There has been a monumental shift in the field of exercise science over the last couple of years, with more scientists and initiatives focusing on the female athlete, the importance of fueling, and the negative consequences of Relative Energy Deficiency in Sport (REDs) and low energy availability (LEA). Most recently, two different rockstar groups of scientists have published big updates in the field, outlining new diagnostic criteria for LEA and an overview on fueling strategies for the female athlete.  Over my next three articles, I will discuss each new publication and their implications in trail and ultrarunning. 

We are going to start with the overview on the current state of research and knowledge around endurance fueling and nutrition for female athletes!

Disclaimer: This article is discussed in terms of biological sex. What I mean by that is that the participants in these studies termed “female” have circulating levels of female sex hormones and were born with an assigned sex of female at birth. This is by no means meant to be exclusionary, however, due to the lack of science on the female sex alone, those who categorize outside of this “neat and tidy” box have not been studied in this space yet. Hopefully, in years to come, the scientific field will also study this area and help us provide knowledge around proper fueling techniques to everyone. This article also discusses a lot of the recommendations around the menstrual cycle, if you do not menstruate, that is okay, the general guidelines are also important to you, and it is even more crucial that you stay in tune with your body and on top of your nutrition!

The review titled “International society of sports nutrition position stand: nutritional concerns of the female athlete” was published in May with lead author Stacy Simms (2). It is quite long, reads well, and has over 300 citations. You can read it here, and/or read my summary of their review below!

First things first

Before diving into the nitty gritty of specific nutrients, blood levels, hormones, and metabolic needs, the authors discuss the general need for athletes to meet energy demands. I’ve said it before, and I’ll say it again: 

Eat enough, always. 

Prioritizing enough calories is way more important than finessing the type of calories for most athletes. Suffering from chronic inadequate energy intake has a lot of negative health outcomes (we will discuss updates in this space in the next article!). Fueling enough will help you handle your training load, recover, get faster, and decrease your risk of injury. The list goes on. In females this is extra important because estrogen (one of our major sex hormones) regulates metabolism and food intake. In states of LEA (a state where we are chronically not matching our energy demands with energy intake intentionally or not), estrogen can become so low that this system gets messed up and we can feel extremely out of touch with our hunger cues and metabolism, further perpetuating the symptoms of LEA. Low energy availability can manifest after as little as five days of inadequate carbohydrate ingestion, so it is especially important to consistently attempt to fuel enough.

One newer development, related to menstruating females, is growing evidence that shows our energy demands may increase during the luteal phase. Obviously, the actual degree of increase is individual, but, if you find yourself really craving extra calories during that time of the month, it’s OKAY to lean into them. Your body is telling you that it needs more, your metabolism is literally increased during this period. Sometimes when we are in a state of LEA, our menstrual cycle will become erratic or disappear completely, this should be a red flag, not a badge of honor.  One thing to note for those who do not menstruate or who are currently on a form of birth control that impacts the bleeding portion of their period, early warning signs of LEA may be trickier to spot. Paying extra attention to other markers like sleep quality, irritability, sex drive, and performance metrics are of utmost importance to all athletes, but specifically those on contraceptives.

For those of us who just can’t seem to keep the luteal and follicular phase straight, I’ve added in a very tidy visual thanks to the team over at Clue. 

When is fueling most important?

Okay, so what about the nitty gritty? How do the female sex hormones specifically impact nutrient absorption and metabolism? Is it true that we are better fat utilizers? Do we have to fuel differently during different phases of the menstrual cycle? During or after menopause? I’m going to attempt to answer these tricky questions with the limited research that is out there by offering summaries of the current data and areas of opportunity. I’ll break it down into the phases of a run: “Before the run, during the run, and after the run.” 

Fueling before the run 

For years, I didn’t fuel before my runs. I’m sure a lot of you can relate, or currently do the same.  It’s easy to wake up, chug a coffee, and get out the door, and for some of us, this is probably all that seems practical. I want to challenge you to sneak in time for even the smallest breakfast, especially one with easily digestible carbohydrates (think a banana). Even something small will help mitigate many of the potential negative impacts you may experience later due to running fasted. 

Due to the wide stream impacts of circulating female sex hormones, specifically estrogen, females may be better adapted for oxidizing more lipids and less carbohydrates compared to their male counterparts. However, this is primarily at submaximal intensities and is different for everyone. This does not mean we should all strive to eat as little carbohydrates as possible; it just means that we can also utilize our fat stores to produce energy during low intensity activities.

Progesterone (a sex hormone that is highest during the luteal phase) impacts protein metabolism and glycogen storage, increasing protein demands and decreasing glycogen (sugar) storage in the skeletal muscles. This helps explain why during the luteal phase, you may need to increase total carbohydrate ingestion over many days, because your storage is impaired, and makes short term carbohydrate loading less effective. However, in the follicular phase, carbohydrate loading (hello extra serving of pasta/oatmeal/pizza) may be more beneficial due to the decrease in progesterone. This all points to the importance of starting your runs with adequate carbohydrate storage – easiest done by eating carbohydrates before exercise.  Since there is limited research on birth control users and menopausal females, it is safe to say that we should all strive to start our runs in a non-fasted state.

Fueling during the run

We all know fueling during our crazy ultra-events is important, despite this only recently have there been some studies in this area, and there are still hardly any studies conducted on females in this space. Fueling at a consistent rate (roughly 30-60g of CHO / hour) may be beneficial at maintaining glucose levels and encouraging utilization of carbohydrates in females during exercise, with more benefits at the 60g of CHO/hour mark. There are currently athletes aiming for 90-100g CHO/hour racing on the trails. Again there haven’t been many studies looking at how menstrual cycle, hormone level, menopause, or birth control impact response to fueling during exercise, so for now practice through all phases and take notes on what works for you. Practicing fueling will only make eating during training and racing easier, and should result in less of those dreaded GI issues that plague many runners.

Speaking of GI distress, can we talk about period poops? Yeah, I said it. And for all of you nodding along, you get it.  Turns out this is common, with some females more likely to experience stomach trouble around their period.  I recommend taking notes around this time of your cycle to try and see what types of foods, life stressors, and time of day trigger your worst response, and try to avoid those things.  For those of you who do not menstruate, or are currently in your menopause years, this trick can also be helpful at figuring out how to keep your gut happy.

Fueling after the run

I have been having a conversation with a lot of my athletes lately around the importance of post-run fueling. It can become an easy part of your post-run routine, and a great way to kick start recovery, even on super busy days where every spare minute is cherished. Most sports recovery beverages contain a 3:1 ratio of carbohydrates to proteins to optimize recovery. It is important to remember that your body needs more than just protein to recover. Carbohydrate ingestion after exercise helps restore glycogen in the muscles that you used up during the activity so you can be ready to go again.

When thinking about your immediate post-run snack. The research recommends that female athletes should seek to consume around 1.2 g/kg of carbohydrate (i.e. if you weigh roughly 60kg, this would be around 72g CHO). While this may seem like a lot most sports recovery products have at least 30g of CHO per serving, so you can get this in rather quickly. Something is also always better than nothing, so don’t stress over numbers too much. For our menopausal cohort, this fueling window is extra important to maximize muscle repair and recovery. Delaying our carbohydrate ingestion post exercise may lead to increased circulating cortisol throughout the day which can impair our ability to repair and recover.

What about the protein?  I emphasized carbohydrates initially because I think it is often overlooked when considering post-run recovery. However, protein is still important for female athletes, menstruating females, and menopausal females, really everyone! Most post-exercise drinks have protein in them also, looking for a good 3:1 ratio of carbohydrates to protein (i.e. 30-60g carbohydrates to 10-30g protein).

We don’t just need protein after our runs. Daily protein needs are a lot higher than many of us may think. The current recommendations are around 1.28–1.63 g/kg per day (most dietians working with endurance athletes are recommending even more) and for runners currently going through their menopausal years should target protein consumption at the  highest end of the range. This is because without or less of your normal circulating hormones, your body is more likely to break down muscle protein – making it critically important to consume enough protein to slow this process. This is one of the reasons why strength training is also important during these years (and helps to maintain bone density!). Finally, there is some evidence coming out that recommends an uptick in protein ingestion during the luteal phase due to the high circulating sex hormones impact on protein metabolism. Basically, when in doubt – more protein.

TL:DR

I know that I just threw a lot at you. You may be wondering, how am I supposed to remember all of this? Lucky for you, I summarized it neatly below.  Like I said in the beginning, this review article is a beast, so I will be continuing this discussion in the next month as well, covering things like sleep, supplements, hydration and electrolytes, and a bit more of a deep dive on menopause. Stay tuned and happy fueling (& running!). 

• Fuel enough, always – Short periods of LEA can accumulate and be detrimental to long term health and performance gains.
  • It may be helpful to increase caloric intake during the luteal phase of your cycle.
• Don’t run fasted – Before runs aim to have an easy-to-digest carbohydrate snack so that your glycogen stores are topped off.
  • During the luteal phase of your cycle, this carbo-loading technique may be even more effective.
• Eat on the run – During your run, aim to ingest ~60 grams of CHO per hour, especially for long endurance bouts.
  • If this seems unattainable, start small, anything is better than nothing. Work your way up slowly to mitigate GI distress.
• Journal – Take notes about your pre, during, and post-run fueling and if you are experiencing GI distress, see if anything in particular causes it more frequently than others.
• Post run carbs are important – Shoot to get in 60-80g of CHO and 20-30g of protein (a 3:1 ratio) as soon as you can after your run to optimize recovery. 
• Don’t skimp on protein – We need a lot of daily protein as female athletes, and this is even more important for menopausal athletes.

References 

• Ray, Laurie. “Clue: Period and Ovulation Tracker for IPhone and Android.” Helloclue.com, Clue, 2019, helloclue.com/articles/cycle-a-z/the-menstrual-cycle-more-than-just-the-period.

• Sims, Stacy T et al. “International society of sports nutrition position stand: nutritional concerns of the female athlete.” Journal of the International Society of Sports Nutrition vol. 20,1 (2023): 2204066. doi:10.1080/15502783.2023.2204066 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10210857/