How to Fast Intermittently vs Prolonged

Intermittent Fasting 101. CC-BY-SA-4.0 By Wilson Fisk https://www.helthyfit.com/2021/01/Intermittent-Fasting-101-Guide-for-Beginners.html

As we have discussed several times in the past, there are many health benefits that come from fasting. These positive impacts range from weight loss and reduced inflammation, to better heart health and increased longevity. However, the benefits you realize depend on the type of fast you do. This leads us to examining the methods and impacts of increasingly-popular intermittent fasting versus those of prolonged fasting.



Before you start a fast, you should understand the goals you are trying to achieve. In general, most fasting regimens that restrict eating beyond 12 hours will help you balance blood sugar, increase human growth hormone, burn fat and lose weight. When you fast beyond 24 hours, you’ll start cellular cleansing and repair via autophagy, and begin entering ketosis. And if you fast beyond 48 hours, your immune system looks to reset and regenerate, and your inflammation response drops considerably. So, there are definite reasons to fast for shorter durations on a regular basis. And likewise, there are additional reasons to extend restricted eating into a multi-day fast. We’ll touch more on these fasting benefits during this post. But you can get even more details about these perks, and when they kick in, via the link below.


Click here to better understand the timeline of fasting benefits.


What is Intermittent Fasting?

Intermittent fasting (IF) is an extremely popular health and fitness trend that people around the world are using to lose weight, improve their health and simplify their life. Important to note, IF (also known as intermittent energy restriction) is not a diet. It is a term used to describe an eating pattern that cycles between periods of voluntary fasting and of feeding. Additionally, intermittent fasting does not dictate what you can or cannot eat. Rather, the focus is more on when you eat.

Our ancestors did not have means to preserve food and often went without eating for extended periods of time. As such, our biology evolved to efficiently handle going without food on a regular basis. In fact, our bodies perform better when we are not constantly feeding all day.

How to Fast Intermittently

Intermittent Fasting Calendar. CC-BY-SA-4.0 By Biochemistry&Love:

To start, there are many methods of intermittent fasting. Some of these include alternate-day fasting, periodic fasting, and daily time-restricted feeding. Those names are fairly intuitive and easily searchable online. But to cut to the chase, here is a re-cap of the most popular styles of intermittent fasting:

  • The “Leangains” protocol (or 16/8 method): Skip breakfast and restrict your eating period to 8 hours, then fast for the 16 hours in between. For example: skip breakfast, and eat only between Noon–8 p.m. Yes, you can adjust these hours a bit. Experienced fasters may reduce the eating window and increasing hours of non-feeding. Their fasting/feeding split may look like 18/6, 20/4, or even 23/1.
  • Eat-Stop-Eat method: Fast for 24 hours straight (drinking only water), once or twice a week on non-consecutive days, but eat normally on the other 5 days.
  • The 5:2 diet: Similar to “Eat-Stop-Eat” but allowing for more food… Consume roughly 500 calories on two non-consecutive days of the week, but eat normally on other days.

Interestingly, because there are so many types of “intermittent fasting”, some experts suggest that we consider stopping use of that term. Dr. Valter Longo, head of the Longevity Institute at USC, has lead considerable research into the effects of calorie-restricted eating and other healthy diets. He does a great job of explaining why “Intermittent Fasting” may be losing meaning. The main point is: it is losing value itself because it is inherently vague and used so broadly. However, he iterates that the benefits of the fasting have been proven over and again.

Benefits of Intermittent Fasting

Even if the significance of the terminology is waning, the positive impacts it can bring to your life are not. I recently delved into the benefits of fasting, which you can read about here. Here are some highlights, from that list, as well as “bonuses” one can commonly expect from the various versions of intermittent fasting:

  1. Simplifying your day: This may not be the first thing that comes to mind, but one less meal a day (or a whole day of not eating) leads to less meals to plan and prepare. Thus you’ll be able to get up and get on your way, and use that time for other productive things.
  2. Fat-burning and Weight Loss: Our bodies don’t burned stored fat until 12 hours after our last meal. Therefore, it’s rare that we are in this fat-burning state if feeding regularly. So even if you don’t change what you eat or how much you eat and exercise, simply changing your eating schedule can help you lose weight.
  3. More balanced blood sugar: No new sugar from food will be coursing through your veins, so your body will get the chance to relax glucagon levels. In the long run you’ll experience less sugar spikes (and crashes).
  4. You’ll actually stick to it: Let’s be real… most diets fail because, as creatures of habit, we aren’t good at changing what we eat. Many find it easier to change when they eat, which leads to more long-term success.

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What is Prolonged Fasting?

Now that we’re clear on what intermittent fasting is all about, let’s revisit prolonged fasting. As the name suggests, this style of fasting requires you to go without food for an extended period. In general, prolonged fasting refers to food-abstention past 24 hours. For the sake of this article, however, we’re really concentrating on multiday fasting of at least two days or more.

Sometimes fasting is done for religious purposes. Image by Sam Kolder.

These sorts of fasts have been performed since centuries ago. Indeed, sometimes it was due to lack of food. However, people have intentionally performed (and still do) prolonged fasts for religious purposes as well as to cleanse the body and mind. They had observed the positive benefits of going without eating, even though they did not have the science we have today to help understand how fasting triggers rejuvenation from within.

Types of Prolonged Fasting

Just like with IF, there are several ways to do prolonged fasting. But at a high level, I like to group them into two buckets:

  1. Water Fasting: You would consume nothing but water for at least 36 hours. The most common of these fasts run 3, 5, or even 7 days with absolutely no food or calories.
  2. Dry Fasting: This is even more extreme. You can likely guess that this will require you to consume nothing at all – not even water – for at least 24 hours, and maybe even up to four days!

I highly recommend that if you are planning on doing either of these fasting methods, please do so with the supervision and guidance of trained (medical) personnel.

Benefits of Multiday Fasting

Prolonged fasting gives many of the same benefits as IF; however, it also unlocks benefits that intermittent fasting cannot. And thanks to modern science and research, we have proven evidence as to how and why fasting works. Here’s a brief recap of the benefits that go above and beyond what you could expect from shorter/intermittent fasting:

Burning. By Pixabay.
  • Weight Loss: Slightly different than what is mentioned above; one can expect notable body fat loss over the course of a five-day fast. Prolonged fasting leads to extended periods of fat-burning. (I lost almost 9 lbs in 5 days!)
  • Ketosis: Speaking of fat-burning… Ketosis begins once you’ve fasted for 24 hours. In this state, your body is fueled by burning fat rather than carbs/sugar. Therefore, you can expect to lose body fat. The trick is, ketosis ends if you ingest (enough) carbs/sugar again. So in order to capitalize on ketosis, you want to limit that intake for as long as possible.
  • Cellular rejuvenation: Autophagy recycles the old, broken parts of your cells into new cells, which helps your body run optimally. This begins after 24 hours of fasting, but ramps up even more as you fast for 72 hours. And like ketosis, the process slows and stops if you start eating normally. So to really get the benefit, you should fast for 5 days (or more).
  • Increased longevity: The cumulative benefits of fasting can add more years to your life. And perhaps more importantly, it can add more years of good health.

Prolonged Fasting Made Easy

As you can see, the benefits of prolonged fasting are pretty amazing. But let’s be honest: starving yourself for 3 days or 5 days (or more) can be quite a daunting prospect. I know it is not something I thought I’d ever consider. However, that was before I heard of ProLon. In many ways, this remarkable product can be considered the culmination of Dr. Longo’s work to date.


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The 5-day Fasting-Mimicking Diet from ProLon was developed by Longo and his team at USC after years of research into the effects of calorie restriction on the body. I’ve discussed much of these studies and results in a previous post, so instead of repeating myself here I encourage you to give that a look via this link. But in summary: Dr. Longo observed all the benefits above, as well as the mechanisms within the body that triggered each of them. He knew these benefits would be helpful in many scenarios, such as helping to put cells into a protective state in order to better withstand chemotherapy and deliver positive outcomes for patients fighting cancer.

He realized that many people could use prolonged fasting to positively impact their lives in both clinical setting and at home. However, he also knew most people would have a difficult time actually refusing food for five days. Luckily, during his studies, Dr. Longo noted the benefits of certain diets complemented the results of fasting. Of note, the Blue Zones diet promoted longevity in much the same way as food-deprivation.

With this in mind, he set out to create a meal plan that would allow a person to eat every day, but still deliver all the benefits of prolonged fasting. Thus, ProLon FMD was born.

Prolon fasting mimicking diet

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Bringing it Home

If you’ve already had some interest in fasting, I hope the information I’ve provided above encourages you to take the next step in going for it. I also hope it helps you understand how to fast intermittently, to harness those benefits that come with daily fasting. You should be able to implement those practices with just a bit of planning and dedications. Of course, if you want to give your body a bigger rejuvenating boost, I encourage you to give prolonged fasting a try. But don’t feel like you need to plunge into the deep end and stop eating altogether for the duration of the fast. ProLon is the perfect bridge in allowing you to capture all the impacts of a week-long fast, while still letting you eat each day. This should allow you to stick to the plan and maximize the benefits of fasting.

If you have any questions about any of the topics I’ve covered above, please drop those in the comments section below. Likewise, we’d love to hear about your experiences with fasting. Please also consider joining our fasting team by entering your information below. We’ll provide tips and encouragement, and will keep you posted as to when we’ll be fasting, too, so we can do it together!

Don’t want to fast alone? Join our next group fast!

ProLon’s 5-day Fasting-Mimicking Diet is scientifically-formulated to nourish your body while keeping it in a fasted state in order to promote cellular rejuvenation and increased longevity. Learn more here.

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Dave Hughes

Editor and Contributing Author at Kaldzar

Certified Biologist and Data Scientist
Constantly curious; Curiously compassionate
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