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Is Intermittent Fasting Good For You?


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You can’t answer this question with a yes or no. There’s no one-size-fits-all approach, and intermittent fasting could be a good idea or it could be a terrible idea, depending on your circumstances.

Revolution Health Radio podcast, Chris Kresser

When you look at the research on intermittent fasting, I would say it’s mixed. There’s definitely some research that suggests that it is beneficial for weight loss and also, more particularly, the improvement of metabolic markers, blood sugar, lipids, and things like that. But I think the confusion arises for the same reason that it arises on a number of different subjects — individual circumstances vary. And those circumstances might change over a given period of time.

In this episode, we cover:

5:15  Situations where intermittent fasting is a good idea
9:10  Who should be cautious about intermittent fasting
10:32  When should you fast?
15:00  Fasting recommendations

Steve Wright: Good morning, good evening, and good afternoon. You are listening to the Revolution Health Radio Show. I’m your host, Steve Wright, co-author at SCDlifestyle.com. This episode of RHR is brought to you by 14Four.me. Now, if you haven’t heard of this program yet, it’s a program that Chris put together that’s designed to reset your lifestyle over a 14-day period. It’s going to do that through the foundational steps that we are usually talking about on the podcast, things like diet, sleep, movement, and stress. If you’ve ever tried to implement healthy habits in your life, you know that it can be very hard to integrate them into daily life and stick with them when things come up, and so what Chris has done is he’s created this program to really walk you through step by step using the best knowledge that we have today from science and habit formation on how you can really implement these throughout your life and do it sort of in one big reset. So if you haven’t yet, check out 14Four.me. That’s 14Four.me.

All right, on with the podcast. With me is integrative medical practitioner, healthy skeptic, and New York Times bestselling author, Chris Kresser. Chris, how is your day going?

Chris Kresser: It’s good. Lots of fun stuff going on. Busy as usual, but also just enjoying the beginnings of summer here and spending more time outside. How about you?

Steve Wright: Yeah, I’m having a delicious day.

Chris Kresser: That’s unexpected! I like it, though. I like it.

Steve Wright: Yeah. I’m trying to be done with the good, great, cool type of things. I’m trying to come up some different words.

Chris Kresser: Well, I will expect a new adjective from you on every podcast. That’s your homework.

Steve Wright: Oh, boy. I’m going to have to think about this.

Chris Kresser: Break out the dictionary or thesaurus.

Yeah, we have a really great question today about intermittent fasting, so let’s give it a listen.

Question from Codi: Hi, Chris. You often talk about your own practice of intermittent fasting on the show, and I’ve been doing some reading about it. There’s some debate about the utility of intermittent fasting for females due to special hormone and reproductive considerations. My own personal situation: My hormones have always been a little bit out of whack, and I have very low adrenal functioning and low hormone production across the board. But I’ve been reading about intermittent fasting as a way to improve my insulin sensitivity and potentially also drop that last 5 to 10 pounds that I’ve been trying to lose. So I’m wondering if you could talk a little bit about intermittent fasting on your show and if you could share some recommendations for how often someone should intermittent fast, say, once a week, twice a week, and if you recommend that they pair that with caloric restriction or simply restrict the window of time that someone eats during the day. And lastly, I’m wondering if there are any special considerations that you have for women or for other health conditions in general. Thanks so much for your time. I look forward to your answer.

Chris Kresser: All right. Well, thank you, Codi. This is, of course, something that’s of interest to a number of people. We get this question a lot either through the podcast or on the blog, from my patients, and it is something that I think there’s a bit of confusion about.

When you look at the research on intermittent fasting, I would say it’s mixed. There’s definitely some research that suggests that it is beneficial for weight loss and also, more particularly, the improvement of metabolic markers, blood sugar, lipids, and things like that. But I think the confusion arises for the same reason that it arises on a number of different subjects. If we try to ask the question, is intermittent fasting a good idea? and just answer it with a yes or no, that’s never going to work because as I always say — at the risk of beating a dead horse — there’s no one-size-fits-all approach, and intermittent fasting could be a good idea or it could be a terrible idea, depending on your circumstances. And those circumstances might change over a given period of time for a given person, so it’s not even accurate to say intermittent fasting is a good idea for this person but not for that person, because those circumstances that determine whether it’s a good idea can change over time.

Steve Wright: I can echo that because I’ve played with this extensively, and I have noticed that over the last six years.

Chris Kresser: Yeah, so I’ll be curious to hear about your experience.

Situations Where Intermittent Fasting Is a Good Idea

Let’s talk a little bit about some of the scenarios and situations where it is a good idea. It’s something that I would think about with patients when rapid weight loss is desirable, when their blood sugar is elevated and there’s some insulin and leptin resistance, maybe dyslipidemia, if they have those circumstances and overall otherwise they are in relatively good health, so they’re not dealing with a really serious chronic infection, they’re not dealing with a chronic fatigue type of problem, their adrenals or HPA axis — you know if you’ve been listening to this for a while I use the adrenal term tongue-in-cheek — but their whole system that governs stress tolerance and stress management is in relatively decent shape, they’re sleeping pretty well. If they meet all those requirements, then I’m certainly happy to entertain intermittent fasting as a strategy for improving their health, helping with weight loss and helping improve blood sugar and lipid markers.

I said something about chronic infection being a contraindication for intermittent fasting. Paul Jaminet and some other folks have written about intermittent fasting as a way of dealing with chronic infection because it upregulates a process called autophagy that may be helpful in dealing with chronic infections. In my own practical experience, I’ve seen kind of mixed results with intermittent fasting for chronic infection. If somebody’s just really exhausted and their HPA axis is really shot — which it often is with chronic infection — intermittent fasting can often, in my experience, take people in the wrong direction who are dealing with those symptoms. But in some cases, I have seen an improvement, and it may be in part from just giving the digestive system a rest and that leaves more energy for fighting the infection, or it may be because of the upregulation of autophagy.

Steve Wright: I have an interesting nugget on that from my personal life. I started playing around with intermittent fasting back in, like, ‘09 when I started my entire health journey, before I even had switched my diet over, and I have done all the different methods out there. You name the person, I’ve tried it. And about a couple years into it — I would always do it for a while and then quit and do it for a while and quit — I started doing 24-hour fasts and sometimes dinner-to-dinner-type fasts, and every once in a while I’d start getting these awful pains in my stomach about 8 to 14 hours into the fast. So I contacted some of the experts who write about intermittent fasting, like, hey, have you ever heard of this? No one had any ideas, had never heard of this, didn’t know what was happening. Fast forward to, I don’t know, about a month ago, and I’m talking with Dr. Steven Sandberg-Lewis. He’s a gastroenterology teacher up in a Portland naturopathic clinic, and he was helping me out with some research on heartburn, and he was saying that it’s very common for people with H. pylori and inflammation of the stomach to get pains if they fast in their stomach.

Chris Kresser: Yeah.

Steve Wright: And it turned out I had H. pylori back then and I had treated it since, and so that’s just to go along with the infection things.

Chris Kresser: Absolutely, yeah. It’s kind of a sidenote. I don’t want to go too far down that road, but it is a big red flag. If you have pain on an empty stomach, that’s a big red flag for H. pylori and other possible gut infections, for sure. That’s a very interesting tidbit there.

Who Should Be Cautious about Intermittent Fasting

So yeah, those are the typical circumstances when we would think about intermittent fasting. Now, on the other side of the coin, the circumstances in which I would be cautious to recommend intermittent fasting include some of the things that Codi mentioned in the question, which is if there is hormone imbalance, if a woman is trying to maximize fertility, unless that woman is really overweight and has blood sugar issues, in which case intermittent fasting may actually move the needle in the positive direction. But if that’s not the case, if weight and insulin and leptin resistance aren’t standing in the way and the woman is just generally trying to maximize fertility, I probably wouldn’t recommend it. If someone has pretty significant HPA axis dysregulation or adrenal fatigue — so that would manifest as feeling tired when you wake up in the morning even if you get enough sleep, having afternoon energy crashes, not being able to fall asleep or stay asleep, your quality of sleep is poor, you have poor stress tolerance, poor exercise recovery or exercise tolerance, these kind of classic signs of — I’m doing air quotes here — adrenal fatigue, in my experience, intermittent fasting usually makes those patients worse.

When Should You Fast?

Now, so far we’ve been talking about intermittent fasting as if you’re doing it every day or you’re not doing it on any days, and of course, it doesn’t have to be like that. As I have often discussed and you know if you’ve been listening to the show for a while, sometimes when Steve asks me what I’ve had for breakfast, the answer is coffee and cream, which is intermittent fasting. Sometimes the answer is a relatively large breakfast. So I’ve mentioned this before, but the way I approach intermittent fasting is I do it when I feel like it or I do it when my life circumstances call for it, like my morning just got away from me and I have a lot going on and it just feels like to rush eating a breakfast, inhaling my food in between commitments, just doesn’t make sense and I would rather just fast and be a little bit more deliberate with my morning. But I have gotten to the point — and I’m curious where you’re at, Steve — where I can just kind of check in with my body and, based on how I’m feeling, determine whether eating makes more sense or not eating makes more sense. The kind of triggers that I look for would be if I had a good night of sleep, if I’m feeling rested, I’m feeling strong overall — all of the cylinders are firing, so to speak — then that’s a good morning for me to fast if I feel like it. If I have had a crappy night of sleep or I’m feeling just unusually tired or run down for any reason, then I’m probably not going to do that because I think I’ll usually feel worse in that situation.

So I think eventually after you experiment a bit and go periods of time where you’re intermittent fasting, periods of time where you’re not, you’ll get a sense of how it makes you feel, and then you’ll be able to make that determination yourself.

Steve Wright: Yeah, I think what you just mentioned is really important. If you’re looking at your life and you’re consistently not getting quality sleep due to life circumstances, like a newborn baby or something like that, or a big project at work, or if your stress is extra high because you’re moving, those are probably not the best times to be intermittent fasting. Whenever I’ve actually attempted intermittent fasting those times, that’s when it’s like agonizing and it doesn’t add value to my life. It seems like more of the times when I’m kind of in flow and, like you said, I just look in the refrigerator and I’m like, I didn’t go to the store and I should’ve. OK, well, I’ll just fast until dinner or something like that. That seems to be how I do it these days.

Chris Kresser: Yeah. That’s sort of like lifestyle-based intermittent fasting, which is fine. I mean, in a way, that mimics the ancestral pattern, right? Like, oops, we didn’t have a successful hunt, so we’re going to be fasting now.

Steve Wright: Yeah. I think the other time that I try to use it — this comes from Brad Pilon; he’s one of the fasting people out there who has a pretty good book — is around events when I know I’m going to overeat. I’ll do it the day after Thanksgiving or something like that. Or if I’m just know I’m going to be eating out a lot, eating a ton of “paleo treats” or whatever, I might fast the day before that weekend or that trip or something like that.

Chris Kresser: Yeah.

Steve Wright: Just to kind of store up some calories.

Chris Kresser: Yeah, that’s a good idea. That’s another circumstance.

Sometimes I’ll do it when I’m flying. We’ve talked about this before. I’ll often bring my own food on a plane, but in some cases I’ll just fast completely from my house to wherever I end up and use that as an opportunity and just focus on other things while I’m traveling.

If I feel like I’m coming down with a cold or some kind of viral thing, I often find that fasting is helpful, or at least just eating more sparingly, so that’s another situation where it might be helpful.

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Fasting Recommendations

In terms of Codi’s question, there are a couple of other kind of subquestions there. One was if it’s recommended to pair intermittent fasting with caloric restriction or simply restrict the window of time that somebody eats during the day. I’d say my recommendation is not to actually count calories for most people when they’re intermittent fasting and just restrict the window of time that you’re eating. So you might eat all of your meals between 12 and 7 p.m. and then not eat anything outside of that. And different people will have different experiences. If you’re trying to lose weight, typically a lot of people will still lose weight even if they’re not purposely restricting calories. If they’re just compressing their food intake into that window, they may still lose weight because there’s an involuntary calorie restriction that happens and they get improvement in insulin sensitivity and leptin sensitivity. Maybe the types of food that they’re eating will change and how they’re metabolizing that food will change. So in most cases, I just recommend that people focus on restricting the window of time that you eat.

If you are doing daily intermittent fasting in a compressed food intake window, like 12 to 7 p.m., and it’s going really well for you and you’re really liking it and you’re getting a lot out of it, one way that you can kind of up the ante is do a biweekly, monthly, or even weekly 36-hour fast, where from 7 p.m. until noon the following day — so let’s say 7 p.m. on Thursday you stop eating. Then you don’t eat again until 12 p.m. on Saturday. That’s another way of fasting intermittently, and in that circumstance, you would definitely be decreasing your overall calorie intake in a given week by skipping that day of food intake.

So there are a lot of different ways to do it, and ultimately it really just comes down to what makes the most sense for you given your health status, your goals, and then your circumstances and lifestyle.

Steve Wright: Yeah, I definitely used to do, like, two or three 24-hour fasts per week, and I think they’re good. I think where intermittent fasting becomes a potential downside if you’re doing it on a month-by-month-by-month basis, other than all the other health stuff you talked about, is if you stop being social because, for instance, everybody’s going to go to a dinner party but today was your fast day and you don’t want to be in that environment and be smelling that kind of stuff. I think that’s one thing I became aware of, too. Like, oh, I think fasting is kind of affecting my social pattern, and I’m not cool with that.

Chris Kresser: Yeah. I mean, that’s fine for short periods of time, too, if you have a particular goal, but that’s a really good example that you bring up, because we’re always having to balance these different choices that we’re making. When we make one choice, that choice tends to have repercussions in other areas of our life, and if you maximize one area of your health and you put all your energy into that — let’s say your nutrition and your diet — then it’s very likely you’re going to go out of balance in other areas of your life. I tried to address this in my book by talking about the importance of pleasure and social connection and fun and having a sense of purpose in your life because I really believe that having this kind of balance is arguably more important than optimizing the last 5% to 10% to 15% of any one particular category. And if you look around at some of the healthiest and most successful people, you’ll see that that’s true for most of them. They have a rich life. That’s what this is all about ultimately, is creating a life that we love living and having a sense of meaning and purpose and rich social connections and fun and that we enjoy our life and we love being here on this planet. Optimizing our nutrition is a big part of that, but it can be easy to get a little carried away there, as we all know.

Steve Wright: Yeah. And I do want to just say that many listeners might not know, but some might know that I used to be 60 pounds heavier than what I am now, and part of how I lost a decent chunk of weight was through changing my diet and then incorporating the intermittent fasting two to three days a week into my life. That, back then, was obviously a really important goal to me, and I think I like the fact that intermittent fasting plays so well into a real food diet. You know, you’re not, like, eating some of the crazy body building diets or any sort of “calorie counting.” You’re just saying, hey, I’m not going to eat from noon to noon or 7 p.m. to 7 p.m. or something like that.

Chris Kresser: That’s right. It’s really not making any changes on those levels. You’re not restricting calories. You’re not counting them. Like you said, you’re just doing what you’re already doing, but you’re doing it less frequently or at particular times during the day.

The other thing we haven’t even talked about, or I guess I alluded to it when I was saying that I will often do it in the morning when I’m busy and doing other things, but I sometimes get tired of eating and preparing food. I don’t know about you. I love food prep, I love going to the farmers’ market, I love everything around the process of food, but I have to say that sometimes it just gets old. I just get really immersed in what I’m doing, and I’m a really passionate, pretty intense person, and so when I get wrapped up in something and I really dive in, the idea of stopping to eat is sometimes not that appealing. And I think there’s something to be said for that as well. There’s some freedom — for me, at least — that comes from not being tied to a schedule of, like, OK, at 8:00 I have to eat breakfast, and at 12:00 I have to eat lunch, and at 7:00 I eat dinner. That kind of schedule and routine, while I generally stick to it because it’s grounding for me and because I’m intense and can easily kind of get so immersed in something that I just forget about everything else, having that routine normally is good me, but it’s also liberating to not be tied to that and to have days where I just have a completely different schedule of food intake, if only for that reason.

Steve Wright: Oh, yeah. I think most people who get more connected to their food and spend more energy on it every once in a while have that moment of, like, wow, this is amazing. I have to eat every day to live, but I’m really not into it right now.

Chris Kresser: Yeah, you’re like, wait, I just… Really? Again?! I just cooked and ate breakfast, and now I’m just about to cook and eat lunch. And wait, then I have to cook and eat dinner later. It can be a lot, especially because that’s not the only thing that most of us are doing during the day. Yeah. It’s just a sidenote, but it’s not really a sidenote because I think that we could call that a kind of spiritual aspect of intermittent fasting, too, where for some people who can get a little addicted to certain aspects of food or certain types of food or our relationship to food starts to feel a little bit out of whack, then intermittent fasting can be one way of resetting that. Or just fasting overall. In the past when I’ve done longer fasts either associated with meditation retreats or longer meditation retreats where I was only eating once a day, I found that to be really liberating and also really instructive. It really kind of shined the light on my relationship with food and certain aspects of that relationship that might not have been as healthy as I wanted it to be, so it’s a way of raising your awareness about how you relate to food, too, I think, which is really valuable.

Steve Wright: Oh, totally. It changed my world when I did a three-day fast six or seven years ago because I grew up and the feedback I got was always, you know, he’s a growing boy and has to eat all the time, and I did eat all the time and it felt great and food tastes wonderful, and so I had bought into the dogma about if I didn’t eat, all these negative hormone consequences would happen. And then there are all sort of priming hormones that can get set based on our rhythms, so if you normally eat around noon, it’s likely that your hormones will be primed for that meal at noon the next day. So I did a three-day coffee-and-water fast just to test it, and it was so amazing to realize, wow, I was just being primed by my environment, my past behavior. I’m totally fine.

Chris Kresser: Yeah.

Steve Wright: It was very liberating.

Chris Kresser: It is really liberating, and I recommend that everybody do that at least once because it can really kind of set you free from some habitual patterns and beliefs around food. I’ve found that to be really valuable.

Codi, hope that answers your questions. Everybody, keep you questions coming. We love hearing from you. Next time I’m going to have an announcement about the clinician training program, which is swimming along at a really increasingly fast pace, and I think we’re going to be starting preenrollment as early as mid August, so look forward to that for another announcement coming soon on the blog and then on the next podcast.

Steve Wright: Awesome, Chris. I know everybody’s waiting for that patiently, so that’ll be good.

In between episodes, if you would like to get your question answered, please go to ChrisKresser.com/PodcastQuestion to submit yours.

And also, if you’re not yet, make sure you’re following Chris on social media. Go to Facebook.com/ChrisKresserLAc or Twitter.com/ChrisKresser. If you’re following him on these modalities, it’s likely that you’ll find out about topics he may be going to write about or we may talk about on the show ahead of time and kind of get the latest access to what’s going on and what he’s thinking about. Thanks, everyone, for listening.

Chris Kresser: Thanks, everyone. Talk to you next time.

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Join the conversation

  1. I have always be taught and told that if there are long periods of time and or you’re not eating enough your body will think it is starving. So when you do eat again it will save and store your food as fat for the next time it is starving. I guess like hibernating. Can you explain?

    • The reason this doesn’t happen is because during a fast, growth hormone is elevated, preserving muscle and optimizing for fat burning. When you eat you’ll fill glycogen stores first, burn some, and if anything’s left it will go to fat yes. Since insulin sensitivity it theoretically improved, you should have maximum uptake and it should drop quicker, allowing fat burning to begin sooner. Metabolism slows after extended caloric reduction, but not after short fasts.

  2. Really enjoyed this topic however, I am curious on how fasting for long periods effect the metabolism. I know for myself that when I eat in the morning my metabolism works extra hard and I feel hungry throughout the day. If I choose to fast until lunch time would that effect how well I am breaking down my lunch time meal?