Protein requirements for female athletes

Are protein requirements for female athletes the same than those of male athletes? Although it makes sense to think that body composition, energy metabolism and sex hormones may play a role in nutrient requirements, there are no fast and hard rules, but sensible guidelines as detailed below.

Protein requirements for female athletes

In theory, female athletes should have slightly lower protein requirements than their male counterparts because oestrogen causes exercising female bodies to increase fatty acid oxidation and decrease amino acid (and carbohydrate) oxidation (1, 2). Moreover, protein catabolism is higher in the luteal phase when oestrogen and progesterone are high (1).

On the other hand, some studies seem to indicate that rates of muscle protein synthesis and balance do not differ a whole lot between young females and males (4).

It is unclear how fluctuations in female hormones during the menstrual cycle nor the use of hormonal contraceptives affect protein balance (1).

Timing of protein intake

The information below refers to all athletes as there is no evidence to show the female body reacts differently to specific protein timings.

Pre-exercise

If the exercise session is shorter than 1 hour, then consuming protein before exercise can make the amino acids available to be used after the session for muscle growth/repair (3).

During exercise

Protein intake during exercise does not act on protein synthesis (3, 4). Therefore, consuming protein during exercise only makes sense for athletes participating in long sessions (e.g. lasting more than 90 minutes) or multiple sessions per day (3).

Post-exercise

The anabolic window which was thought to be as narrow as 30 minutes post-exercise can actually last for several hours (4) and up to 24-48 hours after an exercise session (3). This window tends to be larger when the exercising person is a young male and when exercise intensity is high (4). However, it is true that the ability of the body to build muscle is optimised immediately post-exercise (3, 4). This is especially important in trained athletes, who should take advantage of this heightened anabolic state by consuming a post-workout meal containing adequate protein (3).

Pre-bed

Because the body tends to be in a catabolic state during sleep, athletes looking to maximise muscle protein gains should eat a larger dose (e.g. 0.5 g/kg) of protein before going to bed (3).

How much?

Even though there is no consensus regarding differences in protein requirements between female and male athletes, there is some gender-specific literature worth considering.

Non-gender specific

• Per-meal: 0.25-0.30 g/kg/meal seems to be the optimal dose to stimulate muscle protein synthesis both post-exercise and when not exercising (3, 4).
• Per day: 1.2-2 g/kg/day (1).

Notes:

• During energy restriction, higher protein intakes (0.3-0.4 g/kg/meal) are recommended to enhance muscle protein synthesis (3).
• Protein requirements seem to be similar for aerobic and resistance exercise (3).

Female-specific

• Per meal: 0.32-0.38 g/kg post-exercise supports muscle synthesis, maximal strength and lean mass (1).
• Per day:
  

  Type of exercise	EAR (g/kg/day)	RDI (g/kg/day)
  Aerobic endurance	1.28-1.63	1.59-2.02
  Resistance	1.49	1.85
  Intermittent	1.41	1.75 (1)

Notes:

• The estimated average requirement (EAR) is meant to be optimal for about 50% of female athletes, while the recommended dietary intake (RDI) is meant to cover 97% of that population.
• With resistance exercise, there is evidence that larger doses (e.g. 2.5 g/kg/day) can increase fat-free mass more than lower doses (1).
• In female athletes following a 16:8 time-restricting feeding pattern, a dose of 1.6 g/kg/day has not be shown to have detrimental effects in strength, endurance or fat-free mass (1).

How often?

Hitting the optimal dose every 3-4 hours during the 12 hours after exercise seems to be more effective than hitting smaller doses more frequently or larger doses less frequently (3, 1).

What type of protein?

Proteins with higher content of essential amino acids histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine), especially leucine, seem to be the best to stimulate muscle protein synthesis (3).

Whey seems to be superior to casein and soy protein due to its high essential amino acid and leucine content. The high leucine component stimulates the mTOR anabolic pathway. Whey may also have beneficial effects in immune function and gut health (4).

However, other scientists have found no difference in maximal strength or body composition post-consumption of whey vs casein (1).

Most studies use protein supplements with high biological value (e.g. whey) so it’s safe to assume that requirements are higher for athletes consuming protein with lower biological value (e.g. plant-based) (1, 3).

Factors affecting protein requirements

The following factors may increase protein requirements:

• Higher exercise intensity, longer exercise duration or higher training load
• Higher habitual protein intake
• Energy restriction (e.g. when making weight) (1)

The following factors may decrease protein requirements:

• Highly training status
• Potentially, the menstrual cycle phase (1)

References

1. Mercer D, Convit L, Condo D, Carr AJ, Hamilton DL, Slater G, et al. Protein Requirements of Pre-Menopausal Female Athletes: Systematic Literature Review. Vol. 12, Nutrients. 2020.
2. Desbrow B, Burd NA, Tarnopolsky M, Moore DR, Elliott-Sale KJ. Nutrition for Special Populations: Young, Female, and Masters Athletes. Int J Sport Nutr Exerc Metab [Internet]. 2019;29(2):220–7.
3. Burke, Louise. Clinical Sports Nutrition, 5th Edition. McGraw-Hill Australia, 09/2015. VitalBook file.
4. Poortmans JR, Carpentier A, Pereira-Lancha LO, Lancha AJ. Protein turnover, amino acid requirements and recommendations for athletes and active populations. Brazilian J Med Biol Res = Rev Bras Pesqui medicas e Biol. 2012 Oct;45(10):875–90.

[Photo by Jeffrey F Lin on Unsplash]

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