Cycle-centred fuelling: Optimising nutrition for female athletic performance

Dr Susan Kleiner, a sports nutritionist and founder of the consultancy High Performance Nutrition, has extensive experience working with elite female athletes and understands the importance of optimising female nutrition for peak athletic performance.

During a presentation on the importance of tailoring nutrition strategies for female athletes, she said: “We need convenient, supportive products that are evidence-based and meet the lifestyle needs and biology of the person taking the products.”

Female representation in research is lacking

The gender gap in research is not new. There is a long history of female participants being excluded from medical studies, and research data collected from men and being generalised to women.

Kleiner discussed the underrepresentation of females in research, saying: “Representation is dramatically lacking in exercise science in general when it comes to female participants.”

This disparity means understanding the unique nutritional needs and responses of female athletes is somewhat challenging. Kleiner said that the lack of gender-specific data impedes the development of evidence-based products and interventions tailored to women.

“When I say evidence-based, I mean that we have research data on women who exercise in the age group that is appropriate for the audience that we’re speaking to,” she added.

She pointed to statistics on published journal articles between 2014 and 2020 where just 34% of all study participants were female, and just 6% of studies included female-only study designs. The issue here, according to Kleiner, is that when you put findings from males and females together, you lose female-centric data.

“Having female-centric data is really important to me as a dietitian. It is also really hard for me to ask someone [a female client] to spend dollars on a supplement when I don’t know if it is going to work,” she said.

“Only 3% of sports nutrition products on the market today are targeting women. [...] I can tell you that in 2023, this category alone grew by more than 6%. It is the fastest-growing category across nutritional supplements today,” Kleiner added.

Female athletes are underfuelling their athletic performance

A growing body of research has highlighted the widespread issue of low energy availability (LEA) among female athletes across various sports and levels of competition.

LEA has profound implications for female athletes' health and performance.

“LEA is when you underfuel your body for the level of exercise that you do,” Kleiner said. Inadequate energy intake relative to energy expenditure can lead to LEA, compromising various physiological systems and impairing athletic performance, she added.

“Because energy metabolism works by sort of siphoning off the energy to the area of highest demand, our body will give the energy to exercise and take it away from other very important functions in the body, like your reproductive system, or your immune system, your digestive system, your musculoskeletal system, your cardiovascular system, your nervous system – all of those become underfuelled,” she said.

In the short term, athletic performance may not be impacted, as available energy is being funnelled into the exercise itself.

But, as Kleiner explained: “[Some female athletes’] careers were very short because their bodies break down – because, over time, they're going to start to lose their health.

“They fuel that high-level intensity exercise, and everything else misses out.” 

According to Kleiner, female athletes need to prioritise proper fuelling and nutrition to support the demands of training, optimal performance, and health, and mitigate the risks associated with LEA.

Energy metabolism shifts throughout the menstrual cycle

Women's hormones fluctuate throughout the month, which in turn impacts their nutritional needs. Kleiner discussed the intricate interplay between the menstrual cycle and energy metabolism in female athletes. 

“We can't talk about energy metabolism in the female body without talking about female biology,” she said.

The menstrual cycle, typically represented as a 28-day period, includes various stages that significantly impact a woman's energy needs and metabolic rate. Kleiner explained that during the late luteal phase, energy requirements increase, with the body needing up to an additional 300 calories per day due to its preparation for potential pregnancy.

If fertilisation does not occur, the cycle restarts with the early follicular phase, where hormone levels and energy needs decrease.

“We really are not small men. We really are different. And it doesn't make us abnormal. We are normal within the female gender,” she added.

Kleiner said that these hormonal fluctuations necessitate tailored nutrition strategies and research methodologies that account for the unique biology of women. Ignoring these factors leads to inadequate and irrelevant data.

Opportunities for nutrition products targeted at female athletes

There are myriad opportunities for product innovation tailored to the unique needs of female athletes.

“When it comes to R&D, the sky's the limit in optimising nutrition for female athletic performance,” Kleiner said.

There is potential for brands to develop products tailored to specific points in a woman's menstrual cycle, aligning with the growing trend of personalised nutrition.

Kleiner acknowledged that there is not enough specific data to solve individual nutrition needs definitively, but she believes there is value in cycle-tracking apps and encourages her clients to monitor their cycles to better understand and have confidence in their nutrition and performance.

“We don't really have so much data to say, ‘Yes, if you take this, it's going to solve your problems,’” she said.

“Energy needs are higher during the luteal phase,” she added, suggesting that products higher in protein and carbohydrates could be beneficial during this time.

Despite the challenges of pioneering this research, Kleiner emphasised that every brand's effort is a contribution.

“Each brand that does the research adds to the body of evidence and grows the opportunity for everyone else,” she said.

Additionally, Kleiner advocated for greater representation of women in scientific research and industry leadership roles to drive innovation and address gaps in knowledge.

By fostering diversity and inclusivity, the industry can better serve the evolving needs of female athletes and promote advancements in sports nutrition, she said.