Intermittent Fasting: Who should and shouldn't do it? How can it affect your hormones? What is autophagy? Common pitfalls and Starting and stopping a fast.
Welcome to the Meat Medic Podcast. I'm your host Dr Suresh Khirwadkar.
I'm a GP a lifestyle physician and I'm a practicing carnivore. I've had great success myself personally and with patients by following a carnivore diet and I want to spread the word about the many benefits of eating meat.
What is it?
Intermittent fasting, otherwise known as time restricted eating, has been around for decades. In fact fasting as a therapeutic intervention has gone back thousands of years to the days of Hippocrates around 450 BC.
He used to recommend therapeutic fasting for all sorts of diseases and illnesses, prescribing water-only diets or possibly medicinal teas or predominantly liquid diets for others. Even back then the benefits of fasting were seemingly well known.
Now fast forward 2000 or so years are and intermittent fasting is very popular.
Is it helpful though or is it just a fad?
Is it required or is it harmful?
Well let's discuss.
Intermittent fasting has been around for thousands of years as we said but it's been probably only studied really over the last 100 or so years, however even then it's only recently really been popularized in around 2012 by Dr Michael Mosley with the 5-2 diet. Now most people have probably heard of Dr Mosley or the 5-2 diet. Interestingly outside of the medical world fasting is performed by many cultures and religions around the world such as Ramadan and lent for example.
Intermittent fasting has been shown in literature to be beneficial in weight loss and other medical conditions such as type 2 diabetes, but anecdotally many people report it can be helpful in numerous other health conditions and ailments, even anecdotally as a cure for cancer.
How does it help?
Well we don't know exactly how it helps but we do know that some of the mechanisms of action
Now I briefly discussed the fasted state in a previous episode and if you wanted to watch that about fasting on the carnivore diet please go back and watch episode 4
So there's really two main ways I think in which it could help - fasting can reduce glucose, insulin and other hormone levels within the body and the second thing is called autophagy.
I'll come back to the hormones but first let's discuss autophagy.
Autophagy is the body's process of reusing old and recycling old, damaged parts of cells, or the cells entirely. Cells are required as really the basic building blocks of all components of the human body, and over time they can become damaged or broken, much like broken stuff in our households. If we don't do anything about it,these bits of cells or entire cells can become junk that just kind of clogs up the cells or the rest of the body.
If we don't want them causing issues then it's sensible to either clean them out, repair them, or recycle them, and that's what autophagy is.
These cells can be either repaired or recycled. Autophagy is kind of like quality control for your body. If the cells aren't working correctly then we need to do something about that and we need to repair them or replace them.
Why does this matter though? Well just like in our houses we don't want junk or or litter building up - it'll get in the way of normal processes. You know it's hard to move around your kitchen when it's just full of rubbish. It might stop things working correctly or just start to cause damage to other things around it. So just think about something in your fridge going mouldy because it wasn't thrown out. Eventually it can start to spread to other food.
Another way to think about autophagy is like cleaning up lines of computer code - if you're a bit of a geek like me - you don't really want all that extra stuff in there that could cause an issue or slow the computer down, or a web page down for example or just even worse make the whole system crash.
So autophagy is important for repairing and recycling these damaged cells but also potentially for longevity - that is living longer and healthier. It's not known exactly how fasting induces autophagy or at what point it really starts, but it's likely due to stress on the body which fasting can induce. We don't know exactly how long you need to fast forward to induce autophagy as studies on this do vary, but it's estimated to be at least around 16 hours of fasting, which is why I believe 16:8 is a popular type of protocol.
Now there's other ways to induce autophagy like a low carb high fat diet, exercise and calorie restriction. So autophagy is helpful and as far as we know it has no real downsides.
Intermittent fasting can affect our hormones in primarily a positive way, but also potentially negatively. The main hormonal effect is on insulin. Insulin is our main storage hormone and will primarily store fat, but it will store muscle if giving the incentives. We generally don't want high insulin levels as this can cause a myriad of other issues which we'll cover in another episode, but high levels of insulin also cause high levels of insulin resistance, which is a leading cause of heart disease, weight gain, type 2 diabetes, hypertension and much more.
It's really one of the primary problems if not the primary problem with metabolic syndrome and conditions such as polycystic ovarian syndrome. The longer you can fast for the lower the insulin levels will fall, and then the lower the insulin resistance will go.
This effect is somewhat logarithmic - that is the longer you fast for the bigger the effect is, so it's exponential.
How long can you fast for?
Well believe it or not the longest fast on record is 382 days. That's right, 382 days. This was a Scottish man called Angus Barbieri. He lost 276 pounds in that time. Not surprising as he didn't eat for 382 days. He was under medical supervision the whole time and was consuming vitamins and other supplements to help him, but he wasn't actually in hospital the whole time on a bed hooked up the drips and so forth, no he actually was at home. He just went into the hospital I think every few days for some tests and monitoring.
Now I'm not recommending you do a 382 day fast, and if you do well look I think you probably need some serious medical oversigh, but you know usually 16 to 24 hours is very safe with vew few problems.
So common fasting regimens are 16:8 - most people have heard of that. That's fasting for 16 hours and eating for eight, or maybe 18:6 or 5:2 - that's eating for five days and typically fasting for two days, either complete fast or maybe just a 16:8 on two days.
Some do what we call OMAD or one meal a day, others do alternate day fasting (ADF). So there's many benefits to intermittent fasting particularly for metabolic health and I recommend it to a lot of my patients, but there are also some dangers that you should be aware of.
Now whilst very rare it can cause electrolyte disturbances and there are risks of gallstones and kidney stones forming. It can also trigger gout attacks, thankfully though these are rare and mostly in high risk patients who didn't drink enough water or electrolytes or fasted for far too long. Patients with type 2 diabetes can fast and even patients with type 1 diabetes can fast but really they should be medically supervised.
Intermittent fasting is not that dangerous as long as you're keeping an eye on your glucose levels, but prolonged fasting is much more dangerous for type 1 diabetes.
However some diabetes medications can be dangerous with fasting so you should speak to your health professional before you engage in fasting if you have health concerns.
This topic actually came up on one of my doctor Facebook groups the low-carb down under group, and it was actually today someone was asking about the medications called SGLT2 Inhibitors with type 2 diabetes and a lot of people reporting following low carb diets or intermittent fasting - they've had serious issues when they've been on these medications. That doesn't mean you can't fast if you're on these medications but it means that you probably have to stop them before doing fasting - so speak to your doctor about that.
If your doctor doesn't really know that much about fasting then you can find one like me or other people of course that does to get advice from.
How to do fasting?
So you've decided that you want to try fasting. Well great fantastic but how do you actually start?
Thankfully it's actually pretty easy. Once you've got the go ahead from your doctor or you're very confident yourself in starting then you kind of just get started. Usually you continue your overnight fast into the next day. When you're sleeping you wouldn't normally be eating, so it kind of makes sense to extend this rather than trying to fit in a whole fast somewhere else in the day.
As we said earlier the longer you can fast for the better it is. It's exponential, and a 16 hour fast is actually better than two lots of eight hour fasts. In reality this usually means skipping breakfast and then eating lunch.
It's a little more than that though one of the biggest mistakes I see people making with intermittent fasting is that they think it's just not eating. Now that's actually not fasting it's simply just not eating.
Fasting means not having anything which will break a fast. Unfortunately I can't give you a definitive list of things that will or won't break fast, but for the most part anything other than water could potentially break a fast. Black tea, black coffee, herbal tea, green tea: these are unlikely to realistically break a fast, but if you add anything with any real substance like cream milk even possibly butter then it will probably break your fast.
Now what happens then is you're not fasting, you're just simply not eating and that's when you can get issues. This comes back to what I mentioned in a previous episode about the fasting state, or the fasted state rather. When your body is in the fasted state most people don't get very hungry because the body can actually see its own fat stores and use its own fat stores. The hormone leptin gets unblocked. However if your insulin goes up leptin becomes blocked, your body can't see the fat stores, has very little energy itself because you've used some of your muscle glycogen and so forth overnight, so it will kind of literally think that you're dying because your brain is telling you that you're basically dying because you've got no fuel stores and as far as it knows you've got no no muscle glycogen and no liver glycogen left. You've also told your brain you have no fat stores as far as your body's telling it, and so you just become extremely hungry, and extremely you know angry , and HANGRY basically
Won't I get hungry?
This is a question I often get asked: "won't I feel hungry doing intermittent fasting?" Well actually no surprisingly not because as I said that's your hormones doing what they're meant to, particularly these two hormones insulin and leptin. As I said leptin is a hormone that essentially tells your brain 'it's okay I have enough fat already you don't need to keep eating'.
Think of it like your fuel gauge in your car, and your fat stores are your fuel tank insulin blocks this hormone so if you reduce your insulin your body can actually see your fat stores and not panic because you're not eating.
So another question I often get asked is won't I just overeat when I do eat? Well again really the answer is no, not usually, because your insulin levels will be lower and your leptin won't be as blocked. So you most likely are not going to want to overeat because your body can actually see that you've got plenty of energy already. Of course you can force it and you can just overeat on purpose but obviously that's a little bit silly.
Think back. I'm sure there's been a time when you forgot to eat breakfast. What happened?
- you didn't just die
- you didn't just go out and eat everything inside
- you probably weren't even that hungry
- you probably just got to the end of the work day and thought Oh I haven't even eaten today and then likely when you get home you probably just ate a normal meal
Think again about a time where you've maybe had a super quick breakfast on the go, you've had like a really tiny you know piece of quick toast or or you know coffee. By lunchtime you're probably starving, and just absolutely famished and you're probably just gorge yourself on food. Just try it if you're not sure. Try it - go one day just do black coffee in the morning or nothing and wait till lunch see how hungry you are. The next day have coffee with milk or sugar in it, and see the difference in how hungry you are on that one.
Now some people can struggle a little depending on their own metabolic health, so some degree of willpower may be required to push through at least in the early stages, but it improves pretty quickly.
How to break the fast?
Let's assume that you've done the fast and we're coming up now on let's say 16 hours or whatever other time you wanted to fast for. The question then is how do we break the fast?
I mentioned in a previous episode the breakfast is not the most important meal of the day. I mean after all, I'm talking about skipping breakfast. So breakfast isn't the most important meal of the day but break fast is the most important meal of the day.
When you're doing a 16 hour fast it doesn't really make that much difference. I'll cover this in the next episode on prolonged therapeutic fasting but with a 16 hour fast even 18 or 24 it doesn't really make that much difference what you do for breaking the fast. Generally I'd probably suggest you do a smallish meal, with relatively low to no carbohydrate content and then increase it later again if you're still hungry. The reason we do this is to not spike our insulin levels very high. This is to try and prevent the condition called re-feeding syndrome.
Doing intermittent fasting for 16 hours - refeeding syndrome is incredibly unlikely to happen but we'll cover this in another episode. You do need to be aware of refeeding syndrome but it's really only if you're doing prolonged therapeutic fasting.
If you're interested though do some research into this a lot but I will cover it in the next episode.
Who shouldn't do intermittent fasting?
So fasting can be incredibly powerful but should everybody be doing fasting? Unfortunately like many things we don't have the data to say categorically that it's healthy for everybody. There are some people who are not advised to do intermittent fasting, even though it's almost certainly going to be safe for them because I'm sure they've skipped breakfast at some point, we just don't have the data to support the use of it in all people.
So it's not recommended to do intermittent fasting if you're pregnant or breastfeeding due to the increased metabolic demands on the body. The likelihood is it's not going to cause problems if you do skip a few meals here and there I'm sure you've done it before, as long as you listen to your body and if you're feeling faint or unwell then you should eat. Now it's not officially recommended, I have to tell you that, but I'm sure there's pregnant women all over the world that have skipped a meal here and there by accident probably and they didn't just have any massive problems. In fact intermittent fasting could potentially reduce the risk of gestational diabetes significantly and the possibility of other pregnancy-related issues, although there's no studies to my knowledge that have looked at that specifically. Unfortunately it's pretty impossible to get ethical permission, understandably of course, to test things on pregnant women, so the problem there is the data is always very very lacking. There's some Obstetricians and fertility specialists that do recommend this way of eating intermittent fasting to patients, indeed I was listening to a podcast recently with Dr Anthony Chaffee the plant free MD and Dr Robert Kiltz. Dr Kiltz is a fertility specialist I believe in the US and he was stating that he often recommends intermittent fasting for his patients, or intermittent feasting as he calls it. He stated he found it to be beneficial for nausea in pregnancy, particularly early on and his his theory anyway is that patients following a carnivore diet in pregnancy if they find that they maybe have like a meat aversion which we know can happen, that actually this could potentially be fixed by a short period of fasting and actually eating less.
Now it's also not routinely recommended that children do intermittent fasting for similar reasons again but again if they're just listening to their body and not eating when they're not hungry eating if they get hungry they really shouldn't have any downsides. After all I mean we fast when we sleep, so you're just extending that a little bit.
Of course I hope this goes without saying but I'll say it anyway to be very clear. ** Babies should not be doing intermittent fasting**.
As I mentioned earlier fasting can sometimes increase the risk of things like gallstones or kidney stones so if these are concerns you have then you should speak to your doctor to get health advice.
People with cancer can do fasting, and there is potential for it to help. Now I can't say it will definitely work for you if you have cancer, and I'm not saying it's a cure for cancer, and you should definitely not stop conventional therapy as advised by your oncologist or hematologist, but I would encourage all patients with cancer to speak to their oncologist about intermittent fasting, and particularly what we call the metabolic mitochondrial theory of cancer. I'll discuss this in a future episode.
Basically the metabolic mitochondrial theory of cancer really says that cancer is not just a genetic condition it's actually really a metabolic condition and that the vast majority of cancer cells really can only utilize glucose as a fuel source and if you starve them of glucose by doing things like intermittent fasting and being in the so-called fasted state, nutritional ketosis that theoretically this is a perfect chemotherapy because all the cancer cells will die and all the healthy cells in your body will live.
Now as I said that's the theory it's not proven, and I can't say it's a cure for cancer of course, but it could help.
Do I need to do intermittent fasting?
So I guess the question is do you need to do intermittent fasting?
Well actually no you don't really. There's no real studies comparing intermittent fasting to other types of diet or lifestyle such as the Mediterranean diet or the DASH diet or the ornish diet, but there is data for fasting mimicking diets. This is a diet that puts you in a so-called fasted state. The FMD or fasting mimicking diet does actually show comparable results to the Mediterranean Dash and ornish diet for many health concerns.
So what is fmd or fasting mimicking diet? well it's a diet where you eat foods really designed to maintain nutritional ketosis, the fasted state, which is basically a ketogenic diet. So if you're doing a keto diet or a carnivore diet you'd likely don't actually need to do intermittent fasting on top.
Carniore diet really is by definition a ketogenic diet, so if you're following carnivore you'd probably don't need to do intermittent fasting, at least, not force it, which is what I covered in a previous episode.
Some people however do claim that you do see further benefits, but most people who are doing a carnivore diet naturally fast. Most eat one or two meals a day anyway so I mean really they're doing naturally fasting without even realizing it.
I know I personally saw some small benefit from introducing fasting back into my diet and I did see benefit from when I was doing keto and intermittent fasting on top rather than just plain keto, but now I follow intuitive eating and I eat when I'm hungry, fast when I'm not. Some days it's two meals others it's three and this works well for me sometimes it can be four or five meals, or even one.
Usually it's two meals a day, or 2MAD.
How long can you do intermittent fasting for?
And how long can you fast at any one time? We discussed this previously, but as far as how long you can intermittent fasting for? Well really the answer is as long as you like. There's no upper limit on how many times you can do intermittent fasting or how long in total you can go for. Some do it for a few weeks and then stop others will do it daily for months, sometimes years. For some it's just a way of life and it suits them. Many do it intuitively and don't even know that they're doing it. There's no known harms of long-term intermittent fasting and in fact many studies show multiple benefits.
Fasting for weight loss
The last thing I want to talk about is weight loss and intermittent fasting. You can't really talk about intermittent fasting and not discuss weight loss. Many people will use intermittent fasting to try to lose weight, but does it work?
Well yes actually studies show it definitely does work. There's multiple high-powered studies that demonstrate the people who do intermittent fasting lose more weight, they lose it quicker, and they lose it for longer than controls, whilst following the same daily diet otherwise. Now what does that mean in plain English?
Well it basically means if you compress the same three meals a day into say two meals, you'll probably lose fat and be healthier. It's actually independent of the calories or the content of the food and this has been corroborated by many many studies. You can obviously add a calorie reduction in as well and this could help you to lose more weight, but weight loss isn't really about the calories for most people, more so what your body does with those calories.
I'm going to be covering weight loss extensively in another episode but briefly when this is controlled by hormones like cortisol and insulin and both of these are essentially storage hormones, that is they put your body into a kind of storage mode, if your body is in storage mode it doesn't really matter how many calories you eat you'll likely struggle to lose weight because the body doesn't want to lose weight. If you aren't in storage mode you will probably lose weight naturally.
Intermittent fasting reduces both cortisol and insulin and this can help you flip that switch out of storage mode, which is really how it helps, not the calorie reduction. As we said earlier even eating the same diet, those people who compressed it into one or two meals a day versus three normal meals lost more weight, lost it quicker, and lost it for longer when they returned to their previous diets.
Now this is actually a good time to talk about hormones. We mentioned leptin earlier and of course cortisol and insulin just now. Studies in fasting has proven to affect testosterone levels in men, are very likely to affect estrogen and progesterone levels in females, mostly through a pre-hormone called kiss-peptin.
With regards to testosterone most men find that initially testosterone levels can reduce slightly, but then in the longer term, usually a few months, levels can actually increase back above where their baseline was, and actually produce higher testosterone as a result.
Now interestingly the initial drop doesn't appear to actually be clinically significant, but the rise afterwards actually is which is absolutely fascinating. Testosterone levels going up is actually a good thing.
I'm going to cover this in a future episode, but testosterone has multiple health benefits for men and for women and we don't need to fear testosterone.
In females we are much more concerned with estrogen and progesterone and these can be affected by intermittent fasting. Some women appear to be affected more than others and whilst in men generally the effect is favorable, some women do find the intermittent fasting can adversely affect their cycle and hormone imbalance can occur which can have negative effects. This is a very personal thing and unfortunately cannot be tested for prior to starting intermittent fasting, so you can't know if it will adversely affect you until you try it. Thankfully though most women don't have any issues with intermittent fasting and if you do it's not permanent and will quickly resolve when you stop fasting.
There's also some evidence, anecdotal yes but there's some evidence that women who are affected by fasting will do better with longer but less frequent fasts rather than shorter but more frequent fasts.
Intermittent fasting can be incredibly potent, and potentially has multiple health benefits. It's proven to be beneficial in fat loss and diabetes and anecdotally helpful in many other conditions. It's easy to do, requires no special training, no supplements or pills, and can be done by almost anyone. If you're pregnant breastfeeding or a child it's not routinely recommended so, if you do fall into these categories then you should speak to your doctor about the risks and benefits of intermittent fasting.