You don’t have to spend much time looking through sports research to realize that the majority of research has been done in exclusively male populations.
There is a significant gender research gap in athletic populations. This means that the current sports nutrition recommendations we have, are mostly based on men and have just been applied to all athletes, despite gender.
But of course, there are a lot of fundamental differences between the sexes. Biologically, men and women are different. Our hormone profiles are completely different and this can and does make our nutritional needs different. It also potentially changes what an optimized diet for performance, recovery, and body composition changes should like.
One of the stark differences between men and women is the presence of a menstrual cycle for those with a uterus.
There has been a lot of talk about tailoring nutrition and training for athletes around the menstrual cycle as of late. This is exciting because female athletes are so often overlooked and talking about periods can be seen as uncouth or taboo. So to have it being talked about amongst practitioners, coaches and athletes is pretty darn cool.
But given the state of research amongst female athletes, can we actually give general recommendations around the menstrual cycle?
This article will delve into what we currently know, what we may be able to conclude from that, and potential recommendations as well as what is still left to find out.
The Menstrual Cycle
Before we go any further, let’s do a quick lesson on the menstrual cycle.
So in regards to research, it is the menstrual cycle that makes female athletes “too complicated to study”.
Some of the reason behind the research gap more than likely has something to do with misogyny. Let’s not rule that one out. But unfortunately, the menstrual cycle adds in a whole lot of variables to research that makes it more time-consuming, expensive, and overall straight up complex.
Although, what is really cool about the menstrual cycle for athletes, is it can really give us some incredible insight into our own bodies.
Stress, lack of recovery, and low energy availability can all be indicated through changes to the menstrual cycle!
A typical cycle lasts ~28 days. Although this can differ from person to person, by life stage, due to certain conditions and other confounding factors as well as due to hormonal contraception use.
There are three main phases of the menstrual cycle.
- The follicular phase occurs at the start of menstruation (aka period or the menses) and lasts up until ovulation. During this phase estrogen and progesterone levels are low and this lasts for about half of the menstrual cycle (~14 days).
- The ovulatory phase. This is when the egg is released from the ovary and during this time estrogen levels are high but progesterone remains low. Ovulation is just one day of the whole menstrual cycle but its associated hormonal changes last for a total of around 3 days.
- The third phase is the luteal phase. Here estrogen remains relatively high but progesterone also increases until both levels fall off leading back to the start of menstruation once again.
This may seem like a bit of a useless lesson in biology and hormones but bare with us. These hormonal fluctuations have big impacts on the body (not that we have to tell you that if you have a menstrual cycle). But they also potentially have implications for what optimal sports nutrition may look like at different phases of the cycle.
Is Performance Impacted By The Menstrual Cycle?
Before getting into the nitty-gritty of nutritional recommendations around the menstrual cycle for athletes. I think it is worth asking the question; is performance impacted in different phases of the menstrual cycle?
Because one could argue that if there are no changes to performance, changing training and nutrition at different stages of the cycle is unlikely to provide much value.
And the research on this is mixed. When athletes are asked about their performance and their cycle, many believe their performance fluctuates throughout.
In one study, a large proportion, 50 and 71%, of participants reported feeling their performance in training and competition, respectively, is impaired in certain menstrual cycle phases.
Athletes most commonly perceived performance to be negatively affected in the early follicular and late luteal phases. This is leading up to and during menstruation.
Nevertheless, the perceived impact on performance coincides with the occurrence of premenstrual and menstrual symptoms including changes in mood, fatigue, and menstrual pain. So a reduction in perceived performance may also be attributed to these symptoms.
A review of this topic found that studies measuring objective changes in performance (ie. things that can be measured) actually, did somewhat line up with athletes’ perceived changes in performance.
Seven out of 24 studies that compared performance during the late luteal and early follicular phase found a significant difference compared to other times in the menstrual cycle. Although this is far from the majority of studies, it does provide some evidence that performance may be impaired during this time. Whether this may be due to certain hormonal changes or symptoms, or a bit of both, is unknown.
Overall, 20 out of 35 studies included in this review found no significant improvement or impairments to physical performance throughout the menstrual cycle.
But that does leave 15 studies that did find changes in performance which is worth investigating.
For anaerobic performance, one study found that sprint performance was better in the mid-luteal phase. In another, vertical jump height was greater in the early follicular phase and a third found greater performance in the ovulatory phase during cycle sprints.
For aerobic performance, intermittent endurance performance appeared to be more affected by the menstrual cycle than continuous endurance work. For the most part, continuous endurance exercise seems to be fairly unaffected by the menstrual cycle phases.
However, when looking at the effects shown on intermittent endurance, there are conflicting results.
Muscular strength appears to be the most affected by the menstrual cycle which could be valuable knowledge for strength athletes and coaches.
The review found trends that suggest that strength was unlikely to be different between the late follicular and mid-luteal phases. However, strength outcomes were
- Lower in the early follicular phase (during menstruation) compared to the late luteal phase (leading into menstruation)
- Generally increased in the early and mid-luteal phase
- And potentially increased in the ovulatory phase
Overall, this review summarized its findings in the graphic shown below and their closing remarks were;
“Based on this graphic, endurance performance is likely best early in the menstrual cycle and anaerobic and strength performance may be best in the ovulatory phase. Strength and aerobic performance may be worst in the late luteal phase. Anaerobic performance could be worst in the late follicular phase.”
So What Does This All Mean?
With the research that we have at the moment, we can have hypotheses about how the menstrual cycle impacts performance. But we can’t say for sure that all female athletes will experience the same thing throughout their cycle.
Olympic gold medals have been won by athletes throughout all stages of the menstrual cycle. So I don’t think you are at an inherent disadvantage if a competition date lands at a certain time in your cycle. But hopefully, the research in space will become more clear in the coming decades.
Nutrition Considerations Throughout The Menstrual Cycle
Do You Need More Calories At Certain Points Of Your Cycle?
One of the most common recommendations for tailoring your nutrition to your cycle is that you should have more calories during your period.
Looking at the research, it does appear that resting energy expenditure (REE) might be increased during the luteal phase. One study estimated that this change ranged between an 8-16% increase in REE.
Based on a 2020 meta-analysis it does seem like a bit of a mixed bag though. About a 50/50 split of studies showed a small increase in REE during the luteal phase. Other studies showed no differences in REE throughout the cycle.
But even if we say, yes, REE is increased during the luteal phase. This is actually not your “period”. The luteal phase is the 12-14 days prior to your menses and makes up about half of your menstrual cycle. So this would mean you may have slightly increased caloric needs 2 out of every 4 weeks.
So based on that, it probably can’t be recommended as a general rule that you need more calories during the luteal phase, let alone while you are on your period.
It is likely best to gauge how each individual is feeling and recovering throughout the month, to inform changes to caloric intake.
Should You Change Your Carb, Fat, or Protein Intake Throughout Your Cycle?
Another point that is often raised is that at certain points in your cycle, your body oxidizes (burns) less of certain fuel sources and more of others.
So during the follicular phase, fat and protein oxidation are reduced and carbohydrate oxidation is increased.
And vice versa in your luteal phase.
However, it is really not clear how these changes may impact performance and how that can be mitigated through nutrition and dietary strategies.
There are some people that believe that when you are burning more fat, you should eat more fat and when you are burning more carbs, it makes sense to eat more carbs. Just on a mechanistic basis, this doesn’t make much sense though.
If anything, athletes may consider increasing their carb intake when carb oxidation is low. Even still, based on the lack of research we have and how minute these differences can be, it is all just speculation at this point. It also seems like a bit of an oversimplification.
There is research to suggest that estrogen can inhibit gluconeogenesis. So in the mid-luteal phase (when estrogen levels are high), female athletes use less muscle glycogen during exercise compared with the follicular phase and when compared with male athletes.
It has been suggested that actually increasing carbohydrate intake, particularly before high-intensity exercise, during the luteal phase may help to overcome this deficit. As it is during higher intensity activity where glycogen would be a preferred fuel source. However, how much this would differ (if at all) from general carbohydrate recommendations for athletes is unknown.
From a macronutrient perspective, there is also the fact that progesterone increases protein catabolism which may be a factor to consider in the luteal phase as well. Some researchers suggest that there is a potential need for increased protein intake in this time.
But once again, how this actually affects muscle retention, recovery, and muscle-building capacity is completely unknown. It is worth noting that estrogen is known as an anabolic hormone and is actually protein sparing. During the luteal phase, this hormone is also elevated. So perhaps there is no net difference in protein balance when everything is considered.
What Considerations Are There For Weight Making Sports?
The key points taken from this review in relation to the menstrual cycle, were the discussions around fluid balance, fluid retention and thermoregulation.
Most people with a menstrual cycle will be able to tell you that their body weight can fluctuate pretty dramatically throughout their cycle. This is because high estrogen levels seen during the late follicular phase, ovulation and leading into the luteal phase can increase body weight via up to 2L of additional fluid retention.
On the other hand, higher levels of progesterone can have the opposite effect on fluid balance during the luteal phase leading to lower body weights.
For most athletes, this fluctuation in fluid retention is not going to affect their sport or performance. However, in weight-making sports, knowing where you are in your cycle and how much your weight typically fluctuates by at different stages can be incredibly helpful. Saving some athletes a nasty surprise on weigh-in week with a spike in body weight from additional fluid retention.
The above-mentioned review also made a good point regarding water loading as part of an acute weight cut when fluid retention is present due to the menstrual cycle. Female athletes may be at a greater risk of hyponatremia (blood sodium levels getting too low) if they undertake water loading, with estrogen-related water retention and low or reduced-sodium intakes. There is no evidence to suggest there is a greater risk in this situation but it is an interesting concept given the danger of hyponatremia.
Lastly, there are differences in thermoregulation and sweating capacity between males and females. High progesterone levels during the luteal phase generally increase the core temperature by 0.3-0.7 degrees celsius in comparison to the follicular phase. Paired with the reduction in sweating capacity that we see in women generally, this may mean that women in this phase of their cycle may need to also be more conscious of hyperthermia risk when using active or passive sweating methods. This could include things like saunas and hot baths.
Obviously, this won’t be relevant to a lot of athletes but for those in weight-making sports, it could be very important to consider.
Applying This Information In The Real World
At this point in time, we are barely scratching the surface of what the menstrual cycle means for sports nutrition and performance.
The most we can say is that nutrition should always be individualized to the athlete regardless of gender. That kind of goes without saying.
There may absolutely be value in tracking your period. Getting familiar with how you feel and perform throughout your cycle can be a good idea. Maybe even playing with high-calorie or carbohydrate intakes in certain phases can help too. But we just don’t have the data to give generalized recommendations across the board for women.
There is also the complexity that is hormonal contraception. Which can completely change hormonal profiles and patterns in all sorts of ways depending on what type someone is taking. So not only do we need to know more about how a regular menstrual cycle affects women in sports but also how each type of hormonal contraception can impact them.
So What Now?
Dr. Stacey Simms is a big proponent of making recommendations for women in sports around the menstrual cycle. Whilst I don’t necessarily agree with everything she says. Her saying “women are not small men” rings true.
There are absolutely differences between men and women in sport and this may mean that training and nutrition may need to look different for the sexes. But given the lack of research in women currently, we just have no idea what that might look like as actual recommendations.
Given that women are not a weird anomaly and are in fact 50% of the population, there is a dire need for more research in this space.
