fat not only reduces atherosclerotic and metabolic risks, it also boosts endurance. Speci cally, reduced body fat is associated with increased submaximal and maximal aerobic capacity [28,29]. An athlete with a higher VO2 max relative to their body weight will have better endurance and will outperform an athlete with a lower value [30,31], and the effect of diet on VO2 max relative to body weight is important, not only for high-level competitors, but for individuals who are not trained athletes. In a study of 31 overweight women, the loss of 9.2 kg of body fat was

Nutrients2019,11, 130 4 of 10 accompanied by a 15% increase in VO2 max relative to body weight [28]. Even in the absence of weight loss, a vegetarian, mostly vegan, dietary pattern has been shown to reduce visceral fat and increase VO2 max [32]. 2.2. Facilitating Glycogen Storage Carbohydrate is the primary energy source during moderate and high-intensity aerobic exercise, and endurance is enhanced by a high-carbohydrate intake, not only immediately before athletic events, but over the long term [33]. Many athletes, however, have eating patterns that are de cient in carbohydrate, putting them at risk for an overly rapid depletion of glycogen from the muscle and liver and early fatigue. A 2016 study of athletes participating in full and half Ironman triathlons, winter triathlons, and winter pentathlons showed that fewer than half (46%) reported meeting the recommended carbohydrate intake for athletes training 1–3 h per day ( 6 g/kg body weight per day) [34]. Because grains, legumes, and root vegetables are rich in complex carbohydrate, individuals who begin plant-based diets typically increase their intake of healthful carbohydrate [35]. 2.3. Reduced Blood Viscosity and Increased Tissue Oxygenation A key factor in oxygen delivery to the muscles and other tissues is blood viscosity (resistance to ow, or “thickness”), which is a function of plasma viscosity and packed cell volume [36]. Generally speaking, lowering blood viscosity will improve blood ow and thereby improve athletic performance [37]. In the course of athletic activity, however, the passage of uid from the bloodstream into the tissues leads to hemoconcentration. Gradually rising blood viscosity causes a progressive loss of tissue oxygenation, degrading performance [38]. Aerobic training increases blood volume, and because it increases plasma volume to a greater extent than red cell mass, aerobic training reduces blood viscosity [38]. However, plasma viscosity is also in uenced by food choices. Because plants are typically low in saturated fat and devoid of cholesterol, vegetarian diets reduce plasma lipid concentrations [18], leading to reduced viscosity. In a study comparing 48 individuals following vegetarian eating patterns and 41 matched controls, plasma viscosity, packed cell volume, and blood viscosity were lower in

viscosity [38]. However, plasma viscosity is also in uenced by food choices. Because plants are typically low in saturated fat and devoid of cholesterol, vegetarian diets reduce plasma lipid concentrations [18], leading to reduced viscosity. In a study comparing 48 individuals following vegetarian eating patterns and 41 matched controls, plasma viscosity, packed cell volume, and blood viscosity were lower in vegetarians, and the stricter the avoidance of animal products, the greater the observed differences [39]. Individuals excluding meats entirely had signi cantly lower blood viscosity, compared with those having occasional meat (less than once a week). These observations were initially identi ed as an explanation for the lower blood pressure and lower prevalence of hypertension that are commonly observed among those following vegetarian diets. However, reduced blood viscosity also improves tissue oxygenation, potentially improving athletic performance. Blood ow also depends on arterial exibility. Healthy arteries expand with the pressure of a pulse wave (compliance) and then return to their previous diameter when the wave has passed (elasticity). Over time, hypertension, dyslipidemia, and chronically elevated glucose levels associated with diabetes can injure the artery wall, leading to in ammation and matrix remodeling, making arteries “stiffer” [40,41]. Vasoactivity is also in uenced by diet habits. University of Maryland investigators assessed brachial artery ow-mediated vasodilation in a crossover study in which 18 participants followed a low-fat vegetarian (Ornish) diet, a low-carbohydrate, high-fat (Atkins) diet, and a modi ed low-carbohydrate, high-fat (South Beach) diet, for four weeks each, adjusting energy intake to prevent weight loss. Participants were relatively young (mean age 31 years) and slim (mean body mass index 22.6 kg/m 2 .) The vegetarian diet improved brachial artery ow-mediated vasodilation, compared with the low-carbohydrate diet, while the modi ed low-carbohydrate diet yielded results between the two. The higher the saturated fat intake, the greater the impairment of ow-mediated vasodilation [42]. Arterial compliance can even be impaired by a single high-fat meal. The Maryland researchers measured the effects of a high-fat meal on artery function in 10 healthy volunteers. The test meal consisted of a McDonald's Egg McMuf n, a Sausage McMuf n, two

between the two. The higher the saturated fat intake, the greater the impairment of ow-mediated vasodilation [42]. Arterial compliance can even be impaired by a single high-fat meal. The Maryland researchers measured the effects of a high-fat meal on artery function in 10 healthy volunteers. The test meal consisted of a McDonald's Egg McMuf n, a Sausage McMuf n, two hash brown patties, and a drink,

Nutrients2019,11, 130 5 of 10 providing 900 calories, 50 g of fat, 14 g of saturated fat, and 255 mg of cholesterol. Flow-dependent vasoactivity fell from a pre-meal value of 21% to 11% at two hours and was still low (11%) at four hours postprandially [40]. Although meals rich in animal fats impair arterial compliance, some added oils may have similar short-term effects. A single-meal experiment using a carrot cake and a milk shake prepared with coconut oil (which is high in saturated fat) demonstrated impaired arterial compliance, compared with the same meal prepared with saf ower oil (which is high in polyunsaturated fat) [43]. Studies using olive oil (rich in monounsaturated fat) have yielded mixed results—some showed an impairment of ow-mediated vasodilation, others did not [44–46]. Overall, these studies suggest that, while animal fats are particularly harmful for arterial exibility, there is a bene t from meals prepared from vegetables, grains, legumes, and fruits, without animal products or added oils. The factors described above—blood viscosity, arterial diameter, and arterial compliance and elasticity—are all in uenced by food choices and may all be expected to affect improve tissue oxygenation, endurance, and performance. As we have seen, athletic activity depends on good circulation to provide oxygen and nutrients and carry away metabolic waste products. Blood ow to the muscles is in uenced by blood viscosity, as well as by arterial caliber, compliance, and elasticity, all of which are in uenced by food choices. 2.4. Reduced Oxidative Stress Exercising muscles produce reactive oxygen species (free radicals). These free radicals result from the normal function of mitochondria and other intracellular organelles during exercise, as well as from cellular responses to tissue damage [47,48]. When the production of reactive oxygen species exceeds the body's ability to neutralize free radicals through endogenous and exogenous antioxidants, the result is called oxidative stress. At low levels, oxidative stress upregulates antioxidant defenses [49] and boosts the immune response [50]. However, free radical production that greatly exceeds the neutralizing ability of antioxidant defenses can result in damage to DNA (leading to mutations), to plasma lipids (leading to atherosclerosis), and

This review explores the role of plant-based diets in cardiovascular health and athletic performance.