explain intermittent fasting

[peterm28]

like the title says. what is it, how does it work, etc.

[AdamWW]

like the title says. what is it, how does it work, etc.

It is an eating schedule wherein a person limits their window of feeding during waking hours.

The most common feeding window is 16/8 (8 hours of permitted 'eating time' during the day, 16 hours of total 'fasting'), typically meaning a person delayed eating for several hours after waking, and then halts all calorie consumption 8 hours later. For example: Breakfast at Noon, last meal at 8pm.

This can also be accomplished by consuming all calories earlier in the day, but that is less common.

It does not 'work' or 'not work' in a mechanistic sense, it simply creates a more controlled method for scheduling meals.

[peterm28]

all right, and maybe someone else wants to take this one, but what are the effects on the body? (stuff like fat breakdown, glycogen, all that stuff.)

how does training combine with intermittent fasting, what's the idea here?

[Mrpb]

IF explained: skip breakfast.

Benefits for healthy exercising individuals: none besides convenience for some.

[Nicksosure1]

all right, and maybe someone else wants to take this one, but what are the effects on the body? (stuff like fat breakdown, glycogen, all that stuff.)

how does training combine with intermittent fasting, what's the idea here?

It's really just an adherence protocol. No real benefits or negatives concerning the issues you highlighted that will make or break your training either way. It works well for some people, some people it doesn't.

[Daniel1836]

The reason why I like it is because it makes staying lean easier.
And it's not even very hard, to push your first meal 5 hours or so after you wake up.
And as soon as you get used to it, you find yourself eating fewer calories during the day.

It's just a strategy.
As opposed to using will power to adhere to your daily calories, eating less throughout the day because you had breakfast.

[SuffolkPunch]

You stimulate your appetite less often and find it easier to comply with a calorie restricted diet.

That's it.

[Paulie1986]

It's great for cutting when you never feel full with small meals throughout the day that never satisfies the hunger.

I do about a 5 hour window from about 5PM whilst cutting, but I'll stil eat tiny amounts throughout the day. I do count those calories, but they rarely go above 70cals. So I don't truly fast, but I'm extremely restricted until evening time when I'm generally more hungry. Then I make sure to get my protein in. Fats I'll get through a fried egg sandwich with butter on the bread and peanut butter in my protein shake. Then just have some dry roasted nuts. My frying pan doesn't even require cooking spray or oil, as absolutely nothing sticks, so I'm not wasting calories on things like that.

[AdamWW]

The reason why I like it is because it makes staying lean easier.
And it's not even very hard, to push your first meal 5 hours or so after you wake up.
And as soon as you get used to it, you find yourself eating fewer calories during the day.

It's just a strategy.
As opposed to using will power to adhere to your daily calories, eating less throughout the day because you had breakfast.

I have never been able to go 5 hours without eating and feel 'OK', even when im not lean. If I'm moving around, going to work meetings, etc, I am far more energetic and focused with something in my system.

I naturally get hungry within about 2 hours of waking, MAYBE 3 if I'm totally lazy. The only exception would be if I ate a huge, huge amount right before bed the previous evening.

Not everyone finds it 'easy' to not eat for 5 hours after waking up.

You stimulate your appetite less often and find it easier to comply with a calorie restricted diet.

That's it.

I actually seem to eat less if I eat often... fasting for too long just makes me ravenous and once I start eating, I want more.

[Budjola]

I have never been able to go 5 hours without eating and feel 'OK', even when im not lean. If I'm moving around, going to work meetings, etc, I am far more energetic and focused with something in my system.

I naturally get hungry within about 2 hours of waking, MAYBE 3 if I'm totally lazy. The only exception would be if I ate a huge, huge amount right before bed the previous evening.

Not everyone finds it 'easy' to not eat for 5 hours after waking up.



I actually seem to eat less if I eat often... fasting for too long just makes me ravenous and once I start eating, I want more.

man after 24hrs fasts every day i can eat flock of chickens

[xsquid99]

I have never been able to go 5 hours without eating and feel 'OK', even when im not lean. If I'm moving around, going to work meetings, etc, I am far more energetic and focused with something in my system.

I naturally get hungry within about 2 hours of waking, MAYBE 3 if I'm totally lazy. The only exception would be if I ate a huge, huge amount right before bed the previous evening.

Not everyone finds it 'easy' to not eat for 5 hours after waking up.

Same exact scenario for me. If I don't eat every 4-5 hours I start feeling pretty weak and sometimes get the shakes. I'm absolutely STARVING the second I wake up in the morning.

[rtpmarine]

what are the effects on the body? (stuff like fat breakdown, glycogen, all that stuff.)

how does training combine with intermittent fasting, what's the idea here?

Fasting forces your body into increased fat oxidation and gluconeogenesis. Gluconeogenesis because your blood sugar drops and the brain still has discrete glucose requirements. Fat oxidation because the drop in blood sugar forces the tissues to work with fatty acids more and glucose less—this transition can be VERY difficult for someone with a messed up metabolism.

As for training, it’s really all about forcing adaptations. Remember, your body is constantly trying to adapt to the stresses of its environment. If you fast for 16 hours every day, during the same window, your body is going to adapt to that and the metabolic benefits will come to a halt. You have to change it up often in order to keep the gravy train rollin’. That means fasting for 16 hours one day, then not fasting, then fasting for 36 hours, then not fasting, then fasting for 20 hours, etc. Mix it up just like you would with your training. Sometimes train fasted, sometimes train fed. Always be training with the goal of forcing the adaptation that YOU want. Don’t get into a protocol like IF just for the hell of it.

IMO metabolic flexibility, as in the ability to bench the same 1rm and run the same 400-yard sprint time whether fed or starved, is a key factor in overall health and well-being.

[AdamWW]

Same exact scenario for me. If I don't eat every 4-5 hours I start feeling pretty weak and sometimes get the shakes. I'm absolutely STARVING the second I wake up in the morning.

It usually takes me about 1 hour to feel hungry, and by 2 hours my appetite kicks in full gear. I've never understood how folks can 'forget to eat'... makes no sense to me ;o)

Fasting forces your body into increased fat oxidation and gluconeogenesis. Gluconeogenesis because your blood sugar drops and the brain still has discrete glucose requirements. Fat oxidation because the drop in blood sugar forces the tissues to work with fatty acids more and glucose less—this transition can be VERY difficult for someone with a messed up metabolism.

As for training, it’s really all about forcing adaptations. Remember, your body is constantly trying to adapt to the stresses of its environment. If you fast for 16 hours every day, during the same window, your body is going to adapt to that and the metabolic benefits will come to a halt. You have to change it up often in order to keep the gravy train rollin’. That means fasting for 16 hours one day, then not fasting, then fasting for 36 hours, then not fasting, then fasting for 20 hours, etc. Mix it up just like you would with your training. Sometimes train fasted, sometimes train fed. Always be training with the goal of forcing the adaptation that YOU want. Don’t get into a protocol like IF just for the hell of it.

IMO metabolic flexibility, as in the ability to bench the same 1rm and run the same 400-yard sprint time whether fed or starved, is a key factor in overall health and well-being.

da fuq are you talking about?

[rtpmarine]

da fuq are you talking about?

Using IF as a tool for metabolic advantage rather than as a calorie restriction aid. Not expecting you to love the idea, since you can’t go more than a few hours without eating and are therefore a perfect example of the mal-adaptations that occur when the body does not receive novel stimuli.

[AdamWW]

Using IF as a tool for metabolic advantage rather than as a calorie restriction aid. Not expecting you to love the idea, since you can’t go more than a few hours without eating and are therefore a perfect example of the mal-adaptations that occur when the body does not receive novel stimuli.

There is no metabolic advantage, and I assure you I have tried more dietary approaches than you likely have. This is how my body feels best, to each their own.

[Mrpb]

Before anyone misunderstands what's being said above: intermittent fasting does not cause more fat loss than a normal calorie restricted diet when macros are matched. The fact that it temporarily increases fat oxidation does not make a difference for 24h fat loss.

Use IF if makes it easier for you to adhere to your calories or if you prefer it. The rest is largely nonsense.

And keep in mind that IF is not optimal for muscle gain and retention because it's been shown to reduce 24h MPS and testosterone. But plenty of people still get good results with it regardless. Why? Because lifting and eating sufficient protein are relatively more important than meal timing.

[rtpmarine]

There is no metabolic advantage

Use IF if makes it easier for you to adhere to your calories or if you prefer it. The rest is largely nonsense.

LOL Imagine being so myopically focused on calories that you can't even answer OP's question. Dude comes in here and asks what happens during fasting, and you all go into rants about calorie balance ???

Notice that not ONE single other person in this thread actually spoke to his question about what happens in the body during a fast or how exercise is affected. Not one. The entire thread has nothing to do with weight loss or weight gain, so why do you all jump to talking about the effect fasting has on calorie consumption?

OP--in case you were to discern that I'm somehow advocating IF for fat loss, I'm not. The main point I wanted to get across to you is that using a standard 16/8 IF schedule for several weeks or months will result in diminishing effects because your body adapts to it. Eventually it will be just like eating normally--your body will be completely used to it. We call this effect "homeostasis". My recommendation for fasting is to use irregular-interval fasts so that your body is constantly being challenged. This concept also applies to all other fitness concepts: sometimes you have to change up your exercise routines, or your macro intake, or your sleep times, etc. etc. If not, your body will get really good at doing things the same way every day and you won't have any flexibility or control.

How many people in our society are metabolically healthy enough to fast for 24 hours, then eat 2x their average calorie intake in the next 24 hours, and be able to physically perform the same way throughout? Regardless of your weight loss or weight gain goals, that type of resilience is generally a good thing for overall health because it means you won't get your ass kicked when some challenging circumstance comes along, like not being able to eat for a few hours.

[Mrpb]

LOL Imagine being so myopically focused on calories that you can't even answer OP's question. Dude comes in here and asks what happens during fasting, and you all go into rants about calorie balance ???

First of all, that's not a rant. It's simple objective information. We told him what he needs to hear. Instead of the speculative and misleading half truths that you gave him.

Think about it, when a noob in red literrally asks: "what is it, how does it work, etc." 9 out of 10 times they're just mislead into believing that fasting boosts fat loss, hypertrophy and/or health.

What they need to hear is that fasting is nothing magical, doesn't defy energy balance and there's no reason to believe it's healthier for lean active people.

By the way, I'm done with your posts that constantly try to obfuscate energy balance.

[AdamWW]

LOL Imagine being so myopically focused on calories that you can't even answer OP's question. Dude comes in here and asks what happens during fasting, and you all go into rants about calorie balance ???

How many people in our society are metabolically healthy enough to fast for 24 hours, then eat 2x their average calorie intake in the next 24 hours, and be able to physically perform the same way throughout? Regardless of your weight loss or weight gain goals, that type of resilience is generally a good thing for overall health because it means you won't get your ass kicked when some challenging circumstance comes along, like not being able to eat for a few hours.

I literally answered his question in the first response in this thread

Second, how in the world does not eating for 24 and then gorging in food indicate a healthy metabolism? Sounds like you’re pulling this nonsense out of thin air. If anything, the more often you jump back and forth between feeding schedules, the less optimized you’ll be from an energy production perspective because you’ll never retrain your body to a particular method of eating.

If someone goes from not eating for 24 hours, then eats 2x their TDEE, then consumes 4 meals a day, then one meal, then 6.... explain to me how that person would possibly perform better when energy availability and their digestion/hormonal responses never normalize?

All the best athletes in the world adhere to a protocol which induces a regular feeding timing for optical results... why do you think that is?

[rtpmarine]

By the way, I'm done with your posts that constantly try to obfuscate energy balance.

Are you sure that I am the one obfuscating, and not you? You didn't answer his question, you just assumed that he is an idiot incapable of googling the most basic concepts. He even asked specifically about "fat breakdown, glycogen, all that stuff", implying that he cares about metabolic responses and not calorie balance.

I literally answered his question in the first response in this thread

Touché, i'll give you that. OP clearly didn't find the information useful because he followed up by saying "and maybe someone else wants to take this one" lmao

All the best athletes in the world adhere to a protocol which induces a regular feeding timing for optical results... why do you think that is?

Principle of specificity. If you want to be good at powerlifting, then powerlift. If you want to be good at running, then run. If you want to be good at eating every few hours, then eat every few hours. Athletes use nutrient timing to drive improved adaptations and performance. An example of specificity which goes AGAINST your claim is marathon runners who primarily train in a semi-fed or even fasted state, and then ramp up their sugar-burning and glycogen-mobilizing pathways leading up to race day. Similarly, I assume that pro football players don't eat Sunday's breakfast at the same time every week given that game times vary. The degree of metabolically flexibility someone should have depends on the variance in what they need to accomplish. Plenty of athletes will prefer to not vary their nutrient timing so as to reduce variables in their training.

My whole soapbox here is to use fasting as a tool to drive "good adaptations", such as being metabolically flexible. IMO the typical 16/8 model becomes useless once the body adapts to it, and that only takes a couple weeks. Beyond that point, you'll see a dramatic drop-off in the benefits to insulin sensitivity, leptin response (appetite control), increased energy, enhanced auto****y, boosted immune system, etc.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5513193/

And for God's sake, please don't misconstrue any of those benefits as having anything to do with energy balance, weight change, or calorie intake. I whole-heartedly agree that if WEIGHT change is the goal, then calorie intake and expenditure should be the focus.

[Silencespeaks]

1) don’t eat at all for a long time

2) eat a lot

3) repeat

[Mrpb]

Are you sure that I am the one obfuscating, and not you?

Pretty much.

You didn't answer his question

The question was already answered extensively in the first reply of the thread. Did you mis that?

And I did answer the question: Intermittent fasting 16/8 in most cases is just skipping breakfast. Which happens to be true.

He even asked specifically about "fat breakdown, glycogen, all that stuff", implying that he cares about metabolic responses and not calorie balance.

To me it implies that he wants to hear how it helps him lose more fat. I think it's great that you want to help him understand the more technical implications but to be honest, I'm not sure you're the right person to do so. And no I'm not claiming I'm the right person to do so either.

you just assumed that he is an idiot

No I did not. I called him a noob. A noob is "a person who is inexperienced in a particular sphere or activity". I have looked at his post history and I concluded he's relatively inexperienced when it comes to nutrition.

Here's an example: https://forum.bodybuilding.com/showt...post1590822431

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5513193/

Metabolic flexibility is the ability to respond or adapt to conditional changes in metabolic demand. This broad concept has been propagated to explain insulin resistance and mechanisms governing fuel selection between glucose and fatty acids, highlighting the metabolic inflexibility of obesity and type 2 diabetes. In parallel, contemporary exercise physiology research has helped to identify potential mechanisms underlying altered fuel metabolism in obesity and diabetes. Advances in ‘omics’ technologies have further stimulated additional basic and clinical-translational research to further interrogate mechanisms for improved metabolic flexibility in skeletal muscle and adipose tissue with the goal to prevent and treat metabolic disease.

[...]

Efforts should be continued to interrogate mechanisms and potential treatments for insulin resistance and metabolic inflexibility, including the capacity for fatty acid oxidation, underlying obesity, type 2 diabetes and related conditions.

This happens a lot, people see potential benefits mentioned for obese and diabetic population and then extrapolate to relatively lean healthy active people.

Out of curiosity, which part of this paper do you believe supports your ideas about eating 2x TDEE in 24 hours?

[AdamWW]

metabolically flexible

explain why this matters if you're not obese or already have issues with insulin/glucose, etc.

If i'm turning over substrates by lifting and doing regular metabolic training and not becoming over-fat, I fail to see how this idea of metabolic flexibility matters at all. I also don't see how going hungry when I want to eat and being distracted all day is conducive to a high quality of life.

[rtpmarine]

To me it implies that he wants to hear how it helps him lose more fat. I think it's great that you want to help him understand the more technical implications but to be honest, I'm not sure you're the right person to do so. And no I'm not claiming I'm the right person to do so either.

That's fair. I understand that you and others here get bombarded by people looking for shortcuts to fat loss or muscle gain. I have no problem standing by and observing while you guys respond with the usual "read this sticky". But when follow-up questions ask for technical detail, why should either of us be the right or wrong person? Don't discredit information that answers the question just because you don't like the messenger.

This happens a lot, people see potential benefits mentioned for obese and diabetic population and then extrapolate to relatively lean healthy active people.

Out of curiosity, which part of this paper do you believe supports your ideas about eating 2x TDEE in 24 hours?

I included the link for awareness as to what metabolic flexibility is and the fact that I'm not just pulling the concept out of my butt. I didn't include it to prove any optimal eating schedule or training stimulus. Actually my whole point is that there is no optimal eating schedule. What's optimal is having the ability to vary your nutrient timing and not suffer reduced performance from it. I only used the 2x TDEE for 24 hours thing as an extreme example of the variation.

explain why this matters if you're not obese or already have issues with insulin/glucose, etc.

If i'm turning over substrates by lifting and doing regular metabolic training and not becoming over-fat, I fail to see how this idea of metabolic flexibility matters at all. I also don't see how going hungry when I want to eat and being distracted all day is conducive to a high quality of life.

From a nutritional science perspective, if someone's personal preference is to be more metabolically flexible, then irregular fasting is a huge tool in their arsenal. Hopefully we can agree on that.

From a personal preference perspective, the benefits to being metabolically flexible are that you are better able to handle the **** life throws your way. If you are happily in the "comfort zone" and have everything dialed in, then maybe you don't need to care at all. But consider these examples:

• Somebody who has a bunch of young kids (I have 3 under 3 years old--definitely makes sleeping and eating a rather variable endeavor)
• Someone in the military who gets sent down range and has to deal with eating infrequently
• Something as simple as you can't access food for a few hours because your car broke down and your cell phone died so you have to walk to town and deal with the tow truck guy before Ubering to the nearest fast food joint
• You have a work deadline and would rather hammer it out all at once so you can leave for the day and stopping to eat will just slow you down

I don't know, I'm just slinging crap at the wall here but yeah, it's a personal preference thing. Nothing really to do with nutritional science.

[AdamWW]

That's fair. I understand that you and others here get bombarded by people looking for shortcuts to fat loss or muscle gain. I have no problem standing by and observing while you guys respond with the usual "read this sticky". But when follow-up questions ask for technical detail, why should either of us be the right or wrong person? Don't discredit information that answers the question just because you don't like the messenger.



I included the link for awareness as to what metabolic flexibility is and the fact that I'm not just pulling the concept out of my butt. I didn't include it to prove any optimal eating schedule or training stimulus. Actually my whole point is that there is no optimal eating schedule. What's optimal is having the ability to vary your nutrient timing and not suffer reduced performance from it. I only used the 2x TDEE for 24 hours thing as an extreme example of the variation.




From a nutritional science perspective, if someone's personal preference is to be more metabolically flexible, then irregular fasting is a huge tool in their arsenal. Hopefully we can agree on that.

From a personal preference perspective, the benefits to being metabolically flexible are that you are better able to handle the **** life throws your way. If you are happily in the "comfort zone" and have everything dialed in, then maybe you don't need to care at all. But consider these examples:

• Somebody who has a bunch of young kids (I have 3 under 3 years old--definitely makes sleeping and eating a rather variable endeavor)
• Someone in the military who gets sent down range and has to deal with eating infrequently
• Something as simple as you can't access food for a few hours because your car broke down and your cell phone died so you have to walk to town and deal with the tow truck guy before Ubering to the nearest fast food joint
• You have a work deadline and would rather hammer it out all at once so you can leave for the day and stopping to eat will just slow you down

I don't know, I'm just slinging crap at the wall here but yeah, it's a personal preference thing. Nothing really to do with nutritional science.

My question is: where is the evidence that you can simply MAKE yourself metabolically flexible in this way by constantly changing eating schedules.

Intuitively, if one wanted to argue for the most 'flexible' adaptation, it would be simply going as long as humanly possible without eating, because the primary issue people run into is hunger and food availability.... that doesn't support the idea of going back and forth between diet protocols at all.

But, that also sucks for enjoyment for almost everyone and it certainly sucks for anabolism.

[rtpmarine]

My question is: where is the evidence that you can simply MAKE yourself metabolically flexible in this way by constantly changing eating schedules.

Intuitively, if one wanted to argue for the most 'flexible' adaptation, it would be simply going as long as humanly possible without eating, because the primary issue people run into is hunger and food availability.... that doesn't support the idea of going back and forth between diet protocols at all.

But, that also sucks for enjoyment for almost everyone and it certainly sucks for anabolism.

In the context of nutrient intake, metabolic flexibility is the body's ability to handle both underfeeding and overfeeding. If you only train the underfed state and never train the overfed state, then you won't really become more flexible, you'll just become adapted to underfeeding. Adding variability to your nutrient intake and timing improves your metabolism for the same reason that adding variability to your exercise routine makes you more anabolic: novel stimulus.

[CommitmentRulz]

Adding variability to your nutrient intake and timing improves your metabolism

Proof for this statement? Not just a study saying they are studying it.

[AdamWW]

In the context of nutrient intake, metabolic flexibility is the body's ability to handle both underfeeding and overfeeding. If you only train the underfed state and never train the overfed state, then you won't really become more flexible, you'll just become adapted to underfeeding. Adding variability to your nutrient intake and timing improves your metabolism for the same reason that adding variability to your exercise routine makes you more anabolic: novel stimulus.

I asked for evidence, not statements...

I don't think you're understanding the issue here: what are you seeing as 'improving' metabolism? Making it burn more energy? I see zero reason to believe that... zero.

Your metabolism is the cumulative set of processing occurring in your body which maintain daily functions. So, again, why would this 'improve' it? In what way would it 'improve' it? You're going to secret insulin, produce glucose, etc, regardless of what you do in terms of scheduling, and you're constantly both storing AND burning energy, in the same way you're constantly both breaking down AND building up new muscle tissue/protein...

Whether you start and stop for longer period doesn't matter in terms of 'improving' it....

[rtpmarine]

I asked for evidence, not statements...

Are you expecting scientists to be able to study randomized variability in a meaningful way? The whole "show me the study" approach to dialogue in this forum is bizarre to me. Like, how long did "studies" tell us that dietary fat causes obesity? How long did they say that eggs are unhealthy? Not to mention that so many modern studies contradict one another. I like studies, but there are like 5 or 6 other steps in the scientific method.

I don't think you're understanding the issue here: what are you seeing as 'improving' metabolism? Making it burn more energy? I see zero reason to believe that... zero.

Your metabolism is the cumulative set of processing occurring in your body which maintain daily functions. So, again, why would this 'improve' it? In what way would it 'improve' it? You're going to secret insulin, produce glucose, etc, regardless of what you do in terms of scheduling, and you're constantly both storing AND burning energy, in the same way you're constantly both breaking down AND building up new muscle tissue/protein...

Whether you start and stop for longer period doesn't matter in terms of 'improving' it....

Great call out.

Metabolism: the chemical processes that occur within a living organism in order to maintain life

When I say that something improves metabolism, I'm saying that it expands or enhances those chemical processes and therefore makes the body capable of maintaining life under progressively more varying circumstances. In essence I'm saying: Improved metabolism = increased adaptability.

You're right that metabolic processes such as insulin secretion, glucose production, etc. will happen regardless of whether the metabolism is flexible or not. The nuance here is that if you follow the same schedule day in and day out (eating, exercising, and sleeping the same way at the same times), then your body is going to get very good at the specific metabolic processes required for those circumstances and begins to attenuate and mitigate the metabolic processes that are not. This effect may be desirable if your goal is specificity or if you're happy doing what you're doing and don't desire any flexibility.

[totallypants]

The discussion that is happening in this thread is interesting tbh. Would be nice to see some evidence for what rtpmarine is saying if there is any. Seems like the point he's making is he's not training for results as much as training his body to be able to handle metabolic fluctuations more stably. Like a kind of survivalist training.