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Why Intermittent Fasting Fails Most People
But Is It Right For You?
by Christian Thibaudeau | 03/06/18
The Appeal of Skipping Meals
Changing your body is emotional. If you hate what you're seeing, you want a better body comp... yesterday. And with that strong emotion comes a lack of objectivity. People become easily seduced by the more extreme diets, and one that's making a comeback is intermittent fasting.
People are drawn to it for two major reasons: First, they want to be part of a group. This makes sense because camaraderie helps with compliance. The second reason? They subconsciously believe that the more extreme a diet is, the more effective it'll be.
Simply making better food choices or tracking calories isn't "hardcore enough." They want something that's drastically different than what they're doing – an overhaul feels like the answer.
But it doesn't always work like that. Your body doesn't care how many friends your intermittent fasting group has on Facebook, and it won't instantaneously release all your stored body fat after a few extra hours without food.
The truth is, it's possible to succeed with a fasting strategy. It's possible to improve your health markers and change your body comp. But is it effective long term? Can it be used to gain muscle? What are the drawbacks?
Why We Get the "Feels" For Fasting
It's catching on among the mainstream dieters now, although fasting has gone in and out of style for ages. Its popularity is on the rise because of short-sighted beliefs like this:
"If you don't eat, you lose weight."
And...
"I should be able to eat what I want and lose weight."
It's true, not eating for 16 hours will automatically conjure images of huge weight loss in an average person's brain. So right off the bat they're convinced that it'll work. It even FEELS like it's working when you learn to suppress your hunger that long.
Then if their particular fast allows them to indulge in foods (that are normally off-limits) at the end of the fasting period, they're sold!
My Experience With IF
I used intermittent fasting several times in the past for different reasons. I've also used many variations of it. So I know how it works and what it can and can't do.
I first used intermittent fasting in 1999 after T Nation's interview with the author of the Warrior Diet. I used this approach to lose weight for an Olympic lifting competition. I wanted to drop down two weight classes so I needed to drop a lot of fat while maintaining my strength. I was able to drop from 218 to 182 pounds. My strength dropped slightly but not as much as you'd expect.
I also used intermittent fasting (again using the Warrior Diet structure) after my last bodybuilding competition in 2005. I wanted more freedom with my diet without getting fat after my competition. It worked pretty well: I regained only 5 pounds in the three months after my show, some of which was water and glycogen.
Then I used it in 2010 when I suffered from heart failure. I wanted to keep my body weight down to reduce the load on the heart.
In all the cases you'll notice one thing: I never gained a significant amount of muscle. Every time I used intermittent fasting it was to lose weight/fat or at least avoid gaining it.
Truth be told, I never was able to build a significant amount of muscle while on an intermittent fasting diet, and I've used it at least 10 times at a minimum of three months at a time. At least not while using a typical intermittent fast where you don't eat for 14-16 hours then cram all your nutrition in a 4-6 hour window.
Ways of Going Without Food
There are three main types of intermittent fasting, two of which are true "fasts".
The first one consists of using a fasting period every day followed by a short period where all the nutrition is ingested. Typically it's around 14-16 hours of fasting, with the remainder of your day allotted to a window of eating.
At first during the fast, non-caloric liquids (water, coffee, tea, etc.) are okay and a few green veggies can be used to work into it. But once you're more comfortable with fasting, you don't eat anything at all, but should still drink a lot of water.
If you're training that day, then the end of the fast would coincide with a period starting around 30 minutes before the workout, where you'd have your pre-workout drink.
The second type of intermittent fasting would be something like the 5/2 diet. In the intermittent fasting version, you'd have two non-consecutive days a week where you fast for the whole 24-hour day. The other five days you'd eat normally.
If you're in a mass phase, you could ingest a surplus five days a week and use the fasting days to control and limit fat gain. Or you could get leaner eating at maintenance or a slight deficit during those five days if your goal is maximum fat loss.
The third approach is the same as the first one (14-16 hours of fasting per day) but adding amino acid pulses throughout the day. A good example is the Pulse Feast where you'd use "pulses" of Mag-10® throughout the day. This would prevent the drawbacks of intermittent fasting.
What Intermittent Fasting Isn't
One reason why intermittent fasting doesn't work for many is because they use it as a licence to eat everything they want. If that's the reason why you're looking to start intermittent fasting, you'll run into trouble.
It's not a "diet" – it's an eating pattern. Keto is a diet (don't eat more than 30 grams of carbs and consume at least 60-70% of your calories from fats). The Zone is a diet (every meal has a 40:30:30 ratio of protein, carbs, and fats).
A "diet" gives you specific food choices or a ratio of nutrients. Intermittent fasting only gives you an eating schedule. And the schedule itself can't compensate for poor food choices or too much food.
Yes, you can indulge a bit more when using an intermittent fasting approach. But if you turn it into an all-you-can-eat crap-fest, you'll be in for a world of trouble!
Intermittent fasting can be done with any type of nutrient ratio. You can do keto intermittent fasting, Zone intermittent fasting, high carb intermittent fasting, etc. But what you can't do – if you want to see favorable results – is crap-fest intermittent fasting.
First it'll make you gain fat. You'll also feel like a bloated turd. But more importantly, it'll just reinforce bad eating habits and make it even harder to come back to eating clean.
Love Handles
Intermittent Fasting and Muscle Growth
Intermittent fasting is not a good way to build muscle. Sure, you'll find examples of people who've added muscle using it, but we don't know the whole story. Their fasting may have been what they were doing at the time, but it doesn't necessarily mean that it was the cause of their muscle growth.
Were they beginner lifters? Were they eating a crap diet prior to that? Did they use anabolic assistance? Were they training inconsistently? Did they stop doing tons of cardio? There are a ton of different things that may have lead to their gains.
I do believe a small percentage of people can build muscle on it, but for the rest of us it won't lead to hypertrophy. Some will be able to maintain their muscle mass and others will actually lose muscle.
I used intermittent fasting for 3-4 months at a time, but they were never periods where I wanted to build muscle. Heck, one time I used intermittent fasting because I needed to get smaller! I've used it to lose fat, lose size, to experiment, to be able to eat what I wanted (not always eating shit) without gaining fat, and to create a fat loss program for clients.
But I've never built noticeable muscle mass with it, nor have I used it with a client who wanted to build muscle at an optimal rate.
Who Can Build Muscle With It?
My estimate is about 20% of the population. Those would be the cortisol under-producers. People who have almost zero anxiety, people who don't get stressed about anything, those who have ice in their veins, and are amazing under pressure. They can get away with intermittent fasting when trying to build muscle. Everybody else will either stay about the same (muscle wise) or lose muscle.
Among other things, cortisol is used to mobilize stored energy when you don't have energy readily available (in your bloodstream) from a meal you've eaten. It also helps the body maintain a stable blood sugar level. When blood sugar drops, cortisol is increased to mobilize stored glucose to come back to normal levels.
There are three hormones and one neurotransmitter that primarily increase blood sugar level:
Cortisol
Glucagon
Growth hormone
Adrenalin
If you're someone who's naturally anxious, worries a lot, doesn't handle pressure well, etc. you'll likely be a cortisol-overproducer. When fasting, these guys will release a lot more cortisol to maintain blood sugar levels and mobilize fuel. Whereas the cortisol under-producers will release less and produce more growth hormone.
As you know, cortisol is catabolic – it can breakdown muscle tissue and also makes it harder to build new muscle.
Growth hormone can have an indirect anabolic effect by increasing the release of IGF-1, especially when insulin is also high. With people who produce more GH during fasting, then train (which further increases GH) and eat their "feast" after the fast (which releases a lot of insulin) they get a big anabolic spike which can help them build muscle.
Fasting, Cortisol, Personality, and Gains
If someone produces more cortisol it will be damn near impossible for them to build muscle with IF. And someone who produces a low amount of cortisol will have an easier time building it while fasting.
Think of these low cortisol producers as the neuro type 1A and 1B personalities. These are people who have a high level of confidence, are very competitive, and don't get stressed easily.
Type 2A can gain a small amount of muscle with IF while Type 2B and 3 will lose muscle on it. These guys are people pleasers. Those who have less self-confidence and need others to like them. They need to feel respected to feel good about themselves. They want to be good and look good, but not because they're competitive, rather because they need the respect and admiration of others.
Type 3 are also more likely to gain fat from IF. Why? Because they have the highest cortisol levels of all; it's constantly elevated. Systemic cortisol elevation can decrease T3 (active thyroid hormone) by decreasing the T4 to T3 conversion. And it can also make you insulin resistant.
Both responses will make it harder to lose fat and easier to gain it. These guys are those with the most anxiety. They are routine-based people, they prefer to always do the same thing over and over and follow a plan or structure. They often worry a lot because they can't switch off their brains, which often makes it hard for them to sleep properly.
But even for those 20% that can build muscle from intermittent fasting, it's not the best approach at all to build muscle.
On a related note, the reason why Mag-10® pulses can circumvent some of these issues is because it has just enough carbs (10 grams) to keep blood sugar levels in the normal range, and the type of carbs (highly branched cyclic dextrins) included won't spike insulin. This will prevent or at least greatly reduce cortisol production without leading to rebound hypoglycemia.
Beach Guy
What About The Drawbacks?
Cortisol is one of the hormones that can have the biggest negative impact on body composition. We all understand how bad it can be for muscle growth; cortisol is a catabolic hormone, it breaks down stored energy, including amino acids stored as muscle tissue. While chronically elevated cortisol levels might not always lead to muscle loss, it will drastically decrease muscle growth.
It can also limit muscle gain by increasing the expression of myostatin, the gene responsible for telling your body how much muscle it can build. Increasing myostatin expression will decrease the amount of muscle you'll be able to add to your body.
Cortisol can also impact muscle growth and well being via something called the "pregnenolone steal." How? Well, cortisol, testosterone, estrogen and a few other hormones are fabricated from the same "mother" hormone: pregnenolone. The more cortisol you chronically produce, the less pregnenolone you'll have available to make testosterone and estrogen. This means less sex hormones, which translates into less muscle-building potential. It'll also lead to a drastic drop in libido, and for those who enjoy sex, that's kind of a big deal.
So the impact of chronically elevated cortisol can be significant in limiting muscle growth. It can also negatively impact fat loss.
How Cortisol Can Blunt Fat Loss
Technically, cortisol should help with fat loss, after all, it's a mobilization hormone. One of its functions is to break down stored fat and glucose to make them available for fuel.
So how would it make you GAIN fat? The problem isn't acute cortisol production, which is normal and beneficial. The problem is chronically elevated cortisol production (elevated for most of the day).
When cortisol is elevated chronically it will lead to a decrease in the conversion of the mainly inactive thyroid hormone T4 into the active thyroid hormone T3.
T3 is one of the main hormones that regulate your metabolic rate – meaning, how much fuel you burn even at rest. T4 is mostly a "pro-hormone" for T3. The body doesn't produce a lot of T3, it mostly produces T4. It will only produce as much T3 as the body deems "safe," otherwise the metabolic rate might be too high which the body will deem a danger for survival.
So chronically elevated cortisol levels are one of the main things that will decrease that conversion from happening. This means that over the long run this excess cortisol can slow your metabolic rate, even if you're ingesting plenty of calories.
Bottom line is, intermittent fasting can be detrimental to muscle growth in around 60-80% of the population, and it can slow down fat loss in about 20% of the population.
But there are other potential problems. These come mostly when someone uses intermittent fasting as a licence to binge eat crap. Fasting will reinforce food as a reward which can make it impossible to stop eating garbage.
I've been down that road! And while it's true that you can eat a less "perfect" diet without gaining fat when using an intermittent fasting approach, you can still pile on fat if you turn the post-fast period into a binge.
A lot of people start out only having a small piece of desert. But then it turns to one large piece of desert (or pizza), then half of the food intake turns to crap, and sometimes more. Trust me, I've done it. And I've seen many people who started intermittent fasting with good intentions, but take a turn for the worse.
Plus, you can really overload the digestive system by ingesting a lot of food in a compressed period of time. This can lead to problems in the long run.
In addition, there are "clean" foods that are still calorically dense, and if fasting makes you so hungry that you overeat even the somewhat healthy stuff, you may end up consuming a calorie surplus that makes your body comp much worse off than it was before you began fasting.
And finally there's one more drawback for lifters. While some people report enhanced workouts when training on the tail-end of a fast, that's not true for everybody. Some will feel weak and have less energy when training. Some may even feel the need to skip workouts. Luckily this drawback can be avoided by breaking the fast 20-30 minutes prior to the workout with workout nutrition.
What's Intermittent Fasting Good For?
It can work well for fat loss and muscle maintenance provided that you're not under a lot of stress or someone who produces too much cortisol.
It can also program your body to be more efficient at burning fat for fuel. As such, it can be good as an "induction" phase that'll make a subsequent "normal" fat loss diet more effective.
I still use intermittent fasting from time to time, mostly when I give seminars. By not eating throughout the day, I produce more adrenalin which allows me to be much more confident and dynamic when I present. But I wouldn't use it as a lifetime eating approach.
The biggest advantage of intermittent fasting is that it's convenient and simple. For those who are busy it can be appealing. But in the long run, it's not more effective (if building muscle is among your goals). For 60-80% of the population it'll be less effective than a more traditional approach. And for about 20% it will be completely counterproductive.
A Recap and Final Recommendation
Intermittent fasting (done properly) requires MORE discipline than dieting with a macro ratio or simply choosing healthier foods on a regular basis. But if you're still on the fence, remember these things:
If you're overly anxious, have a lot of stress, or suspect you overproduce cortisol, don't use it.
If you're attracted to it for the perceived freedom to eat whatever you want, don't use it.
If your goal is to put on more muscle mass, don't use it. (Caveat: Unless you're never anxious or are using steroids).
Consider it if you have a busy lifestyle (yet are rarely stressed out from it), if you already have a great foundation of muscle, and you're willing to sacrifice a little bit of growth.
If you're prone to disordered eating (anorexia, bulimia, or binge eating disorder), don't use it.
But Is It Right For You?
by Christian Thibaudeau | 03/06/18
The Appeal of Skipping Meals
Changing your body is emotional. If you hate what you're seeing, you want a better body comp... yesterday. And with that strong emotion comes a lack of objectivity. People become easily seduced by the more extreme diets, and one that's making a comeback is intermittent fasting.
People are drawn to it for two major reasons: First, they want to be part of a group. This makes sense because camaraderie helps with compliance. The second reason? They subconsciously believe that the more extreme a diet is, the more effective it'll be.
Simply making better food choices or tracking calories isn't "hardcore enough." They want something that's drastically different than what they're doing – an overhaul feels like the answer.
But it doesn't always work like that. Your body doesn't care how many friends your intermittent fasting group has on Facebook, and it won't instantaneously release all your stored body fat after a few extra hours without food.
The truth is, it's possible to succeed with a fasting strategy. It's possible to improve your health markers and change your body comp. But is it effective long term? Can it be used to gain muscle? What are the drawbacks?
Why We Get the "Feels" For Fasting
It's catching on among the mainstream dieters now, although fasting has gone in and out of style for ages. Its popularity is on the rise because of short-sighted beliefs like this:
"If you don't eat, you lose weight."
And...
"I should be able to eat what I want and lose weight."
It's true, not eating for 16 hours will automatically conjure images of huge weight loss in an average person's brain. So right off the bat they're convinced that it'll work. It even FEELS like it's working when you learn to suppress your hunger that long.
Then if their particular fast allows them to indulge in foods (that are normally off-limits) at the end of the fasting period, they're sold!
My Experience With IF
I used intermittent fasting several times in the past for different reasons. I've also used many variations of it. So I know how it works and what it can and can't do.
I first used intermittent fasting in 1999 after T Nation's interview with the author of the Warrior Diet. I used this approach to lose weight for an Olympic lifting competition. I wanted to drop down two weight classes so I needed to drop a lot of fat while maintaining my strength. I was able to drop from 218 to 182 pounds. My strength dropped slightly but not as much as you'd expect.
I also used intermittent fasting (again using the Warrior Diet structure) after my last bodybuilding competition in 2005. I wanted more freedom with my diet without getting fat after my competition. It worked pretty well: I regained only 5 pounds in the three months after my show, some of which was water and glycogen.
Then I used it in 2010 when I suffered from heart failure. I wanted to keep my body weight down to reduce the load on the heart.
In all the cases you'll notice one thing: I never gained a significant amount of muscle. Every time I used intermittent fasting it was to lose weight/fat or at least avoid gaining it.
Truth be told, I never was able to build a significant amount of muscle while on an intermittent fasting diet, and I've used it at least 10 times at a minimum of three months at a time. At least not while using a typical intermittent fast where you don't eat for 14-16 hours then cram all your nutrition in a 4-6 hour window.
Ways of Going Without Food
There are three main types of intermittent fasting, two of which are true "fasts".
The first one consists of using a fasting period every day followed by a short period where all the nutrition is ingested. Typically it's around 14-16 hours of fasting, with the remainder of your day allotted to a window of eating.
At first during the fast, non-caloric liquids (water, coffee, tea, etc.) are okay and a few green veggies can be used to work into it. But once you're more comfortable with fasting, you don't eat anything at all, but should still drink a lot of water.
If you're training that day, then the end of the fast would coincide with a period starting around 30 minutes before the workout, where you'd have your pre-workout drink.
The second type of intermittent fasting would be something like the 5/2 diet. In the intermittent fasting version, you'd have two non-consecutive days a week where you fast for the whole 24-hour day. The other five days you'd eat normally.
If you're in a mass phase, you could ingest a surplus five days a week and use the fasting days to control and limit fat gain. Or you could get leaner eating at maintenance or a slight deficit during those five days if your goal is maximum fat loss.
The third approach is the same as the first one (14-16 hours of fasting per day) but adding amino acid pulses throughout the day. A good example is the Pulse Feast where you'd use "pulses" of Mag-10® throughout the day. This would prevent the drawbacks of intermittent fasting.
What Intermittent Fasting Isn't
One reason why intermittent fasting doesn't work for many is because they use it as a licence to eat everything they want. If that's the reason why you're looking to start intermittent fasting, you'll run into trouble.
It's not a "diet" – it's an eating pattern. Keto is a diet (don't eat more than 30 grams of carbs and consume at least 60-70% of your calories from fats). The Zone is a diet (every meal has a 40:30:30 ratio of protein, carbs, and fats).
A "diet" gives you specific food choices or a ratio of nutrients. Intermittent fasting only gives you an eating schedule. And the schedule itself can't compensate for poor food choices or too much food.
Yes, you can indulge a bit more when using an intermittent fasting approach. But if you turn it into an all-you-can-eat crap-fest, you'll be in for a world of trouble!
Intermittent fasting can be done with any type of nutrient ratio. You can do keto intermittent fasting, Zone intermittent fasting, high carb intermittent fasting, etc. But what you can't do – if you want to see favorable results – is crap-fest intermittent fasting.
First it'll make you gain fat. You'll also feel like a bloated turd. But more importantly, it'll just reinforce bad eating habits and make it even harder to come back to eating clean.
Love Handles
Intermittent Fasting and Muscle Growth
Intermittent fasting is not a good way to build muscle. Sure, you'll find examples of people who've added muscle using it, but we don't know the whole story. Their fasting may have been what they were doing at the time, but it doesn't necessarily mean that it was the cause of their muscle growth.
Were they beginner lifters? Were they eating a crap diet prior to that? Did they use anabolic assistance? Were they training inconsistently? Did they stop doing tons of cardio? There are a ton of different things that may have lead to their gains.
I do believe a small percentage of people can build muscle on it, but for the rest of us it won't lead to hypertrophy. Some will be able to maintain their muscle mass and others will actually lose muscle.
I used intermittent fasting for 3-4 months at a time, but they were never periods where I wanted to build muscle. Heck, one time I used intermittent fasting because I needed to get smaller! I've used it to lose fat, lose size, to experiment, to be able to eat what I wanted (not always eating shit) without gaining fat, and to create a fat loss program for clients.
But I've never built noticeable muscle mass with it, nor have I used it with a client who wanted to build muscle at an optimal rate.
Who Can Build Muscle With It?
My estimate is about 20% of the population. Those would be the cortisol under-producers. People who have almost zero anxiety, people who don't get stressed about anything, those who have ice in their veins, and are amazing under pressure. They can get away with intermittent fasting when trying to build muscle. Everybody else will either stay about the same (muscle wise) or lose muscle.
Among other things, cortisol is used to mobilize stored energy when you don't have energy readily available (in your bloodstream) from a meal you've eaten. It also helps the body maintain a stable blood sugar level. When blood sugar drops, cortisol is increased to mobilize stored glucose to come back to normal levels.
There are three hormones and one neurotransmitter that primarily increase blood sugar level:
Cortisol
Glucagon
Growth hormone
Adrenalin
If you're someone who's naturally anxious, worries a lot, doesn't handle pressure well, etc. you'll likely be a cortisol-overproducer. When fasting, these guys will release a lot more cortisol to maintain blood sugar levels and mobilize fuel. Whereas the cortisol under-producers will release less and produce more growth hormone.
As you know, cortisol is catabolic – it can breakdown muscle tissue and also makes it harder to build new muscle.
Growth hormone can have an indirect anabolic effect by increasing the release of IGF-1, especially when insulin is also high. With people who produce more GH during fasting, then train (which further increases GH) and eat their "feast" after the fast (which releases a lot of insulin) they get a big anabolic spike which can help them build muscle.
Fasting, Cortisol, Personality, and Gains
If someone produces more cortisol it will be damn near impossible for them to build muscle with IF. And someone who produces a low amount of cortisol will have an easier time building it while fasting.
Think of these low cortisol producers as the neuro type 1A and 1B personalities. These are people who have a high level of confidence, are very competitive, and don't get stressed easily.
Type 2A can gain a small amount of muscle with IF while Type 2B and 3 will lose muscle on it. These guys are people pleasers. Those who have less self-confidence and need others to like them. They need to feel respected to feel good about themselves. They want to be good and look good, but not because they're competitive, rather because they need the respect and admiration of others.
Type 3 are also more likely to gain fat from IF. Why? Because they have the highest cortisol levels of all; it's constantly elevated. Systemic cortisol elevation can decrease T3 (active thyroid hormone) by decreasing the T4 to T3 conversion. And it can also make you insulin resistant.
Both responses will make it harder to lose fat and easier to gain it. These guys are those with the most anxiety. They are routine-based people, they prefer to always do the same thing over and over and follow a plan or structure. They often worry a lot because they can't switch off their brains, which often makes it hard for them to sleep properly.
But even for those 20% that can build muscle from intermittent fasting, it's not the best approach at all to build muscle.
On a related note, the reason why Mag-10® pulses can circumvent some of these issues is because it has just enough carbs (10 grams) to keep blood sugar levels in the normal range, and the type of carbs (highly branched cyclic dextrins) included won't spike insulin. This will prevent or at least greatly reduce cortisol production without leading to rebound hypoglycemia.
Beach Guy
What About The Drawbacks?
Cortisol is one of the hormones that can have the biggest negative impact on body composition. We all understand how bad it can be for muscle growth; cortisol is a catabolic hormone, it breaks down stored energy, including amino acids stored as muscle tissue. While chronically elevated cortisol levels might not always lead to muscle loss, it will drastically decrease muscle growth.
It can also limit muscle gain by increasing the expression of myostatin, the gene responsible for telling your body how much muscle it can build. Increasing myostatin expression will decrease the amount of muscle you'll be able to add to your body.
Cortisol can also impact muscle growth and well being via something called the "pregnenolone steal." How? Well, cortisol, testosterone, estrogen and a few other hormones are fabricated from the same "mother" hormone: pregnenolone. The more cortisol you chronically produce, the less pregnenolone you'll have available to make testosterone and estrogen. This means less sex hormones, which translates into less muscle-building potential. It'll also lead to a drastic drop in libido, and for those who enjoy sex, that's kind of a big deal.
So the impact of chronically elevated cortisol can be significant in limiting muscle growth. It can also negatively impact fat loss.
How Cortisol Can Blunt Fat Loss
Technically, cortisol should help with fat loss, after all, it's a mobilization hormone. One of its functions is to break down stored fat and glucose to make them available for fuel.
So how would it make you GAIN fat? The problem isn't acute cortisol production, which is normal and beneficial. The problem is chronically elevated cortisol production (elevated for most of the day).
When cortisol is elevated chronically it will lead to a decrease in the conversion of the mainly inactive thyroid hormone T4 into the active thyroid hormone T3.
T3 is one of the main hormones that regulate your metabolic rate – meaning, how much fuel you burn even at rest. T4 is mostly a "pro-hormone" for T3. The body doesn't produce a lot of T3, it mostly produces T4. It will only produce as much T3 as the body deems "safe," otherwise the metabolic rate might be too high which the body will deem a danger for survival.
So chronically elevated cortisol levels are one of the main things that will decrease that conversion from happening. This means that over the long run this excess cortisol can slow your metabolic rate, even if you're ingesting plenty of calories.
Bottom line is, intermittent fasting can be detrimental to muscle growth in around 60-80% of the population, and it can slow down fat loss in about 20% of the population.
But there are other potential problems. These come mostly when someone uses intermittent fasting as a licence to binge eat crap. Fasting will reinforce food as a reward which can make it impossible to stop eating garbage.
I've been down that road! And while it's true that you can eat a less "perfect" diet without gaining fat when using an intermittent fasting approach, you can still pile on fat if you turn the post-fast period into a binge.
A lot of people start out only having a small piece of desert. But then it turns to one large piece of desert (or pizza), then half of the food intake turns to crap, and sometimes more. Trust me, I've done it. And I've seen many people who started intermittent fasting with good intentions, but take a turn for the worse.
Plus, you can really overload the digestive system by ingesting a lot of food in a compressed period of time. This can lead to problems in the long run.
In addition, there are "clean" foods that are still calorically dense, and if fasting makes you so hungry that you overeat even the somewhat healthy stuff, you may end up consuming a calorie surplus that makes your body comp much worse off than it was before you began fasting.
And finally there's one more drawback for lifters. While some people report enhanced workouts when training on the tail-end of a fast, that's not true for everybody. Some will feel weak and have less energy when training. Some may even feel the need to skip workouts. Luckily this drawback can be avoided by breaking the fast 20-30 minutes prior to the workout with workout nutrition.
What's Intermittent Fasting Good For?
It can work well for fat loss and muscle maintenance provided that you're not under a lot of stress or someone who produces too much cortisol.
It can also program your body to be more efficient at burning fat for fuel. As such, it can be good as an "induction" phase that'll make a subsequent "normal" fat loss diet more effective.
I still use intermittent fasting from time to time, mostly when I give seminars. By not eating throughout the day, I produce more adrenalin which allows me to be much more confident and dynamic when I present. But I wouldn't use it as a lifetime eating approach.
The biggest advantage of intermittent fasting is that it's convenient and simple. For those who are busy it can be appealing. But in the long run, it's not more effective (if building muscle is among your goals). For 60-80% of the population it'll be less effective than a more traditional approach. And for about 20% it will be completely counterproductive.
A Recap and Final Recommendation
Intermittent fasting (done properly) requires MORE discipline than dieting with a macro ratio or simply choosing healthier foods on a regular basis. But if you're still on the fence, remember these things:
If you're overly anxious, have a lot of stress, or suspect you overproduce cortisol, don't use it.
If you're attracted to it for the perceived freedom to eat whatever you want, don't use it.
If your goal is to put on more muscle mass, don't use it. (Caveat: Unless you're never anxious or are using steroids).
Consider it if you have a busy lifestyle (yet are rarely stressed out from it), if you already have a great foundation of muscle, and you're willing to sacrifice a little bit of growth.
If you're prone to disordered eating (anorexia, bulimia, or binge eating disorder), don't use it.
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