Know-How: Protein for Women

In sports science, the participation of women in studies has been underrepresented for a long time.. The female menstrual cycle has long been considered a potential confounding factor. This neglect resulted in training and nutrition recommendations often being based on the needs of young men. However, research increasingly recognizes the importance of integrating female athletes, as significant differences exist in physiology and nutritional needs.

A thorough understanding of the physiological differences between men and women is crucial for developing optimal nutrition strategies for various athletic goals. There are significant gender-specific differences in substrate utilization, thermoregulation, fatigue, muscle soreness and recovery, as well as body composition. Before puberty, men and women exhibit similar metabolic patterns; however, estrogen plays a significant role in fat metabolism in adulthood.

After entering puberty and with sufficient calorie intake, women experience regular menstrual cycles, consisting oftwo main phases: the follicular phase and the luteal phase. Menstruation marks the beginning of the follicular phase, during which hormones such as estrogen, progesterone, FSH, and LH are at their lowest levels. In the middle of the follicular phase, estrogen and FSH levels rise to prepare the body for ovulation. After ovulation, the luteal phase begins, during which progesterone and estrogen reach their peak levels. In the absence of pregnancy, hormone levels return to baseline, and menstruation begins again.

These cyclic changes influence the metabolism and performance of women throughout the entire menstrual cycle. Estrogen, as the main regulator of body composition and bioenergetics, undergoes cyclic fluctuations and may influence energy expenditure and food intake. During resting periods, women exhibit increased fat and protein oxidation during the luteal phase, accompanied by higher energy expenditure and potentially increased appetite.

Scientific sources:

• Holtzmann, B. & Ackerman, K.E. (2021). Recommendations and Nutritional Considerations for Female Athletes: Health and Performance. Sports Medicine, 51 (Suppl 1):S43–S57
• Kuo, Y. et al (2022). Effect of Whey Protein Supplementation in Postmenopausal Women: A Systematic Review and Meta-Analysis. Nutrients, 14, 4210.
• Wohlgemuth, K.J. et al. (2021). Sex differences and considerations for female specific nutritional strategies: a narrative review. Journal of the International Society of Sports Nutrition, 18:27

The importance of protein for women is a topic of growing scientific interest, as it becomes increasingly clear that the protein needs of women are often overlooked. In comparison to men, women typically have lower muscle mass and may therefore not engage in as much strength training as men. This is partly because women experience fluctuations in their hormone levels during their menstrual cycle, which can affect their training ability.

The menstrual cycle consists of two main phases: the follicular phase and the luteal phase.. During the follicular phase, the body prepares for ovulation, while during the luteal phase, the uterine lining thickens in preparation for a potential pregnancy. During the luteal phase, the progesterone level rises, leading to increased protein oxidation and thus increasing the need for protein.

Studies have shown that women indeed have ahigher need for protein than previously assumed. This is partly because women exhibit higher protein oxidation, meaning their bodies require more protein for various functions, including the maintenance of muscle mass. Nevertheless, the fact that women actually have a higher protein requirement has often been overlooked.

To achieve similar muscle gains as men, women should particularly focus on higher protein intake during the luteal phase of their menstrual cycle. During this phase, the protein requirement is highest, and the increased protein oxidation means that the body needs more protein to maintain and build muscle mass.

Particularly important amino acids for muscle protein synthesis in women are lysine and leucine. Lysine is an essential amino acid that the body cannot produce on its own and must therefore be obtained through diet. Leucine, on the other hand, is a branched-chain amino acid that plays a key role in stimulating muscle protein synthesis. Both amino acids are therefore crucial for muscle building in women.

Follicular Phase (day 1 of menstruation until ovulation)

The follicular phase of the menstrual cycle is an optimal time for women to focus on strength training . During this phase, the estrogen level, a female sex hormone, rises and exerts an anabolic (building) effect on the body. This anabolism supports muscle protein synthesis, thus creating a conducive environment for muscle building.

The increased estrogen in the follicular phase allows women to build muscle more effectively and recover faster. This makes strength training particularly advantageous during this time to leverage the hormone's positive effects on muscle mass. Through targeted strength training during the follicular phase, women can not only build their muscles more efficiently but also enhance their overall performance and well-being during exercise.

During the follicular phase, nutrition focuses on aspects that support the inflammatory response in the body and strengthen the immune system.

• More protein:In this phase, the uterine lining regenerates while at least one egg matures: proteins are particularly important for your body now. Due to the tendency for increased energy expenditure, a slightly elevated protein intake can help minimize muscle breakdown and support energy supply.
• Antioxidants: Due to the increased energy expenditure and potential inflammation, foods rich in antioxidants, such as pomegranate, can help protect the body from oxidative stress.

Luteal phase (from ovulation to menstruation)

In the luteal phase of your menstrual cycle, where the hormone progesterone is dominant, the challenge is that the body tends to be more susceptible to muscle mass breakdown. Progesterone can cause increased protein oxidation, which can lead to accelerated muscle breakdown.

During the luteal phase of the menstrual cycle, foundational training with moderate intensity can be an effective form of training. This training is characterized by moderate intensity, ensuring sustainable stress on the body without overexertion. Due to the hormonal changes in the luteal phase, especially the increased progesterone levels, it is advisable to refrain from high-intensity training. This training can accelerate muscle breakdown, which the body tends to experience during this phase.

Here are corresponding nutrition recommendations:

• Increased protein intake: Since progesterone levels rise in the luteal phase, increasing the risk of muscle breakdown, increased protein intake can support muscle regeneration. Protein with sufficient leucine and lysine is recommended.
• Antioxidants: Progesterone can lead to an increase in water retention. Foods with anti-inflammatory properties, such as turmeric, ginger, and green leafy vegetables, can help reduce water retention.
• Iron-rich foods: Due to menstrual bleeding, there is a likelihood of increased iron loss. Iron-rich foods such as meat, legumes, and green leafy vegetables should be incorporated more into the diet.

Scientific sources:

• Holtzmann, B. & Ackerman, K.E. (2021). Recommendations and Nutritional Considerations for Female Athletes: Health and Performance. Sports Medicine, 51 (Suppl 1):S43–S57
• Kuo, Y. et al (2022). Effect of Whey Protein Supplementation in Postmenopausal Women: A Systematic Review and Meta-Analysis. Nutrients, 14, 4210.
• Wohlgemuth, K.J. et al. (2021). Sex differences and considerations for female specific nutritional strategies: a narrative review. Journal of the International Society of Sports Nutrition, 18:27

Dietary protein plays a crucial role in regulating skeletal muscle mass. Adequate protein intake is crucial to ensure that muscle mass is preserved. Amino acids are crucial in this regard, especially the essential amino acid leucine.

The current recommended daily protein intake guidelines (RDA) are based on outdated methods and are often misunderstood as minimal values to prevent muscle loss. Studies suggest that the protein intake for young men is around 1.2 g/kg/day, while women may require up to 1.6 g/kg/day due to increased protein oxidation. The menstrual cycle influences protein requirements, especially during the luteal phase when protein oxidation increases.

The timing of protein intake is also important. Studies show that maximum muscle protein synthesis is achieved through an evenly distributed intake throughout the day. For women engaging in strength training, there appears to be a synergistic effect of increased protein intake along with enhanced muscle growth and strength. In endurance sports, protein intake before or after training is also beneficial.

During a calorie or energy deficit, such as during a diet, increased protein intake supports the preservation of muscle mass. Women who consume more calories from protein than from carbohydrates show a better fat-to-muscle mass ratio during weight loss. The menstrual cycle should be taken into account when assessing protein needs, and women may have an increased need for protein during the luteal phase.

It is crucial to emphasize that female athletes who are actively engaged in sports may be at an increased risk of nutrient deficiencies, especially concerning essential components such as calcium and vitamin D. These nutrients play a critical role in bone health, muscle function, immune system support, and injury prevention.

Research has shown that a considerable percentage of female athletes, including high-performance athletes, have low vitamin D levels. The overarching goal should be to aim for a 25-hydroxyvitamin D level above 50 nmol/L to effectively protect bone health.

Scientific sources:

• Holtzmann, B. & Ackerman, K.E. (2021). Recommendations and Nutritional Considerations for Female Athletes: Health and Performance. Sports Medicine, 51 (Suppl 1):S43–S57
• Kuo, Y. et al (2022). Effect of Whey Protein Supplementation in Postmenopausal Women: A Systematic Review and Meta-Analysis. Nutrients, 14, 4210.
• Wohlgemuth, K.J. et al. (2021). Sex differences and considerations for female specific nutritional strategies: a narrative review. Journal of the International Society of Sports Nutrition, 18:27