Nearly 50% of sports participants are female. But less than 10% of research in sport is about the female athlete. From carb loading to creatine supplementation, the guidance is based on male bodies. It begs the question: if you were offered a performance-enhancing substance that had never been tested for your body, would you take it?
In a recent paper published in the International Journal of Sports Medicine, Dr Kathryn Ackerman and Bryan Holtzman presented the most up-to-date knowledge and recommendations on nutrition for female athletes. Never mind marginal performance gains – this paper shows that we have barely covered the basics for female athletes. (The paper, titled Recommendations and Nutritional Considerations for Female Athletes: Health and Performance, is available here). 
In this article, we unpick the key points with Ackerman and speak with Trek-Segafredo professional cyclist Leah Thomas about how she fuels for both health and performance.
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Recommendation 1: Fuel, fuel, fuel
Female cyclists should aim for energy availability (EA) of 45kcal/kg of fat-free mass [the weight of muscles, bones and body mass that isn't fat] each day for optimal health and performance; optimising nutrient composition based on menstrual cycle phase is ineffective without the requisite energy for basic functioning.
“The most basic need for endurance athletes is energy availability (EA),” explains Ackerman. “If you’re worrying about beetroot juice before you’re worried about getting enough calories in, you’re missing the point.”
Ackerman advises eating regularly and planning your calorie intake for big training days. “When an athlete is doing huge volume, their hunger cues might not get them enough calories to make up for the energy expended. Someone doing a five-hour ride needs to fuel the entire time – not just at the end. It’s going to be hard for them to make up the nutritional deficit in one sitting right after the ride.”
“At the same time,” Ackerman continues, “the standard guidance for carb loading can be inappropriate for female cyclists because they generally have a lower caloric intake compared to male athletes.” (Equal to or greater than 8g per kg bodyweight per day.) “Imagine that you have a 60kg endurance athlete who consumes 2,000cals per day. The standard guidance means that 96% of her total caloric consumption is carbohydrate. That’s unrealistic. So when we make statements like ‘you have to carb load’ we have to consider what it looks like in practice.”
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For Leah Thomas, a professional cyclist in a Women’s WorldTour team, her knowledge and experience about fuelling has grown over time. “When I first started, I didn’t eat enough on the bike while I was training and probably not enough after training, either. I used to think that at the end of a long ride I was supposed to feel exhausted and dead because it’s the end of a long ride. I just didn’t have the background or the knowledge.”
Despite a late start in the sport, Thomas more than compensated for it with a desire to learn and improve. (Thomas had an initial career as a middle-school teacher.) These days, Thomas tracks what she eats to make sure that she is eating enough food. “Often, I just don’t feel like I want to be eating anymore,” she explains. “But I know that if I get those nutrients in, I feel much better the next day to be able to do another workout.”
Recommendation 2: Sweat the small things
Micronutrient deficiencies are common in female athletes, particularly iron, vitamin D and calcium. Nutritional strategies should be used to prevent these deficiencies, including increasing consumption of diverse foods and potential supplementation.
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Once you cover the base of your nutritional pyramid, it’s time to start sweating the small things – micronutrients. “Any endurance athlete is susceptible to iron deficiency,” explains Ackerman. “But a female who menstruates has an additional risk of deficiency because she loses blood every month.” Studies suggest that between 25% and 50% of female athletes experience iron deficiency. “Any woman doing a lot of endurance work should test annually for ferritin levels.”
What practical action can female athletes take?
“Endurance athletes need to eat a variety of iron-rich foods rather than leaning on supplements alone,” advises Ackerman. “Even cooking in an iron-clad pan allows for some iron to be absorbed into the food.”
“Vitamin D can be harder to get just through the diet, especially for people living in the UK and other countries where sunshine isn’t plentiful,” continues Ackerman. “We recommend a vitamin-D supplement. Calcium, on the other hand, can be obtained through different foods in the diet. But we only absorb 500mg at a time, so it’s best to spread intake throughout the day.”
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Recommendation 3: Pay attention to your hormones
Micro and macronutrient requirements, as well as hydration needs, may change during various phases of the menstrual cycle as a result of hormonal fluctuations.
“Female athlete monthly hormonal cycles, with fluctuations in oestrogen and progesterone, have varying effects on metabolism and fluid retention,” explains Ackerman. “We do think that there’s probably an opportunity to take advantage of the menstrual cycle for training for performance. But first of all, we need women to 1) track their menstrual cycle, 2) make sure they’re having a menstrual cycle and 3) see how they feel during those different phases, because each woman will experience it differently.” 
“For example, when oestrogen levels are lower, you should be feeling great,” adds Ackerman. “But low oestrogen coincides with a period, when you might also get a lot of cramping and really heavy bleeding. So it’s not just the hormones, it’s understanding all the other things going on.”
The advice is clear – all female athletes need to pay close attention to their hormones. If something changes or your cycle disappears, take it seriously – it could signify a deficiency in energy or in micronutrients. Missing cycles is not “normal for an athlete”.
Putting it into practice and investing in your future
“If someone is spending this much time on training and doing this much thinking about what they’re putting in their body, it’s not too much to spend a little money to go and see a qualified registered sports dietician,” says Ackerman. “A dietician who can talk you through these recommendations may make a huge difference.”
For pros like Thomas, having the expertise of the nutritionist and the chef is a game changer. “At races, they help me to get those nutrients that I need but also to get them in ways that are appetising,” she explains. “Whether you’re with your teammates at a race or socialising at home with your family, eating should be a celebrated thing, not just functional. I think this balance is the best way to approach nutrition.”
Ackerman and Thomas both speak of the danger of “advice pedalled by so-called “experts” on social media. “When there’s a lack of concrete knowledge, it’s easy for fads or unstudied notions to gain traction,” observes Thomas. “It’s great that there are more studies, but it’s important to sort the foundations.”
One of the major reasons for the paucity of female athlete research is the complexity of the female body – researchers need to work hard to control for the menstrual cycle. This costs money and it’s challenging. If you were told to take medicine that had never been tested for your body because it was too difficult or costly to test, would you accept that? So why should female cyclists be any different? Putting female athlete research in the ‘too difficult’ box is no longer an acceptable option.
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“I’m excited that we will get a lot of work done in the next 20 years for the female athlete so we can provide that concrete information,” says Ackerman. “As long as we can get the funding.”
