Fasting, Your Genes & Perimenopause: Why fasting works for some women… and not for others

by Julie Smullen FNC CGP CGC

Fasting is something I get asked about constantly. It comes up in conversations with clients, friends, even people I meet day to day, and more often than not, those conversations are what spark these blogs, which I genuinely love. I’ve explored fasting myself at different points and have experienced just how powerful it can feel when it suits your body.

It’s often spoken about as though it’s universally beneficial, a simple, effective tool to support weight loss, hormone balance, blood sugar regulation, inflammation and overall metabolic health.

And while that can absolutely be true… it’s only part of the story.

Because what is often missing from the conversation is this:

Fasting is not experienced the same way by everybody.

Particularly for women moving through perimenopause, where hormonal fluctuations, stress sensitivity and metabolic changes are already present, fasting can either feel supportive and regulating… or deeply depleting.

So instead of asking whether fasting is “good” or “bad”, a far more useful question becomes:

Who is fasting right for and why? 

Fasting is a stress… and context determines whether that stress is helpful

At a physiological level, fasting is not a passive process.

When food intake is reduced or removed, the body must adapt in real time. Blood sugar regulation shifts, cortisol rises to maintain energy availability, and stored fuel sources begin to be mobilised.

Detoxification pathways are also engaged more heavily as fat stores are broken down.

In a well-supported system, this can be beneficial. The body becomes more metabolically flexible, inflammation may reduce, and energy regulation can improve.

However, in a system that is already under strain, whether from chronic stress, poor sleep, undernourishment, gut dysfunction or hormonal imbalance, this same process can feel overwhelming.

This is why some women report clarity and energy when fasting, while others experience anxiety, fatigue, disrupted sleep and worsening hormonal symptoms.

The difference is not discipline; It's capacity.

Why fasting can feel different in perimenopause

Perimenopause is not simply a decline in hormones, it is a period of fluctuation and recalibration.

Oestrogen levels can rise and fall unpredictably. Progesterone often declines, reducing the body’s natural buffering effect against stress. Cortisol sensitivity tends to increase, and blood sugar regulation can become less stable.

This means the body is already working harder to maintain balance.

When intermittent fasting is layered on top of this, it acts as an additional signal, one that the body must interpret.

For some, this signal is manageable.

For others, it is perceived as a stress that the body is not currently resourced to handle.

This is why fasting for women over 40 often requires a far more individualised approach.

The genetic piece most people are missing

Fasting can affect people very differently, and one of the other reasons for this is individual genetic expression. While we don’t need to go into too much detail, there are several important genetic pathways that influence how your body responds to the stress created by fasting.

These include:

• Methylation and detoxification pathways (e.g. MTHFR, COMT)

• Stress response and nervous system regulation (e.g. COMT)

• Histamine processing and inflammation (e.g. DAO)

• Oxidative stress and antioxidant support (e.g. SOD2, GST pathways)

Variations within these pathways can influence how efficiently your body:

• Processes and clears stress hormones

• Handles the release of toxins during fat breakdown

• Maintains neurotransmitter balance

• Regulates inflammation

For example:

• If detoxification pathways are slower, fasting may increase the release of stored compounds faster than the body can eliminate them, leading to symptoms such as headaches, fatigue or brain fog.

• If stress-response pathways are more sensitive, the cortisol rise that accompanies fasting may feel excessive rather than supportive.

• If histamine regulation is compromised, fasting may contribute to anxiety, irritability or sleep disruption.

  
  

This is why two people can follow the same fasting plan and have completely different experiences.

It is not just what you are doing, it is how your body is equipped to respond.

Tools such as SmartDNA can provide insight into these patterns, helping guide a more personalised approach to fasting, hormone balance and overall health.

Nourishment must come before restriction

A consistent pattern seen in practice is that many women attempt fasting in a state of underlying depletion.

Low mineral intake, inadequate protein, chronic stress, disrupted sleep and long-term under-eating all reduce the body’s resilience.

In this context, fasting does not create balance, it amplifies imbalance.

Particularly in perimenopause, the body is seeking signals of safety and stability. Adequate nutrition, regular meals, blood sugar balance and nervous system support form the foundation upon which any therapeutic fasting approach should be built.

Without this, fasting becomes another stressor layered onto an already overwhelmed system.

A different approach: fasting within a therapeutic, nourished framework

It is important to recognise that not all fasting approaches are the same.

Modern fasting often focuses on restriction, skipping meals, extending fasting windows and pushing through hunger in pursuit of weight loss or metabolic outcomes.

However, traditional therapeutic approaches take a very different perspective.

Within frameworks such as those outlined in Gut and Psychology Syndrome, fasting is not about deprivation, but about strategic digestive rest combined with deep nourishment.

There are multiple variations within this approach, including:

• Structured stages that gradually support gut healing

• Modified fasting using meat stock and easily digested foods

• “No-plant GAPS” variations for sensitive individuals

• Periods of reduced digestive load rather than complete food removal

In this context, the body is not left unsupported.

Instead, it is provided with:

• Mineral-rich meat stock

• Easily absorbable nutrients

• Support for the gut lining

• Reduced inflammatory burden

For many women, particularly those who struggle with fasting, this approach to gut health and fasting can feel far more sustainable and supportive.

So where does this leave fasting for women?

Fasting is neither inherently beneficial nor inherently harmful.

It is a tool for metabolic health, hormone balance and gut support, one that must be applied with consideration of:

• Current hormonal state

• Stress load

• Nutritional status

• Gut health

• Genetic tendencies

For some women, fasting will enhance health outcomes.

For others, the priority will be restoring nourishment, stability and resilience before any form of fasting is introduced, if at all.

Final thoughts

If fasting feels good in your body, supportive, steady, energising, it may be something that aligns with your current physiology.

If it leaves you feeling depleted, anxious, fatigued or hormonally disrupted, that is not something to override or push through. It's information and it is worth listening to.

Because real health is not built on rigid protocols or borrowed routines.

It is built on understanding your body, its signals, its needs, and its capacity and responding accordingly.

Ready to find what works for you?

If you’re unsure whether fasting is right for your body, feel free to reach out.

Or, for a more personalised approach, you can book your SmartDNA wellness test and gain deeper insight into what truly works for you.

References

• Longo, V. D., & Mattson, M. P. (2014). Fasting: Molecular mechanisms and clinical applications. Cell Metabolism

• Anton, S. D. et al. (2018). Flipping the metabolic switch: Understanding the benefits of fasting. Obesity

• Patterson, R. E. et al. (2015). Intermittent fasting and human metabolic health. Journal of the Academy of Nutrition and Dietetics

• Choi, I. Y. et al. (2020). Intermittent fasting and metabolic regulation. Nutrients

• Prior, J. C. (2018). Perimenopause: hormonal changes and clinical implications. Endocrine Reviews

• Campbell-McBride, N. (2010). Gut and Psychology Syndrome

Disclaimer

This blog is for educational purposes only and is not intended as medical advice, diagnosis or treatment. Intermittent fasting for women, particularly during perimenopause, should always be approached with individual consideration, as responses can vary based on genetics, hormone status and overall health. Always seek guidance from a qualified healthcare practitioner before making changes to your diet, fasting routine or lifestyle.