Sports Nutrition Needs for Female Athletes
One of the most underrepresented factors in sports nutrition is anatomical sex. However, research has only recently brought this to light. Much of the previous sports nutrition research has been conducted on males and has assumed that the nutritional requirements of females and males are the same. Studies by the International Society of Sports Nutrition in the last few decades have highlighted distinct metabolic and nutritional needs between the sexes. This work is critical to ensuring every athlete receives his or her exact nutritional needs, especially during high-performance activities. Here we’ll focus on filling in some gaps in understanding how women’s nutritional needs differ from men’s.
Note: This article focuses on the different nutritional needs according to a person’s anatomical sex assigned at birth. Acknowledging that an individual’s gender identity may differ from their assigned sex at birth, this discussion will center around the ways that sex and the physiological differences of the male and female anatomy, regardless of gender identity, influence nutrition.
Physiological Differences Between Males and Females Dictate Nutritional Needs
A key driver of nutritional variances between male and female athletes lies in physiological differences, particularly sex hormones. For instance, estradiol, one of the estrogen hormones, affects the way females store, break down, and distribute carbohydrates throughout the body. The differences in estradiol levels between females and males are one driver that distinguishes the energy intake and use in women from men. Understanding these hormonal influences is crucial, especially as they fluctuate throughout the female menstrual cycle, impacting women’s nutritional needs for exercise performance throughout the month.
For decades, the discipline of nutritional science assumed that the nutritional requirements of women and men were the same and the menstrual cycle was often overlooked in this. However, studies in the last few decades have shed light on the possible distinctions between the genders in terms of caloric intake, energy usage, and nutrient distribution during intense exercise.
Women may not benefit from “carbo-loading” in the way men do
Many athletes engage in a process known as glycogen loading, or “carbo-loading,” prior to intense exercise. This approach involves consuming a diet where approximately 70% of calories come from carbohydrates. Carbo-loading works by increasing the amount of glycogen available in the muscles. In brief, carbohydrate intake signals insulin release from the pancreas into circulation, which promotes glucose transport into the skeletal muscle. The increased levels of glucose in the muscles translates to improved speed and endurance, as evidenced by a study in hockey players. However, research indicates that carbo-loading might not work as well for women as it does for men.
Women generally experience a slower rate of glucose release compared to men, coupled with a higher sensitivity to insulin in their skeletal muscles. Unlike men, women don’t show significant variations in the level of glycogen stored in their muscles. Studies have shown that while carbohydrate loading enhances muscle glycogen levels in men, it doesn’t necessarily lead to similar increases in muscle glycogen or performance improvements in women. This suggests that carbohydrate intake strategies might need to be altered for female athletes.
Furthermore, it’s been found that women tend to have a heightened sensitivity to insulin in their skeletal muscles and are less inclined to oxidize carbohydrates compared to men. During endurance activities, such as marathons, the rate at which glucose becomes available is lower in women than in men.
While one study indicated that carbohydrate loading significantly boosted muscle glycogen levels in men but not in women, there is an ongoing debate in the scientific community regarding these gender differences in glycogen utilization and storage. This is partly because studies on carbohydrate loading vary in their methods and how they report their findings.
Men and women differ in fat, amino acid, and protein needs
Females appear to break down fats more readily during exercise than males. While females use fat to fuel their exercise, men use predominantly amino acids (protein) and carbohydrates. Perhaps that’s because women have a higher lipid content in the muscle compared to men. One study on cycling showed that women derived more energy from fat whereas men derived more energy from carbohydrates. Whereas women use fat to fuel muscles, men have 25% more muscle glycogen utilization than women, demonstrating their use of carbohydrates to fuel their exercise.
Additionally, the bodies of women use fewer amino acids and proteins as a source of energy than men. In particular, the amino acid leucine is more readily broken down by males than females during intensive exercise. This points to differences in the protein needs of males versus females. Elite male athletes require 100% more protein than sedentary males, while elite female athletes require only 50 to 60% more protein compared to sedentary females.
Navigating the Menstrual Cycle in Sports Nutrition
The female menstrual cycle heavily influences nutritional requirements, especially for athletes. Unlike males, whose nutritional needs for athletic performance are relatively stable, females experience significant physiological changes throughout their menstrual cycle, necessitating adjustments in their nutrition plan. As a reminder, the menstrual cycle is marked by menstruation, the follicular phase, ovulation, and the luteal phase.
The Luteal Phase: requires increased protein, fat, calorie, and water intake
The luteal phase of the menstrual cycle begins with the end of ovulation and refers to the time when the egg leaves the ovary and travels to the uterus via the fallopian tubes. This is the last phase of the cycle before menstruation. On average, females expend more energy during the luteal phase of the menstrual cycle and therefore should increase their caloric intake to account for this. Protein metabolism and fat burning are also high during the luteal phase, suggesting that females should increase their protein and fat intake during this time.
Consider eating lean protein like chicken or beans and health fats like fish, olive oil, and avocado. Further, body temperatures often increase during the luteal phase and can lead to more sweat loss during exercise. To counteract this, be sure to stay hydrated.
The Follicular Phase: increases muscle soreness and slows muscle recovery
The follicular phase is marked by the start of menstruation and ends with the beginning of ovulation. In contrast to the luteal phase, the follicular phase is characterized by low levels of estrogen and progesterone. Estrogen is believed to have a protective effect against muscle damage. So, some females may feel increased muscle soreness and longer recovery times during this time when estrogen levels are low.
One study in runners found that women in the early and late follicular phase of menstruation had slower muscle recovery than men or women in other stages of the menstrual cycle. Another study has shown increased muscle soreness during the early follicular phase. Consequently, it’s essential to pay extra attention to recovery strategies and nutritional support during this phase of the menstrual cycle.
For this reason, antioxidant foods like berries and green tea may help with muscle soreness and recovery during the follicular phase, however no studies have confirmed this hypothesis.
Iron and Creatine as Important Supplementation for Female Athletes
Recently, the International Society for Sports Nutrition has published a position on nutritional concerns for female athletes. In particular, the position indicates that iron and creatine have shown the most evidence for the benefits of supplementation.
Iron supplementation in counteracting iron deficiency in female athletes
As we’ve discussed before on the blog, iron is crucial to athletic performance, but maintaining optimal iron levels is particularly challenging for female athletes. One reason is that blood is lost during the menstrual cycle, but another is that iron absorption and regulation are affected by the menstrual cycle.
In short, as female hormone concentrations change across the menstrual cycle, they alter iron absorption and utilization. Research has shown that iron supplementation can help maintain active females’ iron levels and it’s best to take iron supplements weekly rather than just during the menstruation phase.
Creatine supplementation may curb exercise fatigue
The position paper also touts creatine for its strength, energy, and cognitive benefits. Creatine has been used as a sports nutrition supplement since the 1990s, having demonstrated benefits in exercise performance. Its effects stem from the need for creatine to convert ADP to ATP in the muscles to create energetic movement.
One study conducted by Dr. Abbie Smith-Ryan at the University of North Carolina showed that creatine may reduce fatigue in women. Specifically, the study found that women often experience higher levels of fatigue just after ovulation. Creatine supplementation at this phase of the menstrual cycle may yield the greatest benefit in fighting off exercise fatigue.
Although there are many factors that influence the nutritional needs of each individual, such as genetics, the environment, the gut microbiome, activity level, and metabolism, sex is a major component of the equation that shouldn’t be overlooked. As such, it is good practice to consider sex as a dimension of a person’s physiological make-up when evaluating optimal nutritional intake for high performance sports.