Fasting and Muscle: How Long Term 1-2 Day Fasts BURN FAT but KEEP MUSCLE?


– Just because 95% of the
world believes something doesn’t make it true. After all, at one point, 95% of people thought the Earth was flat. In this video, we are
talking about fasting, and not the intermittent kind. Where intermittent fasters
usually fast and feed over the course of a day, this video is on extended fasting, fasts that last between
24 and 72 hours typically. You heard that right, not
eating for 24 to 72 hours. Why even fast this way? Well, as recently as a couple years ago, most people saw fasting as mainly a religious and spiritual act. Recently, though, fasting has been growing in popularity. Aside from a whole range of reported health and cognitive benefits, it is also being utilized by many as a fat loss tool. One single fast can drop
several pounds of fat, which gets some people very excited. However, with its rise in popularity and seemingly extreme nature, many people are wondering if it is the right option for them. A major point of pushback is with people who have spent time
growing their muscle mass. They’re looking to cut body fat, but they’re concerned that fasting will negatively impact their muscle. First, let’s be clear:
all weight loss diets can be boiled down to one simple concept. You are reducing your calorie intake, thereby eating less
calories than you burn. This forces your body to tap into that fat to make up the difference. Converting this fat into energy reduces your fat mass, while making up the additional energy you need. In order to evaluate fasting as a way to lose fat
for people interested in still preserving their muscle, we need something to compare it against. Since the goal here is fat loss with a consideration
for maintaining muscle, it only makes sense to compare fasting against another similarly
effective method of weight loss, a typical cutting diet,
which has participants eating less calories
than they consume daily, meaning they schedule their macros so their deficit shows up
at the end of each day. This means that, day after day, their body is constantly
in a state of malnutrition. It was long held that this
was actually far and away the best way to lose fat
while maintaining muscle. The idea was that eating
at a constant deficit would cause you to lose fat, but keeping protein and
calories from dropping too low would help preserve muscle. Fasting, on the other hand, involves creating a deficit, but just on a larger timescale. While someone on a traditional cut is in a daily deficit, someone doing periodic fasts is looking at the bigger picture, creating, perhaps, a weekly deficit. At the end of the week,
they are in a deficit, but there may be days in that week where their body still benefited from the physiological effects
of being in a surplus. During your fasting window, your body continues to burn calories, it just now needs to turn
to stored fat to get them. This is why, in as little as 72 hours, you can lose one to two pounds of fat. This level of weight loss could take two to four weeks on a traditional cutting diet. Now, the core fear is that, during these extended
windows of not eating, muscle might degrade more rapidly than it would if you lost
the same amount of fat by maintaining a constant
deficit over several weeks. People believe that something about an extended period with no food causes more muscle loss, but what does the science say? Well, it may come as a shock, but not only has it
been studied and proven that this isn’t really the case, but fasting may actually be
better at maintaining muscle– – Wrong. – [Narrator] Because–
– Wrong. – Do you have something to say? – Fasting means not eating anything. That means no protein. Have you ever read a Fitness Magazine? Muscle is made of protein. You even said it yourself in your stupid Logan Paul video that, in order to build muscle, you need X grams per day. So, obviously, if you don’t eat protein, your muscles will shrink away. – Okay, I agree dietary protein is definitely necessary
to build new muscle. But to think that if you aren’t constantly eating protein, you’ll lose all your muscle you already
built is just insane. – Oh yeah, why is that? – It’s easier if I just show you. (crashing) – Where are we? – 5000 years ago, in an
alternate reality dimension. See that tribe down there? In this dimension, their bodies work according to your logic. – [Nay-Sayer] Well, they
look pretty fit to me. – That muscle isn’t for vanity. This is the wild, they gather food by climbing trees and collecting eggs. The nests are very high
up and hard to reach. Luckily, the human body
does something called muscle protein synthesis. When muscles are pushed to their limit, sensors on the muscles
send growth signals. Back in ancient times, when
this mechanism evolved, every activity people
did was about survival, so if a muscle was being
pushed to its limit, it meant survival was at stake. This is how they adapted to have muscles large and strong enough to
reach the top of the tree. But, uh-oh. – [Nay-Sayer] What? – [Narrator] Well, it looks
like there were no eggs today. – So what? He can get eggs tomorrow or the next day. – Sorry, I’m afraid that’s not possible. As I told you, in this dimension, their bodies work the way you described. It takes muscle to reach the nest. That’s why their bodies
adapted to put it on. But remember, without getting
constant food and protein, their muscles are gonna shrink away. Even if they can still
reach the top by tomorrow, the eggs might not be back for a few days. – Now that you put it that way, if muscle is all about survival, it would be pretty dumb if, after a few days of not eating, it all disappeared. If anything, the muscle
was put on to help survive. This is the most
important time to keep it. – Now you’re thinking. While that example was a bit extreme, hopefully you see my point. In ancient times, muscle
wasn’t just for looks, it helped us survive. With food insecurity
and going hungry common, we should expect that our body would’ve developed
systems to maintain muscle during these forced fasts. If anything, going a
few days without eating, then refeeding fully,
sounds like something our body would be more familiar with based on our history. I mean, what are the
odds our tribal ancestors happened to constantly
find food day after day, but it always happened to be 300 to 500 calories short
of what they needed? If you want more proof
that feeding and fasting is something our bodies are
better equipped to handle, look at the way the Swahili Bushmen live. Often studied by researchers, they continue to live in a way which anthropologists believe is similar to the way our ancestors lived. Studying them gives us insight into our ancestors’ habits. They regularly go days without eating while they are pursuing and tracking. Here is a short quote from a researcher who lived with them in the 1930s. During lengthy hunts,
the hunters might eat very little, if anything. They often traveled very far and under extreme conditions. She recounted one story where they went eight days before finding any food. Then, once they reached an animal, they still had to have
sufficient strength to fight it. Okay, so what’s really
happening during these fasts? Why don’t we lose muscle? Well, to understand,
we’re gonna need to take a quick lesson on hormones and what happens to them when you fast, specifically, human
growth hormone and IGF-1. Now, this part might
start to sound familiar, because you’ll hear a lot of YouTubers talking about growth hormone in fasting, but they’re almost never
being fully forthcoming. Usually, they will say
something like this: fasting boosts growth hormone production, leading you to imagine
your body being filled with superphysiological levels of some amazing, muscle-promoting hormone. Those things can make
it sound like fasting is almost the same as steroids. Well, as usual, there’s a bit more to it. To understand what is going on, we need to take a look
at the bigger picture. The story of growth hormone release starts with the interactions
of two hormones. This is detailed in a
fantastic study from 1992 published in the Journal of Clinical Endocrinology and Metabolism. The first of these hormones is responsible for triggering the
release of growth hormone, and is aptly named growth
hormone-releasing hormone. The other is called somatostatin, or also sometimes called growth
hormone-inhibiting hormone. Throughout the day and night, there are periodic release of growth hormone-releasing hormone, which should trigger the pituitary gland to release little blips of growth homrone. However, sometimes this doesn’t work. While sometimes a secretion of growth hormone-releasing hormone, triggers a burst of
growth hormone release. (electronic dance music) If GHIH, growth
hormone-inhibiting hormone, that somatostatin we caled about, is being secreted at the same time, it cancels out the effects of the growth hormone-releasing hormone, and growth hormone isn’t released. The result is small
blips of growth hormone being released throughout
the day into the bloodstream. What makes it even more
difficult to study, though, is once released, growth hormone doesn’t stick around very long. The half life is quite short. In this study, the average half life of growth hormone in the
blood was just 18 minutes. The researchers had to
check the subjects’ blood every five minutes to be
sure they were catching all the little blips that were released before they would disappear. Across the 24 hours, the
mean serum concentrations of growth hormone in the
blood of well-fed subjects was about two micrograms. Levels over the day looked
something like this. Here’s where it gets interesting: they then put the subjects
on a three day fast. After two days of fasting, they remeasured over the final 24 hour period of the fast, and the impact of the fasting was huge. Mean levels of growth hormone in the blood increased by three fold, up to about 6.7 micrograms per liter. After a closer look, they found that the pituitary gland had
kicked into overdrive. Not only did the number of blips of growth hormone release double, the average size of each
blip increased as well. This is where most YouTubers leave off. They’ve told you that fasting increases the release of some hormone
with “growth” in the name, tell you it’s a good
thing, and then move on. But why is this happening? Why is it good, and what
does it have to do with maintaining your muscle? Well, as far as why it’s happening, science isn’t entirely sure, but the mechanism is hypothesized to be a result of an increased in that growth hormone
release-stimulating hormone and a simultaneous decrease
in that somatostatin, which suppresses the
released, as we talked about. (electronic party music) As far as the benefits go, it actually turns out evidence
for growth hormone itself impacting muscle growth
and maintenance is mixed. A 1988 study I reference suggested that growth hormone may
indirectly protect muscles by helping the body mobilize fat for fuel, and also support the liver in generating small amounts of necessary glucose. And while some studies have found that growth hormone increased
muscle protein synthesis, others found no real effect on it. So what is happening? Well, remember how I
mentioned that growth hormone doesn’t stick around very long once it enters the bloodstream? One reason for this is because, when it reaches the
liver, it is transformed into another hormone, known as IGF-1. Unlike growth hormone,
IGF-1 has a robust backing of scientific evidence
supporting its important role in the building and maintenance of muscle, to the point where injectable IGF-1 is a controlled substance
under anti-doping laws. There are several well-studied pathways which allow for muscle
growth and maintenance. IGF-1 is deeply rooted in many of them, including mTOR, p70sk6, AKT, and more. This is also where the pros
aren’t wrong about protein. It turns out, circulating IGF-1 levels are highly correlated
with your protein intake. – [Nay-Sayer] Ah-ha, see,
low protein means low IGF-1. When you fast, you’re getting no protein, so fasting will destroy muscle. – [Narrator] Because of
the relationship between IGF-1 and protein intake, IGF-1 levels in the fasting state should go through a
major drop, that’s true. But strangely, the research shows that, while they reduce a
bit, they don’t plummet, and this gives us a clue as to what is really happening here. By kicking into overdrive
producing growth hormone, the body isn’t directly
maintaining muscle. But by upping the production
rate of growth hormone, the liver has more to make IGF-1 from, and the drop in this important muscle-supporting hormone, IGF-1, is significantly reduced. The body knows that,
without protein intake, IGF-1 levels will drop,
which would risk our muscles, so it is compensating for this by releasing additional growth hormone to make up for some of this difference. To test this out and confirm, researchers conducted a study. Remember when we talked about the two hormones which control
growth hormone release? Researchers took eight subjects and put them through several tests, once during feeding, as a control, and once after a 40 hour fast. Then, for a third test, they
did another 40 hours fast, but researchers injected the
subjects with somatostatin, that same hormone we talked about which blocks the release
of growth hormone. Since somatostatin
affects several hormones, they made sure to replace everything but the growth hormone. This way, they could
measure what would happen to IGF-1 levels during a fast if growth hormone release
didn’t start spiking. First, they measured the baseline
well-fed levels of IGF-1. Then, the subjects did a 40 hour fast, and while the levels changed,
it wasn’t very significant. But, in the group whose
growth hormone levels were prevented from going through the natural fasting increase, their levels of free and total IGF-1 were 35 and 70% lower. And just to tie everything together, the researchers also measured for muscle protein breakdown. When the subjects fasted and had their growth hormone spike suppressed, there was a 50% increase in
the markers of muscle breakdown versus the fasting group who had the natural growth hormone spike. So, when people tout the benefits of elevated growth hormone,
they’re missing the point, since most of the
benefits of growth hormone lay in the fact that it becomes IGF-1. IGF-1 levels being propped up thanks to the added growth hormone is what should be really praised. So now, the real question is, do the systems that kick in during fasting do a good enough job of
helping maintain lean mass that fasting is a viable option for those who want to lose fat while maintaining their muscle gains? Well, this brings us to our final study, which is actually a review. They looked at several weight loss studies where participants used
a fasting protocol, and compared the results
with studies where participants lost weight via a traditional calorie restriction. One thing that jumped
out at the researchers was that the participants
were able to lose an impressive amount of
weight fairly quickly. In just two to three weeks, male and female participants lost 3% and 4% of their
body weight respectively, amounts that actually took longer to lose on many of the daily
calorie restriction diets. Ultimately, though, both
daily calorie restriction and the periodic fasting groups lost similar amounts of body weight over their trails. Doesn’t sound so good for fasting, right? Well, hold on, because everything changed when they took a deeper look and focused not just
only body weight loss, but what kind of weight they lost. During the daily calorie
restriction diets, the body weight participants lost comprised, on average,
75% fat and 25% lean mass, whereas if you look at the groups who lost their weight
through periodic fasting, they might’ve lost the
same amount of body weight, but the ratio was different. On average, 90% of what they lost was fat, and only 10% was lean mass. So, while both groups lost
similar amounts of body weight, the group which did periodic fasts maintained more lean mass,
much of which is muscle. It seems like these fasting groups experienced the best of
both worlds, in many ways. They dropped fat quite quickly, thanks to the hormonal
processes we talked about, their muscles were mostly
protected when they fasted, and they still benefited from being in a calorie surplus
on the days they didn’t fast. In some of the diets, they ate up to 10% more calories over their daily burn on the days they weren’t fasting. This is the beauty of
these periodic fasts. Participants are able to
lose body fat quite quickly while keeping most of their muscle. Then, over the rest of the week, they could benefit from
being in a calorie surplus and replenish any muscle
they may have lost, unlike the cutters, whose body starved day after day after day. If this is something you’re interested in, I would also recommend doing some resistance training during your fast. This triggers various pathways which will further help
protect your muscle. While this video may have convinced you to try fasting, there is still
a lot more you should know. I haven’t even gotten
into most of the benefits, the psychological effects,
and the best practices. If this is something you’re interested in, I can put together a more
comprehensive video guide. One thing you should be aware of is, during a fast, your body will become more sensitive to sugars, which is why I always
like to break my fast with fats and proteins. But these aren’t always
the easiest to cook with. Chicken breasts can come out dry, and it’s always tricky
to get your steak done just how you like it. While most of you know I
make these videos for fun, I actually do have a day job. We sell a sous-vide cooking device. It’s a small, compact device which allows you to cook
amazing meals on your schedule. Imagine coming home to
a juicy chicken breast after a good lift, or breaking your fast with a perfectly good steak. We’re launching on Amazon this November, and if you’re interested in learning more, I’ve put a ink in the description. If you haven’t heard of
sous-vide before, check it out. It’s basically like
science meets the kitchen. Also, if you’re interested
in keeping up with me, you can follow my personal Instagram. Most of my followers are just my friends, and they have no idea I
do this YouTube stuff, but you’re welcome to follow me and make them super confused to how I suddenly have more friends. Anyway, that just about wraps this up. I hope you enjoyed that, and
I hope I was able to clear up whatever question led you to click on this video in the first place. Until next time, D man signing off. (gentle music)

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