Fasting and female hormones – factors to consider

POSTED BY Kimberley | Apr, 16, 2018 |
Fasting and female hormones - factors to consider

Fasting seems to be the new buzz word, particularly in the low carb community, and I’ve noticed an increase in the number of people using fasting as a weight loss strategy.

At face value, I was open to the idea of intermittent fasting due to:

A) The large number of proposed health benefits such as slowing of ageing via autophagy, reduced inflammation and oxidation, weight loss,  improved insulin sensitivity, increased metabolism, and increase in growth hormone.

B) It’s alternative to cutting daily calories – which I hate doing. If there is a way of helping someone break a plateau without having to reduce daily calories (“I like to term it – calorie slashing”) – I want to hear about it.

But after reading Stacey Sim’s book ROAR, with the mantra “women are not small men” I have developed a radar, in which whenever I read about a new diet or eating strategy, I think – okay, but does this research apply to women? And what does it do to hormones?

I’ve mentioned before, that a lot of nutrition research is on done male participants only, as they don’t have to account for the two hormone phases that occur in the female cycle.

Sure enough, when I looked into some the literature on fasting, most (not all) of the research has looked at adaptations in men. Which means we have to be a bit careful…

Let’s have a closer look…

Fasting, Metabolism and Stress

One of the proposed benefits is that fasting increases metabolic rate, based on the increase in stress hormones epinephrine and norepinephrine, and increase in growth hormone.

For example:

  • “Enhanced thermogenic response to epinephrine after 48-h starvation in humans”  Mansell, P. I., et al. (1990)

  • “Resting energy expenditure in short-term starvation is increased as a result of an increase in serum norepinephrine”  Zauner, C., et al. (2000)

  • “Enhanced thermogenic response to epinephrine after 48-h starvation in humans” (Mansell, P. I., et al. (1990).

  • Augmented growth hormone (GH) secretory burst frequency and amplitude mediate enhanced GH secretion during a two-day fast in normal men. Hartman, M. L., et al. (1992).

  • “Fasting enhances growth hormone secretion and amplifies the complex rhythms of growth hormone secretion in man” . Ho, K. Y., et al. (1988).

However, a few things to note:  The studies showing an increase in growth hormone have been done on men (as far as I can find – correct me if I’m wrong here?). , and when it comes to increased metabolic rate from STRESS hormones, well…. I’m not sure if that is actually a good thing.

For example…

Female responses to stress hormone include:

  • Down-regulation of body fat break down (switch to using glucose as a fuel source) –

  • Increased fat storage

  • Suppression of female reproductive hormones

*Side topic: Hunter-gatherer days

One way of trying to understand different responses to stress in males and females is going back to the hunter-gatherer days. When there was famine, the men would have to go and hunt to get more food. An increase in metabolism and growth hormone secretion makes sense; they needed all the strength that could get to go foraging for us women.

But for females?

Well, we’d need to hold onto whatever body fat we had, lay down as much fat stores as possible, and hope they returned with food. And if they didn’t, and we went into a longer fast/calorie restricted diet, ovulation would likely be put on halt.

This might be why men seem to do better on both low carb and fasting diets. I have certainly noticed this in the clinic.


Fasting and female hormones - factors to consider 2


Finally, on the topic of stress:

Morning fasts – why you shouldn’t replace food for coffee!!!

At the women’s hormone seminar Lara and Kira explained that when you wake – your melatonin decreases, followed by a rise in cortisol. We need a bit of cortisol to get us out of bed in the morning. But, as you know, too much cortisol is not good.

Protein buffers cortisol

Protein helps to clear morning cortisol,. So if you are fasting, you are not getting this cortisol lowering effect of a good protein rich breakfast.

Instead, a lot of people are starting their day like this:

  • Wake up; cortisol naturally starts to rise (If you are wake up anxious (like me), it’s probably higher than normal)

  • Skip breakfast, (no cortisol lowering effect of protein),

  • Have a coffee (signal MORE cortisol!),

  • And push through hunger at 10 am (signal MORE cortisol as the body see this as a famine).

  • Throw a few kids in into the mix, and/or battling through morning work traffic, this morning has become a cortisol nightmare.

This is where it becomes very individual. Don’t get me wrong; I think 16:8 fasts are a good option for some people, providing it’s done properly, and not too often (1-2 times a week for example).

BUT they aren’t for everyone, especially those who are waking up stressed, or putting the body under stress (such as high-intensity work outs). And coffee should not be the alternative to breakfast.  I always recommend lemon and water or herbal tea, and starting the morning with a deep breathing ritual.

Thyroid function, fasting, and female hormones:

Despite the claims on fasting boosting metabolism, on the contrary, fasting has been shown to SUPPRESS thyroid function, which results in decreased energy production, and hence, a slower metabolism. So hang on, whats the point in having a metabolic boosting effect from stress, if it’s going to suppress thyroid function??

Another point to make …. Stress is often the CAUS of hypothyroidism due to the communication between out HPA (Stress) Axis  (Hypothalamic, Pituitary, Adrenal) and HPT (Hypothalamic, Pituitary, Thyroid Axis) axis.

AND – Females are also ten times more a risk of becoming hypothyroid than men, because of how oestrogen interplays with thyroid hormone. Oestrogen suppresses thyroid function, while progesterone stimulates it.

Providing they are both balanced; we are fine. However, in the case of oestrogen excess, or simply being under more stress, we are at a much greater risk of developing hypothyroid. This is something I don’ think is being addressed enough in this new fasting craze.

 Fasting and the Female Menstrual Cycle:

” If you’re not thinking about ovulation, you’re not thinking about health” – Lara Briden

When it comes to healthy ovulation, it’s not just about whether or not you are getting your period; it’s also about the cycle length. For example, a longer than average cycle, often (not always) means an anovulatory cycle (you didn’t release an egg), which means no production of progesterone (which is a wonderful hormone for health!)

Indeed, cycle disturbances have been found in fasting studies on women:

For example:

  • In one study, women doing the 5:2 diet resulted in longer the normal cycles.

  • In another study, women doing a 72 hour fast had significantly suppressed LH pulsatility when measured during the fast, compared to the control group. (LH = “luteinizing hormone” which triggers ovulation).


Fasting and Blood Glucose + Insulin response: Males verse Females

I found this study quite interesting.

One of the proposed benefits of fasting is improved insulin sensitivity. However, this study showed that 22 days of alternate day fasting (36-hour fasts), actually IMPAIRED glucose response to a meal in the females, with no change in insulin response. Whereas, the men had no change in glucose response and a significant reduction in insulin.

These results suggest that females may not get that same glucose and insulin sensitising effects of fasts as our male counterparts. Interesting.

Again, 36 hours is quite different to a 16:8 or 12 hour fast. But this highlights how proposed “benefits” may not always apply to females. Or in this case, they may make matters worse.

So where to from here?

Like everything, its a matter of how much and how often. The studies showing high-stress responses, thyroid suppression, and disrupted menstrual cycles have been from protocols with fasting durations over 24 hours.

It might be that shorter fasts (16:8 for example) only 1-2 times per week may be able to provide the metabolic benefit from the initial rise in stress hormones, without this benefit being undone by thyroid suppression.  I just don’t know just yet, but common sense would say that the shorter and less frequent the fast, the less perceived stress, and therefore less risk of hormonal disturbance.

So in summary….

Whether you are promoting fasting, or simply wanting to try it for yourself, please consider these differences in male and female physiology, as well as current stress and hormonal status.

If you have any concerns, with regards to fasting and how it may be impacting on your hormones, make sure you speak to a qualified practitioner.

Talk soon x



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