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Why perimenopausal women should not use Intermittent Fasting for weight loss.

Intermittent Fasting (IF) has become highly popular as a strategy for certain people who want to improve their metabolic markers or lose weight, but it’s not a good solution for perimenopausal women.

For discussion purposes, I will be talking about using Intermittent Fasting, or IF, mainly as a weight loss strategy.

First and foremost, there are not enough studies on IF done in women, and no studies done in perimenopausal women yet.

Most of the claims about the benefits of Intermittent fasting are based on short-termed studies, clinical studies with small sample sizes, and many studies using animals, not humans.

It’s hard to find solid evidence and even harder to apply it to women undergoing the menopause transition.

In my view, just by considering the changes happening in female physiology during perimenopause, I believe there are a lot of side effects and potential risks of fasting for this specific population.

That and the fact that studies have failed to prove significant advantages for weight loss with intermittent fasting as opposed to continuous eating diets that have been controlled for calories.

I view IF as another diet. And, if you’ve been following me for a while, you know my views about diets.

Alongside goes my disbelief in diets in general as a way to evoke long-lasting changes in nutrition habits, and IF, when used for weight loss, doesn’t necessarily improve eating patterns. It’s just another strategy to reduce overall caloric consumption by decreasing the time available to eat.

I believe that diets based on any form of restriction are unsustainable, especially those that:

  • Are not tailored to the individual’s reality as a whole (personal preferences, social and cultural influences, relationship with food, emotional barriers, etc.)

  • Are restrictive (excluding foods, food groups, and time available to eat)

  • Don’t teach the person to eat in a balanced way for the long term.

So, for those simple reasons, I don’t recommend Intermittent Fasting for women, especially perimenopausal women, who are often already experiencing some disruptive symptoms.

What happens to the body in a fasting state

When the body enters a “fasting state, " a series of physiological processes occur in the body as a response to having a deficiency of nutrients. There is hypoglycemia or low blood sugar; there are changes occurring in the HPA axis and changes in the production of neuropeptides such as kisspeptin, which is responsible for hormonal and reproductive function as well as blood glucose regulation and metabolism.

These changes impact more women than men, particularly perimenopausal women, whose sex hormones are fluctuating and causing an additional state of physiological stress.

This additional physiological stress results in the overproduction of the stress hormone cortisol.

During perimenopause, women are more sensitive to stress.

This is a crucial point to remember because cortisol can lead to sleep disturbances, insulin resistance, and behaviors that can result in weight gain as well as other conditions aggravated during the menopause transition by the changes in hormones.

In other words, women at this stage are more at risk of being in a state of fight and flight, and fasting can add another layer of stress.

So we can expect symptoms to have origins from both STRESS and HYPOGLYCEMIA, and if prolonged, MALNUTRITION, especially if the diet quality is poor.


When we enter a state of hypoglycemia (hours without having glucose circulating in our blood), the body starts a set of processes and mechanisms that intensify as time goes by to make sure other vital processes can function (respiration, brain activity, and others) without having glucose to do so.

Many women report the effects of going a long time without eating, such as irritability (felling "hangry"), shaky hands, loss of concentration, and headaches.

Those are adaptations the body is trying to make to adjust to this new state of being.

Here are some symptoms in a bit more detail:

  • Increased hunger - hunger cues (stimulated by hormones like ghrelin) are intensified.

  • Headaches – caused by low blood sugar, caffeine withdrawal, or if a person is more prone to having headaches

  • Irritability – low blood sugar can cause irritability, anxiety, and poor concentration.

  • Fatigue & Brain Fog - Studies show that people who had tried different methods of intermittent fasting experienced more fatigue, lack of focus, and low energy levels than those non-fasting

  • Increase Cravings and Bingeing – Low blood glucose triggers mechanisms in the brain to increase hunger signals, sometimes intensely. IF can exacerbate this situation for women who struggle with emotional eating and bingeing.


With a prolonged state of consuming just a few meals a day, there is a high risk of entering a zone of nutrient deficiency.

One common nutrient lacking in the women I see is protein.

It takes effort to ingest around 100g of protein as an active woman would need. And that’s hard even with, let's say, the standard 12-14 hours to eat. Imagine if you restrict that window to only 8 hours.

The problem is that the body, especially the female body, can absorb only a limited number of protein per 3-4 hours window – around 20-30 grams.

So, consuming 100 grams of protein in 8 hours will be hard.

And that’s not even to mention nutrients such as calcium, magnesium, zinc, iron, and other essential vitamins and minerals that women commonly miss from their diets and that are better absorbed throughout the day, instead of all at once, because of nutrient interactions.

Let’s look at some side effects that can occur from the lack of these essential nutrients:

  • Fatigue – Lack of nutrients and glucose signals the brain to decrease the activities of other systems so it can prepare itself for a potential famine. This includes brain activities and overall energy levels. In the long term, low iron, low vitamin D levels, and zinc levels can cause fatigue.

  • Low Immunity – As with fatigue, the immune system is compromised when different nutrients are missing from the body to perform essential functions.

  • ·Brain Fog – For the same reasons as hypoglycemia, the mind will not be as “sharp” as when it has enough crucial nutrients.

  • Hair loss- Without essential nutrients, the hair follicle loses its strength and is associated with hormonal change. This can be even more prominent.

  • Muscle Loss – Protein intake, which is already low among perimenopausal women, can be hindered even more by a shortened eating time, like what happens with IF. Without enough daily protein, muscle synthesis can be impaired. In the long term, the muscle can even be catabolized to be used as an energy source.

  • Constipation – time-limited ingestion of foods causes the digestive tract’s peristalsis (movement of the GI tract) to be slower, so constipation is quite common.

  • Hormonal Imbalance, disturbed cycles - With insufficient calories or specific nutrients like iron, and overall calories women can have their hormonal cycles affected by the disturbed menstrual cycle and potential fertility problems.

  • Acid reflux, heartburn, canker sores - lack of food reduces stomach acid, which digests food and destroys bacteria. But smelling food or even thinking about it during fasting periods can trigger the brain into telling the stomach to produce more acid, leading to heartburn.

  • Dehydration – dehydration comes partially from the fluids originating from foods (think watermelon), and with less variety of foods available, fewer fluids are available.



As discussed earlier, going through perimenopause results in physiological stress on the body.

Fasting induces an additional layer of stress as the body tries to adapt to the lack of glucose circulating.

These are some of the symptoms related to the other dysregulation of the HPA Axis and adrenal glands:

  • Disturbed sleep – The changes in eating patterns can affect sleep. Studies have found that many people report sleep problems when doing IF.

  • Dysregulated Thyroid – As with any changes in the HPA axis, the thyroid can be affected by the decrease in food intake and metabolism and the changes in stress hormones such as cortisol and norepinephrine levels.

  • Impair glucose tolerance – studies have found that, in fact, for women, there is an increase in glucose tolerance, whereas, in men, there’s a decrease.

  • Slower metabolism – Stress, especially chronic stress, will impact cortisol levels and its side effects, which may trigger for the body to slow down in order to conserve energy.

Implications for women who exercise at high intensity, lift heavy weights or exercise for long hours.

I do not recommend IF or keto, for that matter, to very active women.

Many active perimenopausal women report that they don’t feel their best when exercising in a fasted state. They don’t perform well and feel weak. Much different than the male narrative of feeling super energetic and focused. Well, what can I say... we are different.

There’s an excellent blog post by Dr. Stacy Sims about it that you can find in the reference list below. So, if you’re interested in finding out more about how fasting can impair performance, I suggest reading it.

In short, your performance and overall energy will likely be compromised if you exercise in a fasting state and women are much more sensitive to it than men, as research has shown.


As with any other restrictive diet, I don’t recommend this weight loss strategy for women, particularly perimenopausal women.

For the same reason I don’t recommend any specific weight-loss diet, no matter what name (Paleo, Keto, Atkins, South Beach), the same truth holds: they are non-sustainable, non-personalized, and they won't teach people how to eat in a balanced manner for the rest of their life.

And the chances are... you won’t feel your best while on any of these diets, so... why put yourself through the ordeal???


Front Psychol. 2021 May 19;12:651760.How Experiences Affect Psychological Responses During Supervised Fasting: A Preliminary Study PMID: 34093340

J Clin Endocrinol Metab. 1999 Mar;84(3):883-94. doi: 10.1210/jcem.84.3.5536. Short-term fasting suppresses leptin and (conversely) activates disorderly growth hormone secretion in mid-luteal phase women--a clinical research center study PMID: 10084566

Metabolic Impact on the Hypothalamic Kisspeptin-Kiss1r Signaling Pathway. Front. Endocrinol., 28 March 2018

Short- and long-term effects of continuous versus intermittent restrictive diet approaches on body composition and the metabolic profile in overweight and obese postmenopausal women: a pilot study. 2012 Aug. PMID: 22735163

Glucose tolerance and skeletal muscle gene expression in response to alternate day fasting. Obes Res. 2005 Mar;13(3):574-81. doi: 10.1038/oby.2005.61.PMID: 15833943

Effectiveness of an intermittent fasting diet versus continuous energy restriction on anthropometric measurements, body composition and lipid profile in overweight and obese adults: a meta-analyis

Eur J Clin Nutr. 2021 Jul;PMID: 33293678

Affect regulation and food intake in bulimia nervosa: emotional responding to food cues after deprivation and subsequent eating. J Abnorm Psychol. 2006 Aug;PMID: 16866597

Cortisol Levels during the Menopausal Transition and Early Postmenopause: Observations from the Seattle Midlife Women’s Health Study Menopause. 2009 Jul–Aug; 16(4): 708–718.PMID: 19322116

Fasting headache. Curr Pain Headache Rep. 2010 Aug;PMID: 20490742

Nutrition and Female Fertility: An Interdependent Correlation Front Endocrinol (Lausanne). 2019; 10: 346. Published online 2019 Jun 7. PMID: 31231310

Role of therapeutic fasting in women’s health: An overview.J Midlife Health. 2016 Apr-Jun; 7(2): 61–64.PMID: 27499591

Effect of intermittent versus continuous energy restriction on weight loss, maintenance and cardiometabolic risk: A randomized 1-year trial. Nutr Metab Cardiovasc Dis. 2018 PMID: 29778565

Intermittent fasting versus daily caloric restriction: which diet regimen is more effective for weight lossK A Varady. Obes Rev 2011 July


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