Nutrition and Fueling for the Female Endurance Athlete

How do you train and fuel as an aging female athlete?

When to eat with exercise: before or after?

Morning exercise fueling or fasting?

Ben Greenfield:

  • Stays in mild ketosis 1-3 mmol all day long by not eating carbs 
  • Doesn’t eat carbs all day long 
  • Workout in late afternoon/early evening – increases/induces temporary insulin sensitivity 
  • Carbs at dinner -100g to 200g (helps sleep better)
  • Doesn’t eat carbs again until next evening meal
  • Stays in insulin sensitive state post workout- evening refeed of carbs – restocks up glycogen stores in liver and muscles because you upregulate glute4 transporters- enough fuel is on board for next day’s workout. 
  • The morning cortisol is elevated – more insulin sensitive in the morning

If you can exercise late afternoon – improve insulin sensitivity again post workout so you can enjoy healthy carbs at night

TRAIN LOW -COMPETE HIGH = increases fat metabolism 

Even if slightly lower glycogen stores – training low and competing high or saving carbs for hardest workouts – enhances fat metabolism and increases endurance performance 

Eat low carb diet and occasionally throw carbs in it 

METCON in the morning? the carbs you eat in the evening are going to be enough fuel as your liver and muscle glycogen stores would be topped off. 

If need an extra boost- use essential amino acids and/or creatine pre workout (stave off neuromuscular fatigue- tryptophan crosses over BBB(?), instead of carbs, maintain the ability to burn more fatty acids in the day and stay in autophagy fasting state. Eat your carbohydrates in the evening.

BUT if you are doing two workouts in the day as pro athlete – 

  • you can not adequately replenish carbohydrate stores enough if doing two workouts in eight hour time period.
  • If your workout is in the morning then you have another training session in eight plus hours away from the morning workout then you would want to eat consume carbs in the 20-60 minutes post first workout to replenish the glycogen stores so you can perform as well as you would want to in your second workout of the day (depends on the workout intensity). 
  • If both workouts you are “crushing it” then fuel appropriately after the first workout. 
  • Eat your real food carbs after first workout session then after second workout session. 

If eating carbs after second session- 

  • you can wait 1-2 hours after workout to eat your carb refeed post workout meal as you want to take advantage of the amplified levels of growth hormone and testosterone that occurs when you don’t eat right after the workout and wait for the upregulation (neuro endocrine favorable hormone response post workout) 

Avoid over training!

IF your morning exercise is light, low intensity movement as sauna with yoga, walk in sunshine = not a carb depleting then you can save your carbs for dinner evening meal.

The best time of the day is when you are able to workout but the best time to do a MET CON workout is between 4-6pm. 

  • body temp peaks
  • grip strength peaks
  • reaction time peaks 
  • post workout protein synthesis peaks
  • second rise in testosterone occurs 

 Ideal to start day outside in sunshine or restorative yoga passive – as body naturally surges in cortisol in the morning. 

Wait until dinner to have your carbs unless doing two a day workouts withing eight hours.

BUT what if you are a FEMALE athlete pre-menopausal with hormone fluctuations?

Optimal nutrition is an important aspect of an athlete’s preparation to achieve optimal health and performance. While general concepts about micro- and macronutrients and timing of food and fluids are addressed in sports science, rarely are the specific effects of women’s physiology on energy and fluid needs highly considered in research or clinical practice. Women differ from men not only in size, but in body composition and hormonal milieu, and also differ from one another. Their monthly hormonal cycles, with fluctuations in estrogen and progesterone, have varying effects on metabolism and fluid retention. Such cycles can change from month to month, can be suppressed with exogenous hormones, and may even be manipulated to capitalize on ideal timing for performance. But before such physiology can be manipulated, its relationship with nutrition and performance must be understood. This review will address general concepts regarding substrate metabolism in women versus men, common menstrual patterns of female athletes, nutrient and hydration needs during different phases of the menstrual cycle, and health and performance issues related to menstrual cycle disruption. We will discuss up-to-date recommendations for fueling female athletes, describe areas that require further exploration, and address methodological considerations to inform future work in this important area.

  • Female athletes should aim for energy availability (EA) of 45 kcal·kg–1 fat-free mass·day–1 for optimal health and performance
  • optimizing nutrient composition based on menstrual cycle phase is ineffective without the requisite energy for basic functioning.
  • Micronutrient deficiencies are common in female athletes, particularly in iron, vitamin D, and calcium; nutritional strategies should be used to prevent these deficiencies, including increasing consumption of diverse foods and potential supplementation.
  • Micro- and macronutrient requirements, as well as hydration needs, may change during various phases of the menstrual cycle as a result of hormonal fluctuations.


This supplement is supported by the Gatorade Sports Science Institute (GSSI). The supplement was guest edited by Lawrence L. Spriet, who convened a virtual meeting of the GSSI Expert Panel in October 2020 and received honoraria from the GSSI, a division of PepsiCo, Inc., for his participation in the meeting. Dr. Spriet received no honoraria for guest editing the supplement.

How do we know what is right for the fat-adapted female athlete?

We have hormones fluctuating throughout the month… until post menopause.  Our body changes- so our nutrition, exercise and recovery need to be adjusted.

As I always say… “don’t blame the aging process but embrace the change”

Don’t fuel and train the same as you did when you were 20-30 something year old.  Adjust the timing of your nutrition and vary your exercise.

What about fasting and doing fasted exercise as a female athlete?

There are many claims that intermittent fasting will allow your body to become more “fat adapted.” In other words, fasting will help prime your body to turn to your fat stores for energy. This can lead to fat loss and other purported benefits like blood sugar stability and increased energy.  Even more, intermittent fasting may help promote fat loss simply because you are eating LESS food overall.  Decreasing the window of time in which you eat is likely to lead to you eating LESS food overall. Remember, if you are eating LESS energy than you are expending, you are in a caloric deficit. This deficit will help promote fat loss (considering it is NOT for a prolonged period of time)

While intermittent fasting can offer these positive effects in some cases, it can also be extremely detrimental, especially for athletes and active individuals. Going too long without food can put a lot of extra stress on your body. Extra stress is counter-intuitive when your goal is to RECOVER, ADAPT, and PERFORM!

I agree.

Too much of anything can lead to overload, toxicity and imbalances – METABOLIC CHAOS.

Too little of anything can lead to deficiencies and imbalances.

The Goldilocks Effect:  find the right amount and right dose for YOU to create a positive response!

Nutrient Timing:  WHEN to eat, as well as WHAT, WHY and HOW!

Fueling for Performance points:

  • How to eat but how much to eat… what should your macronutrients be for you varies per day of your cycle and type of exercise session.

This is about 80% of what matters when it comes to fueling for both athletic performance and body aesthetics. Nutrient timing influences about 10% of our fueling priorities, while the remaining 10% comes down to food composition and supplements.

Nutrient timing considers what you eat AROUND the times you are active. We have already discussed the importance of carbohydrates as fuel beforeduring, and after activity to give you an idea of what we mean.  Remember that female athletes who perform at moderate to higher intensities RELY ON CARBS.  Being “fat adapted” only comes in handy when your body kicks in its aerobic energy system, which is used during longer, less intense exercise. This system is meant for slower energy output—not really ideal when we’re looking to run full speed down the court in a breakaway.

After carbs, the next important factor to consider is the timing of your protein intake.  Before you even consider WHEN you eat, you need to first focus on HOW MUCH you should eat (your caloric intake) and WHAT you should eat (your macronutrient ratios, or how much fatprotein, and carbs you should consume).

In the book Roar: How to match your food and fitness to your female physiology for optimum performance, great health, and a strong, lean body for life, Dr. Sims makes the case against fasted training to female athletes with research conducted on only female athletes, an attribute missing in many of these physiological studies, where men or a mixed group of men and women are used. In the morning, cortisol (the body’s stress hormone) levels are at their highest. Exercise is an additional stressor to this system, meaning even more cortisol is produced. However, the body needs the correct building blocks to do so, which are the sex hormones: testosterone, estrogen, and progesterone(2).

In the long-term, a female athlete that is in a chronic state of cortisol elevation due to fasted training can develop hormonal imbalance, potentially risking reproductive health and paving the path to amenorrhea and other symptoms ofRED-S and low energy availability.

Dr. Sims’ research points to the possibility that men may respond better to training in a fasted state, as the muscle adaptation following fasted training programs is greater in men than in women.

This could be because women naturally have a higher fat oxidation, thus have less room to improve through fasted training. 

The health impact of fasting for women casts a wide net.

Hormonal disturbances brought on by low glycogen states can cause fatigue, increased risk for bone stress injuries, and even potential weight gain due to decreased metabolic rate.

Additionally, time spent in a fasted state, independent of total energy consumption in a 24 hr period, can cause reproductive dysfunction(3). In other words, even if you are eating enough food to meet your energy needs, if you spend a significant amount of time fasted throughout the day, it can affect your menstrual cycle and reproductive health. While there are benefits to intermittent fasting for certain populations, a female athlete should take extra scrutiny before deciding that it is right for them

What are the benefits of fasted training for FEMALE athletes?

What if we are fat adapted and efficient fat burners?

What if we are training Zone 1/2 (MAF) max aerobic function heart rate in a workout vs. doing all out glycogen depleting sprints or HIIT training workout with cardio/weights?

There is a theory that female athletes will not improve fat oxidation substantially with fasted runs. According to Dr. Sims, the hormonal state of female athletes results in higher rates of fat oxidation naturally, which is one reason that women can often improve performance relative to men in longer events.

Instead, there are cascades of hormonal responses to low-energy states for some female athletes. Concentrations of the stress hormone cortisol go up, and some research indicates that female athletes can be more sensitive to its effects. In moderation, cortisol isn’t bad, but with chronically elevated levels like those from consistent fasted running, overall hormone balance can go haywire. Reproductive health may be affected, possibly contributing to amenorrhea.

Hormone perturbations can also contribute to fatigue, bone stress injuries, and (possibly counter-intuitively) weight gain from reduced metabolic rate. Recovery and adaptation may slow down too. For example, a 2010 study in the Journal of Science and Medicine in Sport found markers for muscle adaptations responded better in non-fasted female athletes, with male athletes responding more to fasting.

That’s not to say that female athletes should never do fasted runs, or need to have a gel on every run over an hour. While female athletes and male athletes have different physiology, all are homo sapiens, and some of the benefits may still be present in small doses. In addition, for transgender athletes, these considerations could be slightly different, since a transgender/nonbinary person taking hormone-replacement therapy receives hormones through a different mechanism than a cisgender person (though the responses to stimuli are likely similar).

The overall point: there’s a good chance that the strict approaches to fasting and glycogen depletion that may work for some male athletes in moderation will work for very few female athletes.

The overall point: there’s a good chance that the strict approaches to fasting and glycogen depletion that may work for some male athletes in moderation will work for very few female athletes. And as Van Horn says, “Restriction of food is generally not mentally healthy.” Instead, she advises athletes to ask the following question: What can I add to my nutrition to improve my performance and health?

Fasted Training May Have Long-Term Risks, Especially For Female Athletes

Here is another article on Fasted Exercise … each article or blog post is based on Dr. Stacy Sims research as she is the expert in this area.

You (women) could try it by eating early dinner and then fasting until breakfast, (short fast for the autophagy) but it will not give you a huge stimulus to disrupt everything else going on in the body.

Note, that the research spoken of by Dr. Stacy Sims says that the longer women stay in a catabolic state, the more they disrupt their endocrine system and their resting metabolic rate.

There was a study on female endurance athletes who ate before training and then fasted all day and didn’t eat again until night.

Even though they ate the total amount of calories required to keep up the right energy levels (avoiding Low Energy Availability aka LEA) they spent most of their day without food in a catabolic state.  They ended up with reproductive abnormalities.  (Irregular menstrual cycles, anovulatory cycles, amenorrheic, all due to this perturbance in the kisspeptin and not being able to take care of the endocrine cycle, EVEN though they thought they were eating enough.

So, if you do not eat on a regular basis, and are active, you can create this thyroid dysfunction.  This high catabolic state that women stay in purposefully or due to poor lifestyle of not eating regularly  can create this endocrine dysfunction of which the symptoms can be dead-end fatigue, increase in body fat, and in spite of taking time off and trying to rest they are not getting in that proper recovery that they need.

From a health point of view only, if you are looking at exercise, the very long line of research says that exercise is actually in itself a fasted state, because you are using fuel, and creating stress to which your body is responding including a little autophagy (cell regeneration).  You are also getting more blood sugar control and insulin responses.  You are losing body fat and building lean muscle mass.  SO, everything that Intermittent Fasting is purporting to do in the literature, is also the same thing that is purported in the exercise literature!

I always ask “What would Dr. Stacy Sims say…?”

Read the article by Dr. Stacy Sims… and ask yourself how many sources of CHRONIC stress do you experience everyday?  Plus we have HIDDEN internal sources of CHRONIC stress that we may not be aware about unless we run specific functional lab tests (3-5 tests to see WHOLE picture).

It comes down to kisspeptin, is a neuropeptide that’s responsible for sex hormones and endocrine and reproductive function, which also plays a significant role in maintaining healthy glucose levels, appetite regulation, and body composition. It’s also more sensitive in women than men. When it gets perturbed, our sex hormones aren’t produced and released the way we need them to be.

Intermittent fasting and keto both disrupt kisspeptin production. When our brain perceives we have a deficiency in nutrients, especially carbohydrate, we have a marked reduction in kisspeptin stimulation, which not only increases our appetite, but also reduces our sensitivity to insulin. This is why research shows intermittent fasting is more likely to cause impaired glucose intolerance in women, but not men.

What happens when we layer exercise stress on top of the stress of denying our bodies an important fuel source?

Stress hormones like cortisol rise even higher. As you keep increasing that stress, it keeps your sympathetic drive high and reduces your ability to relax. Your thyroid activity is depressed, which messes with your menstrual cycle. Your body also starts storing more belly fat.  So now you’re looking at disrupted menstrual cycles, higher anxiety and stress, impaired performance and often weight gain—pretty much the opposite of what you’re looking for!

The ketogenic diet has very similar effects on women athletes. We hear people rave about the increased mental focus with a keto diet.

In men, yes. They have an increase in their parasympathetic (a.k.a. rest and digest) activity, so they can be more relaxed and present.

In women, keto kicks up our sympathetic (a.k.a. fight or flight) drive, so we’re more anxious, more prone to being depressed, and we can’t sleep very well, which again hurts our hormonal health, performance, well being, and body composition.

Sometimes women will contend that these diets work so well for them. And they might for the first three months, because nearly any diet will yield some effects in the short term. The long term effects for women athletes, however, is endocrine dysfunction, increases in abdominal fat, more depression, and a backlash of subsequent fat gain.

Women athletes perform far better in a fed state. Women athletes need to eat.

Okay, But I’m Not An “Athlete”

While we’re here, let’s address the “A word.” After my Women Are Not Small Men episode on Nuuness TV aired, there were a number of women who took to social media and asked questions like, “So is intermittent fasting okay for me since I’m not an athlete?” and “I’m not an athlete, so is keto beneficial?”

The catch is, these women were athletes. They were runners, bike packers, swimmers, and CrossFit enthusiasts. But like so many women I hear from and work with, despite the fact that they are very active and want to feel and perform their best, they do not consider themselves “athletes.”

I get it. We’ve grown up with the notion that an “athlete” is someone we see on television or on Nike ads. We’re not like them.

But here’s the thing: Yes, we are.

The only thing that separates an “athlete” from someone who regularly works out, exercises, or otherwise pursues physically active endeavors is competition. By strict definition an athlete “competes.” The origin of the word is “one who competes for a prize.”

Otherwise very unhealthy people who drink to excess and smoke cigarettes, but can land a golf ball on a green from 300 yards are “athletes,” even if they don’t otherwise “exercise” every day. In fact, this paper from the American College of Cardiology makes it very clear that many Olympic level athletes have high LDL cholesterol levels and are not necessarily “healthy.” Health isn’t their goal. Winning competitions is.

The bottom line: If you exercise on purpose, you are an athlete–and are maybe even healthier and more active than some professional athletes–and this advice is most definitely for you!

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