An Overview of the menstrual cycle.
As a female embarking on your fitness journey, you will stumble across some road blocks that a male wouldn’t. This isn’t to say that you have to completely overhaul your entire programme or completely disregard what you know about training and nutrition but more that there are a few adjustments you may need to make in order to get the best possible result. The days of women training like ‘little men’ are long gone.
The purpose of this article isn’t to delve too much into the intricacies of the menstrual cycle but more-so the different phases of the menstrual cycle, the main hormones that are involved and the impact that this can have on your metabolism.
While most view the menstrual cycle as a single loop, it actually consists of two cycles that run alongside each other. So rather than view it as one cycle, we’ll instead be discussing it as the ovarian cycle and the uterine cycle. Both of these cycles consist of three phases.
The Ovarian Cycle
The ovarian cycle refers to the changes that occur in the ovary. This cycle is divided into three phases:
The follicular phase
Ovulation
The luteal phase
The Follicular Phase
The is the first phase of the ovarian cycle. Essentially, this is when the ovarian follicles mature and prepare to release an egg. The follicular phase is initiated thanks to two hormones (FSH - Follicle Stimulating Hormone & LH - Luteinizing Hormone) which are released from the brain and travel in the blood to the ovaries. These hormones stimulate the growth of around 15-20 eggs, each contained in its own follicle. Ultimately, one follicle reaches full maturity and releases its egg at the end of the follicular phase, which leads us on to ovulation.
The most dominant hormone present during the follicular phase is Estrogen. As Estrogen levels rise during the follicular phase, it acts to suppress the production of FSH & LH which allows the body to limit the number of follicles that mature. This changes slightly during ovulation.
Ovulation
This is the second phase of the ovarian cycle. This is when the egg releases from the ovarian follicles and into the fallopian tube. During this phase, estrogen reaches a peak, which then triggers a surge in the amount of LH produced by the brain. It is this LH surge that causes the dominant follicle to release its egg. The egg will then sit for around a day or so and if it remains unfertilised it will start to disintegrate.
The Luteal Phase
This is the final phase of the ovarian cycle. During this phase, LH and FSH cause the empty follicle to develop into a new structure called the corpus luteum. The corpus luteum secretes the hormone progesterone, so you could refer to it as a temporary endocrine organ. This secretion of progesterone then causes estrogen levels to rise again, which subsequently causes FSH and LH levels to drop. This causes the corpus luteum to degenerate, progesterone levels begin to fall and this then triggers menses and the whole process starts again.
The Uterine Cycle
Like the ovarian cycle, the uterine cycle is divided into three phases:
Menstruation
The proliferation phase
Secretory phase
Menstruation
This is the first phase of the uterine cycle. During menstruation, estrogen, progesterone and LH fall to lower levels while FSH remains higher. Most will understand this phase to be the time where you start to shed the lining of the uterine wall. The average length of menstruation is around 2-7 days.
It is during this phase where women can encounter cramping in the abdomen. As progesterone and estrogen levels are starting to lower, any irritability felt in the days leading up to menstruation should start to cease.
The Proliferative Phase
This is the second phase of the uterine cycle. During this phase, oestrogen causes the lining of the uterus to grow. This causes the formation of a new endometrium layer whilst also causing the cervix to produce whats known as fertile cervical mucus. Many women monitor this variable when trying to conceive, as detecting fertile mucus is indicative of ovulation and therefore the ‘fertile window’. This phase ends after ovulation as we progress into the luteal phase and the secretory phase.
The Secretory Phase
This phase runs alongside the luteal phase and is the last phase of the uterine cycle. This is the phase where the endometrium becomes more susceptible to implantation due to higher levels of progesterone.
Progesterone increases blood flow and uterine secretions, which also causes an increase in basal metabolic rate. This increase in metabolic rate can cause women to feel both hungrier and warmer than usual, so irritability during the latter stages of this phase tend to be quite high.
Bodyweight & The Menstrual Cycle
The most common problem that women encounter when they first begin their fitness journey is understanding fluctuations in their bodyweight. Men have this to a degree, however it is far more complex with women.
Weight does not decrease in a linear fashion, as a female you will notice quite drastic fluctuations from week to week depending on where you are in your menstrual cycle.
To briefly overview:
You will be at your lightest weight during the early follicular phase. As you progress to the late follicular phase your weight will increase slightly. As you enter the early luteal phase, your weight should drop slightly, but, will likely still be heavier than that of the early follicular phase. As you progress to the late luteal phase you will be at your heaviest weight.
This is down to the different hormonal changes that occur during your cycle as discussed above. The differing levels of these hormones change how much water the body holds and therefore how much you will weigh during each phase.
So it’s important to note, when looking to make adjustments to your training or nutrition programme you should look at progress on a month by month basis as opposed to a week by week basis. So comparing week 1 to week 5, week 2 to week 6, etc.
Menstrual Cycle & Metabolism
Your calorie requirements, how you metabolise carbohydrates, fats, and protein all change throughout your cycle.
The early follicular phase up to the early luteal phase tend to be the most favourable weeks if improved body composition is your goal, as it is during this time that your calorie requirements are the lowest so your hunger would also be lower as a result, your insulin sensitivity is highest so therefore you utilise carbohydrates more efficiently. Your fat metabolism will be increased meaning a better environment for fat loss and your protein oxidation is reduced meaning there is less opportunity for muscle breakdown.
From the early luteal phase onwards, your caloric requirements start to increase, as will hunger. Your insulin sensitivity starts to decrease along with your fat metabolism while your protein oxidation will increase, meaning a higher chance of muscle breakdown.
Summary:
Early Follicular Phase:
Lowest caloric requirements
Increased insulin sensitivity
Increased fat metabolism
increased carbohydrate utilisation
Reduction in protein breakdown
Late Follicular Phase:
Slight increase in caloric requirements
Increased insulin sensitivity
Increased fat metabolism
Increased carbohydrate utilisation
Reduction in protein breakdown
Early Luteal Phase:
Increased caloric requirements
Decreased insulin sensitivity
Decreased fat metabolism
Decreased carbohydrate utilisation
Increase in protein breakdown
Late Luteal Phase:
Further increase in caloric requirements
Decreased insulin sensitivity
Decreased fat metabolism
Decreased carbohydrate utilisation
Increase in protein breakdown
Now, it is important to note that this is all individual. Your own estrogen/progesterone ratio will determine how these fluctuations occur during your cycle. This information can just give a good general overview to how you could adjust your training and nutrition to complement your menstrual cycle.
Taking the above into consideration, if improved body composition is your goal it may be good practice to periodise your nutrition to align with your cycle and hopefully offset any cravings or intense hunger that you may normally feel.
A larger calorie deficit during the follicular phase will allow you to make steady or even aggressive progress with fat loss when you’re most primed to do so whilst experiencing less severe hunger. Following this, bringing calories up to maintenance level or even slightly above during the luteal phase will assist with cravings and increased hunger levels due to the rise in metabolic rate during this stage.
Measuring your progress with these methods on a monthly basis, comparing like week to like week will then allow you to see how this level of periodisation impacts your progress, and whether your dieting experience as a whole is subsequently a little easier now that you are working with your physiology