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Why excessive keto and fasting may be throwing off your cycle, weight loss and shiny hair

Hormone health with keto, fasting and carb cycling

Why excessive keto and fasting may be throwing off your cycle, weight loss and shiny hair

Most that have the slightest interest in health, nutrition and anti-ageing likely have heard of the amazing benefits of a keto diet and intermittent fasting by now. They are all over the media. Keto and fasting have been touted to help with anything from weight loss, cardiovascular health markers, preventing and supporting Alzheimer’s, autoimmune conditions to cancer, and be the magic bullet for anti-ageing (1, 2, 3). Who wouldn’t want to jump on that train!

Sounds too good to be true? It may be. When you read about it, there is generally this small little note at the end saying that keto and fasting may not be suitable for women, that it could cause hormonal havoc, weight gain, irregular periods and even lead to infertility. Finding this terribly confusing? A thing that is meant to be the infinite pool of youth and health could be doing the exact opposite? I hear you. After years of attending many lectures and continued education with our Functional Medicine thought leaders, that always seemed to end with that little sentence of ‘this may not be right for females’ I felt frustrated on what to prescribe for my patients. Many, if not most, of my patients are females, and what was I meant to say to them? Being German it was so very unsatisfying having to say ‘maybe do this, and maybe avoid that’. Being the science nerd that I am, I need facts, and a clear guideline so I can make sure I give the very best advise to my patients, at any point in time. This vague ‘maybe’ was not good enough.


I decided to dig deep into research papers, biochemistry, genetics, on a quest to find the exact how to and when best to use keto and fasting for women, when not to do it, what factors play a role in when it is a good time to use or avoid keto and fasting, and how to reap the biggest benefits without getting into trouble. Hundred research papers later, I connected the dots of already published papers, so that we can take the guesswork out of your health, hormones, weight and wellbeing.


But firstly, in today’s, let’s briefly review what keto and fasting are, their benefits, and how they may lead to irregular cycles, hormone imbalances and hair loss.

What is ketosis


Our body generally uses sugars to create energy for all its processes. When we eat carbohydrates, our body makes the hormone insulin which pulls the sugar from the carbs into our cells to utilize, and store any excess. When there is a lack of sugars, the opposite happens, our body switches off insulin and its fat storing machinery, and instead releases stored fats into the blood stream via the hormone glucagon. Our liver then makes ketone bodies from this fat, which can be used as an energy supply instead of glucose (sugar). When we burn fat for fuel, it burns a lot ‘cleaner’, creating less ‘smoke’ (free radicals), with less damage to our cells. It also allows a process called ‘autophagy’ to ramp up. Autophagy is our very own cleaning company, it’s the process by which the body gets rid of old, sick and mutated cells. Being in a ketogenic state upregulates autophagy.


Why fasting


Fasting has been used for a very long time. Hippocrates, the father of Western medicine, believed fasting enabled the body to heal itself. Paracelsus, another great healer in the Western tradition, wrote 500 years ago that “fasting is the greatest remedy, the physician within.

After a while of fasting, the same process happens as described above in ketosis. Our body switches over to ketosis/ fat burning for fuel, rather than sugar burning, upregulating autophagy, our cellular renewal and cleaning up. Fasting has been shown to reset our immune cells (calming over active cells such as seen in autoimmunity, and activating our defense mechanism where it is too slow). It recycles cells of our skin and organs, serving as the magic bullet of ‘anti-ageing’.

When fasted, our levels of a substance called mTOR drop, which has been shown to be beneficial in preventing mutations (and with it cancer cells).

Fasting (and being in a ketogenic state) has been shown to improve blood lipid profiles like triglycerides, cholesterol, inflammatory markers like HsCRP, can restore insulin and leptin sensitivity which is often thrown off in our society. The common insulin and leptin resistance makes us more prone to type 2 diabetes, obesity, Alzheimer’s, cardiovascular and thyroid disease.

Ketosis and fasting, once the body knows how to use ketones, has further been shown to increase mental performance, keeping the brain sharp and focused (4).


All of this is great news, and many of us have jumped on the wagon of intermittent fasting and a ketogenic diet, as why wouldn’t you if you read all these amazing benefits. Where there was insulin resistance caused by a high carb diet prior with symptoms like PCOS, brain fog, infertility, hangriness and belly fat, I saw my patients’ cycles normalise, body tone, mood and brain performance improve. Studies show just that, where there was too much sugar, too little female hormones previously, short term fasting can improve this and be a great tool to get back to balance (5).

Until one overdoes fasting and keto. The above mentionned benefits stall. Weight creeps back up, maybe the cycle started to get irregular, more crampy, the hair is falling out and energy levels drop.

Many thought leaders in the Functional Medicine and biohacking fields were seeing the same, and either vaguely said to introduce more carbs and do less fasting such as in the newly termed ‘crescendo fasting’ (but wait, what about the benefits of keto and fasting? How much of what is ok?), advised to ignore the symptoms and labs, or advocated for much stricter and longer fasts, like only one meal per day, or only eating every other day. Because, after all, research showed how beneficial keto and fasting is.

What’s the big deal if it throws off you hormones? The importance of a regular cycle for women


Both men and women have estrogen, progesterone, testosterone, thyroid and many other hormones like insulin, glucagon, leptin, ghrelin. They are all intrinsically linked, and when one gets thrown off, it has a domino effect on the entire body and its health pathways. However, as women have monthly cycles with hormones going up and down depending on where in their cycle they are, they are a little more sensitive to the hormone levels (men often get away with things for longer), but also easily show if something is off. The health and regularity of a female cycle not only says something about their fertility, but depicts how healthy all the other pathways in their body are.



Common pitfalls and hormone issues seen in prolonged fasting and a ketogenic diet 


I have always been an advocate of carb cycling, and the importance of keeping some carbs in the diet on the higher end of what is still acceptable on a keto diet, but commonly see my female patients (and myself!) skipping the carb refeed day, and/or the carb portions throughout their week, thinking they will get even better results. However, their complaints of hair falling out, stalling weight loss, and irregular cycles are accompanied by lab test results showing below optimal free T3 (the active thyroid hormone), excess estrogen during day 21/ the second phase of their cycle, and having above optimal blood sugar levels despite being in ketosis. Studies are confirming that excessive fasting, keto and caloric restriction can all cause estrogen dominance in females by increasing their estrogen levels (6) but additionally even upregulating their estrogen receptors (7), meaning the existing estrogen has more of an effect! Why is that, and why are these important?


Estrogen dominance and keto


Estrogen dominance means that you either have too much estrogen, or too little progesterone in relation to estrogen, while estrogen is in the normal range. I commonly see women in their reproductive years (before menopause) to have very high estrogen levels in the second half of their cycle, accompanied with either low, normal or even high progesterone.

While estrogen is a crucial hormone for females, as it keeps our hair shiny, skin radiant, curves curvy and fertility high, if there is too much estrogen, we run into many problems.

Estrogen helps to grow things. Estrogen levels that are above optimal have been implicated in cysts, fibroids, endometriosis, PCOS, cancers, anxiety, gallstones, HPV, excessive curves (big butt and thighs!), histamine intolerance (such as sneezing, runny nose, asthma) and many more problematic situations.


So how come a prolonged keto diet and excess fasting can lead to high estrogen, and why is no one talking about this?


It all has to do with a small enzyme called CYP17a1. One of CYP17a1’s main roles is to convert cholesterol into DHEA, a hormone that gets a lot of great press for its belly fat blasting, mood and resilience boosting, anti-ageing properties. And we do want enough DHEA! DHEA often drops with age, with low DHEA being linked to many age related illnesses. However, as with so many things in our body, we need things to be just right. Not too low, but also not too high. DHEA is the precursor for estrogen and testosterone, and high DHEA levels have been linked with high estrogen and/or androgen levels as a result. So what do keto and fasting have to do with this?

Researchers found that CYP17a1 is also needed in the process of ketogenesis. It gets upregulated when the body is producing ketones from either being in a very low sugar or fasted state (8, 9). It is thought that the higher levels of DHEA are there to increase vigilance and survival. When we are fasting/ are in a ketogenic state for too often and too long, we also risk overproducing DHEA, estrogen (and potentially testosterone), as long as there are enough precursors present in the body. As DHEA is made from cholesterol, which is plentiful in the body as long as we have enough fat stored in the body or are consuming it. And many of us on a keto diet ‘go overboard’ on ‘good fats’.


Next up: Keto, fasting and ovulation


Ovulation, what? Unless you are planning (or have planned) for a pregnancy, chances are you aren’t that familiar with your cycle. Most of my clients and girlfriends walk through life not knowing what ovulation means, when in your cycle it happens, and why it is so important after all. In a nutshell, around day 14 of your cycle (with the count starting on your first day of your period), your brain releases a hormone called Luteinising Hormone (LH), which triggers your ovary to release an egg from a follicle (= ovulation). The follicle turns into a mass called ‘corpus luteum’ which produces progesterone during the second half of your cycle. We need progesterone to balance out estrogen, promote a healthy lining in our reproductive tract for a potential pregnancy, but also to improve mood, reduce PMS symptoms, endometriosis and much more.

LH is crucial to kickstart the ovulation, formation of the corpus luteum, and resulting progesterone production. Now, if our body thinks we are starving (too much), it drops its levels of a substance called kisspeptin. Kisspeptin is needed to stimulate LH release. Without it, there isn’t enough LH, nor resulting ovulation, corpus luteum nor progesterone. Not only does it throw off your cycle, but it also makes you less fertile (you need to ovulate to free up that egg to be ready to be fertilised! Secondly, you need the progesterone to make your lining fertile enough to get the fertilised egg to stick, stay and grow).



Keto, fasting and your thyroid


The next topic generally gets a bit more press. Another very common pitfall is a drop in active thyroid hormone (fT3), and resulting hair loss, cold extremities, stalled metabolism. Basically when your thermostat (the hypothalamus in your brain) measures a lack of food during prolonged fasting, and/or low insulin due to a very low carb intake, it thinks you are starving. It is the same mechanism that links your low food/carb intake to a potential drop in kisspeptin and ovulation (see one section up). To preserve energy and stores, your body drops its metabolism (aka your thyroid), and reduce the amount of thyroid precursors (T4) that get turned into the active form (T3). Some insulin is needed for this conversion to occur. The good news, which often gets stated in the Functional Medicine and keto world, is that a ketogenic diet if done intermittently does not drop the thyroid hormone precursors (such as TSH and free T4) (10). This means your body likely can ramp the metabolism back up quickly when it stops being in perceived starvation. However, the temporary lack of the active thyroid hormone if doing fasting and keto excessively does mean that your hair may be falling out, and your weight loss may stall.


Keto, fasting and inflammation


Being in a ketogenic state, which defined by high levels of the ketone beta-hydroxybutyrate, has anti-inflammatory effects. However, being in a fasted state excessively has shown to downregulate the elimination of an inflammatory substance called COX2 (the one we aim to avoid with NSAIDs- over the counter anti-inflammatories) via the enzyme CYP4f14 (11). COX2 has been implicated in endometriosis and many other conditions (12).


Keto, fasting and your stress hormone cortisol

Another potential problem with doing too much keto and fasting can be its effect on the stress hormone cortisol. Being in ketosis spikes your cortisol levels, which can be a good thing short term, as it helps liberate fat stores and suppresses hunger by increasing circulating dopamine levels (13). However, if that stays ramped up throughout the day, when cortisol should naturally drop to allow for a restful sleep at night, it can disrupt your circadian rhythm, sleep and recovery, which dysregulates our brain- cortisol cycle even more (HPA axis) (13).

Chronically high stress levels have been shown to lead to excess fat storage, especially on your waist line, contributing to abdominal obesity, which has been linked to metabolic syndrome. Studies also show that chronically elevated cortisol has the opposite effect to its acute appetite suppressing effect, and in fact upregulates hunger. It downregulates the region in our brain that helps us make ‘smart choices’, the prefrontal cortex, dopamine levels, and concomitantly upregulates our limbic region, which makes us more sensitive to food cues, emotional eating, the inability to stop, impulsivity and substance abuse, including binge eating (13).

A study done in rodents found that when fasting up to 24 hours, heart rate variability (a marker of health and longevity (14)), goes up, where when fasting extends beyond that, it goes down (=not a good thing) (15). Most of my patients already operate on high stress levels due to executive roles in their jobs or family life, and that extra cortisol may just tip them over the edge.

Cortisol production has also been shown to compete with progesterone, both of which get made from the same precursor. If the body produces excess cortisol, progesterone commonly drops, which contributes to issues in the second half of your cycle, such as spotting, moodiness, PMS and infertility.

I don’t generally recommend extended (beyond 24 hours) fasting for women, unless they have a serious health condition where the upsides of the fast outweigh the downsides of the hormonal havoc. But what about the common intermittent fasting of +/- 16-18 hrs of fasting or the OMAD (one meal a day) approach?


Early vs late time restricted eating (aka intermittent fasting) and meal timing


More recently, our circadian rhythm has received a lot more interest in the research community. Studies on early time restricted eating where the eating window is compressed to earlier in the day has been linked in several studies to improved health markers, such as improved cortisol (stress!) response throughout the day, blood sugar and lipids, autophagy, anti-ageing markers like sirtuins and brain health BDNF, and helps reset the circadian clock of all organs (16).

Another study showed that breakfast consumption acutely affects clock and clock-controlled gene expression leading to normal oscillation. Breakfast skipping adversely affects clock and clock-controlled gene expression and is correlated with increased postprandial glycemic response in both healthy individuals and individuals with diabetes, shown as larger blood sugar swings after meals if breakfast was skipped (17).

A study done on females showed that female breakfast skippers display higher blood pressure, disrupted cortisol (stress hormone) rhythm throughout the day with the cortisol staying elevated later in the day where it should normally drop off naturally (18).

Eating late in the day, post normal dinner time, has been linked to detrimental health outcomes. Compared with patients without night-eating behaviors, those with these behaviors were less adherent with diet, exercise, and glucose monitoring and more likely to be depressed, to report childhood maltreatment histories, to have nonsecure attachment styles, and to report eating in response to anger, sadness, loneliness, worry, and being upset (19).

On the contrary, a contradicting recent study found that there was no significant correlation between skipping breakfast and risk factors of metabolic syndrome (after adjusting for risk factors), but a tendency of skipping breakfast to lower the risk of metabolic syndrome was observed.

This may all sounds quite confusing, but another recent study demonstrated that time restricted eating was beneficial if eating was initiated no later than 1pm, with benefits on health markers found if eating between 1 and 8pm rather than waiting until 4pm (20).


I don’t know about you, but I do know that myself and my patients generally rather stay away from estrogen dominance and its associated risks, irregular and painful cycles, stalled weight and hair loss.


So now what? Where does that leave you in regards to fasting, keto and best strategies for anti-ageing and hormone health? We will dive into how to implement keto and fasting in a safe way, depending on your individual hormone levels, when to upregulate keto and fasting, when to downregulate it, and when to add in more frequent meals and carbs in a next article.

What is your experience with fasting and keto? I would love to know in the comments below. x


  1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6251269/
  2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4534007/
  3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6653417/
  4. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5388543/
  5. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5427116/
  6. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3558496/
  7. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4534007/
  8. https://academic.oup.com/mend/article/23/8/1171/2684005
  9. https://journals.physiology.org/doi/full/10.1152/physiolgenomics.00203.2003
  10. https://pubmed.ncbi.nlm.nih.gov/29344467/
  11. https://www.sciencedirect.com/science/article/pii/B9780080919065000082
  12. https://www.frontiersin.org/articles/10.3389/fphar.2020.01233/full
  13. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4214609/
  14. https://www.health.harvard.edu/blog/heart-rate-variability-new-way-track-well-2017112212789
  15. https://www.nature.com/articles/ejcn201332.pdf
  16. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6627766/#B45-nutrients-11-01234
  17. https://pubmed.ncbi.nlm.nih.gov/28830875/
  18. https://pubmed.ncbi.nlm.nih.gov/25545767/
  19. https://pubmed.ncbi.nlm.nih.gov/16873783/
  20. https://onlinelibrary.wiley.com/doi/full/10.1002/oby.22776
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It is my goal to empower you to become the CEO of your health trajectory, preventing and optimising with precision and science backed strategies to live your best life & thrive.

6 Responses

  1. This article is so enlightening.
    Im 54 and have been through
    Menopause and am so much more heavy then me at 49..hence attempting IF. Its mainly all belly and back fat.
    I never realized how great a roll female hormones played in our lives. This paper really emphasizes this for me. Im no where near doing any of the “proper IF or OMAD” practices. But it has stopped me just gorging and being mindful rather. Funny true story, when i was 22 yrs old i was a dancer in Asia and landed up living in HK. I hated buying my meat from “wet markets” to cook at home..flys and just gross seeing it hanging out all day.
    Long story short,ended up living on salads..I returned home to SA after 2 years, weighing 55kg (Im 1.82) covered in facial serious acne (boil like) and i remember being told it was due to my hormone embalence..
    Oh im now about 100kg
    5 years ago 70kg..

    1. Dear Meme,

      I am glad you found this article helpful! Intermittent fasting is a great first step to cut excess calories and stop mindless eating, you are absolutely right!
      I will be writing about how to cycle carbs in menopause in another article soon.
      Looking forward to chatting then,

      Best wishes,


  2. Hi, I have been suffering for hypothyroid since past 15 years. My current dose of thronorm is 125 microgram. Do you think intermittent fast is OK for me? I do include some carbs in one meal a day and eat a lot of veggies and fruits. I am a vegetarian but eat eggs (once a week) and fish (around once a month) occasionally.

    1. Dear Sasha,
      It is impossible for me to give you a definite answer without having met you/seen your labs and health. However, purely from a thyroid perspective, this should be ok as long as you keep that portion of carbs in. However, the bigger question is, why is your thyroid off? Are you eating enough protein? (sometimes difficult on a vegetarian diet), too many carbs? Not enough iodine, selenium, zinc, vitamin C, iron? Have you tested for thyroid auto-antibodies and food intolerances? They are often a culprit your thyroid may not be functioning properly. I hope this helps!! 🙂

      1. Hello, thank you for your reply. Sorry could not reply earlier. So far no doctor has asked me to do auto-antibodies test and test for food tolerances. I have developed allergies to a few food items after the birth of my children. Whenever I go do a doctor, they simply check TSH, T3 and T4 and prescribe thyronorm.

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