Menstrual Cycle Phases and Hormones Explained

Why Understanding Menstrual Cycle Phases and Hormones Matters

A typical menstrual cycle runs 21–35 days and is governed by four hormones — estrogen, progesterone, luteinizing hormone (LH), and follicle-stimulating hormone (FSH) — cycling in a precise, overlapping sequence. These aren't abstract lab values. Their rises and falls directly influence neurotransmitter activity, body temperature, inflammation response, and metabolism, which is why energy and mood feel meaningfully different from one week to the next. Understanding the mechanism behind those shifts is the first step to working with your cycle rather than against it.

The Four Phases: Hormone Curves and What They Do

Phase 1 — Menstruation (Days 1–5, approximate)

Estrogen and progesterone are at their lowest. The drop in progesterone triggers prostaglandin release, which causes uterine contractions and sheds the endometrial lining. FSH begins a slight rise as the pituitary signals the ovaries to recruit new follicles for the coming cycle. Because estrogen — which supports serotonin synthesis — is at its nadir, some women report low mood, fatigue, and reduced pain tolerance during this window. Research published in Hormones and Behavior (Epperson et al., 2012) confirms that fluctuating ovarian hormones modulate serotonin transporter activity, providing a neurobiological basis for these mood shifts.

Phase 2 — Follicular Phase (Days 1–13, overlapping with menstruation)

FSH stimulates several ovarian follicles to mature; one dominant follicle emerges and begins secreting estrogen. Estrogen climbs steadily across this phase, peaking just before ovulation. This rise has measurable cognitive and energetic effects: a 2018 review in Frontiers in Neuroendocrinology (Rehbein et al.) documented improved verbal memory and faster processing speed during high-estrogen phases. Practically, this is often when focus, sociability, and physical stamina feel strongest. Insulin sensitivity also improves as estrogen rises, which may support better blood-sugar stability.

Phase 3 — Ovulation (Around Day 14)

The estrogen peak triggers an LH surge — a sharp, brief spike released by the pituitary — which causes the dominant follicle to rupture and release an egg. LH and FSH both peak within a 24–48-hour window and then fall rapidly. The LH surge can be detected by over-the-counter tests and is the most precisely timed hormonal event in the cycle. Testosterone also rises modestly around ovulation, which research associates with increased motivation and libido (Roney & Simmons, Hormones and Behavior, 2013). Physical energy typically peaks here.

Phase 4 — Luteal Phase (Days 15–28, approximate)

After ovulation, the ruptured follicle becomes the corpus luteum and secretes progesterone, which rises sharply and dominates the second half of the cycle. Estrogen has a secondary, smaller rise before both hormones fall sharply in the final days if fertilization does not occur. Progesterone has a mild sedative effect — it's a positive allosteric modulator of GABA-A receptors via its neurosteroid metabolite allopregnanolone (Bäckström et al., Epilepsia, 2014). This explains why many women feel calmer, then increasingly fatigued or anxious, as the luteal phase progresses and progesterone metabolites fluctuate. The late luteal drop in both hormones is what underlies premenstrual syndrome (PMS) and, in more severe cases, premenstrual dysphoric disorder (PMDD).

PMS vs. PMDD: The Same Hormones, a Different Sensitivity

Up to 80% of women report at least one premenstrual symptom (ACOG, 2021), but clinical PMS affects roughly 20–40% and PMDD — characterized by severe mood disruption that impairs daily function — affects an estimated 3–8% (Yonkers et al., The Lancet, 2008). Critically, research does not show that women with PMDD have abnormal hormone levels; instead, they appear to have heightened neurological sensitivity to normal progesterone fluctuations, particularly to allopregnanolone. This distinction matters: the problem is not "too much" or "too little" of a hormone but how the brain responds to its natural rhythm. If symptoms are severe or disruptive, a healthcare provider can evaluate evidence-based options.

How Nutrition Interacts With Each Phase

Because hormones influence metabolism, blanket dietary advice misses meaningful phase-specific variation.

• Menstrual: Iron losses from bleeding average 0.5–1 mg/day (WHO, 2020); prioritizing iron-rich foods — lentils, lean red meat, dark leafy greens with vitamin C — may help offset fatigue.
• Follicular: Rising estrogen supports carbohydrate metabolism; complex carbohydrates and fermented foods that support estrogen processing via the gut microbiome are consistent with mechanistic models (Baker et al., Nature Reviews Endocrinology, 2017).
• Ovulatory: Zinc is required for follicle maturation and LH receptor function; shellfish, seeds, and legumes are reliable dietary sources.
• Luteal: Progesterone raises basal metabolic rate slightly — studies estimate a 7–10% increase in resting energy expenditure (Solomon et al., European Journal of Clinical Nutrition, 1994). Magnesium intake may support mood and reduce cramp severity; a meta-analysis in BJOG (Behboudi-Gandevani et al., 2017) found associations between low magnesium and increased PMS symptom severity.

Perimenopause: When the Pattern Becomes Irregular

Perimenopause — the transition to menopause that typically begins in the mid-40s and lasts 4–10 years — is defined by erratic ovarian function rather than a smooth hormone decline. FSH rises as the ovaries become less responsive; estrogen swings unpredictably rather than following the neat follicular curve. This irregularity, not simply "low estrogen," drives hallmark symptoms like vasomotor hot flashes, sleep disruption, and mood variability (Santoro et al., Journal of Clinical Endocrinology & Metabolism, 2016). Cycles may shorten, lengthen, or become anovulatory (progesterone-absent), which is why tracking pattern changes over time — cycle length, flow heaviness, symptoms — gives both individuals and clinicians useful data.

Tracking your cycle phases in detail also shapes practical decisions: knowing which days tend toward heavier flow, for example, helps you plan protection accordingly. Livlit's guide to matching products to your flow walks through how to map usage to your personal cycle pattern.

A Quick-Reference Hormone Chart

• Menstruation: FSH ↑ (early) | Estrogen ↓ | Progesterone ↓ | LH low
• Follicular: FSH ↓ as dominant follicle emerges | Estrogen ↑↑ | Progesterone low | LH low
• Ovulation: LH surge (peak) | FSH secondary peak | Estrogen peak → rapid drop | Progesterone begins ↑
• Luteal: Progesterone ↑↑ (peak mid-luteal) | Estrogen secondary rise then ↓ | LH ↓ | FSH ↓

For a deeper look at how these shifts connect to cycle-related mood changes, see our explainer on PMS vs. PMDD: understanding the difference.

If you experience severe mood disruption, pain, or cycle irregularity that affects daily life, consult a healthcare professional for personalized evaluation.