Podcast Episode 54 Transcript – Thoughts on Intermittent Fasting

Leah

Welcome to the Ideal Nutrition podcast. I’m Leah Higl and I’m here with my co-host Aidan Muir, and this episode we will be discussing intermittent fasting. So there are a lot of big claims made about intermittent fasting. Weight loss is definitely a big one that is always brought up and thrown around, but there are other [00:00:30] ones that we’re going to go over as well. So in terms of claims, there are people saying that there’s reductions in cancer risk, potentially improving IBS symptoms and a handful of other common ones. So we’re going to go through them one by one, like we usually do, and just discuss the research and what we know so far.

Aidan

Awesome. So we’ll start with the obvious, we’ll start with the definition of what intermittent fasting is. It’s exactly what it sounds like. It’s alternated cycles of fasting and eating. [00:01:00] So the most common example of that is 16-8 fasting, which is where you would fast for 16 hours of the day and you would have an eight hour eating window. Obviously it can fit a lot of criteria. It could be as little as a short 12 hour fast, or as much as a 48 hour fast could fit this intermittent fasting window. What we’re not talking about, though, and it’s often lumped in here, is we’re not talking about long fast. So we’re not talking about week long fasts or longer or anything like that. [00:01:30] We’re literally just talking about what we’re talking about, intermittent fasting.

Leah

So let’s start, now that we’ve done the definition, with the number one thing that always comes up and that is weight loss or fat loss. So let’s start simple in that there is no difference between intermittent fasting and not fasting but having the very same calorie deficit. So when calories are matched and you’re in a deficit, weight loss and fat loss is going to be the same, regardless [00:02:00] of if you’re fasting or if you’re eating really regularly throughout the day. At the end of the day, it does come down to calories in versus calories out. Hate to be that dietician, that person, to say that. Obviously there’s nuance, but the nuance just doesn’t really come into play here so much because fasting doesn’t do anything magical to our physiology that helps speed our metabolism up or do anything else magical, or other claims that are made to help with fat loss or weight [00:02:30] loss from that regard alone.

What might be useful and is something that some of my clients have done or people have had success with is use intermittent fasting as a tool to be in a calorie deficit. So some people find that when they have shorter periods of windows of eating throughout the day and those times fasting, that they’re just able to stick to a calorie deficit better, their adherence is better. For those people, fasting can work really well. It doesn’t do anything [00:03:00] magical to our bodies in order to lose body fat or weight.

Aidan

Yeah. That was a good summary and exactly, there’s nothing magical. It can be a good tool for some people. It might be a less good tool for other people. It’s a personal preference thing as to what people find easier to achieve that.

Leah

Totally personal preference, because I find some people try intermittent fasting and then find during the window of time they get to eat, they maybe indulge a little too much or their appetite’s gotten to a point where they’re ravenous [00:03:30] and then they overeat. So for them it might be a start of a restrictive binge cycle or might just not be a good tool for them. But there’s definitely been people I’ve worked with where it has been a useful tool.

Aidan

Yeah. I’m in that mindset, but I did a seminar this morning on relationship with food and one of my things is if somebody has a poor relationship with food, I probably wouldn’t look at fasting, even though it’s a tool that you can use. I’d say on average, most people who fast will end up in a calorie deficit, [00:04:00] but as you said, it has that potential for that restrict and binge and everything that cycle. I’ve seen that to TikTok, you know when people put stars when they say stuff and there’s a TikTok where it’s not actually fasting. It’s just restriction binge with a nice name.

Leah

Just a fancy way to say it.

Aidan

Yeah. But anyway, it can be a useful tool for a lot of people as well anyway. So another thing I want to touch on, which is probably the least interesting thing for people, but I do want to talk about is how could this affect muscle growth? So briefly going through this, [00:04:30] we know that spreading protein intake throughout the day theoretically should help muscle growth. This is backed up by all this research showing that muscle protein synthesis is often maximized by as little as 20 to 40 grams of protein in a sitting, depending on the size, and going above these numbers does not seem to lead to any larger acute spikes and muscle protein synthesis.

But something that I’ve always found really interesting about this research is that during a calorie deficit, when calories and protein [00:05:00] are matched, muscle retention is often similar for people with a higher meal frequency and a lower meal frequency. All the research on intermittent fasting with decent amounts of protein, people seem to be retaining muscle quite well and it’s clearly not the end of the world, particularly in a calorie deficit. The tricky thing is we don’t really have that much research in a calorie surplus for exactly the reasons we were talking about before. It’s harder to over consume calories or create a calorie [00:05:30] surplus when you only have a small eating window. So pretty much all of the research, people just incidentally end up in a calorie deficit.

But that being said, the research is still clear enough to be like, even though total protein intake matters more than distribution, what appears to be ideal for building muscle is spreading it out over four to six meals across the day, that amount of protein, that 20 to 40 grams, or even higher, potentially, over four to six servings across the day. You probably don’t [00:06:00] need to be eating protein from the second you get up until the second you go to bed.

Leah

Yeah, 100%.

Aidan

It doesn’t need to be a massive eating window, but it seems like a 10 to 12 hour eating window is what would be required to maximize this. So even something 16-8 fasting would not be maximizing it, but I am also of the opinion it probably doesn’t make that big of a difference. Hitting your total protein intake is probably 90% of what you could do and to get that last 10% spreading it out over a slightly larger eating window and across the day probably helps a little bit more.

Leah

[00:06:30] Yeah. If there’s an athlete who is, let’s say, in a calorie deficit and their focus is to retain as much muscle as possible, but they know that using some fasting allows them to adhere better to that diet, there’s no reason why I’d go, “Oh, let’s not do that thing that works really well for you based on this fact alone or optimizing muscle retention,” because it’s that tiny little bit so it doesn’t really make the most significant difference. So there’s also the concept of gut [00:07:00] rest. So when we’re talking about intermittent fasting and the claims around IBS, people usually say that it is helpful because your gut needs time to just rest, so it’s not digesting food. This is an interesting one because I don’t really know what their mechanism behind this is, but the gut doesn’t really need to rest.

It’s made to be functioning all of the time, like your other internal organs that are made to be functioning all of the time. It doesn’t necessarily [00:07:30] need to rest. So the concept alone doesn’t have a lot of merit to it. From a practical perspective, if you are limiting food in general, so let’s say in times or periods of time where you are fasting, no food is coming in, you might see a reduction in symptoms during that time because you’re not having any food come in. So I think that’s where things can get a little bit confusing. On the flip side of that, it could mean that you’re eating larger portion sizes [00:08:00] during the times that you do get to eat or those windows of time, which could exacerbate IBS symptoms, because you’re generally having larger portions of food in a single sitting.

So it can go both ways. Again, there’s nothing magical about gut rest or anything. If you are seeing improvements in symptoms, it probably has a little bit to do with the fact there are times where no food is coming in. There also is the fact that maybe it puts you in a calorie deficit so overall you’re just eating less, [00:08:30] less food, less things to trigger your IBS symptoms, less symptoms. So in that way, it does make sense, but there’s not a lot of merit to fasting being particularly beneficial for IBS symptom reduction.

Aidan

It’s something I see in practice a lot. There’s a lot of people who have tried it and they’re like, “Yeah, I definitely felt better doing that,” and often I do like to lean into things that people feel better doing, but it often is exactly what you just said where it’s like there’s this period where they’re not eating. They feel better during that because they’re not [00:09:00] eating obviously, but that’s not to do with gut rest. But I also think a large portion of it is they’re eating less total food, exactly like what you said, that calorie deficit, because a common trend that I’ve just seen amongst clients anyway is say somebody hasn’t told me in the first session that they’re bloated or they have GI symptoms or whatever and they want to be in a calorie deficit and I put them in a calorie deficit, suddenly they’ll come back and tell me that they’re way less bloated and stuff like that. I’m like, “We’re not even working on that. You’re just …”

Leah

Like, “Oh my stomach is so much more [00:09:30] flat. I’m just feeling good. My digestion is good.” It’s like, “Yeah, you’re just digesting less.”

Aidan

Yeah, there’s less to process and it’s the same thing. People who go into a calorie surplus often struggle more with IBS symptoms and the calories matched perspective is something that’s going to be a common theme throughout this podcast because it’s important to look at it through that lens being like, exactly what we said, if you have calories matched, you’re having the same amount of calories regardless of whether you have six meals across the day or whether you have a 16-8, that eight hour eating window, if you’re going to eat the same total [00:10:00] calories, by definition, that would mean that in the eight hour eating window, you’d have to fit more calories into that short space of time and that could potentially lead to more issues.

Then there’s also the practical nature of like, what if you’re just hungrier during that time and then you eat a large amount of food and it’s not calories match, but you just happen to be eating more in that space of time, and you happen to eat foods that happen to be your triggers or whatever and increased amount. Yeah, super complex topic, particularly because a lot of people will feel better doing it, but it’s not for the gut rest reason [00:10:30] or anything like that.

Leah

It’s not for the reason some people like to claim.

Aidan

Going into a bit more of a complex topic, we’re going to be talking about some more health specific stuff. I’m going to start off with a bit of the easier stuff in this broad topic. I’m going to be talking about the effect on cholesterol, blood glucose levels, blood pressure, insulin resistance, those markers of health. So the first starting point is to understand that obviously the majority of studies on intermittent fasting show improvements in these markers of health. [00:11:00] That’s obvious for a few reasons, but it’s one of those things if you look through a study individually, individually, individually, and you look at stuff without context and everything that, it’s going to come out looking like it’s pretty magical for health, but that is where context comes into play. Because a calorie deficit is a driving explanation for a lot of these improvements in health.

If you go into a calorie deficit for six weeks, for example, cholesterol often decreases, blood glucose cells decrease, blood [00:11:30] pressure decreases, insulin resistance improves. All of these things happen regardless of the approach that was utilized for that. Then taking that step further to other studies on an acute basis, short term, you can clearly see how intermittent fasting leads to improvements in these markets. The most obvious one, blood glucose levels. If you’re not eating, there’s nothing coming in that is going to be converted to blood glucose levels. During a fasting window, your blood glucose levels likely are going to decline. I [00:12:00] say likely because there’s a lot of other mechanisms. Your liver could release glucose and all of these things, but just keeping it simple on average is going to be a reduction in blood glucose levels.

That’s why we come back to comparing on a calorie matched basis because if we compare on a calorie match basis where one has a more frequent eating period across the day or whatever, and the other one has a short window, that then gives us a different perspective because let’s talk about that blood glucose levels example I just used. [00:12:30] If somebody was fasting in that case and they were eating less or not at all outside of their eating window, by definition, they’d have to be eating more during their eating window than the other version, that other scenario, would be eating across any individual sitting, which therefore means after a large meal or whatever in that eating window, blood glucose levels would go higher because there’s so much carbs, protein, whatever that could come in that could be converted to blood glucose levels. These things will balance out, even though it’s a bit more of a spike or whatever. That’s why I talk about the [00:13:00] calories match aspect.

Obviously, you can criticize that logic by being like, “Well, fasting typically does lead to a lower calorie intake,” like I just talked about and that’s fair. I think that is a fair criticism, but I also want to talk about it from the calorie match perspective because it gives you flexibility. If you were going to achieve a certain calorie target with a different method, you now know that is going to come with the same outcome for these markers of health, which allows personal preference and allows you to choose whichever way you’d want to go about [00:13:30] doing this.

Leah

So getting into some of the, I guess, more confusing parts-

Aidan

Yeah. Probably leave this one for you.

Leah

Definitely feel free to jump in. So we’re going to talk about cancer risk. So this is a complicated one, but we’ll go over it in the depth that we can in this podcast. So there is a proposed theory that because fasting promotes something called autophagy, it leads to a reduction in cancer risk. So [00:14:00] autophagy is basically the process of clearing out old cells. So in theory, this could be useful because cancer is literally due to cell mutations, so clearing away old and damaged cells could potentially reduce the likelihood of cancer being an issue or starting to grow. This is a really hard area of research to interpret. Even just looking at the few studies I did, it’s a very difficult thing to look into [00:14:30] because going back to the calorie deficit thing, a calorie deficit also causes autophagy. It just causes it, I guess, more chronically where we’re in fasting, we see acute bouts of autophagy.

So whether that has a different outcome, that’s the difficult thing to really interpret. Is it a calorie deficit that is going to be preventative potentially for cancer risk or is it this acute fasting, [00:15:00] making this acute autophagy. It’s a really hard one to look at. Do you have anything to say in that regard?

Aidan

Yeah, it’s one of the things that I get a lot of DMS from people who will send me studies on this topic being like, “You can see the autophagy, this is why it’s going to work,” or whatever, but we can’t compare on a like for like basis with that. We can’t measure autophagy easily in a chronic calorie deficit and be like … what would be perfect [00:15:30] obviously is let’s look over a one month time period and measure total autophagy with total calories matched, except one version does intermittent fasting and the other doesn’t. That would be perfect. Doesn’t exist, and my current stance on it is that I’m of the belief that there would be no difference in that case, which would therefore feed into the whole cancer topic coming out equally, basically. As in there would be no difference between fasting or a regular calorie match diet with the same [00:16:00] total food, the same types of food, the same everything.

But it is a difficult area to interpret, so I’m ready to back pedal on that if I need to. But my current stance is, and it has been my stance for a few years now, because I used to actually have the opposite opinion. My current stance is that there would be no difference.

Leah

No difference between the two. Yeah, I think what, what is interesting is generally a point you made around having a lower body weight can reduce cancer risk. We know that, so it would make sense that a calorie deficit over a longer period [00:16:30] of time leading to a healthier body weight would reduce cancer risk overall potentially. So that from a theoretical mechanism or even from the research makes a bit of sense, just this acute autophagy that occurs in intermittent fasting, I’d say it’s likely not going to have, again, a magical impact on cancer risk.

Aidan

Yeah. The other note that we’re going to touch on is … oh, that we’re actually not going to touch on is fasting as a cancer treatment, [00:17:00] because that’s a completely separate topic to fasting for cancer prevention. Because we to keep these short and sweet, it’s too complex of a topic to touch on here because arguably there is some merit to it under certain situations and it’s very complex topic and the logic is that fasting would reduce glucose available to fuel cancer cell growth. But the reason why we don’t want go into it here is because there are pros and cons, and there are a lot of cons. So it’s about weighing [00:17:30] up whether the pros outweigh the cons and there’s cons like malnutrition. Cancer cachexia is one of the biggest factors in cancer being an issue, amongst others obviously. That’s often not even just intermittent fasting. Often it is prolonged fasting they’re utilizing there and yeah, we’ll just leave that out of this.

Leah

Whole other can of worms for another day.

Aidan

Yeah. It’s interesting. But it’s not for today.

What we will talk about, though, is longevity [00:18:00] and that’s obviously something that feeds in with the cancer prevention thing. That was honestly one of my first interests in fasting and everything that. Early on in my nutrition career, I was more interested in this and I was listening to a lot of people talking about it and everything like that, often that biohacking space, because it’s an interesting topic, and the starting point from this topic is we have a fair amount of research, particularly in animal models showing that calorie restriction, not necessarily fasting, but calorie [00:18:30] restriction is associated with longevity. We can see this far more easily in animal studies, other animals with shorter lifespans, we can study this because, let’s be real, is a human researcher with a finite lifespan going to spend time studying controlled stuff that’s so slow?

But there’s examples of this. The most common example of this is research on monkeys where there’s twin rhesus monkeys is the most common one that has been studied that I’m aware of, where they [00:19:00] obviously have the same genetics, same everything, same environment, but one got fed 30% less calories than the other, or one group got fed for 30% calories less than the other, and there was improved longevity in the ones that had 30% less calories. Theoretically autophagy is a major factor there. You could also talk about other health factors, like in humans, higher calorie intake is associated with a lot of other health outcomes too. So that’s something to consider as well. But then it’s obviously hard to say that fasting provides these benefits more than having the same [00:19:30] total calorie intake over longer timeframes.

Another point that we were briefly talking about off air as well is animal research and fasting and stuff like that. Because of different metabolisms and stuff like that, it doesn’t necessarily always line up with humans. An example, and I’m quoting somebody else here, I’m quoting Menno Henselmans here. He was talking about rodent studies having different metabolisms to a point that’s one day of fasting for a rodent, his words, not mine, but his words were that one day of fasting is the equivalent of about one month for a human just due to [00:20:00] differences in lifespan, difference in metabolism, all of those things. So I was talking about how people send me a lot of studies, rodent studies is the most common that I get and it’s like, that’s great and even if those differences weren’t the same as they were, we’d want to see studies in humans. We are humans. We want to see more studies in humans on that topic.

Then even let’s just go back to the calorie restriction side of things. All of these things are well and good, but let’s talk about that 30% less calorie topic. [00:20:30] The lower your average calorie intake is throughout your lifespan, the lower body weight is going to be, right? Once again, it’s a bit of a lever that you can only pull so hard because you can’t pull it so hard to the point that you are significantly underweight to the point that it causes issues and you don’t want to go to the point of malnutrition. Then there’s implications for once people are past a certain age being like, “How about the risk of falls and stuff that? Is that going to be a factor in not only obviously quality [00:21:00] of life, but also longevity?”

If somebody fractures their hip, are they able to be as active for the next couple of years or whatever? Does that play a role as well in heart health, for example? We know malnutrition causes issues. Then the other last thing I’d probably touch on on that topic is at the opposite end of the spectrum, higher levels of muscle mass in humans are associated with longevity. You can make an argument. It’s like, “Hey, we can have a slightly lower calorie intake on average, do more exercise to achieve that same thing,” but it’s one of those things that instead of saying calorie restriction, [00:21:30] my preferred way of saying it is appropriate calorie average over the long term is probably a better marker for longevity. We don’t have to go super low, but we also want to avoid going overly high as well.

Leah

Yeah. It all comes down to maintaining what would be considered a healthy body weight over the long term, more so than thinking about you don’t need to always be in a calorie deficit to get these outcomes.

Aidan

Yeah. One other thing, actually, that I was just thinking of, but back when I was listening to all those biohackers, I never [00:22:00] actually applied any of this stuff, but it was just an interesting topic obviously, because a lot of people do care about this stuff. One of the points that some of them were making was that let’s say there are benefits of some of these longer fasts or whatever, we could do them infrequently and reap some of these benefits. A lot of people were talking about every three months or every quarter because they’re financial guys, like, “Every quarter I do a 24 hour fast or whatever.”

Because if you’re somebody who cares about growing muscle or whatever, you probably don’t want to be on low calories or [00:22:30] fasting heaps frequently or whatever, potentially because it could make it harder to do that, but fasting every three months or so for 24 hours, that’s probably fine. That way, if you’re somebody who’s listening to this and you’re still like, “Hey, I still want to-“

“I still want to try it. I still want to see if there’s benefits,” or whatever, that’s also an option. It’s not an option I go out of my way to recommend, but it is an option amongst many.

Leah

Yeah. I always like how practical you are. You’re like, “Oh I’m not counting it out just yet. Here’s an option anyway.”

[00:23:00] So in terms of, again, practical takeaway, so fasting can potentially be a useful tool for some in order to create a calorie deficit. But outside of that, in regards to weight loss, it’s definitely nothing magical. We wouldn’t 100% rule out the autophagy aspect that we’ve spoken about. It’s something that we’d like to see more research in, see as things and time progresses, how that goes, but there are likely no inherent benefits [00:23:30] of fasting. I just say it comes down to personal preference. If you want to try it, try it. If you don’t, don’t

Aidan

This has been episode 54 of the Ideal Nutrition podcast and as always, thank you so much for listening.