Nutrition and the Female Athlete: From Research to Practice PDF

Preface

Research examining the effects of nutrition on sports performance (i.e., sport nutrition) has exploded over the last 25 years. The interest in and proliferation of sport nutrition research has led to the creation of two scientific journals, numerous textbooks, and countless Web sites devoted specifically to this topic. Sports dietitians, coaches, and trainers are basing nutrition recommendations to their female athletes on the existing sport nutrition research. Similarly, the existing sport nutrition research is guiding and marketing the manufacturing of sport nutrition products to female athletes. All the while, a key limitation of much of the existing sport nutrition research is being overlooked; with a few exceptions, the majority of studies have employed only male subjects. The results of these studies are then generalized to females with no scientific support for the validity or accuracy of such a generalization. This oversight is not exclusive to sports nutrition research. One need only review the history of sports in general to appreciate the relative dominance by men and limited inclusion of women in all facets of athletics.

In the United States, relatively few women competed in sports until the late 19th and early 20th centuries, when social changes in North America favored increased female participation in society as equals with men (Oglesby 1978). Although women were technically permitted to participate in sports, relatively few did due to the social stigma as well as concerns regarding the effects of strenuous exercise on a woman's physical "constitution" (in particular, her reproductive health) (Oglesby 1978). Two World Wars and a couple of key social "movements" (i.e., the civil rights and women's movements) brought more women onto the athletic playing fields. However, it was not until 1972 when the U.S. Congress passed Title IX of the Educational Movements that the door to women's participation in sports was truly opened (Bell 2007). Subsequent to Title IX, women and girls have become much more involved in sports. College women's athletic participation has increased from 15% in 1972 to 43% in 2001. High school girl's athletic participation increased from 295,000 in 1971 to 2.8 million in 2002–2003, an increase of over 840% (Carpenter and Acosta 2005).

With an increase in women's sports participation has come a greater recognition of and appreciation for the biomechanical and physiological differences between men and women. Over the last 30 years, sports equipment and clothing manufacturers have become more interested in developing and marketing products specifically for women. I have witnessed this "evolution" personally. In the late 1970s, when I first took up distance running, there were no "women's running shoes"; I had to make do with the smallest-sized men's shoe I could find. Similarly, if I wanted nylon running shorts I had to search the boy's or young men's department. Today, every major running shoe manufacturer has not one but several shoes designed specifically for women, and there are numerous clothing lines that cater specifically to women's exercise wear.

Thanks in large part to the innovative studies conducted in the early 1990s by Mark Tarnopolsky and others at McMaster University (Ontario, Canada), researchers are also starting to appreciate that the physiological differences between men and women may translate into different responses and adaptations to nutritional manipulations and, thus, different recommendations in terms of sport nutrition practices.

Therein lies the premise of this book.

It is now well established that females are metabolically unique from their male counterparts; thus, their nutritional requirements for optimal training and athletic performance are likely also unique.

Chapter 1 sets the stage for the discussion of gender-specific nutrition recommendations by highlighting recent research indicating that substrate utilization during exercise differs significantly between men and women. Written by the pioneer in this particular topic area, Mark Tarnopolsky, and one of his recent PhD students, Amy Maher, provide a number of possible explanations for the gender differences in substrate utilization as well as implications for gender-specific nutritional recommendations.

Louise Burke and Christine Dziedzic tackle the topic of carbohydrate needs of female athletes in Chapter 2. More specifically, the validity of generalizing the current guidelines for carbohydrate replacement before, during, and after exercise to female athletes is examined. Examples of ways in which female athletes can address their carbohydrate intake goals in the context of other nutritional needs and dietary concerns are also provided.

In Chapter 3, Nancy Rodriguez addresses the importance of adequate dietary protein in the diets of female athletes by reviewing the myriad of structural and functional roles that protein plays within the athlete's body. The effects of inadequate protein intake, particularly in combination with inadequate energy intake, on the health and performance of the female athlete are discussed and are used to guide recommendations for dietary protein intake.

Proper hydration is as important as carbohydrate and protein intake in terms of optimizing performance and the overall health of the female athlete. Dehydration negatively impacts performance as water increases body core temperature, heart rate, glycogen utilization, and perceived exertion. Nina Stachenfeld has spent a significant portion of her research career investigating the effects of reproductive hormones on the fluid and temperature regulatory systems in women. In Chapter 4, she and her former postdoctoral associate, Megan Wenner, examine sex differences in thermoregulation and fluid balance in order to determine whether female-specific fluid recommendations are necessary.

Although they do not provide energy or support hydration, there is no question that micronutrients (i.e., vitamins and minerals) play a critical role in supporting training, competition, and the overall health of the female athlete. Nonetheless, research indicates that female athletes often have suboptimal micronutrient intakes that place them at risk for deficiency. Nutrients that seem to be of particular concern for female athletes are discussed in Chapters 5 through 7. In Chapter 5, Pamela Hinton highlights the importance of iron and zinc for athletic performance and provides suggestions for helping female athletes meet their iron and zinc requirements. Bone nutrients are covered in Chapter 6 by Kristine Spence. In Chapter 7, Kathleen Woolf, Dara LoBuono, and Melinda Manore provide a comprehensive review of the exercise-related functions, food sources, and recommended intakes for each of the B vitamins.

The final four chapters of the book (i.e., Chapters 8 through 11) are devoted to a discussion of a set of three distinct yet often interrelated disorders including low energy availability, menstrual dysfunction, and poor bone health that have come to be known as the female athlete triad (Triad). Katherine Beals examines the concept of energy availability and summarizes the existing research regarding the etiology, prevalence, and consequences of low energy availability among female athletes. The foremost expert in endocrinology and the female athlete, Anne Loucks, provides a comprehensive review of the research examining menstrual dysfunction among female athletes with an emphasis on its prevalence, causes, consequences, and treatment options. Finally, Michelle Barrack addresses the third and final component of the Triad, bone health. Her chapter highlights genetic and lifestyle characteristics, including sport-specific factors that affect bone health, and provides behavioral recommendations female athletes can employ to optimize bone health and reduce their risk of musculoskeletal injuries.