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Quick biology lesson on 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 – although you can define them differently.
- The follicular phase occurs at the start of menstruation (aka period) 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.
Does performance change around the menstrual cycle?
- This is an important question to frame this discussion
- Because if performance actually doesn’t change around the menstrual cycle, is there really a need to modify our nutrition around it? Probably not
- So the research on this is quite limited but based on my scouring of journal articles these are my main findings
PERCEIVED CHANGE: When athletes are asked about their performance and their cycle, many believe their performance fluctuates throughout.
- In one study, a large proportion, 50%, of participants reported feeling their performance in training 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.
OBJECTIVE CHANGES: A SYSTEMATIC REVIEW: A review
- So most studies (20 out of 35) in this review actually didn’t find a change in performance across the menstrual cycle
- But this leaves 15 which did, which I think is worth exploring
- For anaerobic performance, one study found that sprint performance was better in the mid-luteal phase.
- For aerobic performance, intermittent endurance performance appeared to be more affected by the menstrual cycle than continuous endurance work.
- & Muscular strength appears to be the most affected by the menstrual cycle
- The review found trends that suggest that strength was
- Lower in the early follicular phase (during menstruation) compared to the late luteal phase (leading into menstruation)
- Generally increased during ovulation and during the early and mid-luteal phase
- Relationship between muscular strength and oestrogen
- BUT RESEARCH IS REALLY MIXED AND HARDLY SET IN STONE
Do you need more calories at certain parts 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. – This could equate to an extra 100-400kcals on average
- Based on a 2020 meta-analysis it does seem like a bit of a mixed bag though with about a 50/50 split of studies showing a small increase in REE during the luteal phase with other studies showing no differences in REE throughout the cycle.
- But even if REE is increased during the luteal phase. This is actually not your “period”. In an theoretical 28 day cycle luteal phase starts 12-14 days prior to your period 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.
- It is likely best to gauge how each individual is feeling and recovering throughout the month, to inform changes to caloric intake.
- And if you just feel better eating more on your period or before your period, even if REE is not increased then it is perfectly okay to do so
- Some people just feel better during ovulation and early/mid luteal phase and maybe end up being more active then as well
Should you change your fat, carb or protein intake at certain parts of 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.
CLAIM 1: MORE CARBS IN THE MID LUTEAL PHASE
High oestrogen in this phase can inhibit the utilisation of glycogen stores
- Maybe consuming more carbs during this time could be beneficial for high intensity activity
- This is just a theory though
CLAIM 2: MORE PROTEIN IN THE LUTEAL PHASE
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 this is likely covered by general protein recommendations anyway
Overall, it is probably going to be best to follow general sports nutrition guidelines for carbs, fats and protein intake and then adjust based on how each athlete is performing and recovering
Fluid retention/weight across the menstrual cycle
- Most people with a menstrual cycle will be able to tell you that their body weight can fluctuate pretty dramatically throughout their cycle.
- There can be an increase body weight via up to 2L of additional fluid retention. – this usually occurs in the late luteal phase before menstruation where oestrogen is high and progesterone has begun to decrease
- Oestrgoen = increased fluid retention
- Progesterone = decreased fluid retention
- On the onset of menstruation, oestrogen levels fall and water retention begins to decrease
- Relevant for weight-making athletes
- Best to track your menstrual cycle and have an idea of when your weight is likely to be high and how much it typically fluctuates by
- For general fat loss – monthly averages are better than weekly/daily weights
- There is an excellent 2021 review article called “Nutritional considerations for female athletes in weight category sports”.
- They also discussed the fluid retention and weight component
- But they also brought up a couple of other interesting points
- Water retention & water loading – is there a great chance of hyponeutremia? (when blood sodium levels get too low)
- 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. – Potentially increased hyperthermia risk when using active or passive sweating methods. This could include things like saunas and hot baths.
- Water retention in the late luteal phase – a natural form of hyper-hydration
- Hormonal contraception ?
- 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, and maybe even playing with high-calorie or carbohydrate intakes in certain phases.
- But we just don’t have the data to give generalized recommendations across the board for women.
- Australian female athlete perceptions of the challenges associated with training and competing when menstrual symptoms are present
- The Impact of Menstrual Cycle Phase on Athletes’ Performance: A Narrative Review
- Acute caffeine intake increases performance in the 15-s Wingate test during the menstrual cycle
- 24-hour energy expenditure and the menstrual cycle
- The effect of the menstrual cycle on exercise metabolism: implications for exercise performance in eumenorrhoeic women
- Nutritional Considerations for Female Athletes in Weight Category Sports
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