Exercise And Sport Nutrition - LWW

Chapter 6 Exercise and Sport Nutrition 187 its name to the American Society for Nutrition, it remains a premier research society dedicated to improving the quality of life through the science of nutrition (79). During the early twentieth century, several laboratories were established to advance the understanding of nutrition. In 1904, The Nutrition Laboratory at the Carnegie Institute was created to study nutrition and energy metabolism. Established in 1927, the Harvard Fatigue Laboratory allowed for the further expansion of scientific research in the area of exercise and sport nutrition (78). Early scientific research in nutrition aimed to identify all the essential nutrients and the dietary requirements for each nutrient. Additional work was done to determine the distribution of each nutrient in various foods in an effort to define a nutritionally adequate diet or analyze a diet and determine whether it was nutritionally balanced for good health. This early research provided the foundation for the various computer databases that exist to provide both diet analysis and nutritional prescription (79). Recent History of Nutrition for Health The role of nutrition, particularly as it relates to chronic disease development, has received considerable attention over the last 50 years. Epidemiologic studies have provided us with much understanding of how various nutritional patterns influence the development of cardiovascular disease, cancer, and other diseases affected by individual’s food intake (39). The Framington Heart Study (44), the Harvard Alumni Study (69), and the National Cholesterol Education Program (87) have helped identify specific dietary factors that are associated with cardiovascular disease including the consumption of high levels of saturated fat and cholesterol (62,63). One of the most significant long-term epidemiologic studies about nutrition and health is the National Health and Nutrition Examination Survey (NHANES). NHANES began as a result of the National Health Survey Act of 1956, which was intended to establish a continuing National Health Survey to obtain information about the health status of U.S. citizens, including the services received for or because of health conditions. The first three National Health Examination Surveys (NHES I, II, and III) were conducted between 1959 and 1970. In response to numerous nutrition-related studies, the U.S. Department of Health, Education, and Welfare established a continuing National Nutrition Surveillance System in 1969 in an effort to measure the nutritional status of the U.S. population and monitor changes over time. The National Nutrition Surveillance System was merged with the National Health Examination Survey creating NHANES (64). Table 6.2 provides the dates and specific target groups and foci of the various surveys. Data from NHANES have Direct calorimetry The measurement of heat produced by a chemical reaction or by the body. Indirect calorimetry The measurement of energy production by the body using the amount of oxygen consumed and carbon dioxide produced. Basal metabolic rate The level of metabolism, as measured by energy expenditure, required to maintain the normal physiologic functions of the body. Epidemiologic studies The study of factors affecting the health and disease of large groups of individuals. Potteiger Chap06.indd 187 11/6/2009 11:01:12 AM

188 Chapter 6 Table 6.2 Exercise and Sport Nutrition Overview of NHANES Surveys from 1959 to the Present SURVEY AND YEARS SPECIFIC FOCUS NHES I (1959–1962) Selected chronic diseases of adults between 18 and 79 years of age NHES II (1963–1965) Growth and development of children between 6 and 11 years of age NHES III (1966–1970) Growth and development of adolescents between 12 and 17 years of age NHANES I, (1971–1975) Extensive dietary intake and nutritional status were collected by interview, physical examination, and a battery of clinical tests and measurements NHANES II (1976–1980) Expanded the age of the first NHANES sample by including individuals as young as 6 months of age; children and adults living at or below the poverty level were sampled at higher rates than their proportions in the general population (“oversampled”) because these individuals were thought to be at particular nutritional risk NHANES III (1988–1994) Included infants as young as 2 months of age, with no upper age limit on adults; African Americans, Mexican Americans, infants, children, and those over 60 years old were oversampled; NHANES III also placed a greater emphasis on the effects of environment on health 1999, NHANES became a continuous survey Surveys are conducted over a period of approximately 4 years with a break of at least 1 year between survey periods provided considerable insight into how dietary patterns have changed during the past 50 years and how these changes have contributed to the development of disease conditions. The American Dietetic Association (ADA) has been instrumental in promoting the dietetics profession, the enhanced understanding of nutrition, and the education of nutritional professionals. The ADA was founded in 1917 during a meeting of approximately 100 dieticians in Cleveland, Ohio. The first president, Lulu Grace Graves, helped estab Thinking Critically lish the initial areas of practice: (a) dieto-therapy, In what ways has our knowledge (b) teaching, (c) social welfare, and (d) administraabout nutrition contributed to a tion. These areas of practice remain at the heart of the broader understanding of how indimission of the ADA, which is to serve the public by viduals can improve physical fitness promoting optimal nutrition, health, and well-being and promote good health? (17). Federal, state, and many private foundations continue to support nutritional science research in an effort to help better understand the role of nutrition intake in disease development and disease risk reduction. Sport Nutrition The role of nutrition for enhancing sport and athletic performance has a rich history. The areas that have received the greatest attention and contributed most Potteiger Chap06.indd 188 11/6/2009 11:01:12 AM

Chapter 6 Exercise and Sport Nutrition 189 significantly to the development of sport nutrition have been carbohydrate and protein consumption, and vitamin and mineral supplementation. For example, historic recordings (ca. 500–400 BC) indicate that consumption of deer liver and lion heart would enhance bravery, speed, and strength in the athlete and warrior (5,60,81). Although early writings demonstrate people’s awareness of the role of nutrition in promoting physical development, most of what we know about the role of nutrition for enhancing sport and athletic performance comes from more recent times. Early in the twentieth century, scholars described the importance of carbohydrate during prolonged exercise and the role of carbohydrates in maintaining adequate stores of muscle and liver glycogen (22,50). During the 1924 Boston Marathon, measures of blood glucose were made of the first 20 runners to cross the finish line. Many of the runners displayed hypoglycemia, symptoms of fatigue, stupor, and poor concentration (55). During the following year, runners were given large amounts of carbohydrate the day before the race and sugar candy during the race. The result of this nutritional strategy was a normalization of blood glucose levels and the alleviation of the symptoms of nervous system fatigue and poor concentration (34). The development and use of the muscle biopsy procedure by Swedish researchers in the 1960s allowed for the determination of how fast muscle glycogen was depleted during exercise (2). This information eventually led to the development of the carbohydrate loading procedure for improving endurance performance and the influence of carbohydrate consumption on muscle glycogen replenishment (9). Continued research in this area led to the use of sports drinks for delaying muscle fatigue and improving performance during prolonged exercise (86). Experiments conducted in the 1940s demonstrated that increased protein consumption could enhance the development of skeletal muscle mass in individuals involved in resistance exercise training (5,49). Throughout the 1950s and 1960s, the increased consumption of milk and beef products led to greater protein consumption (5). The development of isolated protein powders and amino acids in the 1970s and early 1980s resulted in athletes using these products for increasing dietary protein intake. Additional research in the 1990s led to many athletes closely matching amino acid intake and resistance exercise training in an effort to secure the greatest enhancement of lean muscle mass development (5). The use of amino acid supplements by all types of athletes continues into the twenty first century, with athletes mixing various amino acids and growth-promoting agents in an effort to maximize protein synthesis and skeletal muscle mass during training. Many water- and fat-soluble vitamins were discovered during the 1930s. The use of these compounds quickly spread through the sporting world so that by 1939, cyclists in the Tour de France reported performing better after taking vitamin supplements (60). Early scientific research did not support the use of vitamin supplements for enhancing athletic performance, but athletes remained committed to heavy vitamin supplementation. For example, during the 1972 Olympic Games athletes reported consuming large quantities of vitamins in an effort to enhance performance during competition (24). Athletes continue to use high doses of Muscle biopsy A procedure whereby a small sample of muscle tissue is collected using a special needle. Potteiger Chap06.indd 189 11/6/2009 11:01:12 AM

190 Chapter 6 Exercise and Sport Nutrition vitamin supplementation in an effort to improve performance or at the very least as an insurance mechanism to ensure adequate levels of vitamins in the body (61). Within the ADA, a dietary practice group called the Sports, Cardiovascular, and Wellness Nutritionists (SCAN) was established in 1981. The SCAN Dietetic Practice Group works to promote healthy, active lifestyles through excellence in dietetics practice in sports, cardiovascular, and wellness nutrition, and the prevention and treatment of disordered eating. Registered dieticians can also acquire board certification as a Specialist in Sports Dietetics indicating they are specialty trained to work with high school, collegiate, Olympic, and professional athletes to enhance sport performance (http://www.scandpg.org/). Exercise and sport nutritionists working with other exercise science and allied health professionals continue to explore ways that nutrition can be used to promote good health and improve sport and athletic performance. Future research work and advancements in policy initiatives and educational program development will be a central focus as nutrition is used to address diet-related health problems, and Thinking Critically individuals try and meet the dietary guidelines In what ways has our knowledge about for good nutritional practices. Table 6.3 provides nutrition contributed to a broader a list of significant recent events in the historic understanding of how to enhance development of nutrition for health, sport, and sport and athletic performance? athletic competition. Table 6.3 Potteiger Chap06.indd 190 Significant Events in the Historic Development of Nutrition for Health and Sport YEAR EVENT 1903 W.O. Atwater and Francis Gano Benedict invented a respiration chamber 1904 The Nutrition Laboratory at the Carnegie Institute was created to study nutrition and energy metabolism 1917 American Dietetic Association was founded 1925 First experiment on carbohydrate supplementation during exercise was conducted at the Boston Marathon 1927 Harvard Fatigue Laboratory was established 1933 American Society for Nutrition was founded 1937 Clive McCay demonstrated that restricting energy intake of rats by 33% led to increased longevity 1939 First report of vitamin supplementation improving performance in cyclists in the Tour de France 1956 First NHANES was administered 1981 The SCAN group of the ADA was formed 1999 NHANES became a continuous survey 11/6/2009 11:01:12 AM

Chapter 6 Exercise and Sport Nutrition 191 BASIC NUTRIENTS Each of us needs to consume adequate amounts of the macronutrients and micronutrients in our diet to ensure proper physiologic and structural function and good health. Although individual circumstances and preferences will dictate food intake, many individuals will meet the recommended dietary intake (RDI) for carbohydrate, fat, protein, vitamins, and minerals by consuming a diet that is consistent with general nutrition guidelines. Proper nutritional intake promotes optimal growth and development, appropriate energy balance and body composition, health and longevity, and normal physiologic function. Table 6.4 provides a list of the macro- and micronutrients and their primary functions related to physical activity, exercise, sport and athletic competition. The information contained in the following sections is designed to provide an overview of macro- and micronutrient function. Carbohydrate Carbohydrate is a macronutrient that provides energy to the body. Dietary carbohydrates exist in two forms: simple and complex. Simple carbohydrates, sometimes called simple sugars, come from the carbohydrates found in milk and Table 6.4 NUTRIENT The Macronutrients and Micronutrients and their Primary Functions Related to Physical Activity, Exercise, Sport, and Athletic Performance PRIMARY FUNCTION RELATED TO PHYSICAL ACTIVITY, EXERCISE, SPORT, AND ATHLETIC PERFORMANCE Carbohydrates Provide energy during moderate to high intensity physical activity or exercise Fats Provide energy during low to moderate intensity exercise Protein Important component of skeletal muscle Part of various compounds that regulate metabolism during rest and exercise Vitamins Important for controlling metabolic pathways that produce energy during rest and exercise Minerals Part of the structure of bone Part of various compounds that regulate metabolism during rest and exercise Macronutrient A chemical substance (such as protein, carbohydrate, or fat) required in relatively large quantities in an individual’s daily nutritional intake. Recommended dietary intake The recommended intake level of a nutrient that is considered to meet the daily needs of nearly all healthy individuals. Simple carbohydrate A carbohydrate, such as glucose, that consists of a single monosaccharide unit. Potteiger Chap06.indd 191 11/6/2009 11:01:12 AM

192 Chapter 6 Exercise and Sport Nutrition FIGURE 6.4 Complex carbohydrates. (Photo by Tetra Images/Getty Images.) fruit. A large percentage of the simple sugars consumed in the diet of individuals living in the United States are added to processed foods during the manufacturing process. These refined sugars, with sucrose and high fructose corn syrup being most popular, are frequently added to soft drinks, fruit drinks, candies, and desert items. Complex carbohydrates, also called starches, are found in whole grains (Figure 6.4) and certain vegetables such as potatoes, beans, and peas. Complex carbohydrates are generally considered healthier and more beneficial when performing exercise and participating in sport and athletic activities. Complex carbohydrates also contain large amounts of vitamins and minerals and result in a slower release into the body (35). When carbohydrates are consumed in the diet, they are broken down in the gastrointestinal tract and absorbed in the small intestine as small six-carbon molecules such as glucose and fructose. Glucose is the most common and useful form of carbohydrates in the body. Glucose provides energy to the various tissues of the body in one of two forms; blood glucose or liver and muscle glycogen. Although almost all cells can use carbohydrate, fat, or protein for energy, the brain and nervous tissue depend almost exclusively on glucose to provide energy (35). The storage form of glucose in the body is called glycogen. The liver and the skeletal muscle are the primary tissues for glycogen synthesis and storage. Normal fasting blood glucose levels are between 70 and 100 mg·dL 1. When blood glucose decreases below 70 mg·dL 1 the condition of hypoglycemia occurs and symptoms such as drowsiness, irritability, and fatigue may appear. The body responds to hypoglycemia primarily by breaking down liver glycogen into glucose and releasing it into the blood. At the same time, various signals from the brain stimulate hunger and the desire for the individual to eat. Combined, these two actions serve to elevate blood glucose levels (35). When blood glucose levels increase after food consumption, the body releases insulin from the beta cells of the pancreas. Insulin works with protein receptors (called glucose transport proteins) in the tissues of the body to promote glucose uptake for immediate energy use or conversion to glycogen for storage. This process results in a return of blood glucose to normal levels. A disease condition called diabetes mellitus occurs when either the pancreas does not produce sufficient amounts of insulin (Type 1 diabetes mellitus) or the insulin does not facilitate glucose uptake into the tissues of the body (Type 2 diabetes mellitus). Potteiger Chap06.indd 192 11/6/2009 11:01:12 AM

Chapter 6 Exercise and Sport Nutrition 193 If the fasting blood glucose level is 100 mg·dL 1 to 125 mg·dL 1, the individual may have impaired fasting glucose, commonly known as prediabetes. A fasting blood glucose level of 126 mg·dL 1 or higher is consistent with either type 1 or type 2 diabetes when accompanied by classic signs and symptoms of diabetes, including increased thirst or hunger, frequent urination, weight loss or blurred vision (35). Fat Dietary fat and cholesterol are critical to the normal functioning of body tissues and overall good health of the body. Dietary fat is vital for the absorption of the fat-soluble vitamins (A, D, E, and K) and to provide key biochemical precursors that can be transformed into essential cellular products. Dietary fat also contributes to the flavor and texture of foods, and it is believed that fat maintains satiety and helps to keep us from being hungry. Fat also provides a concentrated form of energy for our body. Cholesterol is important in the formation of cell membranes and some hormones in the body (35). Most consumed fats are broken down in the gastrointestinal tract into free fatty acids and monoglycerides for absorption in the small intestine. Dietary fat and cholesterol enter the blood stream and travel to the liver for further processing by the body. The fat absorbed from the small intestine is largely stored in the liver and adipose tissue and is later used in the body to provide energy at rest and during physical activity and exercise. Cholesterol travels through the circulatory system for use by various tissues of the body (35). Excessive intake of dietary fat can result in the development of assorted disease conditions, including atherosclerosis, hyperlipidemia, and obesity. The consumption of a high fat diet, which often results in high total calorie intake, has been shown to be related to excessive weight gain and the development of obesity (6). Individuals who are obese have a higher risk of developing cardiovascular disease, type 2 diabetes, and certain types of cancer (16,28). The consumption of a high fat diet can also lead to excessive levels of blood lipids. The conditions of hyperlipidemia and hypercholesterolemia can increase an individual’s risk of cardiovascular disease and stroke (26,87). Complex carbohydrate A carbohydrate, such as sucrose or starch, that consists of two or more monosaccharide units. Hypoglycemia An abnormally low level of sugar in the blood. Type 1 diabetes mellitus Condition chara

Nutrition After completing this chapter you will be able to: 1. Describe the importance of proper nutrition as it relates to enhancing health, physical activity, exercise, sport, and athletic performance. 2. Describe the key highlights in the historic development of nutrition and sport nutrition. 3.