What this article will show you is that perimenopause doesn’t break metabolism – it reveals where metabolic capacity has been lost. Fasting helps only when it restores metabolic flexibility, not when it adds stress to an already overloaded system.

The Perimenopause Challenge

As women move through perimenopause, many discover that the same habits that once kept body fat in check suddenly stop working. Without eating more or exercising less, abdominal fat increases, inflammation rises, sleep worsens, and confidence in the body erodes.

In the search for helping these women, fasting has become a topic of contention, with two legitimate schools of thought, both existing for good reasons. 

The cautionary view expresses the following concerns:

• Women are more stress-reactive to calorie restriction
• Fasting may worsen sleep or cycle irregularity
• Chronic under-fueling can suppress thyroid and reproductive hormones
• Many women are already under-eating protein
  

The adaptive view looks to emerging evidence and clinical experience to suggest:

• Short, consistent fasting windows can improve insulin sensitivity in midlife women
• Reduced late-night eating improves sleep and cortisol rhythm
• Metabolic flexibility matters more than total calories*
• Context (protein, strength training, sleep) determines outcome

*Metabolic Flexibility – your body’s ability to efficiently switch between burning carbohydrates (glucose) and fats for energy, adapting to available fuel sources and activity levels, a key indicator of metabolic health.

 

Both perspectives are partially correct – but incomplete without context. Perimenopause changes insulin and stress physiology, meaning fasting helps only when it supports metabolic function, rather than adding another stressor.

Perimenopausal Hormonal Changes & Fat-Burning Effects

How to define perimenopause

Menopause is clinically defined as 12 consecutive months without a menstrual period, and marks the end of a woman’s reproductive years. 

The transition from fertility to non-fertility is called perimenopause. This phase lasts an average of 4–7 years, though it can extend up to 10-14 years in some women.[1] Because the average age of menopause in the U.S. is 51-52, perimenopause may begin as early as the late 30’s to early 40’s.

This transition is not subtle for many women. 

• “While most women will have an experience of hot flashes limited to just a year or two, others will experience them for a decade or more, and a small proportion of women will never be free of them.”[2] 
• “At least 20% of women experience symptoms to an extent which significantly impacts their quality of life”[3] including changes in body composition, sleep, mood and metabolic health.

Female hormones: primary role & fat-burning effects

The chart below highlights three key female hormones, their primary roles, and how they most directly influence fat metabolism.

Female Hormones: Primary Role & Fat-Burning Effects
Hormone	Primary Function	Most Direct Effect on Fat Burning
Estrogen	Regulates ovulation, menstrual cycling, and reproductive tissue signaling	Improves insulin sensitivity by increasing muscle glucose uptake. Because insulin is a primary fat-storage signal, lower insulin demand supports fat burning.
Progesterone	Supports implantation, pregnancy, and nervous system calming	Indirect; supports sleep quality and nervous system regulation, helping limit chronic cortisol elevation and downstream fat storage.
Cortisol	Mobilizes energy during stress by increasing glucose availability	Acute cortisol releases fuel; chronic elevation promotes insulin resistance and abdominal fat storage.

 

Together, estrogen, progesterone, and cortisol regulate insulin – the body’s primary fat-storage signal. As estrogen and progesterone fluctuate during perimenopause, insulin signaling becomes more forceful and less predictable, while cortisol’s fat-storing effects become amplified. The result is easier fat storage and harder fat loss, even without changes in calories or exercise.

Female hormones: perimenopause effects & fat-burning effects

Estrogen and progesterone evolved primarily to support reproduction, but also play roles in energy metabolism and fat burning. 

What happens when the hormones that once stabilized insulin, sleep, and stress begin to fluctuate unpredictably for five or more years?

While menopause represents a relatively stable low in both estrogen and progesterone, perimenopause is defined by erratic, unpredictable swings in these hormones – sometimes high, sometimes low, often out of sync. [4,5] These fluctuations, rather than the eventual decline itself, are what drive many of the metabolic, emotional, and body-composition changes women experience during this transition.

This is why fat loss often feels hardest before menopause, not after it.

Female Hormones: Perimenopause Effects & Fat-Burning
Hormone	Peri→Menopause Effect	Effects on Fat Burning
Estrogen	→ Reducing	Fluctuations mess with estrogen’s usual role of helping glucose & insulin balance.
Progesterone	→ Reducing	Fluctuations mess with progesterone’s usual role of managing stress, sleep and cortisol.
Cortisol	Increased impact — cortisol effects are amplified due to reduced estrogen buffering and progesterone sleep disruption.	Chronic elevation promotes insulin resistance and preferential abdominal fat storage.

 

Overview of transition phases

Menstruating years

• Hormones are relatively high and cyclically predictable:
  Estrogen rises → ovulation → progesterone rises → both decline predictably (assuming no pregnancy).

Perimenopause

• Marked by hormonal instability, [6,7] especially estrogen and progesterone, with irregular timing and amplitude—leading to fluctuating and often confusing symptoms.

Menopause

• A new low-hormone baseline. Once ovarian function winds down, estrogen and progesterone settle into consistently low levels.

This explains why fat loss often feels hardest during perimenopause—not after menopause, when hormones stabilize again.

Fasting During Perimenopause

Fasting can be classified by duration

Fasting can be categorized by duration:

• Time-restricted eating (TRE) or Intermittent Fasting (IF) (16–18 hrs): improves insulin sensitivity with low risk.
• 24-hour fasts: deeper ketosis and autophagy, higher cortisol risk. (Example: eat dinner Monday, and your next meal is dinner on Tuesday.)
• 36–48+ hour fasts: stronger autophagy, but increased muscle loss, sleep disruption, and metabolic suppression risk – especially in perimenopause. (Example of 36-hour fast is to eat dinner on Monday, and then your next meal is breakfast on Wednesday.)

One of the main physiological reasons to do longer fasting is to achieve autophagy. Autophagy is your body’s natural cellular recycling system, where cells break down and remove old, damaged, or dysfunctional proteins and organelles to create new, healthy components, providing energy and building blocks, to maintain cell health and function.

Metabolic flexibility is key

Metabolic flexibility is the ability to switch easily between burning carbs and fat, handle carbohydrates without large insulin spikes, mobilize stored fat during fasting or exercise, recover from stress without prolonged cortisol elevation.

In the age range of 20s-30s, estrogen helps with all of this: improving insulin sensitivity, enhancing muscle glucose uptake, buffering stress responses, and protecting lean mass. So even if someone ate late, under-recovered, dieted aggressively, trained hard, and slept poorly, they often still looked metabolically resilient.

Perimenopause acts like turning down the “hormonal noise-canceling headphones.” Suddenly you can hear poor sleep, under-protein intake, excess training, chronic stress, late-night eating, aggressive dieting. These factors mattered before – but they weren’t punished as severely.

Fasting benefits & risks

One of the main benefits of fasting is improvement of metabolic flexibility.  Metabolic flexibility improves when the body repeatedly practices switching fuel use across fasted and fed states, as well as due to exercise training and circadian alignment (sleep).[8,9]

In general, fasting benefits increase with duration – but so do the risks, especially during perimenopause.

Fasting Options: Benefits vs Trade-offs
Fasting Type	Main Benefits	Biggest Downsides / Risks
Intermittent Fasting (IF) / Time Restricted Feeding (TRF) (6-hour eating window : 18-hour fast)	• Improves insulin sensitivity & metabolic flexibility* • Mild ketosis (so  increased fat burn access)	• Limited autophagy • Can elevate cortisol if sleep, protein, or calories are inadequate • Metabolism preserved or increased if refeeding is adequate
24-Hour Fast	• Deeper ketosis (fat burning potential) • Autophagy initiation (cellular cleanup) • Clear insulin suppression	• Increased cortisol for many people • Greater lean tissue breakdown if repeated frequently • (Preserved metabolism if refeeding is adequate)
36-Hour Fast	• Stronger autophagy signaling  • Sustained ketosis  • Appetite reset for some	• Higher risk of muscle loss • Sleep disruption common • [Metabolic rate may be preserved with strong refeeding and recovery (sleep, stress reduction, strength training, removal of “scarcity”)]
48-Hour Fast	• Deep ketosis  • Robust autophagy activation	• Significant muscle and protein loss risk • Cortisol often elevated • Thyroid and metabolic suppression possible
72+ Hours	• Maximal ketosis • High autophagy and immune recycling	• Strong metabolic slowdown • Substantial lean mass loss possible • Hormonal stress response

*Notice that the shorter fasting timeframes of IF/TRF may actually be more effective at improving metabolic flexibility due to the fuel-demand flipping back and forth regularly.[10]

How fasting affects female hormones & fat burning

Fasting is a form of physiological stress, similar to exercise, heat exposure (sauna), or cold exposure. Like all stressors, the effect depends on dose and recovery.

• Too much stress can overwhelm the body and disrupt hormones.
• Too little stress fails to trigger beneficial adaptations such as improved metabolic flexibility, insulin sensitivity, and cellular repair.

The goal is hermetic stress – enough to stimulate adaptation without tipping into chronic strain.

Hormones: Fasting Effects & Fat-Burning
Hormone	Intermittent Fasting Effect *Primarily referring to short, consistent fasting windows – not multi-day fasts.	Effects on Fat Burning
Estrogen	Intermittent fasting does not inherently lower estrogen, unless it creates chronic under-fueling that elevates stress hormones – particularly cortisol.	Cortisol is the primary hormone to manage during fasting, as stress level – more than fasting itself – determines fat-burning vs fat-storage outcomes.   Short-term (acute) cortisol rises are beneficial (hormesis), supporting fat mobilization and metabolic adaptation.   Chronic cortisol elevation promotes insulin resistance and preferential abdominal fat storage.
Progesterone	Progesterone is highly sensitive to stress load. Fasting can reduce progesterone if it significantly elevates cortisol. This effect is driven more by perceived stress (sleep loss, under-eating, excessive training) than by fasting length alone.
Cortisol	Cortisol is the hormone most directly affected by fasting. Fasting can temporarily raise cortisol, especially during early adaptation. Poor sleep, inadequate protein intake, and excessive exercise amplify this response.

 

Notes on Cortisol Adaptation

• When someone is new to fasting, the body often interprets it as a novel stressor, producing a higher cortisol response.
• As metabolic flexibility improves (better fat and ketone use), the cortisol response typically diminishes – assuming adequate sleep, protein intake, and recovery.

Fasting itself is not the problem – poor recovery turns a beneficial stressor into a hormonal liability.

“Is fasting good or bad for women?”

Perimenopause shifts the rules of fat loss, and fasting only helps when it restores metabolic flexibility rather than adding stress to an already overloaded system. 

The question often asked is, “Is fasting good or bad for women?”

But a more accurate framing is:

“Is today’s fast going to bolster or detract from my client’s health at this time period of her life?” Or more specifically, “Will this woman gain or lose metabolic flexibility with this fast?”

Fasting tends to help when:

• Protein intake is sufficient
• Strength training is present
• Sleep is protected
• Eating windows are consistent
• The goal is insulin regulation, not restriction

Fasting tends to hurt when:

• Calories are already too low
• Protein is insufficient
• Training volume is high
• Sleep is poor
• Stress load is unmanaged
  

So, fasting benefits are dependent upon one’s current overall health & stress status. Perimenopause is an inherently stressful period of life due to the erratic hormonal changes, which makes fat burning a little more tricky.  

Perimenopause itself does not break one’s metabolism, however it does expose where metabolic flexibility has been lost. 

During perimenopause:

1. Fasting can retrain metabolic responsiveness
2. Strength training preserves the metabolic engine
3. Sleep protects the hormonal signal
4. *Note that HRT (hormone replacement therapy) can help stabilize the hormonal environment
   

None of these work well in isolation.

Do we have studies showing fasting effects during perimenopause?

As of January, 2026, most fasting research in women actually excludes perimenopause (performing research on those who are either completely pre- or post-menopausal instead). These studies help us infer mechanisms, not provide definitive perimenopausal guidance.

Key: 

• IF = Intermittent Fasting
• ADF = Alternate Daily Fasting
• TRF = Time-restricted Feeding

2013. Harvie et al. British Journal of Nutrition

IF can help reduce body fat in women.

Examined: Compared intermittent energy and carbohydrate restriction (IECR) (two very low-calorie, low-carbohydrate days per week) versus daily energy restriction (DER) in 115 overweight women (ages 20–69) to assess effects on insulin resistance and body fat loss over 3 months, with a short maintenance phase.

Conclusion: “In the short term, IECR is superior to DER with respect to improved insulin sensitivity and body fat reduction.”   Intermittent restriction produced greater improvements in insulin sensitivity and greater body fat loss than daily calorie restriction, and these benefits were largely maintained with one restricted day per week – suggesting intermittent approaches can be metabolically advantageous for women, though this study was not specific to perimenopause.

2018. Antoni et al. British Journal of Nutrition

IF and CER both produced weight loss, but IF also improved metabolic health.

Examined: Compared intermittent energy restriction (IER) (2 very-low-calorie days/week) versus continuous energy restriction (CER) (daily calorie restriction) in overweight/obese adults (both men and women), after both groups achieved the same ~5% weight loss, to determine whether fasting confers metabolic benefits beyond weight loss—particularly in postprandial (after-meal) glucose, insulin, and lipid handling.

Conclusion: With matched weight loss, IER and CER produced similar changes in body composition and glucose control, but IER (IF) led to greater reductions in postprandial triglycerides and showed trends toward altered insulin secretion dynamics, suggesting fasting may improve lipid metabolism and insulin handling beyond calorie reduction alone, though findings require confirmation in larger studies.

2020. Palla et al. Journal of Endocrinological Investigation

Perimenopause is biochemical, and biochemistry is governed by nutrition, exercise, sleep, and recovery.

• Examined: Whether excess body weight and metabolic syndrome (MetS) in perimenopausal women are associated with adverse changes in metabolic, inflammatory, and hormonal biomarkers, independent of menopausal symptom severity.
• Conclusion: “Perimenopausal women with [excess BMI] and [metabolic syndrome] showed an altered metabolic profile, but no differences in menopausal symptoms which also did not correlate with changes in studied biomarkers.” In other words, perimenopausal symptoms do not reliably reflect underlying metabolic dysfunction. Women may experience significant insulin resistance, inflammation, and adverse metabolic signaling even when classic menopausal symptoms (e.g., hot flashes) are mild or similar across groups.
  • This study reinforces that perimenopausal fat gain and metabolic inflexibility are biochemical – not merely symptomatic – processes. While hormonal changes initiate the transition, metabolic health, inflammation, insulin sensitivity, and stress physiology play a major role in shaping body composition and risk—and these factors are highly responsive to nutrition, exercise, sleep, and recovery.

2021. Lin et al. Nutrition, Metabolism and Cardiovascular Diseases

ADF can support weight loss for some women.

Examined:  Whether the weight loss and metabolic effects of alternate-day fasting (ADF) differed by sex or menopausal status in adults with obesity, using pooled data from three 12-week ADF trials on premenopausal women, postmenopausal women, and men. Alternate-day fasting protocol:

• Fast day: ~500 kcal
• Feast day: eat as much as you want
• Duration: 12 weeks

Conclusion: “The weight loss and metabolic benefits of ADF do not generally vary according to sex or menopausal status in adults with obesity.”  Weight loss with ADF appears possible in midlife women with obesity, but this study does not address the hormonal instability, stress sensitivity, or metabolic variability characteristic of perimenopause.

2021. Cienfuegos et al. Experimental Gerontology

TRF can support weight loss in pre- and post-menopausal women.

Examined:  Whether an 8-week time-restricted feeding (TRF) (4–6 hour eating window) protocol produced different weight loss or metabolic effects in premenopausal vs postmenopausal women with obesity (perimenopausal women were excluded).

Conclusion: “These findings suggest that the weight loss and metabolic benefits of TRF do not differ between premenopausal and postmenopausal women with obesity.”  Short-term TRF resulted in similar weight loss (~3.3%) and metabolic improvements in both premenopausal and postmenopausal women, indicating that menopausal status alone did not alter outcomes, but the findings do not apply to perimenopause.

2024, Veltri, Karen. Dissertation

Fasting had no effect on perimenopause cognition.

• Examined whether a short-term 16:8 intermittent fasting protocol (2 weeks), with exercise controlled as a covariate, affected working memory in perimenopausal women.
• Conclusion: A 2-week 16:8 intermittent fasting intervention neither improved nor impaired working memory in perimenopausal women, and exercise levels did not influence outcomes. Findings suggest short-term fasting during perimenopause appears cognitively neutral, with potential effects requiring longer duration, larger sample sizes, or direct hormonal and metabolic measurements to detect meaningful changes.

2024. Zunaidy et al. Nutrition and Metabolism 

Fasting improved pre & post menopausal fat loss & health.

• Examined the effects of Ramadan intermittent fasting (~14:10 time-restricted eating for ~4 weeks) on cardiometabolic, inflammatory, oxidative stress, and hormonal markers in pre-menopausal (ages 21–42) and post-menopausal (ages 43–68) healthy women.
• Conclusion: A month of daily dawn-to-sunset fasting improved body composition, lipid profiles, inflammatory balance, and antioxidant status in both pre- and post-menopausal women. Estrogen decreased slightly in pre-menopausal women and increased modestly in post-menopausal women, while progesterone remained unchanged in both groups. Benefits appeared driven by fat loss and metabolic improvements rather than hormonal restoration, supporting short daily fasting windows as metabolically beneficial—but hormonally neutral—when overall nutrition and lifestyle remain stable.
  • Note that this study did not include perimenopausal women.

2025. Ruchika, et al. Journal of Mid-Life Health

Narrative review: IF shows potential benefits in menopausal women. 

• Examined: Reviewed existing human and mechanistic research on intermittent fasting (IF) in menopausal (post-menopause) women, focusing on weight management, metabolic syndrome, cardiovascular risk, inflammation, oxidative stress, and hormonal changes associated with estrogen decline. (Not a perimenopausal study; no original intervention data.)
• Conclusion: Intermittent fasting shows potential benefits for weight control, insulin sensitivity, lipid profiles, and inflammatory markers in menopausal women, but evidence remains limited and heterogeneous. IF may improve health outcomes when individualized and paired with adequate nutrition, resistance training, hydration, and medical oversight. The authors emphasize that IF is promising but not universally appropriate, and more menopause-specific clinical trials are needed.

Fasting & Longevity Experts Vary in their Opinions

In this section, we will briefly explain the opinion of various fasting or longevity experts, so that you can get a birds-eye-view of this charged topic. For each, my intention is to provide his or her core philosophy, and then any specific mention for women, especially perimenopausal women if that opinion could be found as of this writing. 

Valter Longo – Cell biologist known for his studies on fasting

• Core philosophy: Valter Longo is one of the most prominent & scientifically recognized figures in fasting research, especially his Fasting Mimicking Diet (FMD). He promotes longevity via periodic stress (FMD), not continuous restriction. Fasting-mimicking is a 5-day low calorie diet designed to mimic prolonged fasting benefits without complete starvation. Non-starchy vegetables and healthy fats are the staple of this 700-1100 calorie-per-day diet, suggested to be done anywhere from 1-12 times per year.

Sara Gottfried, MD – Author of Women, Food, and Hormones

• Core philosophy: “Let’s address the biggest concern of perimenopause: weight. When it comes to weight loss, or preventing weight gain, in perimenopausal women, the issue is blood sugar and keeping insulin levels in the optimal zone. Whether women are at a healthy weight or overweight, blood sugar rises with age. Maintaining a balanced diet made up of mostly vegetables and clean proteins may prevent women from gaining fat.”[11]
• Perimenopause guidance:  “Intermittent fasting. Since aging can also throw off insulin levels and tip the scales, one of the best ways to correct insulin is with intermittent fasting. I recommend a 16/8 protocol: sixteen hours of overnight fast followed by an eight-hour eating window. Women with thyroid or adrenal issues may need a slow onramp, starting first with twelve- to fourteen-hour fasts twice per week. The problem with intermittent fasting is that many women know about it, but don’t know how to perform it correctly for the female body. Learn more about metabolic health and the role intermittent fasting can play in regulating insulin in my book Women, Food, and Hormones.”[12]

Aviva Romm, MD – Author of Hormone Intelligence and The Adrenal Thyroid Revolution

• Core philosophy: Root-cause, holistic women’s medicine with a “do no harm” lens.
• Perimenopause guidance: Generally cautious with fasting; prioritizes blood sugar stability, sleep, and nervous-system regulation.  Time-based Eating. “TBE with an eating window of 10-12 hours and fast of 12-14 hours is a more natural daily eating pattern for me. And in my clinical experience, a 12:12 or 14:10, TBE window is highly achievable, sustainable, and not psychologically challenging for many women. It also reduces sleep disturbances, as well as reflux at night, which independently causes or exacerbate sleep problems, both of which are often even more problematic in perimenopause and early menopause, when inflammation and weight gain may also start to creep up.”[13]

Gin Stephens – Author of Fast. Feast. Repeat. and Delay, Don’t Deny.

• Core philosophy: Focuses almost entirely on timing of meals. “Delay, Don’t Deny.” Emphasis is on IF timing, and less-so on quality foods.
• Perimenopause guidance: Anecdotally supportive via testimonials that support Gin’s own journey from 210 pounds down to 130 pounds.  “In January 2019, I started officially fasting…skipping one meal.. then two. Now I average 20:4. I am happily wearing size 4-6. More than that, my pre-menopausal symptoms gone, my eczema gone, my plantar fasciitis gone. I have thick hair, strong nails, smooth skin, I look and feel like my 20’s and I’m 48! The best thing is I can finally say the weight DID NOT creep back on, and my husband does not have to leave on Navy orders for me to lose weight 🙂 And I am no longer a “closet” faster. I am proud to shout it loudly -clean fasting is the answer!!”[14]
• Delay, Don’t Deny (DDD): “Someone mentioned IF and Dr. Fung’s book. I read his book August 16th and 17th, started 16:8 on the 18th. Someone in THAT facebook group made mention of Gin and DDD and I read it the beginning of September. Gin’s approach made so much sense to me and I began “delaying, not denying” and started to wean myself off the Contrave (doctor approved)….I don’t really weigh anymore but I think I am down around 40 pounds and down from a size 14/16 and XL to 8/10 and sm/med…Thanks so much for taking the time to read our IF story. I am eternally grateful to Dr. Jason Fung and Dr. Herring and so many IF pioneers, but my heart belongs to Gin and the DDD Facebook folks for the sense of community, love and support for this IF lifestyle.  My dream is to take my sister on the next DDD Cruise to Cuba and make it a surprise trip for her. Until then, we will “fast on”, stay healthy and, God willing get her back in remission!”[15]

Dave Asprey – “father of biohacking;” author of Bulletproof Diet. 

• Core philosophy: Biohacking for performance and longevity, often through fasting and ketosis.
• Perimenopause guidance: “IF done right helps women balance hormones, improve metabolic health, lift brain fog, get more sleep and crank up physical and mental energy.”[16]  “Fasting diminishes your body’s glucose reserves — its primary energy source from food. Without glucose, your body switches over to burning fat for fuel… I recommend eating all your daily calories within a shortened period of between 8 and 10 hours, primarily during the afternoon and early evening. Fasting too much can be taxing for women, which is why I suggest doing it 4 or 5 days of the week…if you feel dizzy or nauseous, eat something. It can take up to 2 months before your body is accustomed to intermittent fasting, and has built up enough resilience to accommodate exercise in the morning.”[17]

Mindy Pelz, DC – Author of Fast Like a Girl and The Menopause Reset

• Basic approach: The body is brilliant and inherently capable of healing itself, provided one applies the correct, science-based “tools” of fasting and diet variation tailored to individual hormonal needs, particularly for women. She views fasting not as a diet or a form of calorie restriction, but as a lifestyle practice and a powerful self-care tool for restoration and metabolic health.
• Perimenopause focus: “Fasting during perimenopause, menopause, and post-menopause requires a tailored approach because hormonal changes significantly affect metabolism and energy. These shifts can influence how your body responds to fasting, making it crucial to adjust your fasting routine to support hormonal balance.”[18] “Perimenopausal women with regular cycles: Vary fasts to sync your cycle. Perimenopausal women with irregular cycles: Vary fasts until signs of low progesterone show up, then stop fasting until bleed.”[19] For regular cycles, Pelz is wanting to place longer or more aggressive fasts earlier in the cycle, and pull back when progesterone should be rising. For irregular cycles, instead of syncing to a cycle that no longer behaves predictably, she uses symptoms as the stop signal to prevent excessive cortisol dominance. Dr. Mindy Pelz’s 4-2-1 method [20] is a weekly fasting rhythm designed to align fasting intensity with female hormonal physiology:
  • 4 days of 17-hour fasts
  • 2 days of 13-hour fasts
  • 1 day of 24-hour gut-healing fast

Jason Fung, MD – Author of The Hunger Code, and Life in the Fasting Lane

• Basic approach: “Calorie restriction combined with increased exercise (Eat Less, Move More) is proven to fail.”[21] But fasting is convenient, simple, and free. The two main problems with caloric restriction is that it (a) slows metabolism, and (b) increases hunger. The Biggest Loser correlation showed that, over 30 week, one participant went from burning 3500/3600 calories daily to burning only 1600/1700 calories per day (ts 13:00). After one year of losing weight from caloric restriction, ghrelin grows much higher (ts 21:00), and Peptide YY falls much lower (ts 21:08), meaning that you increase hunger and decrease satiety. This is part of why people always regain whatever weight has been lost during caloric restriction. Contrary to common belief, “Over 4 days of fasting, the metabolic rate doesn’t go down…[in fact] it went up by 10%.”  (ts 30:00). As insulin and glucose go down, you are making up for it with ketones and fat. Even after 32 weeks of alternate daily fasting (ADF), there was no statistical difference in metabolic rate  (ts 31:40).
  • Alternate Day Fasting (ADF) is a type of intermittent fasting where you alternate between a “feast day” of normal eating and a “fast day” with very low calories (around 500) or no calories, allowing fluids like water and broth.
  • After 70 days of ADF: fat mass goes down (43.5 to 38.1kg) while fat-free mass stays the same (51.4 to 51.9kg)   (ts 35:10) “If you’re talking about preservation of lean mass, fasting…is something like four times better.” (ts 36:00)

• Difference between Men and Women: When it comes to fasting in general, as well as long-term ADF, Fung says, “Some people say ‘women should never fast.’ What’s fascinating is that…men have [a drop in ghrelin] but women have this huge effect  where the hunger just goes down and down over time. So, is it effective for women? One, yes. And two, it may actually be more effective in women than men.”  When it comes to 30 days of fasting, Fung says, “Both men and women show really the same rate of weight loss. It averages half a pound of fat mass per day of fasting, so it’s for both men and for women.” (ts 36:22)

Stacy Sims – PhD in exercise physiology, author of ROAR

• Basic approach: “Women are not small men.” “Most of the guidelines out there come from research done on men. Fasting is no different. While some studies show benefits for active men, the data tells us that fasting often has the opposite effect for active women. Research shows definitively there are sex differences in energy metabolism and metabolic homeostasis, which is why women (as compared to men) are more efficient in conserving energy stores (aka fat) and proteins (for fuel, not to conserve lean mass) in times of food scarcity or prolonged exercise. (Quick clarification: I’m talking about active women—those who exercise with intention. For sedentary populations, fasting may offer some benefits. But for active women, it often leads to more harm than good.) So, why does fasting negatively affect women more than men? One word: neuropeptides.”[22]  Essentially Sims teaches that women show a stronger neuropeptide-driven response to low energy availability. When women fast or under-eat, appetite hormones rise more strongly than in men, signaling the body to conserve energy, increase hunger, and favor fat storage over fat loss. “So if you’re an active woman, the message is clear: Train hard, eat well.”[23]

 

• Perimenopause focus: Sims notes that during perimenopause, rising stress sensitivity and declining estrogen make women less tolerant of fasting and under-fueling, increasing cortisol load and impairing recovery unless nutrition and training are carefully supported. (ai synopsis)

Suzan Galluzzo – Holistic Nutritionist

• Basic approach: “Regardless of your age while eating delicious foods, balance your hormones, take control of your weight and look 10 years younger in four months or less.”[24] “You don’t need longer fasts to lose more weight, what you need is stable blood sugar. When you overfast, especially without proper re-feeding, your body panics. That means stress hormones rise, metabolism slows, fat loss plateaus. So what works better? Strategic fasting, 2 to 4 times a week with quality meals in between. Enough protein, enough fat and carbs that work with you. Fasting that supports insulin and leptin sensitivity, not just the scale. Fat loss isn’t about doing more, it’s about doing what’s right for your body at your stage. Fasting can work, but not if it’s triggering survival mode. Smart over extreme.”[25]

    

• Perimenopause focus: “Keto, fasting, Ozempic, cutting carbs, lipo… sure, they might start the weight loss. But what happens next? It creeps back in. Because the root cause was never addressed. If you’re in peri or menopause, your hormones have shifted and your body is no longer responding the way it did in your 20s. That’s not failure. That’s biology. You don’t need another crash diet. You need to rebalance your hormones. Heal your gut. Work with your body, not against it.”[26]  “So many women believe fasting is the key to weight loss…But what if it’s actually working against your hormones? The truth is: your metabolism isn’t broken, it’s reacting. Here’s what the research shows. When we skip meals, cortisol (our stress hormone) spikes, hunger hormones go wild, and our bodies cling to stored fat instead of burning it. Your metabolism can slow down over time, especially for women 35+. Eating breakfast with protein helps regulate blood sugar, support thyroid function, and balance hunger hormones like ghrelin and leptin. Fasting too long can also mess with your sleep and make you more likely to overeat at night. Here’s what happens when you start fueling again: Steadier energy and fewer cravings. A metabolism that actually works with you. Balanced hormones and better sleep. Your body changes with age, hormones, and lifestyle… so your nutrition should, too. It’s time to nourish, not deprive.”[27]

Peter Attia, MD – longevity researcher, author of Outlive

• Fasting for Females: “If any woman is having an issue with fertility, i…can’t make a compelling case for nutritional ketosis if a woman is trying to get pregnant…If you think about it from an ancestral standpoint, the higher level of ketones during evolution, the more likely we were separated from food. And the more likely you’re separated from food, the less genetic pressure you should have to be reproducing at that point in time.”[28]

• Note: Ketosis is when your body burns fat for fuel, instead of carbs. Fasting promotes ketosis by lowering insulin and increasing fat use, but being in ketosis doesn’t automatically mean fat loss, because total energy balance and stress hormones still determine whether body fat is reduced.

Rhonda Patrick – PhD in biomedical science

• Basic approach: “It is Dr. Patrick’s goal to challenge the status quo and encourage the wider public to think about health and longevity using a proactive, preventative approach.”[29]
• Fasting for Females: 
  • 2022: “While no studies have been done in humans, research in rats has found that intermittent fasting does not interfere with estrous cycling, but extreme caloric restriction halts the estrous cycle. The safety of intermittent fasting in adolescent girls with or without being overweight has not been studied. While intermittent fasting does increase stress hormones in animal studies, this stress response promotes longevity, unlike the response to chronic, uncontrolled stress.”[30]
    • Estrous cycle – cyclic ovarian function in non-human mammals
  • 2025: “Probably one of the biggest things I’ve changed my mind on over the past few years is my stance on meal skipping…Somehow this has become synonymous with IF, [but] that’s not [really] IF.”[31]  Rhonda explains how many people just skip breakfast when IF. She explains that after consulting with many experts, “I’ve come to this conclusion that not getting enough protein in that really important meal after we’ve been fasting all night – [because we don’t store amino acids] – we start to experience muscle breakdown…Breakfast is so important because you’re essentially at the point where you need protein.”[32] She discusses how lifting weights can give the signal to keep protein synthesis going, but how protein would have to be made up for in the next meals of the day (which many people don’t do).   

Expert disagreements seem more-so about whether fasting restores metabolic flexibility or adds stress during this hormonally sensitive life stage.

CONCLUSION

In perimenopause, the question is less “Should I fast?” – it’s more “Will this fast reduce or increase my total stress load?”

We now have a clearer understanding that: 

1. Perimenopause disrupts hormone-insulin signaling
2. Erratic hormones make fat loss harder 
3. Fasting is a stressor, not a magic tool
4. Short fasts are more likely to restore metabolic flexibility
5. Long fasts or too intense fasting can compound stress
6. The sum of lifestyle and stress factors – nutrition, exercise, sleep, work, home-life, etc – must be taken into account alongside the fast to ensure that metabolic health is restored rather than further stressed.

Fasting is not inherently good or bad for women in perimenopause. It is a tool that amplifies whatever physiological context it’s applied to. When paired with adequate protein, strength training, sleep, and recovery, short fasting windows can help restore metabolic flexibility. When layered onto chronic stress, under-fueling, and poor sleep, fasting can magnify hormonal disruption and fat storage.

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If you love fun & research-based guidance as a fitness professional, or during your own pregnancy & postpartum, please check out these Fit For Birth offerings:

• For Fitness & Wellness Professionals:
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• For Pregnancy, Pre-conception & Postpartum:
  • Zoom virtual personal training.  Contact us HERE if you’d like professional training to help you implement exercise & fasting through your perimenopause transition!
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James Goodlatte is a Father, Holistic Health Coach, Corrective Exercise Practitioner, Speaker, Author, Educator, and the founder of Fit For Birth and Exercise For Longevity. Since 2008, when he found out he would be a father, his passion for holistic wellness shifted to children and families. Today, he is a driving force in providing Continuing Education Credits for the pre and postnatal world, with Fit For Birth professionals in 64 countries. James is a member of the First 1000 Days Initiative at the Global Wellness Institute, and professional longevity researcher & educator.

 

REFERENCES

[Note that most links to Scientific Journals, in the section sub-titled “Do we have studies….” are direct-referenced in their titles (ie. “2013. Harvie et al. British Journal of Nutrition), and direct-linked by clicking each unique title.(And therefore are not duplicated in the reference list below.)]

[1] 2025. Wegrzynowicz, et al. Women (Basel) Retrieved 1/11/26 from https://pmc.ncbi.nlm.nih.gov/articles/PMC12014197/

[2]   2016. Santoro. Journal of Women’s Health. Retrieved 1/11/26 from https://www.liebertpub.com/doi/abs/10.1089/jwh.2015.5556

[3] 2025. Wegrzynowicz, et al. Women (Basel) Retrieved 1/11/26 from https://pmc.ncbi.nlm.nih.gov/articles/PMC12014197/

[4] 2011. Prior, JC. Facts, Views, & Vision in ObGyn. “Evidence shows that with disturbed brain-ovary feedbacks, E2 levels average 26% higher and soar erratically – some women describe feeling pregnant! Also, ovulation and progesterone (P4) levels become insufficient or absent. The most symptomatic women have higher E2 and lower P4 levels.” Retrieved 1/14/26 from https://pmc.ncbi.nlm.nih.gov/articles/PMC3987489/

[5]  1998. Klein & Soules. Clinical Obstetrics and Gynecology. “The degree of unpredictability of the perimenopause is such that the diagnosis of menopause can only be made retrospectively.” Retrieved 1/14/26 from https://journals.lww.com/clinicalobgyn/abstract/1998/12000/endocrine_changes_of_the_perimenopause.17.aspx

[6]  2011. Prior, JC. Facts, Views, & Vision in ObGyn. “Evidence shows that with disturbed brain-ovary feedbacks, E2 levels average 26% higher and soar erratically – some women describe feeling pregnant! Also, ovulation and progesterone (P4) levels become insufficient or absent. The most symptomatic women have higher E2 and lower P4 levels.” Retrieved 1/14/26 from https://pmc.ncbi.nlm.nih.gov/articles/PMC3987489/

[7]  1998. Klein & Soules. Clinical Obstetrics and Gynecology. “The degree of unpredictability of the perimenopause is such that the diagnosis of menopause can only be made retrospectively.” Retrieved 1/14/26 from https://journals.lww.com/clinicalobgyn/abstract/1998/12000/endocrine_changes_of_the_perimenopause.17.aspx

[8] 2017. Goopaster & Sparks. Cell Metabolism. “The more common concept of metabolic flexibility has been promulgated in the context of fuel selection in the transition from fasting to fed states, or fasting to insulin stimulation to explain insulin resistance.” Retrieved 1/14/26 from https://www.cell.com/cell-metabolism/fulltext/S1550-4131(17)30220-6

[9]  2018. Smith et al. Endocrine Reviews. “Exercise training regimens can be used as an intervention to improve metabolic flexibility.” “An overnight fast already induces changes in metabolic flexibility in healthy humans.” Retrieved 1/14/26 from https://academic.oup.com/edrv/article/39/4/489/4982126

[10]  2020. Mishra & Singh. Biomedical and Pharmacology Journal. “Periodic flipping of metabolic switching not only provides ketone bodies as a fuel source during fasting period, but also regulates expression of many proteins and molecules that can influence health and aging.” Retrieved 1/14/26 from https://biomedpharmajournal.org/vol13no3/intermittent-fasting-and-metabolic-switching-a-brief-overview/

[11]  2018, May 28. Sara Gottfried, MD. Article. Retrieved 1/11/26 from https://www.saragottfriedmd.com/navigate-perimenopause-menopause-naturally/

[12]  2018, May 28. Sara Gottfried, MD. Article. Retrieved 1/11/26 from https://www.saragottfriedmd.com/navigate-perimenopause-menopause-naturally/

[13] 2023, May 17. Aviva Romm, MD. “Intermittent Fasting and Time-Bas…” On Health for Women. Episode 212. Retrieved 1/11/26 from https://avivaromm.com/intermittent-fasting/ 

[14]  (nd). Gin Stephens Website. Success Stories. Jaya Wilkin. Retrieved 1/11/26 from https://www.ginstephens.com/success-stories.html

[15]  (nd). Gin Stephens Website. Success Stories. Two Fasting Sisters! Retrieved 1/11/26 from https://www.ginstephens.com/success-stories.html

[16] (nd). Dave Asprey Website. “How intermittent fasting works for women.” Episode #919 with Cynthia Thurlow, NP. Retrieved 1/11/26 from https://daveasprey.com/cynthia-thurlow-919/ 

[17]  (nd). Dave Asprey Website. “Why you’re putting on weight during menopause and what to do about it (meal plan included). Retrieved 1/11/26 from https://daveasprey.com/menopause-weight-loss/

[18]  2024, Sept. 27. Dr. Mindy Pelz Facebook Post. Retrieved 1/11/26 from https://www.facebook.com/drmindypelz/posts/fasting-during-perimenopause-menopause-and-post-menopause-requires-a-tailored-ap/1099476998201174/

[19]  2024, Sept. 27. Dr. Mindy Pelz Facebook Post. Retrieved 1/11/26 from https://www.facebook.com/drmindypelz/posts/fasting-during-perimenopause-menopause-and-post-menopause-requires-a-tailored-ap/1099476998201174/

[20]   2025, July 3. Dr.MindyPelz Instagram. Retrieved 1/13/26 from https://www.instagram.com/reel/DLqV_ZTINs-/?hl=en

[21]  2017, Nov. 5. Public Health  Collaboration YouTube Channel (41:36). Lecture. “Therapeutic Fasting – Dr Jason Fung.” See various timestamps (ts). Retrieved 1/11/26 from https://www.youtube.com/watch?v=iatPAjf5I_Y&list=WL&index=6

[22]  2025, June 25. Dr. Stacy Sims. “Why Fasting Doesn’t Work for Active Women.” Retrieved 1/11/26 from https://www.drstacysims.com/newsletters/articles/posts/fasting-for-active-women-risks 

[23] 2025, June 25. Dr. Stacy Sims. “Why Fasting Doesn’t Work for Active Women.” Retrieved 1/11/26 from https://www.drstacysims.com/newsletters/articles/posts/fasting-for-active-women-risks   

[24]  (nd) Suzan Galluzzo Website. About Page. Retrieved 1/13/26 from https://www.suzangalluzzo.com/about/

[25]  (nd) Suzan Galluzzo Facebook. Retrieved 1/12/26 from https://www.facebook.com/reel/1270171464426646

[26]  2025, Dec. 2. SuzanGalluzzo Instagram. Retrieved 1/12/26 from https://www.instagram.com/reel/DRw46GhjfxV/

[27]  2025, Dec. 21. SuzanGalluzzo Instagram. Retrieved 1/12/26 from https://www.instagram.com/reel/DSicP0LkR4e/

[28]  2018, October 29. Peter Attia MD Youtube (7:21).  Retrieved 1/12/26 from https://www.youtube.com/watch?v=4f-gbJLw5no

[29] (nd) Rhonda Patrick website, Found My Fitness. About page. Retrieved 1/13/26 from https://www.foundmyfitness.com/about-dr-rhonda-patrick 

[30] 2022, April 2. Rhonda Patrick Podcast: Found My Fitness. Interview with Dr. Mark Mattson. Retrieved 1/12/26 from https://www.foundmyfitness.com/episodes/fasting-affect-women-stress-hormones

[31]   2025, Dec. 19. FoundMyFitness Clips, YouTube (10:46). Retrieved 1/12/26 from https://www.youtube.com/watch?v=TNOUXQSgcgYb

[32]  2025, Dec. 19. FoundMyFitness Clips, YouTube (10:46). Retrieved 1/12/26 from https://www.youtube.com/watch?v=TNOUXQSgcgYb