Dear Mark: Women and Intermittent Fasting
Many differences exist between the two sexes. We look different. We sound different. We dress differently from each other. We like different things. Different genres of movies cause men and women to cry (differently). And although society, media, and culture drive and/or inform many of our differences, some are inherent and physiologically-driven. For example, men and women have different biological equipment – both external and invisible to the naked eye – that change how we interact with and respond to our environments, our exercise, our sleep, and our eating habits. Nowhere are these gender differences more evident than in the realm of health and nutrition, and yet it seems that I’ve overlooked a big one: different sex responses to intermittent fasting.
Let’s take a look at a couple recent reader emails:
Hi Mark,
I’m a woman (28 years old) who followed your recent fasting series with great interest, gave it a shot, but had mixed results. Then I read this post, which mentioned your series and questioned the suitability of intermittent fasting for women. Is it true? Do we respond differently than men? What do you think of that post? Thanks!
Claire
Dear Mark,
Paleo for Women blog says that fasting may not be for women: that it’s more suited for male physiology. I have been fasting for three years and never experienced any missed periods/sleeplessness, etc. Moreover I got a handle on my mindless eating. Can you give your word on IF for women?
Varsha Tiwary
Thanks for writing in with your questions.
First of all, I really, really liked Stefani’s post. I should say “posts,” actually, since Stefani Ruper (who wrote the post linked in the reader question) also just did a guest post on Free the Animal, in which she discussed the treatment of women’s issues in the community at large. While I don’t agree with everything she said, both were quite well done.
Even though her articles – for lack of a better phrase – “called me out” (in a completely non-confrontational way), I was actually quite happy to read them. Heck, I was happy to read them because of it. After all, I’ve always encourage people to be critical about what they think they know about nutrition and fitness, and to be skeptical about what they read on the Internet – my articles included. The beauty of MDA is that it isn’t one-sided. I get constant feedback from readers that send me down new paths of inquiry, and it’s through this kind of crowd-sourced effort that the Primal Blueprint message grows and becomes stronger than it already is.
I also appreciated Stefani’s articles because they do highlight a blindspot – not just in my own series of posts, but in nutritional science as a whole. In the push to eliminate the confounder known as inherent endocrine gender differences, they’ve forgotten that real life is a series of confounding variables all pushing, pulling, poking, and prodding at the results we get. They’ve forgotten that while their results may represent fodder for publishing and accolade accumulation and hypothesis confirmation (or rejection), real live humans in normal living situations are not placebo-controlled. That women are not the same as men and respond differently to stimuli and stressors isn’t a “confounder”; it’s a fact deserving of further study! Because what are we ultimately trying to do here – put together nice, neat, peer-review-ready trials, or help real people living real lives?
Since I’m trying to do the latter, I happily accept constructive criticism. So should we all.
So, what did Stefani’s research find?
Fasting has different endocrine effects on male and female rats.
In male rats:
No matter the duration or degree of nutritional stress, male rat brain chemistry responds with similar changes. Nocturnal activity and cognition stay fairly stable, regardless of the intensity of the fast. If you push the fast long enough, males will get a little wonky and frantic, but overall they maintain pretty well. It’s like they’re equipped with the ability to handle nutritional stressors.
In female rats:
Any degree of nutritional stress (fasting or mere caloric restriction) causes increased wakefulness (during the day, when they normally sleep), better cognition (for finding food), hyper alertness, and more energy. In short, female rats become better at finding and acquiring food when they fast, as if their bodies aren’t as well-equipped to deal with the stress of going without food. They also become less fertile, while the males actually become hornier and more fertile (probably to account for the females’ plummeting fertility). Ovary size drops (bad for fertility), adrenal gland size increases (which in rats indicates exposure to chronic stress), and menstrual cycles begin to dysregulate in proportion to the degree of caloric restriction.
In humans, the male-female fasting literature is quite scant, but Stefani also found considerable differences beween the sexes, when data was available:
- One study, which I’ve cited before as evidence of a benefit to fasting, found that while IF improved insulin sensitivity in male subjects, female subjects saw no such improvement. In fact, the glucose tolerance of fasting women actually worsened. Ouch.
- Another study examined the effect of alternate day fasting on blood lipids. Women’s HDL improved and their triglycerides remained stable; men’s HDL remained stable and their triglycerides decreased. Favorable, albeit sex-specific results.
- Later, both obese men and women dropped body fat, body weight, blood pressure, total cholesterol, LDL cholesterol, and triglyercides on a fasting regimen. These people were obese, however, and perimenopausal women were excluded from the study, so the results may not apply to leaner people or women of reproductive age.
I figured I’d look through my other recent fasting posts for data on female (preferably pre-menopausal) responses to fasting. Here’s what I found:
- In the only heretofore extant human study on fasting and chemotherapy, seven females (including a 44-year old woman who was likely premenopausal, given when menopause usually onsets, though it wasn’t explicitly stated) and three males found that IF improved their tolerance to and recovery from chemotherapy. Takeaway: male and female (mostly middle aged, though that’s the population that generally gets cancer and undergoes chemotherapy) chemotherapy patients appear to benefit equally from IF.
- Although both men and women displayed greater increases in VO2 max and resting muscle glycogen concentration in response to fasted cycling training, only men showed greater skeletal muscle adaptations when fasted. Women had better muscle adaptations when fed. Takeaway: fasted endurance training, then, may work better for women than fasted weight training.
As it stands right now, I’d be inclined to agree that pre-menopausal (and perhaps peri-menopausal) women are more likely to have poor – or at least different – experiences with intermittent fasting, at least as a weight loss tool. That said, it appears to be a potentially gender-neutral therapeutic tool for chemotherapy, cancer, and age-related neurodegeneration patients.
As I alluded to earlier, this is what I love about this open forum we call the Internet: the fact that if you leave something out, or overlook a key point, someone will call you out on it, most likely publicly. When that happens, you grow despite yourself. If not for Stefani’s posts, I may never have taken a closer look at the inherent differences in men’s and women’s metabolic responses to fasting. I certainly receive enough feedback from female readers for whom fasting has been helpful, so it’s good to see another side.
To sum things up – if such a thing can even be done – and answer the questions in the intro, men and women have inherent metabolic and hormonal differences, and it’s evident that these differences in part determine how we respond to a stressor like intermittent fasting. I’ve never prescribed intermittent fasting as a requisite piece of the Primal lifestyle, but rather as an adornment, a choice, a potentially therapeutic strategy that each individual must test for him or herself. Although my recent series on fasting might have thrown some people off, I want to reiterate that I am not a huge IF guy. For myself, I generally fast when it makes sense – if I’m traveling and good food isn’t available, if I’m just not hungry, stuff like that. I periodically do 16/8 or 14/10 (i.e. eating in an 8 or 10 hour window) and find it works great for me because I am fully fat-adapted. But even I don’t hold rigidly to that. It’s not for everyone. And that hasn’t changed.
So who should and shouldn’t consider fasting? Have my recommendations changed?
If you haven’t satisfied the usual IF “pre-reqs,” like being fat-adapted, getting good and sufficient sleep, minimizing or mitigating stress, and exercising well (not too much and not too little), you should not fast. The pre-reqs are absolutely crucial and non-negotiable, in my opinion, especially the fat-adaptation. In fact, I suspect that if an IF study was performed on sugar-burning women versus fat-adapted women, you’d see that the fat-burning beasts would perform better and suffer fewer (if any) maladaptations.
I would also caution against the already lean, already calorie-restricted woman jumping headfirst into IF. I mean, fasting is ultimately sending a message of scarcity to your body. That’s a powerful message that can get a powerful response from our bodies. If you’re already lean (which, depending on the degree of leanness, arguably sends a message of scarcity) and restricting calories (which definitely sends a message of scarcity), the response to fasting can be a little too powerful.
I’d also say that daily fasts, a la 16/8 or even 14/10, run the risk of becoming chronic stressors and should be approached with caution by women. Same goes for ultra-long fasts, like a 36 (or even 24) hour marathon. Most of all, though, I’d simply suggest that women interested in fasting be cautious, be self-aware, and only do so if it comes naturally. It shouldn’t be a struggle (for anyone, really). It shouldn’t stop your cycle or make it harder for you to get pregnant. It should improve your life, not make it worse. If you find that fasting has those negative effects, stop doing it. It should happen WHEN (When Hunger Ensues Naturally), if it happens at all.
I’m not going to say that women should or shouldn’t fast. I’ll just echo Stefani’s advice “to look at options, to be honest about priorities, and to listen to one’s body with awareness and love.” Frankly, everyone should be doing that, but with regards to fasting, it looks like women should probably hew a little closer to her words.
Of course, if I had to make one minor quibble with the content of Stefani’s otherwise outstanding posts, it would be her source for the number of unique visitors Mark’s Daily Apple gets each month. Nowadays, we’re actually getting closer to 1.5 million monthly uniques, not 250-300,000… but who’s counting?
That’s it for me, today. What about you? If you’re a woman who has tried fasting, or know someone who fits the description, let us all know about your experiences. I’m intensely curious to hear from as many of you as I can. Thanks for reading.
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Posted By: Mark Sisson
Last year I went a few weeks of alternate day fasting. Not only did I not lose weight, but after I stopped doing it completely my body gained 10 pounds eating how I normally ate before it. I still have on the extra 10 pounds and my body seems pretty resistant to getting it off. Maybe a 2 day a week fast would have worked instead of every other day, but all I know is that it messed something up for me that I hope can be fixed!
I will say, though, that even though IF doesn’t achieve weight loss for me…fat FASTING does. You all know about a “fat fast”, right? (Dr. Atkins wrote about it in his book)–90 percent fat, 1000 calories a day through 4 to 5 mini meals of macadamia nuts,cream cheese, etc… My body gets lean super quickly doing that but I seem to be annoyed more doing it, maybe because it’s easier to not eat at all. I have been dreading doing it, but I have to do something to get this weight off from IFing!
Oh, I forgot to mention…I just turned 30, mother of 3 (not sure if having babies changes anything but probably, everything seems to matter!) and I’m a size 10 and pear shaped. I have been doing kettle bell swings a couple times a week (30 to 50 swings) and that has made my shape more pear-ish than usual, but that’s for another post.
A little late to the comments here, but I’d like to share my experience because many of the comments above made me feel much less alone and crazy.
I’ve been a natural IF’er my whole adult life. The minute I got to college, I quit eating breakfast and lunch. College roommate’s slogan for me to this day “she doesn’t eat during daylight.” You cannot imagine the grief I’ve gotten for this. I’ve also always been a natural low carber.
Yet, I eat when I’m hungry. Yesterday morning, I was super hungry so ate some leftovers at 5 am.
My “normal” IF is 24 hours, 7 days a week. I’m 45 YO, pre-menopause, 5’7″, about 123 lbs.
Fascinating, I know. The other two tidbits I’d like to offer are that I’ve realized my parents were pretty similar: Very light breakfast, never ate anything else under dinner. My husband has sort of naturally followed me to eat something smaller mid-morning and then dinner.
It’s not something I think about. I’ve made my peace with the “social lunch” and eat to be polite. Only to find out I’ve doing something that’s “a thing!”
I have been sooo happy IF’ing. I’ve actually hit a weight that I never could before even on a low carb/high protein diet.
I realize that I used to do this as a kid – I would never eat in the morning.
I make sure I don’t eat too much when I break the fast so I don’t get a tummy ache after. Yes, I am a female and I’m glad I didn’t listen to the IF naysayers!
I’m a pre-menopausal woman and I have been losing weight taking the adapted form of 5:2 fasting as advocated by Dr Michael Moseley. I eat 500 calories on 3 days a week (not consecutive) and eat normal ( not binge) the rest but that means classes of wines, desert sometimes and YES allelujah – carbs.
It is really easy to limit your intake to 500 calories and not feel hungry – there are excellent filling soups that come in at 150 calories a serve, a two egg omelette is about $175, grilled fish and salad is also an option – hell there are lots of options
And it works for women.
I find that the fat loss from my boobs is accelerated during IF
compared to regular diet and exercise. Has anyone experienced that?Otherwise its great
I don’t IF intentionally. However, I have noticed a pattern in my own eating habits over the years. I go through periods where I have a very large appetite and want/need to eat a lot (prolly close to 3000 calories a day) and periods where I eat nearly nothing (about 1000 calories a day), one point in college my roommates thought I had developed an eating disorder. I can’t explain why this happens, and I cannot pinpoint when I start my low calorie intake (stress, sleep habits, happiness, etc). I am trying not to sink I to the lows as I am breastfeeding my LO, but it still happens. I think this goes in line with our DNA make up that Mark was talkin about, times where food is scarce, times when food is in abundance.
You wont gain FAT unless you eat too much! If you eat more cals than you burn – in a eating window of the day at 6-12 hours OR if you don’t do IF you eay too many cals at the end of the day you get same result – a cal is a cal! So if any of you gained wieght and in bodyfat at IF you are eating junk when you finally can eat! Then IF isn’t for you if you can’t control it after a fasting period!
I just wanted to add something since I commented a couple times already about having a hard time fasting. I am fairly lean now (under 12% bf) and have been for about a year and a half. Prior to that I had been over weight most of my life and never this lean. I found I could easily fast when I had more body fat. I’ve found that it’s hard when I am lean.
I think it comes down mainly to the difference between intermittent FASTING and intermittent FEEDING. If you mostly don’t eat, then eat during a small window day after day it’s going to be hard on you and at some point you will feel like crap. I made the mistake of doing this and I was fine until I got lean. I also workout really hard, and long workouts, even though I am not a competitor. I just love both lifting and running… and I mean LOVE both and have for over 30 years.
If you are a lean athlete and you intermittently FEED (mostly fast) or eat too low for your level of work and leanness, yes you will feel like crap. If you are a lean athlete then you can eat low if you don’t work hard, or you can work hard and not eat low, one or the other and not both.
Not that there are not other hormone issues for some people but in general I think this is the case.
Hi,
I’ve been following Mark’s Daily Apple for a few years and went Paleo about 3 years ago. I also had a lot more energy (at first) but about a year ago I noticed my hair was getting much thinner and falling out. It happened really gradually (I didn’t fast, only no carb and practically no sugar ever) so I only noticed it late. I do believe there is a hormonal link, since many high starch vegetables, beans and legumes contain Phytoestrogens, but I came to another conclusion as well. Just for the record, this is a speculation, but it makes sense to me. I started taking Biosil (a product that promotes hairgrowth) and after a little research I found that the main component of this product is Orthosilicic acid (OSA). OSA is found in many plants (vegs, fruits) but the highest concentration is found in grains and beer (which uses grain fermentation). I also noticed I just couldn’t relax anymore, even though I practiced yoga and meditation (maybe going Paleo was affecting my serotonin levels as well?) and my muscle strength decreased (even thoug I ate high quality protein – all organic – daily) I’m now eating grains again but not without soaking them first (I use Sally Fallon’s book, Nourishing Traditions for recepies). There may be more to it than that, but I just wanted to share my story so women are aware that there might be down sides to going totally grain free.
In any case, I wish to thank Mark for his excellent blog. I refer to it very very often and really love it. Thanks a lot for all the energy you’ve put into this!
For me, fasting once a week isn’t a problem. I actually feel much better 10 hours into a fast than I usually do on a regular eating-day. But I can’t exercise on fasting days, or even if I’ve just skipped a meal immediately before.
I have noticed with my metabolism that it’s highly sensitive to the amount and type of exercise I do as well – right now I’m weight training every other day, and don’t really get hungry at all, but if I’m weight training or running 6x a week like I usually do, I’m ravenous. If I haven’t worked out at all in three days, a six inch Subway sandwich feels like far too much food and I’m not interested in eating the rest of the day.
For some reason, there is no way to “Reply” to the 41-year-old female pro-fitness model, chef and yoga instructor’s comment about her – in her words – “positive” experience with low calorie intake and fasted training (her “thriving on 6hrs. of sleep, mental clarity and increased ability to multi-task). So my reply is ending up here randomly. But I couldn’t help but have deja vu when reading her experience. Didn’t the study that Mark just quoted state:
“In female rats:
Any degree of nutritional stress (fasting or mere caloric restriction) causes increased wakefulness (during the day, when they normally sleep), better cognition (for finding food), hyper alertness, and more energy. In short, female rats become better at finding and acquiring food when they fast, as if their bodies aren’t as well-equipped to deal with the stress of going without food. They also become less fertile, while the males actually become hornier and more fertile (probably to account for the females’ plummeting fertility). Ovary size drops (bad for fertility), adrenal gland size increases (which in rats indicates exposure to chronic stress), and menstrual cycles begin to dysregulate in proportion to the degree of caloric restriction.”
Umm, Michelle…doesn’t this sound familiar? If you have to do this to yourself to get down to the 8% required to win these events, then perhaps the “fitness” competition should be more aptly named…
Being in the “fitness” industry myself, I tire of the increasing disconnect that is happening between the world of fitness and the world of health. “Fitness” has become more and more about fitting into a certain look, no matter the consequence to your health. Unfortunately, the vast majority of people don’t see this.
Hi guys,
I apologise if this has already been asked and answered, I did try searching but couldn’t come up with anything.
I’m trying out the Eat Stop Eat method of fasting (24hrs once or twice a week) and was just wondering whether it is advisable to fast for 24hrs during your period?
It seems to me that it wouldn’t be a good idea due to the blood/iron loss and general grumpiness that accompanies menstruation, but is there any actual data on this? How do the rest of you approach it?
Cheers,
Emma
I’ve always considered myself an IF dropout. I have a seriously difficult time going beyond 10am without eating. I’ve tried 5:2, and IF. I get that hyper-alert thing going where I can’t settle down and concentrate. I know that hunger comes and goes, so I can wait out the hunger pangs, but I can’t fix the restlessness.
I never really lost weight or saw major differences in my blood sugar either.
Am I fat adapted? I have been low carb for about 10 years, but I’m not someone who produces a lot of ketones.
I am 54 years old and finally into menopause, or post-meno.
To be fair, I think there’s something wrong with me metabolically. I have extreme difficulty losing weight.
Chiming in to say I started IF a few weeks ago after watching the Mosley/BBC documentary. (5:2 – 2x a week, 500cal dinner only. I drink loads of green and herbal teas thru the day until then, then right before dinner I usually make a cup of organic broth just for something savoury. My boyfriend has much less to lose but was curious to try it to improve muscle definition in his abdomen (the only place he needed to really lose anything). In the evening, I prepare a 500 calorie meal, always lowcarb (tonight for instance was spinach, tomato and cucumber salad with balsalmic dressing and grilled halloumi), and my SO has his with extra crispbreads or portions to add the additional 100 for men.
As for me, I’d previously lost about 21kg (50ish pounds, I believe?) over two years of what I’d say was lowcarb/primarily paleo eating (I say “primarily” because I did continue to eat organic yoghurt almost daily and relied on the odd Atkins bar when in a bind)….but weight loss had stalled after 21kgs, and I have felt – even though I’ve kept it off – that I needed to shake things up a bit. I also felt I was eating healthy calories overall, but still too many of them. (I don’t eat junk food and I rarely touch sugar or wheat – but calorically its easy for me to get too many, since many beneficial foods that I rely on – coconut oil, macadamia nuts for instance – are not exactly low-calorie. I take a few supplements daily (based on the Jaminets’ “Perfect Health” recs – Vitamin D and K2, a B complex, a probiotic, Magnesium, Copper, etc).
Still – I feel these choices laid a good foundation for IF, because I don’t have issues with blood sugar “crashes”, headaches, I sleep very well if not better since I started this…..so when I see irritability/headaches/blood sugar crashes being described by people for whom it’s not working, I would only question if that could be in part due to nutritional deficiencies or bad diets.
I see a few stories now and then about people who experienced some issues like this – but then in the same story talk about the gorging on “feed” days, describe junky or carby meals, etc – and I have to wonder if IF has gotten a bad rap when in truth, other factors can be the root cause. I feel like my body isn’t needing anything because nutritionally, I’ve given it what it needs and fuel-wise, it’s already fat-adjusted and not seeking carbs for a quick fix.
Of course, we’re all different, and I know what works for one won’t for another – but I for one find the research compelling not just for weight loss but improving quality of life as we age and as long as I’m feeling better on it, and feeling my body streamline somewhat, I’m all for it.
For my part I’m in my 40s, have about 13kg (30 lbs or so?) left to lose and IF has, at least so far, been not that hard at all.
For what it’s worth, my 2p/tips:
I deliberately choose my 2 busiest days to fast until the small dinner meal, Tues and Thurs
I keep lots of herbal and green teas around to enjoy through the day – helps me stay hydrated, keeps my taste buds entertained.
I have a cup of 5cal broth before the evening meal, takes that edge off if I’m hungry so I don’t eat too quickly, and it tastes surprisingly good.
On my “feeding” days I make an effort to eat normally and I actually use an app to track calories even on THOSE days so I am sure I have a “feel” for what my suggested goals actually amounts to.
on Wednesday and Saturdays, we opt for more indulgent foods but keep the day’s food within an 8 hr window and usually just have 2 meals that day.