Nutrition for Female Athletes

Note: Some sections of the following work are excerpted from the book “The New Power Eating” by Susan Kleiner, PhD, RD, with Maggie Greenwood-Robinson (Human Kinetics, Champaign, IL), publishing in September.

There is a host of inadequacies and inaccuracies surrounding the practice of female-athlete fueling. While women and girls make up 50 percent of all sports participants only a third of all subjects in exercise science studies are female — and that percentage is likely smaller in the narrower focus of sports nutrition. This lack of research has led to inadequate nutritional recommendations and guidelines and has allowed biased marketers to drive the narrative on the dietary needs of active women and girls. While I am no longer an academic researcher, it is my hope that my voice and my pen (or keyboard) will elevate the call for more female-centric research. It is a wide-open area of opportunity.

The other way that I try to drive a wedge between marketing mumbo jumbo and evidence-based practice is by working directly with women and girls in sport on nutrition for female athletes. Based on my experiences and the growing available data, I’ve formulated models for their macro- and micronutrient needs, determined how to fuel them for training without causing gastrointestinal distress, and developed nutrition plans to meet both their performance and aesthetic goals. (You can find those models in The New Power Eating at http://www.humankinetics.com/products/all-products/New-Power-Eating-The)

The first step in coming up with a nutrition plan for female athletes is calculating their fueling needs correctly. In the past, this was done by determining energy balance—the point at which energy expenditure equals calorie input. However, being in energy balance does not always reflect an optimal state. For instance, if a female athlete has low calorie intake, she will have low energy output. Although she is in energy balance, it does not reflect her potential peak output—if she increased her caloric intake, she’d be able to expend more energy. Since our culture often tells women that less is better, energy balance is not a useful concept.

Instead, energy availability (EA) is the preferred method of calculating fueling needs. In addition to factoring in calorie input and energy output, it accounts for the calories needed to maintain fundamental physiological processes. It is expressed as: dietary energy intake (EI) – energy expended in exercise (EEE), normalized for fat free mass (kg FFM), using the leftover calories to support life processes. To obtain optimal energy availability, female athletes should take in at least 45 calories per kilogram of fat-free mass per day, and no less than 30 calories per kilogram of fat-free mass per day, at an absolute minimum.

EA = EI – EEE
Kg FFM

When female athletes’ diets are assessed by percent of total calories from macronutrients like carbohydrates, protein, and fat, the carbohydrate intake will often appear high. Yet because total energy consumption is commonly low in female athletes, their absolute carbohydrate consumption may also be low. In fact, when it comes to macronutrient needs, the largest gap in female athletes’ diets is usually carbohydrate fuel.

To address this, they should consume five to six grams of carbohydrate per kilogram of bodyweight per day when participating in moderate-intensity (off-season maintenance) training and seven to 12 grams per kilogram of bodyweight per day for high-intensity work. The carbohydrate should come from a variety of nutrient-dense sources, such as starchy vegetables, fruits, whole grains, beans, and dairy.

Whenever possible, recommendations for carbohydrate consumption may change based on what phase of the menstrual cycle a female athlete is in. In particular, during the luteal phase—which begins after ovulation, lasts about 14 days (unless fertilization occurs), and ends just before a menstrual period—studies have shown that carbohydrate oxidation is reduced at rest and at moderate-intensity exercise levels. So there may be a reduced need for carbohydrate intake during rest days and steady-state training days in this phase.

Protein needs are also linked to energy availability for female athletes. When energy levels are high, protein is used primarily for physiological functions that require nitrogen, such as the structure, function, and regulation of the body’s tissues and organs. During periods of low energy availability, protein is used to meet energy needs by removing and excreting nitrogen as urea from the urinary tract, and when a female athlete is in an energy deficit, protein needs increase to fulfill energy requirements.

The balance needed between protein, carbohydrate, and energy availability is particularly profound for women in sport because female reproductive hormones are linked to the metabolic pathway. When energy and/or carbohydrate and protein intakes are deficient, reproductive function declines. This has a domino effect on overall health, leading to diminished thyroid function, bone mineral metabolism, immune function, gastrointestinal function, and maintenance of body tissues and organs. Ultimately physical performance declines.

To maintain adequate protein levels, female athletes should take in high-performance, nutrient-dense sources of protein such as meat, fish and seafood, eggs, dairy, vegetable proteins, grains, beans, nuts, and seeds. However, it is very difficult for women and girls in sport to eat enough to fully meet their daily protein needs, so the recommendations listed below have a built-in margin of safety to account for the likelihood that energy consumption will often, if not always, be insufficient. When athletes are in energy deficit, increase protein intake by 10 percent:

• Endurance athlete: 1.4 to 1.6 grams per kilogram of bodyweight
• Strength athlete in a maintenance phase: 1.4 to 1.6 grams per kilogram of bodyweight
• Strength athlete in a building phase: 1.8 to 2.0 grams per kilogram of bodyweight

Female athletes need fat to support conditioning, recovery, tissue growth, and joint mobility, as well as immune, reproductive, endocrine, and nervous system functions. Fat intake should comprise 25 to 35 percent of their total daily energy intake, and female athletes should stick to “high-performance” fats, such as those found in fatty fish, nuts and seeds, nut and seed butters, avocados, olives, extra virgin olive oil, and other vegetable oils.

Regarding micronutrient needs, decades of research have shown that female athletes are at a high risk of iron deficiency. They also frequently lack in calcium and vitamin D. All of these factors will impact their performance and overall health.

The best food sources of iron are dark meats and oysters, while calcium can be found in dairy products. Green, leafy vegetables are great sources for both iron and calcium. For vitamin D, being out in the sun with face, arms and legs exposed without sunscreen for 15 minutes between the months of April to September can help address the deficiency, as well as consuming fortified dairy products and fatty fish. Additionally, to ensure micronutrient needs are met, it may be a good idea to supplement female athletes’ diets with 18 mg iron, 1,000 mg calcium, and 2,000 IU vitamin D per day (can be lowered with sun exposure during summer months).

Structuring a day’s worth of food for women and girls in sport should focus on eating a plant-rich diet, with plenty of vegetables, fruits, grains, beans, nuts, and seeds. Each meal should contain two or more servings of plant foods, one to two servings of high-performance fats, and one serving of a protein-rich food. I encourage two to three dairy servings throughout the day, especially following training to enhance rehydration and recovery.

Finally, female athletes will need to consume snacks between meals to maintain optimal nutrient and energy levels. A good snack combines foods rich in carbohydrate, protein, and fat. Pre-workout snacks should be very low in fat and moderate in protein to allow the stomach to empty quickly.