How Does Fasting Affect Your Cycle?

I want to go deeper this week into the effect of fasting on the female cycle. It’s one of the most common biohacking tools right now, across men and women of all ages, and we’re seeing some thrive and others crash.

That’s why this topic matters, as I don’t want women to feel another sense of failure when that’s absolutely not the case.

Fasting impacts your cycle, hormones, and energy, especially for the ‘constant woman’ of today. As let’s face it, women are providing equally in careers and finances, but still carry the roles of caregiver, organiser, and nurturer.

It’s a lot. So this blog is about how fasting truly affects us, and why the key to vitality and longevity lies in listening, not forcing.

Effect of Fasting on Menstrual Cycle Hormones

We’ve been taught, just like men, to follow a straight line, when our biology moves in seasons. You can feel like a completely different person from one week to the next, and that’s simply your intelligent physiology.

A reminder from last week’s blog: almost all medical data before 1995 was based on men. So much of what we see pushed as standard health advice overlooks the complexity of female hormones.

Women’s bodies aren’t designed for constancy as our hormones, metabolism, and stress responses change week to week, influencing everything from hunger and energy to insulin sensitivity.

Fasting can alter ovulation timing, shorten the luteal phase, or even delay periods. When under fuelling becomes chronic, it can reduce oestrogen and progesterone, slow thyroid hormones, and raise cortisol, your key stress hormone.

This can result in tiredness, low mood, poor sleep, or irregular cycles. And not because fasting is bad, but because your body is trying to protect you. It reads restriction as survival mode.

Fasting According to Your Menstrual Cycle: Phase by Phase Guide

Shall we talk about the four phases? So many women don’t fully know how their cycle changes. I’ve written a deeper guide on this which you can read here. 

Every phase of your cycle has different needs, and understanding them allows you to work with your biology.

🩸 Menstrual Phase (Days 1–5) Winter Season.

During this phase, your body is renewing and releasing. Energy is low, inflammation rises slightly, and you need warmth and nourishment. 

Some studies, and many women’s personal experiences, show that a longer fast on Day 1 can support blood sugar balance. I’ve personally found it beneficial at times too.

However, others find it a time of nourishment only, and this is one of the nuances of the female body, another example of how different we all are.

So, if you feel best with nourishment, honour that and focus on slow cooked meals and magnesium rich foods. If you feel drawn to fast, then work with your body and trust your cues. 

And remember: one month can feel completely different to the next, depending on stress, nutrition, sleep, and how supported your body feels going into your bleed.

🌱 Follicular Phase (Days 6–14) Spring Season.

Oestrogen rises, metabolism steadies, and energy lifts. This is when short, gentle fasts, around 12–14 hours, may feel fine for some women. 

Keep hydration high and meals balanced with quality protein, healthy fats, and fibre.

🌸 Ovulation (Around Day 14) Summer Season.

Metabolism speeds up and calorie needs rise. It’s normal to feel hungrier, as that’s your body preparing for potential conception.

This is also the phase where your body is more resilient to fasting. However, I recommend this only if fertility is not a goal. If you’re hoping to conceive, your body needs the extra nourishment.

For those who do want to fast, a 24–36 hour fast can feel incredible. Oestrogen peaks during ovulation, reducing inflammation and giving women a beautiful window of metabolic flexibility.

But as always, listen to your body and support it depending on your goals. What feels amazing one month may feel completely different the next.

🍂 Luteal Phase (Days 15–28) Autumn Season.

Progesterone takes the lead, increasing body temperature and appetite. This is not the time for fasting or calorie restriction. Instead, support your nervous system with magnesium, complex carbs (to support progesterone production), and rest.

Nourishment Over Restriction, Your Body Knows Best 

I know it’s a big ask to ‘just listen to your body’ when life is busy and our intuition feels distant.

A gentle first step I teach my clients is tracking your cycle. Once you understand each phase, pause each morning and check in: What am I drawn to today? Am I ovulating and craving movement? Or am I in my luteal phase, needing warmth and comfort?

I call this biohacking the feminine way, using intuition and biology together. When you fuel your body properly, you balance blood sugar, support your nervous system, and naturally reduce visceral fat, all without extremes.

Support Your Cycle: The Feminine Biohack Approach

I know it’s really trendy and exciting trying out the new biohacks, like infrared saunas, tracking devices, or elaborate supplements. But before you go there, I want you to pause and ask yourself one simple question - Do I have the foundations covered?

So many women skip the basics that actually keep the body grounded. These nutrients, which are found in my bestselling bundle The Woman of Wellness, are the 5 key pillars that help hormones, gut, brain, and metabolism work in harmony:

✨ Vitamin B Complex + Vitamin C: The spark plugs for energy, focus, and stress resilience. They help convert food into fuel, regulate mood, and support adrenal health. Essential for women feeling drained, fatigued, or mentally foggy.

✨ Magnesium Complex: The mineral everyone needs, because most of us are deficient! It helps calm the nervous system, eases PMS, soothes headaches and supports deep sleep, while stabilising blood sugar and energy throughout your cycle.

✨ Vitamin D3 (with or without K2): Vitamin D is essential for hormone production, bone strength, and immune health. I recommend Vitamin D3 with K2 for most women, especially those who are peri-menopausal, menopausal, or have a history of bone weakness, as K2 supports calcium absorption for stronger bones and cardiovascular health.

✨ Microflora Complex (Probiotic + Prebiotic): Your gut is the epicentre of health. A flourishing microbiome supports hormonal balance, nutrient absorption, and reduced inflammation. It also helps metabolise oestrogen, supports mood and brain health, and even strengthens your immune system. Honestly, the list is endless, this is why the gut needs regular, ongoing support.

✨ Pure & Wild Omega 3 (or Vegan Omega 3): Omega 3 is one of the most powerful anti-inflammatory nutrients you can take. It’s key for brain health and fog, and it’s essential for hormone production (hormones literally need fat to function properly). It’s also proven to soothe cortisol, nourish the skin, and reduce visceral fat by supporting metabolic flexibility.

These five form the foundation every woman should build first. Once in place, you can layer in more targeted supplements.

A little note: If fasting still feels non negotiable for you right now, you can make it gentler by adding collagen, MCT and/or a dash of unpasteurized butter to your morning coffee to ease cortisol spikes and keep your nervous system steady.

Biohacking That Honours Her

From today, let’s focus on biohacking that honours the female body. And just to reiterate, fasting is fantastic when it’s used at the right moment. We don’t need to fast all month long. We need to ebb and flow, just like our hormones do.

Some phases support fasting beautifully, like ovulation. Some phases benefit from a longer fast, like Day 1 of your cycle (for certain women). And other phases need softness and nourishment instead, especially the luteal phase.

So try to understand the season of your cycle and plan your workouts, fasting windows, and lifestyle around it. When you start listening to your body’s rhythm, fasting becomes optional and a powerful tool when it’s honoured correctly.

Let’s make the future of wellness less about extremes and more about alignment. Still honouring the brilliance of science, but also the brilliance of your own body.