SHOULD WOMEN FAST?
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Episode 279:
Show Notes
In this week’s episode, Dr Mary Barson and Dr Lucy Burns from The Real Health and Weight Loss Podcast discuss intermittent fasting—particularly its relationship with protein intake and key considerations for women. The episode explores how to manage protein goals while practicing intermittent fasting, different fasting protocols, and practical tips tailored specifically for women who fast.
Protein and Fasting Balance
On fasting days, don't worry about hitting protein goals, but prioritize protein on eating days with roughly one gram per kilogram of body weight (minimum 90 grams). During fasting, the body enters a catabolic state where it recycles damaged proteins and cellular components through autophagy, reusing existing protein stores.
Common Fasting Mistakes
The "fast and furious" mistake occurs when highly insulin-resistant people begin fasting too quickly before becoming fat-adapted, leading to fatigue and hunger because high insulin levels prevent access to fat stores. New practitioners should wait several weeks after starting a low-carb, higher-protein diet before attempting fasting.
Fasting Protocols
Common approaches include 16:8 (16-hour fast, 8-hour eating window), 18:6, OMAD (one meal a day), and 24-hour fasts. Modified fasting allows black coffee or tea with small amounts of milk/cream and bone broth, which makes fasting more sustainable.
Building Fasting Capacity
Fasting should be treated like building a muscle, starting with 12-hour overnight fasts and gradually extending to 16, 18, or 24 hours over several weeks.
Avoiding Excessive Fasting
Daily OMAD or excessive fasting can lead to metabolic adaptation, where metabolism slows down due to chronic calorie and nutritional deficits. Balance between fasting and feasting days is essential.
Fasting for Women
The blanket statement that women shouldn't fast is overly simplistic. During the luteal phase (post-ovulation), progesterone dominance increases insulin resistance, making fasting harder and increasing cravings. Fasting can help with perimenopausal symptoms including hot flashes, mood fluctuations, and sleep issues, though flexibility is important due to unpredictable hormonal changes.
Who Shouldn't Fast
Pregnant and breastfeeding women, people with anorexia nervosa history, underweight individuals, and children under 18 should avoid intentional fasting beyond overnight periods.
Fasting Benefits
Benefits include improved insulin resistance, ketone production for mental clarity, reduced inflammation, autophagy for cellular repair, and potential cancer prevention. The goal should focus on health benefits rather than weight loss to avoid triggering disordered eating patterns.
Key Rules
Always stay hydrated during fasts, include electrolytes (salt), and stop if feeling nauseated, overly tired, or excessively hungry. Individual responses vary significantly, so personal experimentation is essential rather than following one-size-fits-all research recommendations.
Episode 279:
Transcript
Dr Mary Barson (0:04) Hello, my lovely friends. I am Dr Mary Barson.
Dr Lucy Burns (0:09) And I'm Dr Lucy Burns. We are doctors and weight management and metabolic health experts.
Both (0:16) And this is the Real Health and Weight Loss podcast!
Dr Lucy Burns (0:21) Good morning, friends. How are you? Dr Mary and I are having a tortle just offline before we got going on tonight's episode. Laughter is medicine. I think we have an apron that says real food is medicine. But every now and then I think, God, I could have laughter is medicine, sleep is medicine. Maybe we'll have a whole medicine range when we've got nothing else to do. We'll create some merch.
Dr Mary Barson (00:49) Yep, morning sunlight is medicine. We could do lots. We could do fasting is medicine. This is a good segue, wasn’t it?
Dr Lucy Burns (00:55) It is, it is. So I am, of course, joined by my beautiful and smiley, laughy co-host, Dr Mary. And, yeah, we are today talking about fasting. We're talking about fasting and protein. We're talking about fasting for women. So there’s a lot of, again, a lot of noise. A lot of noise. Yes. You know, summary is going to be no one-size-fits-all, but we’re going to dive into a little bit around some of our recommendations and why we might make those.
Dr Mary Barson (01:23) Absolutely, yeah.
Dr Lucy Burns (01:24) All right, lovely. So to, I guess, carry on from last week where we talked about protein goals and, you know, roughly aiming for a gram per kilo a day of your current body weight per day and what that might look like and, you know, maybe a minimum of 90 grams, yada, yada, yada. The question obviously that then follows that is, well, what if I’m fasting? How do I get my protein then?
Dr Mary Barson (01:48) That's a great question. That's it. So if you choose to do some intermittent fasting, and there are lots of good reasons why you might want to, the short answer is on that day, on the day that you are doing fasting, don't worry about hitting your protein goals. Like, that is not something you need to worry about for that day. But on the days that you do eat, on the days that you are choosing to nourish your beautiful body, then it's really important to prioritise protein on those days. So you don't want to get into a situation where you're doing, you know, two intermittent fasts or three intermittent fasts a week, and on those days, sure, you're probably going to be getting less protein just because you're eating fewer meals. But then on the days that you are eating, you don't want to be only getting, you know, 30, 40 grams on those days because then you really could get into a situation where you're not getting enough protein. So it's about balance. When you're in the fasted state, you flick on this metabolic switch. Beautiful things start to happen in your metabolism—nearly magical things—as we go from a fed state into a fasted state. It's called an anabolic state into this catabolic state. Amazing things are happening. And one of the great things that is happening in our bodies is recycling. Our bodies start sifting through the cells. They start recycling all the old, slightly broken-down organelles, the broken-down cells, the damaged proteins. They get sifted through, repaired, recycled, and we actually can just reuse a whole lot of the protein that already exists in our body when we're in this fasted state. And it's a great thing. It's fantastic. It's very healing. It's very healthy. But you can't stay there all the time. You must balance that fasted state with the fed state. And then when you are eating, on your eating days, prioritise your protein and you'll do well. So that's the short answer to that question. Well, actually, it was quite long, but in my head, it was short.
Dr Lucy Burns (03:40) I do love that because it is all about balance, and we will talk about sometimes fasting mistakes that people might make. And certainly, the first mistake that I often see is something I call the fast and the furious, which is when people are very insulin resistant, and you will hear that fasting is very good to improve insulin resistance—and that is absolutely true. But if you're very insulin resistant, so that basically just means that your body needs to produce a lot of insulin to overcome that resistance, you might have quite high blood insulin levels. And we know that insulin stops fat breakdown. So when people go to what we call too fast and furious, so they get out of the blocks and they're going, “Yep, I'm going to just do a fast,” that can be quite hard for their body because they run out of fuel. So you then find yourself tired and hungry, and so then you're having to do the hunger battle, which is no fun at all, and you've got no energy, which is no fun at all.
Dr Mary Barson (04:46) Yeah, it is not. That's right. I mentioned that fasting is when we flick this metabolic switch, and it allows us to enter into this fasted state where we're burning fat for fuel and lots of beautiful things are happening metabolically. But when we've got high insulin—and that happens early on when people are just starting to sort of manage their insulin resistance, maybe they've only just started a low-carb, higher-protein diet to try and manage their insulin—and their insulin levels are still quite high, their body has not yet been able to adapt to be an effective fat burner yet. In that state, as you mentioned, fasting is hard because that high insulin state switches off our ability to get to those fat stores. So I think fasting is fabulous, but if you are just new to metabolic healing, then you really should probably wait a few weeks until you're in a more fat-adapted state, and then go for it. And, in fact, not only is that a good time to do it, it's actually an easy time. Like, it becomes relatively easy. Lucy, could you explain to our beautiful people what we mean by intermittent fasting?
Dr Lucy Burns (05:54) Yes. What actually is that? That's funny. I was just having that question in my mind because you're absolutely right. People have different ideas on what fasting means, what intermittent fasting means, and there's a lot of chitchat around it. I mean, look, fasting has been done for centuries in various cultural and religious groups, but the popularisation of it probably came more recently with the late Dr Michael Moseley and the 5:2 diet, which was really around, you know, five days of your normal eating and two days of low eating. His methodology is not quite in keeping with ours, but it was around just having 500 calories a day. So his 5:2 is what often people will think of with intermittent fasting, but it's probably not what we would think of. So I think the first thing you mentioned earlier is that you've got a fed state, so a period in which you are eating. Some people will call it their eating window, so it might be several hours. It doesn't mean you need to eat continuously for those hours, but it is the hours in which you might eat some food. And then you have the fasted state, which is the hours in which you don't eat any food. So the majority of us have some fasting going on overnight when we're asleep, and I'll say the majority because I know some people don't, and that's a separate issue. But, yeah, so the majority of us, if you go to bed at, you know, 10 o'clock and get up at 6 o'clock and you stop eating, even if you stopped eating at 8 o'clock and got up at 6 o'clock and had your first meal, then you've already kind of entered a 10-hour fasting state by doing that. So when people make big blanket statements like, “Oh, fasting is not safe for women,” we're going to talk a bit more about that later—what exactly are they talking about? And that's the critical thing. So I think it's really important to define when I'm talking to somebody about fasting or when we're talking to people about fasting in our programs, we define what we actually mean for that particular moment. So there are some formulas, if you like. So there's the 16:8, which is where you fast for 16 hours and you eat within an eight-hour window. There's the 18:6, which is very similar—fast for 18 hours, eat within a six-hour window. There's something called OMAD, which is where you just eat once a day. So, you know, probably doing a 23-and-a-half-hour fast, yes, give or take. Yeah, that's right. There will be people that do alternate-day fasting, so they might fast for 36 hours, eat. And then there's more prolonged fasting, which is, you know, people that might not eat for 72 hours. And then there's even longer fasting protocols that, again, we're not particularly experienced in and probably don’t particularly recommend them. I think there are some dangers that, you know, the law of diminishing returns and the law of increasing dangers the longer you go.
Dr Mary Barson (09:02) Absolutely. And so how we help people to fast, how we would say you actually do it, that it is pretty simple. It's just a period where you're not eating food, but we do strongly encourage people to drink. And then, you know, what do you drink? Then there are some components that say, you know, sort of pure fasting is just water, probably also some salt as well. And you could totally do that—just have a bit of salt and lots of fluid, a lot of water. That's absolutely fine. But we are big fans of what could be called a modified fast where you can include other drinks, other drinks that are either, you know, just low in energy. So black coffee, black tea. We say have a splash of milk or a splash of cream with it if it's just the difference between you being able to do it and not do it. You say, well, I can't fast because I can't have black coffee, and I can't have a coffee. I can't not have a coffee. Therefore, I'm not going to do it. Oh, just have a little bit of milk in your coffee. Technically not fasting, but it's not going to make a big enough difference, and you're still going to get all of those fabulous health benefits. And broth too—big fan of broth, big fan of bone broth in particular because it's so nutritious. But, you know, you could do other broths if you wanted to do a veggie broth if you want. You just want to make sure that it's nice and salty so that you're getting some good electrolytes. And there are a few kind of rules about fasting. The rules would be that you need to drink. You really do. I think that's really important. And that if you feel bad, stop. Fasting is natural. It's normal. We're designed to do it. Like I said, we don’t all starve to death every night when we sleep. We just enter a fasted state overnight, we’re fine, and you can prolong that fasted state. And that's a very healthy and natural, normal thing for our metabolisms to do. And, in fact, it's a very healthy thing for us to do. But there are times when it still just isn’t right. It just doesn’t feel right. If you’re nauseated, if you’re tired, if you’re just more hungry than you really think you should be—just eat. Just eat. You know, fasting is free. You can just come back to it. There’s no need to push it when it doesn’t feel right. Just come back to it. For me, if I’m sick, I don’t want to fast. If I’ve got psychological stress, I don’t want to fast. If I’m really sleep-deprived, I don’t want to fast because it just adds an extra layer of stress to my body, which is unhelpful for me. You might find that, you know, there are circumstances where it just doesn’t work for you.
Dr Lucy Burns (11:18) Yeah, absolutely. And I think the psychology of it is really important because, as you said, you know, if you're already stressed—I mean, look, there are some people out there who, when they're stressed, can't eat. Sadly, I was never one of those. I was one of those people—the more I stress, the more food I needed. So we don't need to make things hard for ourselves, but we also need to recognise that there are people that we don't want to get caught in the diet trap of fasting. So fasting is not about weight loss and calorie restriction. Identifying the reason you want to fast in the first place is really helpful. So, you know, if I'm doing fasting, part of the reason I like to fast is that, for me, I do get ketones. I know we’re talking in a few weeks about our evolution of the ketogenic diet, but ketones are really helpful for me because they do give me good energy and good, particularly, mental clarity and good brain energy. So I quite like being in nutritional ketosis, and fasting is helpful for that. Fasting, you know, can be really helpful, as we mentioned, to lower insulin. So that’s great because that’s when you can then open your woodshed and start burning your own fat for fuel. Fasting is also really good for inflammation. So some people find if they’ve got a chronic inflammatory condition, even an autoimmune, like arthritis-type condition, that it improves when they’re fasted. And some people are wanting to look for the autophagy benefits, which you mentioned, Miss, around recycling your proteins. And so, again, for those people, you may find that if that’s your goal, and you might want to do that for various reasons—maybe, again, it can be helpful for prevention of cancer. And, again, that’s a general. That’s not the only thing that is useful for preventing cancer. But you get to decide what the goal of it is. What we don’t want you to be doing it for is to be thinner, because that’s actually a really unhelpful goal. Because, again, if you’re finding that when you’re fasting that your brain moves into deprivation mindset, and then once it comes out of fasting it goes into eating everything in sight—so if fasting is provoking a binging episode, then we would advise don’t fast. So fasting is really only helpful when you’ve really got a good relationship with food and your body. Yeah.
Dr Mary Barson (13:47) And I suppose we could elaborate on the other sort of people who probably shouldn't fast beyond, you know, a 12-hour overnight fast. Pretty much everyone could do that. But, you know, more prolonged and intentional fasts—I'd say pregnant women, breastfeeding women, it's probably just not a good idea. And people who've got, yeah, like you mentioned, that if it can trigger binge eating, people who have a history of anorexia nervosa, you'd want to be really, really cautious. And people who are underweight, you shouldn't do that. I also think kids too—under 18, I probably wouldn’t recommend it, not without, you know, very, very, very specific medical advice and medical supervision because children need a lot of nutrients because they're growing.
Dr Lucy Burns (14:31) Yeah, and again, adolescents are very susceptible to disordered eating. It's a really peak time for disordered eating. So, yeah, we definitely want to make sure that, and again, if you're the parent, that you're also modelling behaviours that are going to be helpful for kids. So, I mean, which brings us into this next point because there's a lot of talk around this—you know, if you're going to do intermittent fasting, you should have breakfast. If you don't have breakfast, you're spiking your cortisol and you shouldn't have your dinner. So just have breakfast and lunch and then do your fasting. And I don’t know what you think about that, Miss. I suspect there’s probably some evidence for that as far as, you know, eating within our circadian rhythm. What are your thoughts?
Dr Mary Barson (15:17) Totally, yeah. So I think that there is some evidence that from chronobiology that, you know, fast from, you know, breakfast to breakfast probably is a teeny, tiny, eeny, weeny, maybe, but we’re not sure, possibly a little bit better than fasting from dinner to dinner. However, this is what we’re talking about—24-hour fasts. The fasting that you do is the fasting that you will benefit from. So I think that we need to, like, put off our perfect hat and just stomp on it and ground it to dust because we don’t want to try and be perfect fasters here. And so just do what works for you. If you want to do a 24-hour fast—and we think that, you know, that’s a good aim for a lot of people once you’ve fat adapted—you know, one or two 24-hour fasts a week can be really great, can be really healing. It’s also probably safe to do that more often than that, but you also probably don’t need to. If it works for you to have your breakfast and then, you know, not have dinner, not have lunch, not have dinner, go to bed, wake up, and then have your breakfast again, go for it, absolutely. And you may be working with your natural sort of chronobiology in doing that. It doesn’t work for me. For me personally, you know, the meal that my family comes together with, the meal that I, you know, is dinner. So it just works for me in my life to have dinner with my kids. So when I choose to do intermittent fasting, I go from dinner to dinner. I have my dinner with the kids, then I stop eating, and then I wake up, I don’t have breakfast, I don’t have lunch, then I have dinner again. And it’s helpful for me and that works. So I don’t think you need to get too wound up in the minutiae. I think do what works for your lifestyle because you will only benefit from the fasting that you actually do.
Dr Lucy Burns (17:00) Yes, I agree. And I think, again, you know, you've got a teenage daughter, so, you know, you're wanting to model family eating, that you're not fearful of food, that, you know, there are good behaviours around social coming together for food like that. And, again, for anybody who's listening out there thinking, God, 24 hours, that sounds like an enormously long time. Dr Mary just didn't wake up one day and think, oh, I think I'll do 24 hours. Like, she's been building up to that.
Dr Mary Barson (17:30) Yeah, totally. And I think that's important because I mentioned that, you know, that metabolic switch, that we go into this metabolic state. We flick into this different metabolic state, but it's probably more useful to think of fasting as like a muscle because our metabolism needs to get better at it. And I think that we want to build it up over time. So starting with a 16-hour fast is actually maybe even less than that, maybe a 12-hour fast. Just, you know, give yourself that. Don't eat after dinner and, you know, go from 7 p.m. to 7 a.m. and see how you feel, and then start stretching it out. A 16-hour fast is achievable for most people, and I think that's a great one to aim for. And then once that is comfy and it feels good and you feel fine and you're in your stride, maybe you push it out to 18 hours and see how that goes. Once that's comfy and in your stride, then you can go 20, and, you know, do these strides a few weeks at a time if you're new to it. If you are fat adapted, you absolutely can dive straight in. It just might be harder than it needs to be. It's better, I think, to allow yourself to build up.
Dr Lucy Burns (18:32) Yeah, absolutely. And I think it's important that there's a threshold. So more fasting isn't necessarily better. So when people go, oh good, I can do a 24-hour fast, I'm going to do one every day now — that is not always helpful either. So, Miss, what happens if we do too much fasting?
Dr Mary Barson (18:50) Yeah, so if we do too much fasting, then we run the risk of getting ourselves into a calorie deficit and into a nutritional deficit as well. So it's going to be difficult to get all of the protein requirements that you need if you're only eating one meal a day, every day, day in, day out. It's also going to be difficult for you to just get your nutritional requirements and your energy requirements. So going back to thinking about this idea of the metabolic switch, so let's say that—I love easy math—so let's just say that the amount of energy that it requires for me to be me, to do all the things I need to do, is like 2,000 calories. Let's just say that. And there will be days where I'm getting my energy from my food and days where I'm getting my energy from my food and from my fat stores, and a bit of a mixture of both. And if I'm keeping my insulin low, when I go into a fast, I can just flick that switch and I can really easily get that energy that I need from my fat stores. However, if day in, day out, day in, day out, I am not getting enough energy—if I'm not eating enough day in, day out—then I will get this metabolic adaptation to that lower intake of energy, to that lower calorie intake, to use that loaded C word. Then my metabolism will actually slow down. So whereas fasting helps improve your metabolism—in that fasted state, we have this increased upregulation of what we call our counter-regulatory hormones that help improve our metabolism, help speed it up—day in, day out, calorie restriction does the opposite of that, and that is not what we want. So one meal a day, day in, day out—tricky. Be cautious to the point where I would probably actually advise against it. I think we want balance. Your fasting days and your feasting days.
Dr Lucy Burns (20:36) Absolutely. And, you know, you may have even fasting periods. So this is where it's so flexible. You know, you might do OMAD five days in a row, let's say, and then you might have a period where, you know, you've got a few things on and suddenly you're having two meals a day and you might do that for two weeks. Then you might have a period where you think, oh, I wouldn't, you know, I don't know, I feel like I need some intermittent fasting benefits, and so you might do five days in a row again. Again, you can mix it up. But what we don't want is just prolonged—and it really is, it’s prolonged low-calorie eating—because, as you said, Mary, it will reduce your metabolic rate. We've seen that. Any of you who have watched the Biggest Loser documentary recently, we've seen that. We've also seen it, you know, in the Minnesota Semi-Starvation Study. So this is well known. So it's a really important step to be mindful of. But, again, I would just go slow and steady—boring, old-fashioned advice—slow and steady.
Dr Mary Barson (21:40) Yeah, that's right. That's right. But what about if you're a woman? As we both are. You will see blanket recommendations out there in social media land and elsewhere that women should not fast. Fasting is bad for women. And I would argue that that is highly simplistic advice, to the point where it is, in fact, wrong. But there's some nuance there which I think is important to be aware of. If you are a menstruating woman, we're going to have hormonal fluctuations throughout our cycle, and it often happens in a relatively predictable way. There are times when fasting is going to be harder—not necessarily that you can't do it, but it might be harder. So, in particular, the luteal phase, which is like from ovulation onwards, that second half of our cycle—during that part of our cycle, progesterone, that hormone, it dominates. And as progesterone dominates, our insulin sensitivity decreases—or it might be easier to say our insulin resistance goes up. And during that time, it's really normal for women to have increased cravings, increased hunger. And it may be that fasting is more difficult for you to sustain in that luteal phase. And if that's the case, don't fast at that period of time. But there will be women out there listening to me and like, I've got no idea what you're talking about. I don't get hungry at the second half of my period. I don't notice increased cravings. And if that's you, just do whatever you want to do. But just be aware that there might be times when it is harder for you. And fasting in perimenopause is another time that some flexibility may be required, because the same things are happening with fluctuations in estrogen—relative fluctuations in estrogen and progesterone—but it's happening in a less predictable way during that perimenopausal transition. So being flexible might be even more important. And if there are days when you're just feeling like, I don't know why, but this is just too hard today, then eat and try it another day. Just allow yourself to be flexible and understand that you're going to have fluctuations in your insulin resistance and insulin sensitivity during this time. But also understand that fasting can be really helpful in perimenopause for treating many of the issues that arise for us during that time—not just the decrease in our metabolic health. It's really helpful for that. But there are also studies looking that for some women it is helpful for hot flushes. For some women, it is helpful for mood fluctuations. It can be helpful for sleep. So just be your own scientist. Do it safely, do it sensibly, and figure out what works for you.
Dr Lucy Burns (24:17) Yes, absolutely. And I think this is the tricky bit around studies. When you look at a study, any study, there is never—it's not 100% of women will behave in a certain way. So even research, you know, there are some fairly popular researchers on socials who are pretty anti-fasting in women, and particularly one who's particularly anti-fasting in saying it decreases athletic performance, which may be true if you're a high-level athlete. But the majority of women we see aren't really high-level athletes—they're just living their lives. And again, it doesn't matter what study, anything that happens, there will be an average—so the average amount of such and such. There will be people for whom they've had, you know, morning fasting makes no difference to their cortisol levels or their metabolism or anything. And there will be other people for whom morning fasting or drinking black coffee in the morning, they get a highly exaggerated response. So like everything, the summary is doing things sensibly but test and measure your own response because you are your own individual with your own set of hormones, your own set of circumstances, your own set of neurotransmitters, and we now know that there is no one-size-fits-all.
Mary Barson (25:41) That's right. One-size-fits-one sometimes.
Dr Lucy Burns (24:46) Absolutely. All right, lovely friends, we will talk to you very shortly. Have a wonderful week and we will see you all soon.
Mary Barson (25:53) Bye now.
Dr Lucy Burns (26:57) The information shared on the Real Health and Weight Loss Podcast, including show notes and links, provides general information only. It is not a substitute, nor is it intended to provide individualised medical advice, diagnosis or treatment, nor can it be construed as such. Please consult your doctor for any medical concerns.
