Since last month’s review of Intermittent Fasting, I feel like I’ve been bombarded with this topic everywhere I look. So much more information has come to my attention, I’ve been reading books, listening to podcasts, searching more scientific articles, etc. etc. so I thought I’d use the February round-up to provide a little more information and clarification. If you have specific questions not covered in this report or the last one, please leave a comment and I’ll see what I can find out. There are very few published, well-designed studies on humans regarding intermittent fasting, there is a lot of “bad science” out there and even medical doctors don’t often agree on topics like this, so getting accurate information can be tricky. And ultimately, there is a great deal of experimentation involved in figuring out if Intermittent Fasting (IF) is right for you and if so, in what form.
Why should you even care about intermittent fasting? It has been shown to promote health in so many areas: immune system health, weight/fat loss (which has many positive side-effects), treatment of cancer, Alzheimer’s disease, ALS and on and on. This seems to be a powerful tool with basically no downside. And it’s easy in terms of food prep, which is the biggest deterrent for many people when it comes to changing their eating habits. If you’re the kind of person who says it’s easier for you to eat ZERO cookies rather than have just ONE, fasting is definitely something you should consider.
Let’s dive in:
Understanding Fasting:
Some of this is a repeat of the last article, but as I’ve done more research, I found additional information and ways of explaining these concepts that I think brings clarity.
A person is considered to be in the fasted state once their body has digested and stored their last meal, usually 3-5 hours after eating. Here’s what happens: You eat a meal, your body produces and releases insulin, that insulin causes your cells to store the food that was just consumed. Now it’s just sitting there waiting for your body to use it – it’s in a sort of short-term storage (in the liver). Most people eat again about the time that last meal has been used up. So the body produces more insulin, the most recent meal is stored and used until the next meal. Do you see why this is a problem for someone who wants to lose body fat? Body fat is stored fuel that your body wants to be able to use, but it’s locked away in long-term storage. If you are constantly feeding it another meal that it can put in short-term storage, it can’t ever get to that long-term storage. Even if you reduce your calorie intake while eating multiple small meals per day, you will lose weight initially, but your body quickly adapts to the reduced amount of fuel and begins to burn less each time it is fed. And if you are constantly feeding, your body will not get into that state of autophagy that I talked about in the last article. Autophagy is the body “cleaning house,” getting rid of all the cellular junk. More on that below.
Insulin is 100% the key to fat storage and fat loss, so it bears driving this home a bit: During the time that you eat, your insulin goes up. There are other hormones involved; other things that are happening, but the most impactful is that insulin goes up. And that insulin gives your body the instruction to store food energy. You store it in two different ways; as sugar, which is glycogen in your liver. And when that’s full, then you store body fat. That’s all that happens. When you don’t eat; when you fast, then your insulin levels fall, and the falling insulin levels, send information to the body that nothing is coming in. We need to start pulling out those calories that we stored away.
And that’s why you don’t die in your sleep every single night. Because your body stores it and brings it back. Kind of like your wallet. You put some money in your wallet, you take it out. It goes in, it goes out. And every day, there’s a sort of balance to that. So it’s about time, letting your body have a period of time where your insulin levels fall. To let your body digest the food and start to use it. That’s the real metabolic advantage. – Dr. Jason Fung
Back to autophagy for a bit: autophagy is the breakdown of sub-cellular proteins that are old and junky. If your body senses that you’re not eating, this is what it does. There’s a period of time where it burns through the sugar, but then there’s a period of time; somewhere, 16 to 36 hours in where it actually starts to break down some protein to produce glucose. People think this is a bad thing, but it’s actually good. Because when you break down the protein, you’re taking old, sort of defective, junky old proteins and breaking them down for energy, but at the same time your growth hormone levels go up so that when you feed again, you’re going to rebuild that protein. So you are, in fact, rejuvenating yourself. You’re actually reversing a lot of the processes that can lead to disease. Certain diseases are caused by the build-up of all this cellular junk in your body.
Alzheimer’s disease, for example, is a buildup of excess protein in the brain. Same with cancer – build-up of excess proteins. This is all very interesting, but not proven, but perhaps this knowledge will lead to the prevention of Alzheimer’s disease. Maybe your body will be able to prevent the development of cancerous growths because they’ll just get fed into the fire to get burned. And then when you rebuild them, you’ll rebuild normal cells.
So to greatly simplify, fasting turns on two important processes in the body: fat burning (lipolysis) and autophagy and these two processes have many subsequent positive side-effects.
Clean vs. dirty fasting
Clean fasting means zero calories consumed during the fasting window and dirty fasting means you are consuming a few calories or even zero calories but including some artificial sweetener.
By fasting, you are not releasing insulin. That is a fact and it is what you want. Your body releases insulin in response to the stimulus of food or beverage consumption. Even a calorie free sweetener can cause an insulin release. Published studies have shown clearly that a sweet taste, even without the consumption of any calories, can cause the body to release insulin. One rat study demonstrated this clearly when the researchers cut the nerve that connected the taste buds to the brain. With that nerve intact, the rats were fed a sweet substance and their body released insulin in response. The nerve was then cut, the rats were fed the same calorie free, sweet substance and there was no insulin release. A similar study conducted on humans produced the same results. These study participants were given a sweet liquid to swish around in their mouths, but not swallow. Even just tasting the sweetness caused insulin to be released.
Some people will say you can consume fat only, protein only, calorie-free drinks, bone broths, etc. etc. during a fast and still stay in the fasted state. Remembering that every body is different and some personal experimentation is necessary, the data and most anecdotal evidence suggest that a clean fast is the most beneficial.
Remember, a clean fast means zero calories consumed and excludes calorie-free sweeteners.
Allowing your body to keep on going during the fasted state is key to burning body fat and turning on autophagy. When you feel a pang of hunger, just wait. Drink some water. The hungry feeling will pass fairly quickly. If you fixate on food, it will be much harder to continue to fast. Try to keep busy. If you have stored body fat, your body will start to use that for it’s fuel source. Think of the hunger pangs as your body saying, “I’m just about to start working really well. Please don’t feed me yet.” I think just about everyone has experienced being so busy that they either forgot or simply didn’t have time to eat and you survived just fine. The hunger pangs went away, eating was the furthest thing from your mind and you went about your business. It’s because your body is designed to work this way. If we were designed to need to eat every 2 hours on the hour around the clock, we would never have survived as a species! Food just wasn’t always that readily available.
If you decide to give Intermittent Fasting a try – with a clean fast and a long fasting window – you may experience some unpleasant symptoms at first – headaches, dizziness, lightheadedness, weakness, but that will pass within a few weeks as your body learns that you are not going to be feeding it constantly and it has to tap into that stored fuel. This is called becoming fat adapted or metabolically flexible. Not everyone experiences negative effects at all. Each body is different.
What you are more likely to notice is a lot of positive effects, especially a sense of clear-headedness and lots of energy. How many of us would like to have more energy and not feel that we’re in a fog? There’s a scientific reason for this: when you are fasted and your body is running on it’s stored fuel, that fat is turned into ketones, which is a highly efficient energy source for the body and happens to be the brain’s preferred energy source. That is why you so often hear people talk about how fasting got them out of their brain fog!
Please note, if you have tried fasting and were consuming artificial sweeteners in any form and felt a “crash” and therefore decided fasting wasn’t for you, you may want to try a clean fast. That sweet taste, even if it didn’t come with calorie consumption, most likely caused your body to produce insulin, which in turn caused your blood sugar to tank because there were no calories on which the insulin could work.
If you’re someone who enjoys coffee or tea in the morning, it is fine to continue to consume those beverages as long as you don’t add anything to them. And be careful with teas, because many of them now have stevia or other sweeteners added. Even an orange or lemon flavor can be sensed by the brain as sweet and cause an insulin response.
Optimal fasting window
I touched on this in the last research round-up, but again, I’ve been studying it in more detail since that time. If you have tried intermittent fasting and found it appealing for some reason – maybe simply for the convenience – but are not seeing actual health benefits you desire, you might need to extend your fasting window/shorten your eating window. A 16:8 plan (fast 16 hours: eat 8 hours) is fairly common, but has been shown to be less effective for most women. Yes, men have an easier time seeing benefit from a shorter fasting window than women. Most women need to get to a fasting window of 18-20 hours. The length of fasting window necessary to see optimal results varies by person, however, anecdotal evidence suggests that a fasting window of at least 18 hours is most beneficial, both for fat loss and for autophagy to kick in.
Sparing Muscle
One argument against fasting that I see frequently is the concern over muscle wasting during fasting, meaning you lose weight but that it is coming from muscle rather than fat. In fact, this has been studied and that argument is completely without merit. Fasting is actually considered a protein sparing diet, which means that the physiological processes that occur during fasting, shuttle the “burning” away from muscle and to other tissues. In fact, people who lose a lot of weight through fasting typically don’t have the excess skin issue that people have from other weight loss methods because the body slowly “digests” that extra skin. I know that sounds gross, but it’s actually a very good thing.
If you’re interested in the physiology of how this is possible, here are some details: During fasting, when the body begins burning fat for fuel, the actual fuel being produced and used are ketones. These ketones are transported into cells with high metabolic activity (muscle cells and neurons/brain cells primarily), where they are eventually metabolized into ATP – our body’s energy source. What’s happening through these processes is that the ketones are sustaining the function of muscle and brain cells during fasting and extended periods of physical exertion/exercise. Thus, it appears that when the metabolic switch is flipped, when someone becomes fat adapted, the primary energy source for the body shifts from glucose to free fatty acids derived from adipose tissue breakdown and ketones, which serve to preserve muscle. Retention of lean mass is increased following IF regimens for weight loss, as compared with continuous calorie restriction regimens in humans. Additionally, in mice, the decline in muscle mass that occurs during normal aging is prevented by time‐restricted feeding involving 40% caloric restriction.
Fasting early or late
In the previous report, I told you about the study that showed fasting later in the day is better for insulin resistance, inflammation and other health markers (meaning eat breakfast and lunch, but skip dinner). That study has really bothered me. A few years ago, I was diagnosed with *almost* insulin resistance (you can read all about that here) and that was a huge wake-up call for me. In brief, those test results came at the end of an indulgent holiday season and everything was back to normal a few months later, but even still, it was a shocking diagnosis to accept. There is a lot of Type 2 Diabetes in my family and I know the dangers. If my fasting early and eating later was possibly putting me at risk for Diabetes and more inflammation in general, that study was something I was going to have to seriously consider.
So I went back to that study and really dissected it carefully. This is what I found: One problem with this study is that it lasted only 4 days. Clearly, that is not long enough to make significant conclusions. Another issue with this study with relation to our question of which is better, fasting early or fasting late, is that this is not what the study authors were comparing. They compared fasting late to a normal eating window of 8 am – 8 pm. This is huge! To my knowledge, there is no long-term study of intermittent fasting in humans comparing those who fast early, those who fast late and those who do not fast at all (like their normal eating window group). This is the study that needs to be conducted in order to say unequivocally that one is better than the other.
Tips for getting started:
A natural, easy progression might look like this:
- Drink black coffee or tea upon waking
- Take a walk or do some sort of light, non-strenuous exercise
- Drink a big glass of water
- Hold off on breakfast until around 10. Assuming you finished dinner by 8 PM, you will have fasted for 14 hours. That’s a great start and very doable for many people.
Then slowly add something in – either a more intense workout before eating or extend your fasting window by 15 minutes at a time.
Then continue to slowly increase your fasting window until you reach the point where you are comfortable and seeing the results you desire.
One other technique for getting started if you experience too many unpleasant side effects of fasting, is to have a small, high fat, low or no carb breakfast and lunch (eg. just eggs, heavy cream in your coffee, bacon). The lack of carbohydrates will keep your body from producing much insulin and help you become fat adapted while still putting food in your stomach.
My personal experience with Intermittent Fasting – apparently the wrong way
When my functional medicine doctor first told me to try intermittent fasting, he suggested I still have my morning coffee, with the addition of MCT oil, collagen and butter, AKA Bulletproof coffee. The average bulletproof coffee contains 300 calories. This would not constitute fasting in any sense. While I was following his instructions, I didn’t notice any positive benefits to my “fasting” other than the convenience of not having to cook breakfast. Although, I did still have to get out my blender to make the coffee, which was a hassle. I quit doing it for that reason alone.
After a couple months of my Bulletproof fast, I switched to just some Nutpods (dairy free creamer), collagen and stevia in my coffee. This was easier, felt lighter, was much more convenient, but still didn’t really provide any benefits to me other than the convenience. I had been told that as long as you keep your calorie intake below 100, your body would still be in a fasted state.
I’ve continued with this version of “fasting” for years because I feel fine and as I’ve said, it’s convenient and works well for my lifestyle. However, my goal is to build more muscle and lose some body fat and of course, be as healthy as possible. My BMI is in the normal range, but based on body fat analysis, I do have too much fat and frankly, I can feel it in my clothes and I can see it in the mirror. I have felt, prior to now, that it was just a losing battle – me vs. my genetics, my age and the state of my hormones. I’m more active than ever, my diet is very clean, I’m not actually gaining weight, but things aren’t changing for the positive. I think IF can help me here, but I need to change some things from what I had been doing. If it’s not working, time to make a change!
So it seems that my Nutpods and collagen coffee was actually “dirty fasting.” Or some experts would say that it is not even fasting at all. Period. There is clean fasting and there is not fasting. So perhaps that is why I was not feeling all the magical benefits of fasting that I kept hearing about. I certainly didn’t have boundless energy and that is something I would LOVE! Wouldn’t we all!
In the for what it’s worth category: I have been “clean” fasting for at least an 18 hour window most days for the past two weeks. During that time, both of my children had some sort of cold virus and then my husband caught it. I never got it. I took vitamin C and was diligent about sanitizing the house and washing my own hands, but you all know how hard it is to avoid catching something when it’s in your house – and in your bed!
I chalk this up to the immune-boosting effects of my fasting. I obviously have no way of proving that, but I do think it goes in the interesting category.
In my last Research Round-up I mentioned that I was getting a body fat analysis scale (I have this one and recommend it). I’ve had it for two weeks and this is what I’ve seen:
- weight down 2.2 lbs.
- BMI down .5
- body fat down .7%
- body water up .3%
- skeletal muscle mass up .5%
*Based on my last “advanced” body composition analysis at my doctor’s office, this at home machine is accurate and I can trust it’s readings.
All of those changes are very positive. The problem with many “diets” is that people end up losing water and muscle more than fat. My goal is definitely to gain muscle and lose fat. Fasting has long been considered a protein sparing type of diet, meaning it does preserve muscle and I have seen that myself, albeit in a very small way so far.
I honestly wouldn’t believe it if I were not seeing the numbers for myself. It’s way too early to notice any significant changes in how I feel or even how my clothes are fitting, but I love seeing the numbers all move in the right direction.
I should note that I am not restricting myself during my eating window. I eat the same things I always ate (a paleo type diet). I tend to consume most of my calories at my earlier meal and eat a lighter dinner because I’m generally not very hungry by dinner, but I’m still eating balanced meals and some of my more indulgent paleo food like biscuits and some treats.
I have also not changed my workouts, my sleep habits or anything else. All I’ve changed is when I eat. I feel like this is as controlled of a study as I can conduct on myself.
One book I recommend you read for a good overview of fasting in a very easy to understand format is Delay, Don’t Deny. One of my favorite parts of the book is that the author references many published studies and other reliable resources so if you want to dig in further, you can. I particularly love the title of this book and think it sums up this version of IF really well. I’m not denying myself any particular foods and I can eat as much as I want during my eating window, I’m just delaying when I start eating each day.
My husband and I recently went away for a quick day trip and I wondered how I would feel not eating breakfast with him and how he would handle eating a late lunch (he has Type I diabetes and just doesn’t have the same level of flexibility with his meals that I do) and it was totally fine. I stuck to my 18 hour fast and we had a great and indulgent meal around 1:30.
The only negative for me so far is that I’m pretty hungry all morning. I still get up early, drink black coffee, work out first thing, but I used to eat when I finished working out and now I don’t. I am drinking a lot more water, but I’m not eating anything. A lot of my work revolves around food: I’m researching recipes, writing up recipes, practicing recipes, videoing myself cooking, etc. etc. so it is hard for me to simply not think about food. Once I get to 1:00 I’m generally feeling fine and could in fact fast longer. But I really want to eat by that point and I’m usually done with my 18 hour fast so I go ahead and break my fast. I just want to eat; I don’t necessarily need to eat. I’d like to try extending my fast a bit – to maybe 20 hours, but haven’t done it yet. One of my favorite hobbies is eating so long-term fasting may be too hard for me. 🙂
So I get it – if you are wanting to give this lifestyle a try, but have hesitations or doubts about your ability to do it.
All I can suggest is that you try it. If you are currently not fasting at all (other than while you sleep) consider dipping your toe in.
I will say that unequivocally, I do love the convenience of a longer, clean fast. Black coffee – easy. Plain water – easy. Something else – I used to read to my kids while they ate lunch. When they were little and we were just in the weeds over here, I would eat separately from them so I could have a little peace and quiet. We all loved the reading time together and I got a peaceful lunch. It was a win win. Well, the way I had been doing my fasting, I would often eat with them, thus no more reading. So now that I’m back to not eating while they eat, I can read to them again. I’m always looking for the upside!
Final thoughts:
One argument against the paleo or autoimmune paleo diets that I hear frequently is that it’s not sustainable because it’s SOOOO much cooking and SOOOO expensive. Well, fasting is a great way to combat both of those issues! Instead of cooking three meals a day, you’re only cooking one or two. This saves both time and money.
Fasting is such a complex topic and we still have so much to learn. What is pretty clear now is that fasting seems to be a very effective strategy for fast loss, while preserving muscle mass, and for health in general, including strengthening the immune system.
As with most things in the functional medicine world, you will need to try this for yourself and see how you feel. If your diet is dialed in, you are getting regular exercise, your stress is under control, you’ve removed as many environmental toxins from your life as you can and you are sleeping like a baby and yet you still don’t feel as well as you would like, intermittent fasting might be worth trying.
I still have a couple unanswered questions that I’m continuing to research so look for another brief follow-up to come. One of those big questions is how IF might help someone who is already lean but has health concerns that could be helped with IF. I’m thinking of a friend who is fighting cancer, but is very lean and is dealing with nausea that is often settled by eating. How might IF work for her? I’ll let you know what I find out.
References (in case you’re interested in doing some research yourself):
https://onlinelibrary.wiley.com/doi/full/10.1002/oby.22065
https://www.mdpi.com/2072-6643/11/6/1234
https://www.cell.com/cell-metabolism/pdfExtended/S1550-4131(19)30429-2
https://www.ncbi.nlm.nih.gov/pubmed/?term=intermittent+fasting+and+insulin
The Intermittent Fasting Podcast – listen wherever you find your podcasts
The Balanced Bites Podcast – episode with Dr. Jason Fung