Fasting has enjoyed a remarkable surge in popularity. Unless you have been living in a cave for the past two years, I’m sure you have noticed this trend.

Now, this might give the general impression that fasting is merely a fad, but the truth is that fasting as a health practice is nothing new. Indeed, we know that Hippocrates — the father of modern medicine — advocated periodically abstaining from food as a way to stave off disease. And of course, for most of our history as a species, humans fasted (involuntarily) for periods of time due to a lack of continuous food availability. Indeed, some research suggests that our bodies may have actually evolved to endure that kind of stress. This could be a subtle hint that doing so intentionally might be advantageous.

But going without food is pretty hard, right? Sure, it’s easy enough to implement fasting with lab animals living in cages, who can only eat whatever is given to them. It is way more challenging with free living humans. This is especially true in the modern environment, where we have relentless access to hyper-palatable foods, and other people encouraging us to eat at all hours. Everything seems to work against us.

We have been contemplating the challenges and the benefits associated with fasting, and how to make it work. In this blog, I’ll very briefly review what fasting does in the body, and some of the basic methods out there. Then, I’ll talk about our own super easy approach to fasting – that pretty much anyone can do – and how you can implement it yourself.

 

HOW FASTING WORKS

When you periodically abstain from eating, your cells are subject to a certain degree of stress. That might sound kind of bad, but stress can be physiologically beneficial, provided that your body is able to adapt to it. Probably the best example of this is weight lifting. The exercise, in the short term, damages your muscles. But when you rest and recover, your body repairs the damage and builds new muscle fibers to make you stronger. This is known as hormesis.

Fasting, at the cellular level, is surprisingly similar. When you fast, a number of cellular processes are initiated that appear to be health-promoting. For instance, fasting ramps up autophagy. During autophagy, cells generate membranes that scoop up damaged proteins in cells and sends them to be broken down by lysosomes. Concurrently, you see a spike in growth hormone (perhaps as much as five-fold), which facilitates cellular repair. Together, the body essentially experiences a state of rejuvenation, cleaning up the junk and replacing older cells with newer and more functional tissue. A number of other molecular processes occur with fasting as well, but articulating those is beyond the scope of this blog.

In response to these cellular effects, we can detect signals that the body is functioning better. For instance, you see a drop in fasting insulin levels, which indicates that the body is now more sensitive to this important hormone. You also see reductions in inflammation and oxidative stress, both of which are key contributors to a wide range of chronic diseases.

Obviously, most folks who adopt a fasting regimen do it to lose weight. However, it’s worth noting that the benefits mentioned above can occur even when there is no weight loss involved. This indicates that the processes that occur during fasting are promoting certain health effects independent of weight loss. And even if you don’t need to lose body fat, you can probably benefit from a smart fasting regimen.

 

METHODS OF FASTING

There are many different ways to fast, but protocols can generally be divided into two main categories: one that is based on limiting the time-frame in which you eat, and the other on limiting how much you eat on a specific day.

Let’s start with the first form, which is often referred to as time-restricted eating. The idea is that you consume all of your calories for the day in a shortened eating window. Let’s say you normally eat from, say, 7am to 10pm. This, incidentally, is actually pretty common (research suggests that more than half of adults eat for 15 hours or more every day). Instead, you limit all of your food intake to 10am-6pm. Thus, you are compressing your eating window from 15 hours to just 8 hours.

This doesn’t sound like a big deal, but it can make an astonishing difference. One study found, for instance, that reducing the daily eating window to 8 hours per day decreased daily calorie intake by around 300 calories, without any intentional calorie counting. This resulted in spontaneous weight loss as well as clinically relevant reductions in blood pressure. Pretty cool.

But some people might find that tricky for social reasons, or they just don’t want to have to focus on food timing every day. Another method that has gained traction recently is alternate day fasting. Here, you eat normally most of the time, but on certain days of the week you intentionally restrict your calories dramatically downward — generally around 20–25% of your normal energy requirements.

Some studies suggest that alternate day fasting may produce somewhat more weight loss than time-restricted feeding. But really the main advantage here is simplicity. You only have to restrict on fasting days, the rules are pretty black-and-white, and you don’t have to worry the rest of the week. That removes all the willpower and guesswork out of your diet, which is huge!

 

FASTING FRIDAY

Okay, so we’ve reviewed some of the benefits of intermittent fasting. Let’s talk about implementing all of this in your life.

We like the idea of alternate day fasting — again, just to keep things simple. But maybe the prospect of fasting two days a week sounds a bit daunting, or just socially untenable. Or perhaps you’re an HIIT junkie like me, and you’re concerned that fasting that frequently will interfere with your exercise regimen.

That’s how we came up with Fasting Friday. The basic idea is that you pick one day per week to take in about 25% of your daily energy needs (that’s 500 calories for a 2000 calorie diet, which is gonna be a reasonable target for most people). So you do get some food, rather than a total fast, but it’s low enough to elicit the physiological benefits associated with fasting.

Importantly, the eating window is also set around the time when the sun is out — in alignment with your biological rhythms. And although we call it Fasting Friday (because, well, it’s kind of catchy), it’s totally flexible. You can schedule the fasting day for whichever day of the week is most advantageous for you.

 

MAKING IT EASY

When you have a super tight calorie budget like this, it helps a ton to determine what you are going to eat well in advance. That way, it’s easy to stick to the plan and you’re less likely to “cheat” when you’re in the kitchen grabbing food (I speak from experience here!). I recommend just weighing and measuring everything that you’re going to eat for the day the night before, and having it all ready to go.

If you want something that is damn near foolproof, you might go for something that is already made for you, and even pre-packaged. One good option would be Splendid Spoon.

Splendid Spoon offers a Soup Cleanse, which seems almost ridiculously perfect for this purpose. It is comprised of four low-calories drinkable soups, plus one more substantial bowl. Conveniently enough, this lineup is very close to 500 calories. The current soup cleanse menu, for instance, comes in right at 520 calories. Close enough for a somewhat arbitrary target, I think.

(Just don’t forget that you only want to consume half of each bottle for this cleanse, since each contains two servings. Otherwise, this won’t be much of a fast! Save the rest for another day.)

These products are all high in fiber and plant phytochemicals, both of which should help keep you energized and satiated during your mini fast. As an added bonus, soups in particular may be uniquely effective for keeping your appetite at bay, due to their physical and sensory properties.

Some very cleverly designed trials have found that soups make people feel fuller and eat less, compared to consuming the same volume of ingredients and fluid separately. For instance, one study found that eating a chunky vegetable soup was more satiating than a serving of the same veggies accompanied with a glass of water. Better still, that was reflected in how much they ate later. Subjects consuming the 95 calorie soup subsequently decreased their energy intake by 157 calories at lunch, compared to the vegetable plate. So veggie soup seems like a very safe bet if you’re trying to stick to a fast.

 

WANT TO LEARN MORE?

This blog only barely scratches the surface on the topics of fasting.

You can get more practical information about various fasting protocols, including Fasting Friday, by becoming a humanOS Pro user and checking out our How-to Guide to Fasting.

And for more in-depth education on fasting, you can also refer to our fasting program, co-created by Jeff Rothschild. Really good stuff in there!

Final quick medical caveat: Short term fasting should be perfectly fine for healthy folks, but it is not for everyone. Individuals with certain health conditions – like diabetes – should definitely check with their doctor before adopting a plan like this.