• Jacqui Niehaus

The darkside of intermittent fasting for female reproductive health

Updated: Feb 9

So many people in the health space are advocating for intermittent fasting (IF) these days. I see articles about IF popping up everywhere with huge promises for improved health, from weight loss, to better cognitive function, to enhanced longevity. However, from personal experience, as well from working with many ladies who have tried IF, there is definitely a dark side to IF.


After spending hours and hours digging through the research, my current stance is that IF is not optimal for health. In this article, I go through some papers that show detrimental effects to pre-menopausal woman in particular. I will then explain why so many papers show benefits, and how I believe we can achieve the same benefits without having to actually skip meals.


Firstly, most of the studies on IF are done on men or post-menopausal woman. Pre-menopausal woman are excluded from many research studies as it is difficult to standardise for hormonal effects that differ for each lady depending on where she is in her cycle. The few studies on IF that were done on pre-menopausal women actually show overwhelmingly negative consequences.


The hormones that regulate key functions (like ovulation and metabolism) are extremely sensitive to energy intake, especially for woman. Going long periods of time without eating forces our bodies to create fuel by using stress hormones (cortisol and adrenaline) to break itself down.


Over time, the continual over-production of stress hormones has many side effects, including irritability, loss of ovulation, estrogen dominance, rapid aging, hair loss, and more. This is because when the body is in a state of stress, it shuts down ‘non-essential’ processes (like reproduction).


Here we see evidence of this in the literature:

  • ‘Reproductive processes, including the hypothalamic-pituitary-gonadal (HPG) system and the mechanisms that control sex behavior are most proximally sensitive to the availability of oxidizable metabolic fuels.’ [1]

  • ‘Thus, in states of severely altered energy balance (either negative or positive), fertility is compromised’ [2]

  • ‘In female track and field athletes, functional hypothalamic amenorrhea as consequence of Low Energy Availability has been reported among 60% of elite middle- and long-distance athletes and 23% among elite sprinters. Health concerns with functional hypothalamic amenorrhea include impaired bone health, elevated risk for bone stress injury, and cardiovascular disease.’ [3]

  • ‘menstrual abnormalities during Ramadan month reach to their peak and three months after Ramadan reduce but do not return to previous condition.’ [4]

  • ‘The mild energy-restriction diets (20% CR and IF) significantly increased the proportion of animals displaying irregular cycling patterns, whereas the 40% CR animals displayed an almost complete loss of estrous cyclicity. The females on the HFG diet continued to cycle but exhibited an increase in cycle irregularity.’ [5]


We can see that being in a low-fueled state can be detrimental to the reproductive health of females. One may argue that IF should therefore only be excluded when trying to conceive. However, the health of our fertility is about so much more than getting pregnant. Fertility is an indicator of the state of our overall health, and an irregular cycle is an early warning sign of an underlying health problem.


But what about all the papers that do show benefits? Well, I wonder if the benefits of fasting are really due to the fact that you aren’t eating anything during the fasting window, or due to the fact that you simply aren’t eating gut-irritating foods during the fasting window.


Whenever someone sends me a paper showing the benefits of intermittent fasting, I always ask the same question:


“WHO WAS THE CONTROL GROUP?”


We can only really assess the ‘benefits’ of intermittent fasting in relation to what the control group was eating while the test group was fasting.


The benefits of IF are often attributed to modulating gut bacteria, thereby reducing inflammation. To which I say there are far less stressful ways to achieve the same results. This includes reducing the consumption of hard-to-digest foods such as excess amounts of nuts and seeds, cruciferous vegetables and underprepared grains.


If we compared IF to those eating easier-to-digest foods, I suspect we wouldn’t see the same benefits. And perhaps the negative side effects would be highlighted, such as our body having to rely on stress hormones to bring our blood sugar back up. Elevated stress hormones come at a cost - in the form of slowing thyroid function, reproductive function, immune function, and eventually systemic degeneration.


Some may argue that the main benefit of IF is autophagy (the clean-up process in our cells). While cleaning up damaged components is beneficial, it is important to remember that the main thing that increases autophagy is stress and damage. My thought is that is better to have a situation where there is minimal cell breakdown and stress so there is no need for lots of autophagy.


I also really worry that IF is giving young girls an excuse for eating disorders. It used to be called ‘starving yourself’ and now it has a fancy new name so it seems justified. We really need to change from a mindset of restriction to a mindset of nourishment.


I focus on helping my clients learn to nurture their bodies by providing themselves with the fuel they need to function optimally. Eating within an hour of waking and then every 3-4 hours helps you balance your blood sugar and regulate key bodily functions. My hope is that we can move away from priding ourselves on how restrictive we can be, to priding ourselves on how well we can nourish ourselves.


Fasting is not more beneficial than providing our bodies with sufficient, nutrient-dense foods on a consistent basis.


[1] J. E. Schneider, “Energy balance and reproduction,” Physiol. Behav., vol. 81, no. 2, 2004, doi: 10.1016/j.physbeh.2004.02.007.

[2] J. A. P. De Bond and J. T. Smith, “Kisspeptin and energy balance in reproduction,” Reproduction, vol. 147, no. 3. 2014, doi: 10.1530/REP-13-0509.

[3] A. K. Melin, I. A. Heikura, A. Tenforde, and M. Mountjoy, “Energy availability in athletics: Health, performance, and physique,” Int. J. Sport Nutr. Exerc. Metab., vol. 29, no. 2, 2019, doi: 10.1123/ijsnem.2018-0201.

[4] M. Yavangi, M. A. Amirzargar, N. Amirzargar, and M. Dadashpour, “Does Ramadan fasting has any effects on menstrual cycles?,” Iran. J. Reprod. Med., vol. 11, no. 2, 2013.

[5] B. Martin et al., “Sex-dependent metabolic, neuroendocrine, and cognitive responses to dietary energy restriction and excess,” Endocrinology, vol. 148, no. 9, 2007, doi: 10.1210/en.2007-0161.

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