Nutritional guidelines for female athletes

Chapter 4
Nutritional guidelines for female athletes


Louise M. Burke


Sports Nutrition, Australian Institute of Sport, Belconnen, ACT, Australia


Introduction


Good nutrition is important for optimal performance for all athletes, but particularly so for females. Female athletes have increased requirements for some nutrients compared with males. In addition, due to their smaller body size and often a relative smaller training load, female athletes need to achieve their nutritional requirements from a smaller energy intake. Finally, female athletes in at least some sports appear to be at greater risk of developing issues related to eating and body image compared with their sedentary counterparts or male athletes. Therefore, there are some challenges but great rewards for achieving a sound eating plan. This chapter overviews the key concepts of sports nutrition considering whether the current guidelines are suitable for female athletes and providing special insights into issues that might be different to those of their male counterparts.


Specificity and periodization of nutrition goals


A variety of nutrition goals can be identified in the training and competition elements of sporting involvement (see Table 4.1). It is important to realize, however, that these goals and nutritional requirements are not only specific to the individual athlete and her event, but specific to the phase of the athlete’s program. Athletes incorporate a range of training sessions (type, duration and intensity) within the microcycles and macrocycles of their conditioning programs, and compete in events with a range of different nutritional challenges. There are also differences in individual responses to many nutritional interventions, and a need to integrate the athlete’s range of sports nutrition and other “everyday” or clinical nutrition goals into her overall eating program. Therefore, each athlete needs an individualized plan to achieve her unique set of nutrition goals and requirements and should expect that her eating plan will differ from day to day and over the season to accommodate changes in the exercise load and other goals of the periodized approach to conditioning and performance.


Table 4.1 A summary of sports nutrition goals





In training, the athlete should aim to

  • Meet the energy and fuel requirements needed to support her training program
  • Achieve a physique (body mass, body fat, and muscle mass) that is consistent with long-term health and performance using sensible strategies
  • Refuel and rehydrate well for key training sessions where it is important to perform at her best
  • Enhance recovery and adaptation between training sessions by providing all the nutrients associated with these processes
  • Practice any intended competition nutrition strategies so that beneficial practices can be identified and fine-tuned
  • Reduce the risk of illness and injury during heavy training periods by maintaining healthy physique and energy balance and meeting requirements for key micronutrients (e.g., iron, calcium) and health-promoting food chemicals (e.g., antioxidants, omega fatty acids)

In competition, the athlete should aim to



  • In weight-division sports, achieve the competition weight division with minimal harm to health or performance
  • “Fuel up” adequately prior to an event; consume carbohydrate and achieve exercise taper during the day(s) prior to the event according to the importance and duration of the event; and utilize carbohydrate-loading strategies when appropriate before events of greater than 90-minute duration
  • Use opportunities to drink before and during the event to minimize dehydration by replacing most of the sweat losses, but without drinking in excess of sweat losses
  • Consume carbohydrates during events >1 hour in duration with a sliding scale of intake according to the need to prime the brain or to provide an additional source of muscle fuel.
  • Achieve pre-event and during-event eating/drinking strategies without causing gastrointestinal discomfort or upsets
  • Promote recovery after the event, particularly during multiday competitions such as tournaments and stage races

Overall



  • Make use of supplements and specialized sports foods that have been shown to enhance training goals or provide a competition performance gain after considering the potential risks associated with their use
  • Eat for long-term health by paying attention to community nutrition guidelines
  • Continue to enjoy food and the pleasure of sharing meals

Can research on male athletes be applied to females?


Expert groups that develop sports nutrition guidelines typically make universal recommendations without specific adjustment for the sex of the individual athlete. The absence of sex-specific guidelines could mean that females do not have special considerations regarding exercise metabolism or nutritional requirements for sport. Alternatively, it could mean that there is no information on which the effect of sex can be based. It is of importance to differentiate between these two options since the absence of evidence for an effect is not the same as evidence for the absence of an effect. Three broad categories of studies would be useful in either confirming the suitability of present sports nutrition guidelines or developing separate recommendations for female athletes: (i) studies in which female subjects have been included within the group outcomes without distinguishing any differences based on sex; (ii) studies that focus on female subjects alone, and (iii) research in which direct comparisons have been made between the response of male and female subjects to a sports nutrition intervention. It is clear, notwithstanding the difficulties of undertaking such research, that these types of studies are under-represented in the literature and should be encouraged.


There are several issues that might explain or call for differences in recommendations for sports nutrition for female athletes. The first is the different hormonal environment and its changes over the menstrual cycle experienced by females. The small number of factors in which this has been investigated in terms of exercise metabolism (e.g., protein synthesis and carbohydrate metabolism) suggests that such differences, if they occur, are sufficiently subtle that they do not merit separate recommendations in terms of sports nutritional strategies. The second issue is the smaller body size or muscle mass of females. This issue is covered to some extent in that old sports nutrition recommendations for absolute nutrient amounts have been replaced with targets expressed relative to body mass (e.g., carbohydrate intake) or in terms of developing an individualized and tolerated plan (e.g., fluid intake during exercise). A final consideration is the observation that many female athletes consume diets that are low in energy availability; apart from impairing health and function, this can indirectly alter nutritional requirements.


Low energy availability


An inadequate intake of energy in relation to the energy cost of exercise prevents the body from having sufficient energy to fuel the functions underpinning optimal health and performance. This situation, termed low energy availability, is frequently observed among female athletes related to their management of optimal body mass/physique. However, it can also occur when appetite or opportunities to consume food fail to adapt to an increase in training/competition load. The chapter on the female athlete triad (Chapter 9) describes the causes and outcomes of this syndrome in more detail. Here, we will quickly consider the effects of low energy availability on sports nutrition requirements. Although the clear objective is for female athletes to avoid scenarios of energy deficiency, there are some situations in which some reduction in energy availability may be required or tolerated. In such cases, some secondary nutritional issues should be considered.


An outcome of the reduction in energy intake below energy expenditure is an adjustment to physiological function to conserve energy and preserve against starvation. A reduction in metabolic rate ultimately reduces energy requirements, whereby in extreme cases, a female may regain energy balance (intake = expenditure) despite a low level of energy availability (where EA = intake minus the energy cost of exercise < level required for healthy function). In these cases, nutritional counseling of the female athlete may need to take into account a current energy requirement below predicted/healthy levels. A gradual intake in energy may be required to help restore energy availability, metabolic rate, and health. Even when this takes place, however, the female athlete will need to make sound dietary choices from a range of nutrient-dense foods to ensure that all requirements for micronutrients and beneficial food constituents are met from a restricted energy budget. The case for reduced EA and the protein and carbohydrate guidelines covered later in this chapter merit special comment.


Older studies of female athletes and carbohydrate loading made observations that they are less efficient at storing glycogen than their male counterparts (i.e., females store less glycogen from a given carbohydrate intake or fail to super-compensate muscle glycogen stores). More recent research has shown that this finding is related to energy deficiency and females can store glycogen effectively when they consume adequate energy intake. Alternatively, when carbohydrate intake is below the targets identified for optimal refueling, the addition of protein (∼20 g) to the meal/snack enhances glycogen storage. Meanwhile, although protein targets can be set for meals and snacks to optimize protein synthesis in response to exercise over the day, recent studies show that these targets need to be increased even when energy availability is reduced by amounts normally considered to be “safe” for weight loss (30 kcal/kg fat-free mass).


Guidelines for everyday training


Everyday eating must support the athlete’s training load and allow her to stay healthy and uninjured. The fuel cost of training varies according to the frequency, duration, and intensity of workouts, and causes a change in the athlete’s daily carbohydrate use. Sports nutrition guidelines have changed from recommending that all athletes consume “high carbohydrate diets” per se to considering carbohydrate intake in relation to the fuel cost of training and refueling (“carbohydrate availability”). The guidelines recommend that for days/scenarios where the training program calls for high-intensity, high-quality or technique-based workouts, athletes should consume carbohydrate over the day and in relation to the workout to provide high carbohydrate availability (carbohydrate targets met). General targets have been set (Table 4.2) but need to be individualized according to the athlete, her energy budget, and feedback from training outcomes and long-term performance gains. Meanwhile, in other scenarios, carbohydrate availability may not be crucial for training outcomes, and the athlete can allow carbohydrate intake to be below theoretical exercise costs. In fact, there are even potential advantages to periodizing training to include some sessions involving low carbohydrate availability (training after an overnight fast, training with low glycogen stores, etc.) to promote a greater training stimulatory response.


Table 4.2 Carbohydrate intake targets for athletes


Muscle protein synthesis is a desired response to an exercise session, with the specific stimulus of training targeting specific increases in protein types. There is a greater increase in myofibrillar proteins in response to resistance training, while endurance athletes are interested in an increase in the mitochondrial or sarcolemmal proteins that underpin metabolic goals. Insights from the latest protein research have moved guidelines away from a focus on over daily protein intake targets or the concept of nitrogen balance, to targets for chronically maximizing the protein synthetic response to training or competition. Although the period immediately after key exercise sessions is an important time to consume protein for this purpose, it is also important to consume protein over the next 24–48 hours to take advantage of the long stimulatory response to a workout. The new guidelines promote an intake of ∼20 g (perhaps 15–30 g depending on body size, with the high-end of this range being required when in lower energy availability) of high-quality protein soon after exercise and at meals/snacks every 3–4 hours over the day. A protein-rich snack prior to bed will also assist with overnight protein synthesis. Lean meats, eggs, and low-fat dairy products provide a good source of such protein, as well as other micronutrients such as iron and calcium that can be in short supply in the diets of many female athletes. Vegetarian protein sources (e.g., soy milk, tofu, beans, and lentils) are typically limiting in some of the essential amino acids, but mixing and matching these sources together, or adding dairy or eggs in the case of lacto-ovo-vegetarians, will enhance the protein quality of the meal.

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Jul 18, 2016 | Posted by in SPORT MEDICINE | Comments Off on Nutritional guidelines for female athletes
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