Guest blog post by James Clear:
What is Intermittent Fasting and Why Would You Do It?
Intermittent fasting is not a diet, it’s a pattern of eating. It’s a way of scheduling your meals so that you get the most out of them. Intermittent fasting doesn’t change what you eat, it changes when you eat.
Why is it worthwhile to change when you’re eating?
Well, most notably, it’s a great way to get lean without going on a crazy diet or cutting your calories down to nothing. In fact, most of the time you’ll try to keep your calories the same when you start intermittent fasting. (Most people eat bigger meals during a shorter time frame.) Additionally, intermittent fasting is a good way to keep muscle mass on while getting lean.
With all that said, the main reason people try intermittent fasting is to lose fat. We’ll talk about how intermittent fasting leads to fat loss in a moment.
Perhaps most importantly, intermittent fasting is one of the simplest strategies we have for taking bad weight off while keeping good weight on because it requires very little behavior change. This is a very good thing because it means intermittent fasting falls into the category of “simple enough that you’ll actually do it, but meaningful enough that it will actually make a difference.”
To understand how intermittent fasting leads to fat loss we first need to understand the difference between the fed state and the fasted state.
Your body is in the fed state when it is digesting and absorbing food. Typically, the fed state starts when you begin eating and lasts for three to five hours as your body digests and absorbs the food you just ate. When you are in the fed state, it’s very hard for your body to burn fat because your insulin levels are high.
After that timespan, your body goes into what is known as the post–absorptive state, which is just a fancy way of saying that your body isn’t processing a meal. The post–absorptive state lasts until 8 to 12 hours after your last meal, which is when you enter the fasted state. It is much easier for you body to burn fat in the fasted state because your insulin levels are low.
When you’re in the fasted state your body can burn fat that has been inaccessible during the fed state.
Because we don’t enter the fasted state until 12 hours after our last meal, it’s rare that our bodies are in this fat burning state. This is one of the reasons why many people who start intermittent fasting will lose fat without changing what they eat, how much they eat, or how often they exercise. Fasting puts your body in a fat burning state that you rarely make it to during a normal eating schedule.
Fat loss is great, but it isn’t the only reason to try intermittent fasting.
1. Intermittent fasting makes your day simpler.
I’m big on behavior change, simplicity, and reducing stress. Intermittent fasting provides additional simplicity to my life that I really enjoy. When I wake up, I don’t worry about breakfast. I just grab a glass of water and start my day.
I enjoy eating and I don’t mind cooking, so eating three meals a day was never a hassle for me. However, intermittent fasting allows me to eat one less meal, which also means planning one less meal, cooking one less meal, and stressing about one less meal. It makes life a bit simpler and I like that.
2. Intermittent fasting helps you live longer.
Scientists have long known that restricting calories is a way of lengthening life. From a logical standpoint, this makes sense. When you’re starving, your body finds ways to extend your life.
There’s just one problem: who wants to starve themselves in the name of living longer?
I don’t know about you, but I’m interested in enjoying a long life. Starving myself doesn’t sound that appetizing.
The good news is that intermittent fasting activates many of the same mechanisms for extending life as calorie restriction. In other words, you get the benefits of a longer life without the hassle of starving.
Way back in 1945 it was discovered that intermittent fasting extended life in mice. (Here’s the study.) More recently, this study found that alternate day intermittent fasting led to longer lifespans.
3. Intermittent fasting may reduce the risk of cancer.
This one is up for debate because there hasn’t been a lot of research and experimentation done on the relationship between cancer and fasting. Early reports, however, look positive.
This study of 10 cancer patients suggests that the side effects of chemotherapy may be diminished by fasting before treatment. This finding is also supported by another study which used alternate day fasting with cancer patients and concluded that fasting before chemotherapy would result in better cure rates and fewer deaths.
Finally, this comprehensive analysis of many studies on fasting and disease has concluded that fasting appears to not only reduce the risk of cancer, but also cardiovascular disease.
4. Intermittent fasting is much easier than dieting.
The reason most diets fail isn’t because we switch to the wrong foods, it’s because we don’t actually follow the diet over the long term. It’s not a nutrition problem, it’s a behavior change problem.
This is where intermittent fasting shines because it’s remarkably easy to implement once you get over the idea that you need to eat all the time. For example, this study found that intermittent fasting was an effective strategy for weight loss in obese adults and concluded that “subjects quickly adapt” to an intermittent fasting routine.
I like the quote below from Dr. Michael Eades, who has tried intermittent fasting himself, on the difference between trying a diet and trying intermittent fasting.
“Diets are easy in the contemplation, difficult in the execution. Intermittent fasting is just the opposite — it’s difficult in the contemplation but easy in the execution.
Most of us have contemplated going on a diet. When we find a diet that appeals to us, it seems as if it will be a breeze to do. But when we get into the nitty gritty of it, it becomes tough. For example, I stay on a low–carb diet almost all the time. But if I think about going on a low–fat diet, it looks easy. I think about bagels, whole wheat bread and jelly, mashed potatoes, corn, bananas by the dozen, etc. — all of which sound appealing. But were I to embark on such a low–fat diet I would soon tire of it and wish I could have meat and eggs. So a diet is easy in contemplation, but not so easy in the long–term execution.
Intermittent fasting is hard in the contemplation, of that there is no doubt. “You go without food for 24 hours?” people would ask, incredulously when we explained what we were doing. “I could never do that.” But once started, it’s a snap. No worries about what and where to eat for one or two out of the three meals per day. It’s a great liberation. Your food expenditures plummet. And you’re not particularly hungry. … Although it’s tough to overcome the idea of going without food, once you begin the regimen, nothing could be easier.”
— Dr. Michael Eades
Diets are easy in the contemplation, difficult in the execution. Intermittent fasting is just the opposite — it’s difficult in the contemplation but easy in the execution.
In my opinion, the ease of intermittent fasting is best reason to give it a try. It provides a wide range of health benefits without requiring a massive lifestyle change.
Examples of Different Intermittent Fasting Schedules
If you’re considering giving fasting a shot, there are a few different options for working it into your lifestyle.
Daily Intermittent Fasting
Most of the time, I follow the Leangains model of intermittent fasting, which uses a 16–hour fast followed by an 8–hour eating period. This model of daily intermittent fasting was popularized by Martin Berkhan of Leangains.com, which is where the name originated.
It doesn’t matter when you start your 8–hour eating period. You can start at 8am and stop at 4pm. Or you start at 2pm and stop at 10pm. Do whatever works for you. I tend to find that eating around 1pm and 8pm works well because those times allow me to eat lunch and dinner with friends and family. Breakfast is typically a meal that I eat on my own, so skipping it isn’t a big deal.
Because daily intermittent fasting is done every day it becomes very easy to get into the habit of eating on this schedule. Right now, you’re probably eating around the same time every day without thinking about it. Well, with daily intermittent fasting it’s the same thing, you just learn to not eat at certain times, which is remarkably easy.
One potential disadvantage of this schedule is that because you typically cut out a meal or two out of your day, it becomes more difficult to get the same number of calories in during the week. Put simply, it’s tough to teach yourself to eat bigger meals on a consistent basis. The result is that many people who try this style of intermittent fasting end up losing weight. That can be a good thing or a bad thing, depending on your goals.
This is probably a good time to mention that while I have practiced intermittent fasting consistently for the last year, I’m not fanatical about my diet. I work on building healthy habits that guide my behavior 90% of the time, so that I can do whatever I feel like during the other 10%. If I come over to your house to watch the football game and we order pizza at 11pm, guess what? I don’t care that it’s outside my feeding period, I’m eating it.
Weekly Intermittent Fasting
One of the best ways to get started with intermittent fasting is to do it once per week or once per month. The occasional fast has been shown to lead to many of the benefits we’ve already talked about, so even if you don’t use it to cut down on calories consistently there are still many other health benefits.
The graphic below shows one example of how a weekly intermittent fast might play out.
In this example, lunch on Monday is your last meal of the day. You then fast until lunch on Tuesday. This schedule has the advantage of allowing you to eat everyday of the week while still reaping the benefits of fasting for 24 hours. It’s also less likely that you’ll lose weight because you are only cutting out two meals per week. So, if you’re looking to bulk up or keep weight on, then this is a great option.
I’ve done 24–hour fasts in the past (I just did one last month) and there are a wide range of variations and options for making it work into your schedule. For example, a long day of travel or the day after a big holiday feast are often great times to throw in a 24–hour fast.
Perhaps the biggest benefit of doing a 24–hour fast is getting over the mental barrier of fasting. If you’ve never fasted before, successfully completing your first one helps you realize that you won’t die if you don’t eat for a day.
Alternate Day Intermittent Fasting
Alternate day intermittent fasting incorporates longer fasting periods on alternating days throughout the week.
For example, in the graphic below you would eat dinner on Monday night and then not eat again until Tuesday evening. On Wednesday, however, you would eat all day and then start the 24–hour fasting cycle again after dinner on Wednesday evening. This allows you to get long fast periods on a consistent basis while also eating at least one meal every day of the week.
This style of intermittent fasting seems to be used often in research studies, but from what I have seen it isn’t very popular in the real world. I’ve never tried alternate day fasting myself and I don’t plan to do so.
The benefit of alternate day intermittent fasting is that it gives you longer time in the fasted state than the Leangains style of fasting. Hypothetically, this would increase the benefits you receive from fasting.
In practice, however, I would be concerned with eating enough. Based on my experience, teaching yourself to consistently eat more is one of the harder parts of intermittent fasting. You might be able to feast for a meal, but learning to do so every day of the week takes a little bit of planning, a lot of cooking, and consistent eating. The end result is that most people who try intermittent fasting end up losing some weight because the size of their meals remains similar even though a few meals are being cut out each week.
If you’re looking to lose weight, this isn’t a problem. And even if you’re happy with your weight, this won’t prove to be too much of an issue if you follow the daily fasting or weekly fasting schedules. However, if you’re fasting for 24 hours per day on multiple days per week, then it’s going to be very difficult to eat enough of your feast days to make up for that.
As a result, I think it’s a better idea to try daily intermittent fasting or a single 24–hour fast once per week or once per month.
Frequently Asked Questions, Concerns, and Complaints
I’m a woman. Should I do anything differently?
I haven’t worked with women on implementing an intermittent fasting schedule, so I can’t speak from experience on this one.
That said, I have heard that women may find a wider window of eating to be more favorable when doing daily intermittent fasting. While men will typically fast for 16 hours and then eat for 8 hours, women may find better results by eating for 10 hours and fasting for 14 hours. The best advice I can give anyone, not just women, is to experiment and see what works best for you. Your body will give you signals. Follow what your body responds favorably to.
Also, if you’re a female, there is an all‐female page on Facebook that discusses intermittent fasting. I’m sure you could find a ton of great answers and support there.
I could never skip breakfast. How do you do it?
I don’t. Breakfast foods are my favorite, so I just eat them at 1pm each day.
Also, if you eat a big dinner the night before, I think you’ll be surprised by how much energy you have in the morning. Most of the worries or concerns that people have about intermittent fasting are due to the fact that they have had it pounded into them by companies that they need to eat breakfast or they need to eat every three hours and so on. The science doesn’t support it and neither do my personal experiences.
I thought you were supposed to eat every 3 hours?
You may have heard people say that you should have six meals per day or eat every 3 hours or something like that.
Here’s why this was a popular idea for a brief period of time:
Your body burns calories when it’s processing food. So the thought behind the more meals strategy was that if you ate more frequently, you would also burn more calories throughout the day. Thus, eating more meals should help you lose weight.
Here’s the problem:
The amount of calories you burn is proportional to the size of the meal your body is processing. So, digesting six smaller meals that add up to 2000 calories burns the same amount of energy as processing two large meals of 1000 calories each.
It doesn’t matter if you get your calories in 10 meals or in 1 meal, you’ll end up in the same place.
This is crazy. If I didn’t eat for 24 hours, I’d die.
Honestly, I think the mental barrier is the biggest thing that prevents people from fasting because it’s really not that hard to do in practice.
Here are a few reasons why intermittent fasting isn’t as crazy as you think it is.
First, fasting has been practiced by various religious groups for centuries. Medical practitioners have also noted the health benefits of fasting for thousands of years. In other words, fasting isn’t some new fad or crazy marketing ploy. It’s been around for a long time and it actually works.
Second, fasting seems foreign to many of us simply because nobody talks about it that much. The reason for this is that nobody stands to make much money by telling you to not eat their products, not take their supplements, or not buy their goods. In other words, fasting isn’t a very marketable topic and so you’re not exposed to advertising and marketing on it very often. The result is that it seems somewhat extreme or strange, even though its really not.
Third, you’ve probably already fasted many times, even though you don’t know it. Have you ever slept in late on the weekends and then had a late brunch? Some people do this every weekend. In situations like these, we often eat dinner the night before and then don’t eat until 11am or noon or even later. There’s your 16–hour fast and you didn’t even think about it.
Finally, I would suggest doing one 24–hour fast even if you don’t plan on doing intermittent fasting frequently. It’s good to teach yourself that you’ll survive just fine without food for a day. Plus, as I’ve outlined with multiple research studies throughout this article, there are a lot of health benefits.
What are some good resources on intermittent fasting?
You can learn a lot about intermittent fasting by reading articles like this one and the resources below, but the best way to learn about what actually works for you is to experiment. That said, I’d recommend the following resources.
Martin Berkhan’s site on the Leangains version of intermittent fasting is great. You can find it here. If you’re looking for a few articles to start with, I’d recommend this one, this one, and this one.
Andy Morgan has also created an excellent site that covers the Leangains model of intermittent fasting, which you can find here. I particularly like his method of counting macros instead of counting calories, which you can read about here. (That said, I don’t count anything. I just eat.)
There is a very active forum on Reddit where people post their own progress with the Leangains style of intermittent fasting. You can check that out here.
Brad Pilon wrote a good book on intermittent fasting called Eat Stop Eat, which you can buy here.
And finally, John Berardi’s report on intermittent fasting is a great example of testing the ideas in practice. You can download it here.
That’s intermittent fasting in a nutshell.