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Intermittent Fasting with Natalie Bourke

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Intermittent Fasting with Natalie Bourke

There is a growing body of research supporting a range of clinical benefits for intermittent fasting (IF). For those of us who aren't early adopters - what is it and when is it a clinically relevant choice for patients?

In today's podcast, we're joined once again by Natalie Douglas, who shares her own clinical rationale for determining if intermittent fasting is the right choice for her patients. Nat expertly navigates us through outcomes for women vs. men, the impact on blood sugar and hormonal systems and talks specifically about what to be aware of for a range of chronic health conditions like diabetes, thyroid disease, metabolic syndrome, autoimmune disease and much more. 


Covered in this episode

[01:12] Welcoming back Natalie Bourke
[01:58] What is intermittent fasting?
[04:18] Intermittent fasting vs. calorie restriction
[06:28] Mechanisms of action
[09:30] The impact of stress and cortisol
[13:59] Intermittent fasting and immune modulation
[16:04] Intermittent fasting and gut conditions
[17:17] Intermittent fasting and chemotherapy
[20:14] Overcoming hunger
[23:00] Who else is intermittent fasting good for?
[26:05] Who is it not suitable for?
[29:46] Be aware of the differences in males vs. females
[34:14] Where to start with intermittent fasting?

Andrew: This is FX Medicine, I'm Andrew Whitfield-Cook. Joining us on the line today is Natalie Bourke who's a holistic dietitian and nutritionist, author, podcaster, speaker and fitness instructor. Nat is passionate about helping women build a healthy relationship with food and their body. She achieves lasting results for her clients using wholefood nutrition, functional medicine, and holistic lifestyle advice. 

You can catch her fortnightly on the The Holistic Nutritionists podcast. Her eBook, Healing Digestive Discomfort, is an industry-leading guide with accessible guidance for anyone looking to start improving their gut health.

Welcome back to FX Medicine. Nat, how are you?

Natalie: Thank you for having me. I'm great. 

Andrew: Let's first cover the concept of this. It was popularised by Michael Mosley's book, the 5:2 Diet. But I think it's been around a lot longer than that. Take us through a little bit of the history or more importantly where we are today with intermittent fasting. 

Natalie: Yeah. Look, I think intermittent fasting is eating, well, basically just for anyone who doesn't know it - is eating within a shortened window. So usually people are fasting anywhere from 12 to 20 hours although I'd say the most common kind of time is about 16 hours and then eating within an 8-hour window. And, I think it began a long time ago from an evolutionary standpoint. You know, how long have humans been in existence I guess would be more of a question and where the answer lies. 

So historically we didn't have the food availability that we have now so you couldn't just walk out the door and be met with a supermarket, a café, and a vending machine. There were times of course when there was adequate food available, but then there were times where there wasn't and this is how we evolved. We didn't come here with a setup breakfast, lunch, and dinner eating schedule. And we certainly didn't historically eat five to six meals a day to "keep our metabolism firing". 

So, it's been around for a long time, and I guess it's hard to say how, like when it began to be more popular from a modern-day perspective. All I can do I guess is speak from my personal experience and what I've noticed. And I think over the last let's say five years as diets like the paleo diet and keto have become more and more popular. A lot of the key health proponents in these circles have also been speaking about the benefits of and uses of intermittent fasting. 

And because, I guess, if we look at things like the paleo diet and a big foundation of eating that way is getting back to eating in more of an ancestral way. So eliminating processed foods and then from there, I think there have been increasing inquiry around not just what our ancestors ate but how did they eat? And, you know, they could definitely be more of a sophisticated answer than that. But that's what I have seen in my observation in the wellness industry at least.

Andrew: And how do you tease apart intermittent fasting versus overall calorie restriction?

Natalie: Well, there are differences. So, calorie restriction doesn't necessarily follow a fasting period, like a structure. Whereas intermittent fasting, you are eating within a certain window of time but you're not calorie-restricting. So, in calorie restriction, there is calorie restriction, but in intermittent fasting, there isn't. 

Andrew: So it's got to with the window of fasting and how long you're actually not eating for rather than just caloric restriction? I would imagine though that intermittent fasting would lead to less calories, is that right? 

Natalie: Well, I do think so in a lot of situations, I think that particularly when you've got a lot of the population taking it on because they want weight loss, they often do end up calorie-restricting. Or if they're not paying attention to doing it how it's intended, then, yes, it does. 

But I actually think that it's more beneficial, even for weight loss, to actually do intermittent fasting but without the calorie restriction. We've seen a lot of the benefits still come about from just doing that.

Andrew: This is something that really interests me because like, I remember years ago, there was this...it was a fad but it was popular at the time about "keeping your blood sugar level by eating small amounts more frequently". 

So there was the six, seven snacks rather than meals per day. I wonder though whether the intended purpose of keeping your blood sugar levels even led to more calories, not less? And that was the overall problem. 

Natalie: Yeah, I mean it's always more than one thing and I'd say like, it potentially could be some kind of mechanism happening there. And, look, I do think that eating frequently for someone who has really fluctuating blood sugar levels can be an advantage. But when we're talking about pre-diabetes or insulin resistance, definitely intermittent fasting, like, there's a reason to use it in that situation. 

Andrew: Let's discuss the mechanisms of action, because I could imagine that it would have effects on a multitude of hormones, not just insulin. Is that right? 

Natalie: Yeah, absolutely, but I guess insulin is an awesome one to start with. So, let's take it back to basics, and excuse any oversimplification but just stay with me for a minute. 

Andrew: Okay. 

Natalie: So, when you eat and your body breaks down your food, the glucose from your food goes into your bloodstream for transport to your cells. Glucose gives your cells the fuel they need to do whatever their job is. Now, when your body gets the signal that you've eaten, beta cells in your pancreas produce insulin, which is what tells your cells to open the door and let the glucose in from the bloodstream. 

When you don't have insulin or you're resistant to insulin or what we know as insulin resistance, then your cells don't allow glucose in and the glucose stays in your bloodstream. Once your body senses that glucose has been hanging around in your bloodstream for a while, it's stores it as fat for later because it thinks your cells don't need it now because it's not being let in as it should. 

So, for insulin resistance to develop, it's obviously not just going to happen overnight. Usually it requires high blood glucose levels for a long time and consistently. So, you've got three factors there - high blood glucose levels, a long time, and consistent. So that's important to remember.

So then how does this relate to fasting? Well, the easiest way to explain one mechanism by which insulin sensitivity is increased with fasting is that you're basically taking away the amount of time that there is larger amounts of insulin released into your bloodstream. So it kind of reduces that whole consistency element of the equation that predisposes someone to developing insulin resistance. As in you're not continuously hitting your body with insulin. And just to point out, insulin is released in response to other foods too, like not just carbohydrates but obviously carbohydrates has more of an impact. 

Anyway, hopefully that makes sense. I mean I'm certain again there's probably further research going into more complex mechanisms but that is my understanding and it's an easy one to wrap your head around. And for those of you listening who love a study to back things up, there's plenty of research relating to improved insulin sensitivity and blood glucose levels when following an intermittent fasting or fasting regime. However, interestingly enough, which we'll go into shortly, is most of these benefits are exclusive to men. 

So one example of the many was a 2005 study where Danish researchers showed that intermittent fasting quickly increases insulin-mediated glucose uptake rates. So, I believe there was about 80 men in their mid-20s who fasted for 20 hours every day. Sorry, every other day for 15 days. And at the end of the trial, their insulin had become more efficient at managing blood sugar. 

So that's kind of the insulin side of things, but as you mentioned, there are other hormones that are affected by it, like cortisol of course. 

Andrew: I guess my concern with intermittent fasting is the blocks for accessing the benefits of intermittent fasting. And of course one of those is stress and hunger. Largely driven by a hormone called cortisol. Let's discuss that. 

Natalie: Yeah, yeah. So, look, when you fast, there obviously isn't any exogenous or dietary sources of glucose coming in to balance or regulate your blood sugar via the mechanism we discussed before, right? But, your body still needs to regulate blood sugar. 

So one way that it does this is via cortisol. So, when blood sugar dips too low, cortisol is released and helps to bring your blood sugar back up to a stable range. So, with that being said, fasting can actually definitely increase cortisol if someone has dysregulated blood sugar already, and it's constantly going up and down and needing cortisol to come to the party to help regulate it. 

So in someone with blood sugar regulation issues, as in they're fluctuating quite a bit, then fasting can actually make them worse. And I guess from a clinical practice perspective, you can track this in a few ways depending on the motivation of your client and if you have your fancy pants on that day. But one way is just to ask questions around blood sugar regulation. Like, do you feel lightheaded between meals? Do you feel super tired after you eat? Do you have strong sugar cravings? Does your energy fluctuate noticeably throughout the day? Do you get shaky? And, if the answer is yes to any of those questions, then I'd argue that fasting right now, for that person, is not going to provide a net benefit. 

Now, if you want to get fancy, you can. You could get them to buy a blood sugar monitor and take their fasting blood glucose levels and if you postprandial glucose level throughout the day for a week or so. But for most people, that's going to be a bit too hard basket. But, you know, we all have clients that are really into that stuff, so options, right? 

But, there are two kind of ways that you can assess that and make more of an informed decision around whether intermittent fasting is going to be the idea or correct strategy for that patient at this time in their life.

Andrew: So would you say a pre-prandial/before food test, so a fasting test plus let's say, immediately after food and then say two or would you wait four hours after food?

Natalie: I'd probably do two hours after food. And you're looking for...like, I guess the reference range is about 3 to 7.7 millimoles per litre 2 hours postprandial. But from a functional medicine perspective, I would say it's best to sit in the middle of that kind of range. 

Andrew: Yep. 

Natalie: So if it starts creeping up, we don't pay attention. Once it's out of range, if it's starting to creep up, then you would start to pay attention. 

Andrew: Yeah, that's right and that's where you'd be looking at seeking other advice, correct?

Natalie: Absolutely, yes.

Andrew: People speak about intermittent fasting like it's taking away the stress of food that food places on the system but I must ask the question, is it a reliever of stress or is it indeed a stressor in itself? 

Natalie: Yeah. It is a stressor in itself. Because you are essentially restricting nutrients and you're causing the body to have to synthesise glucose from stores. Or, you know, it is a stress on the body but it's a positive stress in some ways just like exercise is if it's done in the right amount by the right person at the right time. 

So, whenever I'm assessing whether intermittent fasting is going to be a good intervention for a patient, I look at all of the other stressors in their life. How much stress is actually coming in their life elsewhere, and then I make a decision as to whether, yes, adding this stress is going to still provide a net benefit. 

But if you've got someone that is, you know, working a ridiculous amount, they're training a lot, they're emotionally stressed, or they've got a history of "adrenal fatigue" or HPA axis dysregulation as I prefer to call it...

Andrew: Yes, thank you. 

Natalie: Then you know, yeah, the benefit probably isn't going to outweigh the cost for them right now. It's not to say that that strategy isn't going to be of benefit down the track, but it's all about assessing the situation right now as it is in front of you. 

Andrew: What effects then, if this is a positive stress, what effects are seen on say the immune system for instance? I remember people talking about a study where medical students were pushed into a cold-water pool, and they immediately saw decreases in the immune signals if you like in their saliva. But can intermittent fasting have a positive effect on immune modulation at all?

Natalie: Yeah, it can. So, when it comes to immune modulation, I do think there is some good research in this area. A lot of it is animal-based but there is also some human studies, too. 

So I think part of the way fasting is helping with regulating the immune system is via autophagy, which plays a crucial role in immunity and inflammation. And also there's evidence showing that intermittent fasting can reduce inflammatory cytokines. In particular, interleukin-6 and TNF-alpha, but as always I like to think about, okay, how does this translate into practice in patients I'm seeing? 

So, for me, a lot of the patients I see have autoimmune thyroid conditions; in particular, Hashimoto's. And I think for most people with an autoimmune condition, it's a fine line between benefit versus cost with fasting. So, benefit being the autophagy and some regulation that's happening there. But then the cost being that these people often are under quite a lot of stress emotionally, or physically, or whatever it may be. And for me, if someone is under a lot of stress, fasting is not right for them. 

But as a general rule, I'd say doing a couple of intermittent fasting days a week is fine. See how they feel but don't insist if they're not getting the benefit or they are starting to have issues with sleep. Because when we're getting into a net cost...like, then we are getting into a net cost as opposed to a benefit. So maybe focus on other ways to turn on autophagy like exercise or I think infrared saunas is another way you can upregulate it, too.

Andrew: What about gut conditions? I'm noting you're reducing IL-6 and TNF-alpha. In my mind, I've got things like Crohn's swimming around in there. What effect does intermittent fasting have on Crohn's? I do remember gastroenterologists using, well, they were using, let's say, an oligoantigenic approach to give the gut a rest, but that was not fasting per se. What effect does fasting have?

Natalie: Yeah. Look, I'd say the benefits would be two-fold, in that yes, giving the digestive system a rest in that case can be beneficial. Because you're obviously not putting the things that could potentially create inflammation in the body into the system on a consistent basis. So I'd definitely give it a go, and there still are going to be immune modulation type mechanisms happening in that case. 

So, absolutely I would use it in Crohn's disease and just see how that patient responds. So it's always about, here's what the literature says, here's what the mechanism of action is according to that, and here's the person in front of me. I'm going to try it and I'm going to see how they respond. And their body will tell you whether it's working for them or it's not.

Andrew: Yeah, I think the caveat would be obviously they've got to be reasonably nourished. They can't be malnourished as I've seen in a couple of patients. But, to me, it's really interesting how, for instance, intermittent fasting is being researched in, say, not necessarily its effect on cancer. That's an inappropriate comment but it's a positive effect on how people react to chemotherapy i.e. how they tolerate it better. That's really interesting to me. And it's not just staying away from something that'll make you nauseous. It's not that concept. It's actually helping the chemotherapy to work more effectively.

Natalie: Yeah, definitely. And I can't say I'm an expert in that area at all, but I definitely have seen some research flagged around that. And I think that, as you said, part of it is making the chemotherapy work better. Also, I think the concept of autophagy comes up again..

Andrew: Yep, yep. 

Natalie: Which is basically just a fancy word for cellular cleaning. So, turning on that process helps clear damaged cells inside tissues, organs, etc. which is a good idea since letting these cells linger can trigger inflammation. And there's lots and lots of different steps in autophagy but basically the damaged cells get transported into a lysosome and destructed. Then they can come back out and be recycled or repurposed. I like to think of it as spring cleaning and chucking out the junk and then rediscovering stuff you forgot you had that could be repurposed and used.

Yeah, just to point out though that autophagy does actually already exist in all living cells but certain things increase it. So, the two main ways is in response to stress or nutrient depravation, and you know, fasting is one way to do that. And also, as I mentioned before, exercise would be the other big way. And both of these have been linked with benefits like weight control, longevity, reduced risk of autoimmune conditions, all that good stuff.

Andrew: You know, this is something that I think we're finally learning is that the concept...if we go back 10 years, the concept would be that you need to feed to support cellular function. You know, you need nutrients therefore more nutrients is better. And now what we're learning is that the stressor that indeed exercise causes and things like that, this period of "have not" can wake a body up, can wake cellular processes up, and reset them to a degree. 

Natalie: Yeah, exactly. It's kind of like that Goldilocks Zone. There's a sweet spot for it all and I think that there really needs to be individual care around that if someone is in that situation. And making an informed decision, and constantly reassessing their decision as the patient progresses or whatever they're trying to move through.

Andrew: So let's talk about the previous period of having too much and then you're used to it. And now you're in that hunger phase. You're driven by your sugar levels, your cortisol, and all of those other hormones and even habits; your secretin, and somatostatin, and all of these other hormones. Hunger. How do you intervene once hunger is already set in, it's already a habit?

Natalie: Yeah. Well, I guess there is that question around, as you mentioned, like stress, and hunger, and hunger drivers and does stress undo all of the positive effects that intermittent fasting is doing? And, well, like, yes and no. Stress, which is going to drive up hunger, won't necessarily decrease the benefits in terms of autophagy, but obviously it's going to have an impact on HPA axis and trickle down into dysregulated cortisol production, and we know cortisol has a close relationship with blood sugar, and insulin, and also thyroid health. So that whole axis is going to be put off.

And I guess this is where sensible use of intermittent fasting needs to come in. Is the person in front of you really going to benefit from intermittent fasting more than it's going to stress their body out? And this, in my opinion, should always be the question. It should never be a matter of is intermittent fasting always good, always bad? And being open to the fact that that may change throughout time. But it is a positive stress, as I mentioned, but you'd have to be assessed on an individual basis because, yes, if you are...we all kind of know intuitively that, when we're stressed, or when we're super tired, or there is just additional stressors in our life, our hunger drivers are increased. And adding the stress of fasting into that is only going to further dysregulate our blood sugar and further contribute to that problem. 

And to give listeners more of an example they might be able to relate to in that context, is that I found for myself is that, when I'm on holiday and I'm generally pretty relaxed, getting plenty of sleep, and not caught in the ‘rat race.’ I can get away with fasting in the morning and actually drinking more coffee without any noticeable effect on my blood sugar. But if I try to do those two things regularly when I'm not on holidays, it just doesn't work. And, again, does that mean that intermittent fasting is bad for me full stop? Absolutely not. It means that, in that context, it's not very good for me.

Andrew: We've mentioned a few obvious sort of things about insulin resistance, and therefore I would include people that have gotten that metabolic syndrome type picture. I would also assume that it would help with controlling weight. You've mentioned autoimmune conditions, and I'd love to discuss more on that. But who else is intermittent fasting suitable for?

Natalie: Yeah. So, yeah, as you mentioned, definitely weight loss, insulin resistance, metabolic syndrome type picture. And just to point out there, so I did mention before that a lot of the research doesn't show benefits in females in the context of regulating blood sugar. But one exception to that rule is that research done on females who are overweight or obese, that actually does have a positive effect in that specific population. So, just to point that out for listeners that it's not a blanket no for all women. In relation to regulating blood sugar, that group of people do benefit from it. 

But another one that I actually find a benefit in would be patients with SIBO. And so just, SIBO being small intestinal bacterial overgrowth. So, the reason why fasting can be beneficial in SIBO is because we have something called a migrating motor complex that is kind of like this wave-like movement moving undigested food and waste out of the small intestine which prevents overgrowth there. 

Now, this whole process or this switching on the migrating motor complex happened in stages. Generally speaking, it will start about one and a half to two hours after eating. Then there is like a calm period lasting about 45 to 60 minutes, followed by a period of peristaltic contractions which increase in frequency and last for about 30 minutes or so I think? And then there's a period of rapid, evenly spaced peristaltic contractions lasting about 5 to 15 minutes, and then a short transition period until the whole cycle like phase 1 kind of begins again.

So, all that translates into practically is leaving a good 4 to 5 hours between eating is necessary for that whole process to be really effective. And of course 4 to 5 hours isn't a complete intermittent fast by any means and you obviously don't need to fast for really long periods to experience the benefit of optimal migrating motor complex function. But I definitely do think it can be used and I have used it successfully in a number of my SIBO patients. So I think that that can be particularly good as a therapeutic intervention in that context. 

And then the only other group that I'd probably add to that or the only other benefit I would say, just from a longevity point of view and more from...I guess where that comes in is the autophagy, cellular cleaning. You're obviously allowing the body to have more opportunities to clean itself basically. And that can obviously help with, you know, longevity. 

Andrew: Okay, but it can't be suitable for everybody. Who's it not suitable for? When do you have to be really careful? I've got obvious things floating around in my mind; people who are malnourished. We've reported before with regards to Crohn's disease. What other conditions do you have to be particularly aware of?

Natalie: Yeah. Look, I have a little list myself that I have in the back of my head when people are inquiring about it. And for me, there's a few red flags. People doing a significant amount of glycolytic, like high-intensity-interval-training-based exercise tend to not do great with it. In my experience, it just doesn't work. There's already quite a lot of stress going into their system, and also these people who are engaging in a lot of that activity often have higher energy demand. And it's really quite hard to get enough food into a shortened eating window, so I don't tend to use it in that context. 

I also - a bit of an obvious one - would not use it in anorexia or bulimia or any kind of eating disorder. Because we're trying to detach any kind of restrictions or rules around food in order to help these people develop a healthier relationship with food. These people already have strong emotional ties to their dietary habits and self-worth, and to add in something else that they must follow in order to consider themselves worthy, it's just not indicated or helpful at all. 

The next one would probably be in any kind of HPA axis dysregulation, "adrenal fatigue". This comes back to the effects of fasting on cortisol and blood sugar regulation. So, it can increase cortisol production in an attempt to regulate blood sugar. In someone who is going through a stressful period, it's just not wise to keep adding on. Heal first, then reassess if it's an option. I actually find in people with blood sugar regulation issues which often accompany the HPA axis dysregulation, getting them to eat regularly is helpful as an intervention. And again treat and then reassess.

And then probably a couple more that I'd add would be hypothyroidism, and I'd lump this with the same reason as above. You've got a dysregulated HPA axis or HPT axis in this situation. For managing hypothyroidism, it's often necessary to support the adrenals to focus on decreasing inflammation, increasing sleep quality, and ensuring they have adequate carbohydrates. So, I think there are more important strategies that provide more of a benefit in that kind of context. 

And then the last one I'd really like to flag because I see this just go wrong so often is hypothalamic amenorrhea. So, what's happening is basically how I like to explain it, which everyone giggles a little bit, but basically the brain stopped communicating with your lady garden or female reproductive organs for the more professional terminology. 

This is happening because there's too much perceived stress. So we often see in this condition that it's driven by undereating and/or over-exercising or just too much stress. Physiologically the body will preferentially produce stress hormones at the expense of sex hormones. And if you're adding the stress of fasting in, then it's just going to further drive this mechanism and not to mention a lot of people with HA have gotten this because of disordered eating patterns.

Andrew: Are there any major differences between men, when it comes to intermittent fasting given that there is some poor data on both sexes in certain instances?

Natalie: Yes, absolutely and this is something I'm really passionate about shouting from the rooftops. Because I think there's so much information out there in the blogosphere declaring all the benefits of intermittent fasting with limited discussion around the differences in the research between men and women. 

So, here I am playing devil's advocate. So, in a lot of women, intermittent fasting causes issues with sleep, anxiety, and irregular periods or amenorrhea. Some people also experience weight gain, and the question then becomes, well, what the heck is going on when most people promoting intermittent fasting are saying that you will get the opposite? As in, you'll experience weight loss, then great hormonal balance, and an abundance of energy. And the answer is both simple and complex. 

So let's start with the simple version. Biologically we're in a quite different cement. We have way more sensitive hormonal systems that are more in tune with energy availability. And that energy availability has a very close relationship with our hormonal health. Because from a biological perspective, we were designed to be fertile and reproduce. And why would the body want to reproduce if it feels like its survival is being threatened by energy restriction? It just wouldn't. 

And when it comes to the research, there are a few examples I can give. So in women, a two-day fast shifted nervous system activity towards more of a sympathetic-dominant state. Whereas in men, a two-day fast shifted the nervous system into the other direction, as you mentioned, more of a parasympathetic state. And interestingly there's also something called the hypocretin neurons which were only relatively recently discovered, and I think it might have been like 1998 or something. 

Anyway, I don't know everything about them but I will share what I do know. Which is that they're like little neurons that have the ability to cause wakefulness and prevent a person from being able to fall asleep. And they're pretty complex but basically in the context of this discussion, their excitation occurs in reaction to the body detecting a starved state. So, hypocretin neuron activation is one way in which intermittent fasting may dysregulate a woman's normal hormonal function. 

Andrew: Wow!

Natalie: Yeah, so like again it's kind of a relatively new thing and only came up on my desk for research recently. So I haven't gotten to dive deep into it but I found that a really interesting little addition.

Andrew: That's really, really interesting - hypocretin neurons. I'll be sure to put something up on the FX Medicine website about that. And if you've got any research to share, I'd love to put that up on the FX Medicine website for our listeners. Please, Nat, that'd be great. 

Natalie: Yeah, absolutely. And, I guess moving on from that, another example relates to a study done on autophagy where male neurons respond to starvation as we'd expect by undergoing autophagy. Whereas female neurons respond by resisting it. 

And again there is a bit of conflicting research in this area because there are also studies that do show positive benefits in women in relation to autophagy. But it just isn't as straighty-180 in men. So my thoughts on that is perhaps, if autophagy is the main goal, again, until we have more solid research, maybe using exercise as the key way to switch that process on is wise. Or simply not using intermittent fasting every day. 

And finally I'd like to add my own clinical practice experience. I see a lot of women undertake intermittent fasting regimes and end up with difficulties sleeping, low thyroid function is a big one and signs of dysregulated blood sugar. And usually issues with their menstrual cycle. And again does that mean I never use intermittent fasting or see benefit in women? Definitely not. I have plenty of women who have benefited from it as a short-term intervention or even, some people just do well off it a few days a week. But it's just like, what I want practitioners to take away, is it's just really important to know the differences between men and women and o make an informed decision if you are going to use it in women.

Andrew: How do you start intermittent fasting? And I guess I have to ask here, when you're seeing these issues with men and women and particularly in certain patients, do you tend to look at the intermittent fasting as a per day phase or a per week phase like, you know, the 5:2 diet? 

Natalie: Yeah, I don't tend to get women to do it daily and, in terms of how to start, I'd say slowly. So my advice would actually to first be clean up your diet. If you're coming from a processed food diet or even just a diet quite high in carbohydrates, I'd suggest first switching to a wholefood-based diet, then incorporating maybe some cyclical low-carb eating if it's not contraindicated for you. 

Then I'd work on adding in one intermittent fast day a week and go from there. It shouldn't just be, you know, I'm eating a standard Australian diet, and I just need to go and fast. Because it's just not going to be an easy ride. And the point isn't to make our patients suffer, it's to have simple solutions that create lasting results that aren't impossible to achieve.

Andrew: And so when you're discussing these sorts of issues with your patients and I've brought it up previously with regards to hunger, what should they be prepared to endure and how easy it for these people?

Natalie: Yeah. So, if you do it sensibly as suggested above. The only symptom that should or may come up is a little bit of hunger as your body kind of adjusts. If you're getting wild blood sugar swings, lots of cravings or issues with sleep or your cycle, then I'd say that it's a red flag for not being the right move for you at this time. 

So, I don't believe it's something that you should just kind of tough out. If your body is sending you a lot of signs, it may be something you need to step into more slowly and that will give you more of a benefit than if you were to just tough it out and wait for all that to pass.

Andrew: And obviously there are these red flags of things like dizziness and anything that might affect the daily activities of living or things like driving and safety issues, correct?

Natalie: Yeah, yeah, absolutely changes in sleep, changes in menstrual cycle, all those kinds of red flags would be what I'd look out for in women.

Andrew: So, just a last little point. Any tweaks then? For say, women, if they've insisted on using it but you've seen these red flags or you've seen these cautions, what do you advise your female patients to do?

Natalie: Yeah. So, for women I find, as I mentioned, doing it less frequently on non-consecutive days. And on days when they're not doing high amounts of activity seems to be more helpful to start with. 

Another tip that some people have benefited from is, instead of just doing straight fasting with nothing but water, they can incorporate like a bulletproof coffee or bulletproof caffeine-free drink depending on what's most appropriate for them as an individual. So what that is just combining water, organic coffee, because it's low in toxins, or using a caffeine-free alternative like dandelion tea with some MCT oil is my favourite and/or some grass-fed butter. And basically just fat as opposed to carbs and proteins. So, it kind of can get the benefit of protein-restricted fasting but still supply some energy source for the brain. And the fat takes your body in ketosis so you get the cell-renewing benefits of intermittent fasting in that regard. And the fat also provides enough fuel for your brain so you don't get the same kind of stress response in most cases. 

So again if someone does that and they get signs of low blood sugar after having that, then it's not the right answer and I'd go back to putting them on a high-protein breakfast and reassessing the intermittent fasting at another time. 

Andrew: Your expertise, and this is obvious, and I love the way...I've got to so I'm so impressed the way that you personalise everything and you bring it back to that person right there with their conditions and their experiences. I really admire you for that, Nat, both in our previous podcast but also in this one on intermittent fasting. Thanks so much for joining us on FX Medicine.

Natalie: Thanks for having me, Andrew.

Andrew: This is FX Medicine. I'm Andrew Whitfield-Cook.

Additional Resources

Natalie Bourke 
The Holistic Nutritionists Podcast
eBook: Healing Digestive Discomfort by Natalie Bourke
Dr Michael Mosely: The Fast Diet

Research explored in this episode

Halberg N, Henriksen M, Söderhamn N, et al. Effect of intermittent fasting and refeeding on insulin action in healthy men. J Appl Physiol (1985). 2005 Dec;99(6):2128-36. 

Varady KA, Hellerstein MK. Alternate-day fasting and chronic disease prevention: a review of human and animal trials. Am J Clin Nutr. 2007 Jul;86(1):7-13.

Mehrdad Alirezaei, Christopher C. Kemball, Claudia T. Flynn, et al. Short-term fasting induces profound neuronal autophagy. Autophagy. 2010 Aug 16; 6(6): 702–710.

Antunes F, Erustes AG, Costa AJ, et al. Autophagy and intermittent fasting: the connection for cancer therapy? Clinics (Sao Paulo). 2018 Dec 10;73(suppl 1):e814s.

Du L, Hickey RW, Bayir H, et al. Starving neurons show sex difference in autophagy. J Biol Chem. 2009 Jan 23;284(4):2383-96.

Heilbronn LK, Civitarese AE, Bogacka I, et al. Glucose tolerance and skeletal muscle gene expression in response to alternate day fasting. Obes Res. 2005 Mar;13(3):574-81.

Arguin H, Dionne IJ, Sénéchal M, et al. Short- and long-term effects of continuous versus intermittent restrictive diet approaches on body composition and the metabolic profile in overweight and obese postmenopausal women: a pilot study. Menopause. 2012 Aug;19(8):870-6.

Kumar S, Kaur G. Intermittent fasting dietary restriction regimen negatively influences reproduction in young rats: a study of hypothalamo-hypophysial-gonadal axis. PLoS One. 2013;8(1):e52416


Other podcasts with Nat include:


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