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TL;DR
- The Ancestral Why: Fasting isn’t a fleeting trend; it’s a biological heritage. Our bodies evolved in a feast and famine cycle, making us metabolically optimized for periods of scarcity.
- Hormone Harmony: For women in their 30s, IF can be a tool for balancing insulin and supporting PCOS, but it must be done crescendo style to protect cortisol and thyroid health.
- Keto Synergy: Fasting is a fast track to ketosis. If you’re already keto, intermittent fasting becomes significantly easier because your body is already fat-adapted.
- The Myth: Fasting doesn’t break your metabolism or cause muscle loss. As with all things, there’s an optimal way to do it and a sub-optimal way.
- Safety First: Women should cycle their fasting intensity with their menstrual phase. Quick tip: more fasting in the follicular phase, less in the luteal phase.
Table of Contents
The Evolutionary Blueprint: Why We Are Born to Fast
We live in a world of 24/7 caloric abundance, but our DNA is still calibrated for a time when we had to work to find food. For 99% of human history, the concept of breakfast – or a meal that breaks your fast – didn’t exist until something was hunted or gathered.
Although many of us are living a life where your next snack is steps away in your pantry, or a few clicks away on your favourite food delivery app, our bodies are still operating on an old-school model for feeding ourselves.
The Feast and Famine Cycle
Our ancestors didn’t eat three square meals a day with snacks in between. They practised involuntary intermittent fasting. This created an evolutionary pressure that favoured people who could remain physically active and mentally sharp during a fast.
The people who survived and ultimately passed on their genes all the way down to the present generation are the ones who could survive days without a proper meal. This evolutionary pressure made us good at fasting so that when a meal would come along, we had the mental focus and physical energy to hunt it down with the same force as we would if we had just eaten.
This is why, when you fast, your body increases adrenaline and norepinephrine. This is the energy boost that’s common to experience when you’re well into your fasting period. Your body is trying to give you the energy to go find food.
Metabolic Flexibility: Our Lost Superpower
Metabolic flexibility is the ability to switch between burning glucose (sugar) and burning fat (ketones). In the modern world, most people are sugar burners, meaning they feel shaky and hangry if they miss a meal.
One of the many benefits of intermittent fasting restores the ancient ability to tap into our own body fat for fuel, a process that is essential for long-term longevity and preventing metabolic disease. It also frees you from feeling like you’re always thinking about your next meal.
I regularly practice intermittent fasting and love the moment when I feel like I’ve been released of a nagging sense of “I need to find a sweet treat right now!”
It’s crazy, but I also want you to know that I am not judging you if that’s your experience. Multi-billion dollar corporations with tons of money for research and development have designed a world of addictive snacks.
I am someone who can really get stuck in a snacking vortex. The dopamine hit combined with the high-sugar and high-salt content of my favourite snacks means that I genuinely do feel like something else is controlling my body, and if I don’t get another hit of my favourite salty-sweet snacking combo, I will go crazy.
I get it. I really do. Which is why I feel so passionate about intermittent fasting, because it was one of the tools I discovered to break that snacking cycle that was affecting my skin, my mood, and my overall health.
I know there are a lot of opinions out there about intermittent fasting, so I am going to take the next section to myth-bust some of them.
Myth-Busting: Debunking the Top 5 Intermittent Fasting Lies
Before we dive into the “how,” we have to clear the air. There is a lot of misinformation circulating about fasting, especially for women.
- Myth #1: “Fasting Will Damage Your Metabolism.”
- The Reality: Chronic caloric restriction (eating 1,200 calories every day for months) slows metabolism. Short-term fasting actually increases metabolic rate by up to 14% by boosting norepinephrine.
- Myth #2: “You’ll Lose Your Hard-Earned Muscle.”
- The Reality: Fasting triggers a massive surge in Growth Hormone (GH), which is muscle-sparing. As long as you hit your protein targets during your eating window and keep lifting, your muscle mass is safe.
- Myth #3: “Breakfast is the Most Important Meal of the Day.”
- The Reality: This was a marketing slogan created to sell cereal in the early 20th century. Your cortisol is naturally highest in the morning; adding a high-carb breakfast can actually cause a massive insulin spike that leads to a mid-afternoon crash.
- Myth #4: “Fasting Causes Eating Disorders.”
- The Reality: For most, IF is about when to eat, not how much and at its best, can fix broken hunger signals (leptin and ghrelin). However, it is not recommended for those with a history of clinical EDs.
- Myth #5: “Women Simply Shouldn’t Fast.”
- The Reality: This is the biggest myth of all. Women can benefit immensely from fasting, but we have to fast differently than men to respect our more complex hormonal feedback loops.
The Female Factor: PCOS, Insulin Resistance, and Hormones
For women in their 30s, the our bodies are changing and so much of this change is driven by how our hormones are changing during this period.
This is the decade where insulin resistance often starts to creep in, and conditions like PCOS (Polycystic Ovary Syndrome) can show up and become more symptomatic.
PCOS and the Insulin Connection
PCOS is, at its core, a metabolic disorder driven by high insulin.
The cycle goes like this: High insulin levels tell the ovaries to produce more testosterone. Higher testosterone leads to acne, hair thinning, and irregular cycles. And if you’re anything like me, acne, irregular cycles and stubborn weight gain are the perfect storm of stress that makes me want to “treat myself” with something sweet. And so the cycle continues!
Intermittent fasting is one of the most potent ways to lower your fasting insulin, which in turn helps lower androgen levels and can restore regular ovulation.
Related Content: Inositol Deep Dive
Stubborn Weight and Mood Swings
The stubborn weight around the midsection in our 30s is usually cortisol and insulin-driven. Something I learned from Cat Bohannon’s book “Eve”, is that our body stores fat with a specific chemical make-up in specific areas of the body. When certain signals from the body require those fat cells, it is released from that specific area of the body to support whatever call was made from the other part of the body.
This is a bit confusing, but to use Cat’s example, the fat stored in our hips and thighs has specific nutrients that are used to help develop the brains of a growing fetus. So, when the body is in a state of dysregulation due to insulin sensitivity and high testosterone levels, our bodies store fat in our midsection.
By creating a fasting window, you give your insulin levels a chance to drop to baseline, allowing your body to access stored adipose tissue (fat), finally. Moreover, stabilised blood sugar means an end to the glucose roller coaster that causes irritability and mood swings.
Intermittent Fasting and the Keto Connection
If you’re already following a Ketogenic lifestyle, you have a massive advantage when it comes to fasting.
The Fast-Track to Ketosis
When you eat a standard high-carb diet, it takes about 24–48 hours of fasting to deplete your liver’s glycogen stores and enter ketosis. If you are already keto, you are already in a state of fat-adaptation. Your body will experience less hangry panic when you skip breakfast because it simply continues burning the fat you ate the day before, or the fat that is stored on your body.
Related Post: Why Do We Have Fat? (one of my favourite articles I’ve ever written)
Why Keto and Intermittent Fasting are a Perfect Pair
When I was talking with my sister earlier this year about doing keto again, one of the things we both mentioned we were excited for was how easy it was going to be to fast again. Going back to my previous point, being able to access fasting for us meant that we weren’t beholden to sugar-crashes or relentless cravings.
A ketogenic lifestyle and intermittent fasting really are the perfect pair, and here’s why:
- Appetite Suppression: Ketones naturally suppress ghrelin (the hunger hormone). This makes a 16-hour fast feel like a breeze.
- Mitigating the Keto Flu: Fasting helps your body reach deeper levels of ketosis faster, which can shorten the transition period of keto-adaptation.
- Enhanced Autophagy: Both keto and fasting trigger autophagy (cellular cleanup), but when combined, they act synergistically to deep clean your cells.
My mind is clear, my keto flu symptoms are non-existent, and my body is clearing out old cells, which is better for long-term health.
The Benefits Beyond the Scale: Autophagy and Mental Clarity
While many start intermittent fasting for weight loss – which is a nice perk if you’re feeling stuck – they stay for the brain gains.
Those brain gains are another one of the benefits my sister and I discussed before starting a keto lifestyle this year. She’s planning a wedding, managing a household, and working a demanding job. I am managing a busy social life, ambitious career goals, and building this community. Having a brain that is clear and running on the best fuel possible makes a huge difference.
Autophagy: Your Internal Recycling System
Autophagy (aw-taw-fudgey) is a natural process that is happening all the time in the body. Cells use resources and break down other cells, and there needs to be a system to clean up and recycle those used cells.
Enter: autophagy.
During a fast, your cells begin to break down old, misfolded proteins and damaged mitochondria. This process is essential for anti-ageing and longevity. For women with fair skin autophagy is a key player in maintaining skin elasticity and clearing out cellular damage.
You want to keep that youthful glow? Encourage more autophagy in your daily routine!
The Fasted High: Mental Clarity
Around hour 14 of a fast, many people report a sense of euphoria or intense focus. This is due to an increase in BDNF (Brain-Derived Neurotrophic Factor). BDNF acts like rocket fuel for your brain, supporting the growth of new neurons and improving synaptic plasticity.
When I was working full-time as a personal trainer, I used to do an extended fast every Wednesday. It was my longest day at work (6AM – 9PM) and I didn’t want to have any energy crashes throughout the day.
I remember that as my body got used to doing this fast, at around 2 PM every day I would get this surge of energy. It honestly felt like I could see more clearly, hear more sounds, and like there was all of this fresh, clean energy running through my body. It was an incredible feeling and I started to look forward to it every Wednesday!
Intermittent Fasting Comparison Table
Everyone has their own idea of the ideal fasting routine. When I was first introduced to fasting in college, my classmate talked about eating between 10AM and 6PM, a classic 16:8 fasting to feasting ratio.
I am a big fan of the 16:8, but have also dabbled in 24hr fasts, 18:6 and 20:4 fasts. It all depends on the day, really. But I would say that 16:8 is a good target if you are starting out. Here are some other fasting options and what they are best for:
| Method | The Protocol | Best For |
| 12:12 (Circadian) | 12h fast / 12h eating | Beginners, High-stress weeks |
| 16:8 (Leangains) | 16h fast / 8h eating | Daily maintenance, Fat loss |
| 14:10 | 14h fast / 10h eating | Women with thyroid issues |
| OMAD | One Meal A Day | Deep autophagy, Advanced |
| 5:2 Method | 5 days normal / 2 days 500kcal | Breaking weight loss plateaus |
| Crescendo | Fasting 3 non-consecutive days | Protecting the menstrual cycle |
Step-by-Step Crescendo Fasting Guide
Don’t jump into a 24-hour fast on day one. The experience will be unpleasant, and from experience, this usually leads me to eat like it’s my last day on earth when I finally end my fast.
To ease yourself into fasting, and dip your toes into this practice, follow these steps:
- Week 1: The 12-Hour Reset. Simply stop eating after dinner (e.g., 7 PM) and don’t eat until 7 AM. No late-night snacking, but also perfect for making fasting easy – you’ll be sleeping for most of the time!
- Week 2: The 14-Hour Window. Push breakfast back by 2 hours. Eat from 9 AM to 7 PM.
- Week 3: The Crescendo. Fast for 16 hours, but only on 3 non-consecutive days a week (e.g., Tuesday, Thursday, Saturday). On other days, stick to 12:12 or 14:10, depending on how you feel.
- Week 4: The 16:8 Standard. If you feel great, move to a daily 16:8 window, but remember to listen to your body.
Cycle-Syncing Your Fast: A 28-Day Strategy
I’ve seen a lot of chit chat online about how fasting is the worst possible thing for your menstrual cycle. I can promise you, it is not the wrost thing for your menstrual cycle. As we’ve already discussed, there are so many benefits to intermittent fasting when done with intention and a balanced approach.
Part of being intentional about fasting is to consider your menstrual cycle and how the fluctuations in hormones can influence the fasting experience. Basically, you shouldn’t fast the same way every week of the month.
Here’s a cycle-synced plan to help you optimize your fasting with your fifth vital sign.
- Days 1–10 (Follicular Phase): This is when you are on your period and the week after your period. Estrogen is low and then rising. Your body is more resilient to stress. This is the best time for 16:8 or even the occasional 20-hour fast.
- Days 11–14 (Ovulation): Estrogen peaks. You might feel extra energetic. Stick to 14:10 or 16:8.
- Days 15–21 (Early Luteal): Progesterone is rising. Your body is preparing for a potential pregnancy. Keep fasts gentle (12-14 hours).
- Days 22–28 (Late Luteal/PMS): Listen to your body and don’t be too extreme with your fasting windows. This isn’t the time test your first 20 hour fast. Your body is most sensitive to stress right now. Pushing a fast will spike cortisol, ruin your sleep, and make PMS worse. Focus on nutrient-dense keto meals and restorative movement. But again – listen to your body. She will always tell you what she needs when she needs it.
Safety, Precautions, and When to Stop
Intermittent fasting is a hermetic stressor, ie. a good stress that makes you stronger. But too much of a good thing becomes a “bad” stress.
Signs you should stop or scale back:
- Your period disappears (Amenorrhea): This is a red alert that your body feels unsafe.
- You can’t fall asleep: High nighttime cortisol from over-fasting causes “wired but tired” insomnia.
- Hair thinning: A sign of thyroid slowdown or protein deficiency.
- Constant coldness: Your body is down-regulating your basal metabolic rate to save energy.
Who should NOT fast:
- Pregnant or breastfeeding women.
- Anyone with a history of disordered eating.
- Type 1 Diabetics (unless under strict medical supervision).
- Those with advanced adrenal fatigue or burnout.
Frequently Asked Questions (FAQ)
Black coffee is fine and can actually enhance autophagy. However, once you add cream, sugar, or MCT oil, you are technically breaking the fast (though “fat fasting” with MCT oil is a valid strategy for keto-beginners).
Yes! For many, fasted cardio or a fasted lifting session (like HYROX prep) leads to better fat oxidation. Just ensure you have your electrolytes (and maybe that Magnesium Malate we talked about!) ready.
Over-fasting can lower T3 (active thyroid hormone). This is why “cycle syncing” and eating enough calories during your window is so critical for women.
Avoid a “carb-bomb.” Break your fast with high protein and healthy fats—like eggs with avocado or a protein shake. This prevents a massive insulin spike.
No! In fact, you need more salt while fasting because your kidneys flush sodium when insulin is low. A pinch of high-quality sea salt in your water is a fasting essential.
Final Thoughts
Intermittent fasting isn’t about restriction; it’s about rhythm. It’s about aligning your modern life with your ancient biology. When done correctly it can be a powerful and freeing tool for you to reclaim your energy, and balance your hormones.
