The Beginner’s Guide to Intermittent Fasting

“…But Tony the Tiger tells us that breakfast is the most important meal of the day!”

This rule has become so commonplace throughout the health and fitness community that it’s readily accepted as fact:

“Want to lose weight? Make sure you start off with a healthy breakfast, so you can get that metabolism firing first thing in the morning!  Eat breakfast like a king, lunch like a prince, and dinner like a pauper.”

“Want to lose more weight? Make sure you eat six small meals throughout the day so your metabolism stays operating at maximum capacity all day long”.

There are even studies that show those that eat earlier in the day lose more weight than those who ate later in the day or skipped a meal.

So, eat breakfast to lose weight and obtain optimal health.  Case closed…right?

Maybe you’re not getting the whole story. As skeptics, what we need to ask: what if there’s science and research that promotes SKIPPING BREAKFAST (the horror! blasphemy!) for optimum efficiency, maximum muscle retention, and body fat loss?

After firmly being on “Team Breakfast” for 28 years of my life, I’ve skipped breakfast for the past three months and might never go back to eating it.

I want to share with you a concept about skipping breakfast (and other meals), and how your health will benefit as a result.

Tony ain’t gonna be happy, but today we’re talking about intermittent fasting.

This is a topic that is very controversial, as it turns a LOT of conventional wisdom on its head. This is why this article is filled with more sources and citations than Jim Carrey’s glove compartment.

What is intermittent fasting?

Seal

Intermittent fasting is not a diet, but rather a dieting pattern.  

In simpler terms: it’s making a conscious decision to skip certain meals.

By fasting and then feasting on purpose, intermittent fasting means eating your calories during a specific window of the day, and choosing not to eat food during the rest.

Now, there are a few different ways to take advantage of intermittent fasting:

  • Regularly eat during a specific time period.  For example, only eating from noon-8 PM, essentially skipping breakfast.  Some people only eat in a 6-hour window, or  even a 4-hour window.  
  • Skip two meals one day, taking a full 24-hours off from eating.  For example, eating on a normal schedule (finishing dinner at 8PM) and then not eating again until 8PM the following day.

Now, you might be thinking: “okay, so by skipping a meal, I just eat less than normally overall, and thus I will lose weight, right?”  

Well, that’s partly true.  

Yes, by cutting out an entire meal, you are able to eat MORE food during your other meals and still consume a caloric deficit (which is an important for losing weight).  

However, as we already know that not all calories all created equal, the timing of meals can also influence how your body reacts.  

How does intermittent fasting work?

Cog

With intermittent fasting, your body operates differently when “feasting” compared to when “fasting”:

When you eat a meal, your body spends a few hours processing that food, burning what it can from what you just consumed.   Because it has all of this readily available, easy to burn energy in its blood stream (thanks to the food you ate), your body will choose to use that as energy rather than the fat you have stored.  This is especially true if you just consumed carbohydrates/sugar, as your body prefers to burn sugar as energy before any other source.

During the “fasted state,” your body doesn’t have a recently consumed meal to use as energy, so it is more likely to pull from the fat stored in your body, rather than the glucose in your blood stream or glycogen in your muscles/liver.

Burning fat = win.

The same goes for working out in a “fasted” state.  Without a ready supply of glucose and glycogen to pull from (which has been depleted over the course of your fasted state, and hasn’t yet been replenished with a pre-workout meal), your body is forced to adapt and pull from the only source of energy available to it: the fat stored in your cells!

Why does this work?  Our bodies react to energy consumption (eating food) with insulin production.  Essentially, the more sensitive your body is to insulin, the more likely you’ll be to use the food you consume efficiently, which can help lead to weight loss and muscle creation.

Along with that, your body is most sensitive to insulin following a period of fasting. 

Your glycogen (a starch stored in your muscles and liver that your body can burn as fuel when necessary) is depleted during sleep (fasting), and will be depleted even further during training, which can further increases insulin sensitivity. This means that a meal immediately following your workout will be stored most efficiently: mostly as glycogen for muscle stores, burned as energy immediately to help with the recovery process, with minimal amounts stored as fat.

Compare this to a regular day (no intermittent fasting).  With insulin sensitivity at normal levels, the carbs and foods consumed will see full glycogen stores, enough glucose in the blood stream, and thus be more likely to get stored as fat.

Not only that, but growth hormone is increased during fasted states (both during sleep and after a period of fasting).  Combine this  increased growth hormone secretion, the decrease in insulin production (and thus increase in insulin sensitivity), and you’re essentially priming your body for muscle growth and fat loss with intermittent fasting.

The less science-y version: Intermittent fasting can help teach your body to use the food it consumes more efficiently.  For many different physiological reasons, fasting can help promote weight loss and muscle building when done properly.  

But why does every health book say “6 small meals?”

small plate

There are a few main reasons why diet books recommend six small meals:

1) When you eat a meal, your body does have to burn extra calories just to process that meal.  So, the theory is that if you eat all day long with small meals, your body is constantly burning extra calories and your metabolism is firing at optimal capacity, right? Well, that’s not true.  Whether you eat 2000 calories spread out throughout the day, or 2000 calories in a small window, your body will burn the same number of calories processing the food.  So, the whole “keep your metabolism firing at optimum capacity by always eating” sounds good in principle, but reality tells a different story.

2) When you eat smaller meals, you’re less likely to overeat during your regular meals.  I can definitely see some truth here, especially for people who struggle with portion control or don’t know how much food they should be eating.  However, once you educate yourself and take control of your eating, I would argue most people find that eating six times a day is very prohibitive and requires a lot of effort.  Along with that, because you’re eating six small meals, I’d argue that you probably never feel “full,” and you might be MORE likely to eat extra calories during each snack.

Although grounded in seemingly logical principles, the “six meals a day” doesn’t work for the reason you think it would (#1), and really only works for people who struggle with portion control (#2).

If we want to think back to the caveman days, we’d have been in serious trouble as a species if we had to eat every three hours.  Do you think Joe caveman pulled out his pocket sundial six times a day to consume his equally portioned meals?  Hell no!  He ate when he could, and his body adapted to still function optimally during the rest of the day.

A recent study (highlighted by the New York Times) has done a great job of challenging the “six-meals-a-day” technique for weight loss.  

Martin from LeanGains points out two important quotes from the study:

“…The premise underlying the present study was that increasing meal frequency would lead to better short-term appetite regulation and increased dietary compliance; furthermore, it was hypothesised that these predicted beneficial effects of increased meal frequency could have resulted from more favourable gut peptide profiles, potentially leading to greater weight loss. Under the conditions described in the present study, all three hypotheses were rejected.”

“…We had postulated that increasing meal frequency would enhance the compliance to the energy restricted diet thus leading to greater weight loss, an effect possibly mediated by increased fullness. The present results do not support this hypothesis.”

Remember, the type of food you eat matters. Meal frequency is not nearly as important as the quantity and quality of food consumed.  This study reached similar conclusions.

Why intermittent fasting?

IF fast plate

Because it works.  Although we know that not all calories are created equal, caloric restriction plays a central role in weight loss.  When you fast (either for 16 hours per day, or 24 hours every few days), you are also making it easier to restrict your caloric intake over the course of the week.  This will give your body a chance to lose weight as you’re simply just eating less calories than you were consuming before.

Because it simplifies your day. Rather than having to prepare, pack, eat, and time your meals every 2-3 hours, you simply skip a meal or two and only worry about eating food in your eating window.

It requires less time (and potentially money). Rather than having to prepare or purchase three to six meals a day, you only need to prepare two meals.  Instead of stopping what you’re doing six times a day to eat, you simply only have to stop to eat twice.  Rather than having to do the dishes six times, you only have to do them twice. Rather than having to purchase six meals a day, you only need to purchase two.

It promotes stronger insulin sensitivity and increased growth hormone secretion, two keys for weight loss and muscle gain.  This was already explained in the previous section with relevant sources, but intermittent fasting helps you create a double whammy for weight loss.

Plus, Wolverine does it.

What are the drawbacks with intermittent fasting?

refrigerator

In my own experimentation, I have found very few negative side effects with Intermittent fasting.  

The BIGGEST issue I’ve found, and the biggest concern most people have, is that intermittent fasting will lead to lower energy, focus, and the “holy crap I am hungry” feeling during the fasting period.  People are concerned that they will spend all morning being miserable because they haven’t consumed any food, and thus will be miserable at work and ineffective at whatever task it is they are working on.

Yes, the initial transition from EATING ALL THE TIME, to intermittent fasting can be a bit of a jolt to the system. However, once you get through the transition, your body can quickly adapt and learn to function just as well only eating a few times a day:

This study explains that in participants after 48-hours of fasting, ”cognitive performance, activity, sleep, and mood are not adversely affected in healthy humans by two days of calorie-deprivation.”

“So why do I feel grouchy when I’m not eating breakfast?” In this nerd’s humble opinion, a good portion of the grumpiness is a result of your eating habits. If you eat every three hours, your body will start to get hungry every three hours as it learns and becomes used to expecting (and receiving) food every three hours. If you eat breakfast every morning, your body is expecting to wake up and eat food.

It turns out, quite a bit of it is mental.

Once you retrain your body to NOT expect food all day every day (or first thing in the morning), these side-effects become less of an issue (thanks to a substance our bodies produce called Ghrelin).

Think about it in caveman terms again.  We certainly found ways to survive during periods of feast and famine, and that remains true today.  It actually takes our bodies about 84 hours of fasting before our glucose levels are adversely affected.  As we’re talking about small fasts (16-24 hour periods), this doesn’t concern us.

AN IMPORTANT CAVEAT: Intermittent Fasting can be complex for people who have issues with blood sugar regulation, suffer from hypoglycemia, have diabetes, etc.  If you fit into this category, I highly recommend you check with your doctor or dietitian before adjusting your eating schedule.

I believe more research needs to be done for these particular cases and thus would recommend you do what works best for YOU.

Can I build muscle and gain weight while intermittent fasting?

muscle hypertrophy

Absolutely!

In fact, I have been intermittent fasting for the past three months or so while building muscle, with minimal increase to my body fat percentage.  I still eat the same number of calories I was consuming before, but instead of eating all damn day long, I condense all of my calorie consumption into an eight hour window.

  • 11 AM Work out with heavy strength training in a fasted state.
  • 12 PM Immediately consume 1/2 of my calories for the day (a regular whole-food meal, followed by a massive Calorie Bomb Shake.)
  • 7 PM Consume the second portion of my calories for the day in a big dinner.
  • 8 PM – 12 PM the next day: Fast for 16 hours.

This method has been borrowed from one of the best resources on intermittent fasting and muscle building on the internet: Lean Gains.

In a different method, my friend Nate Green packed on a crazy amount of muscle while fasting for a full 24 hours on Sundays.  

I’m not kidding when I say this has revolutionized how I look at muscle building and fat loss.  Ultimately, this method flies in the face of the typical “bulk and cut” techniques of overeating to build muscle (along with adding a lot of fat) before cutting calories to lose fat (along with some muscle) and settling down at a higher weight.

I prefer this method to the bulk-and-cut technique for a few reasons:

  • There’s far less of a crazy swing. If you are putting on 30 pounds and then cutting 25 to gain 5 lbs of muscle, your body is going through drastic swings of body mass. Your clothes will fit differently, you’ll have different levels of definition, and your body will wonder what the hell is going on.
  • You’re consuming less food and thus spending less money.  Rather than overeating to put on 1 pound of muscle and 4 pounds of fat in a week or two, you’re aiming to eat exactly enough to put on 1 pound of muscle without adding much fat on top of it.  Yeah, it’s a delicate balance, but there’s far less swing involved. You are just slowly, steadily, and consistently building muscle and strength over many months.
  • There’s never a need to get “vacation-ready”: we all want to look good naked, right?  When you are just adding muscle, you don’t need to worry about getting your body ready before by drastically altering your diet (going on a miserable crash diet for a month). I like Anthony Mychal’s technique of never being more than two weeks away.  Keep your body fat percentage low, build strength and muscle, and if you happen to notice your body fat creeping up, cut back on the carbs. Within two weeks you should be back at your preferred body fat percentage and can continue the muscle building process.

Does intermittent fasting have different effects on men and women?

boy girl

Yes, intermittent fasting does affect men and women differently.

This article over on Paleo For Women goes extensively into the negative effects of intermittent fasting for women.

This article on Mark’s Daily Apple does a fantastic job of breaking down the differences between men and women and how they are affected by intermittent fasting, ultimately explaining:

  • “One study, which I’ve cited before as evidence of a benefit to fasting, found that while IF improved insulin sensitivity in male subjects, female subjects saw no such improvement. In fact, the glucose tolerance of fasting women actually worsened. Ouch.
  • Another study examined the effect of alternate day fasting on blood lipids. Women’s HDL improved and their triglycerides remained stable; men’s HDL remained stable and their triglycerides decreased. Favorable, albeit sex-specific results.
  • Later, both obese men and women dropped body fat, body weight, blood pressure, total cholesterol, LDL cholesterol, and triglyercides on a fasting regimen. These people were obese, however, and perimenopausal women were excluded from the study, so the results may not apply to leaner people or women of reproductive age.”

Long story short: Yes, men and women will have different experiences with intermittent fasting; we’re all unique snowflakes (yep, even you), and your body will be affected by intermittent fasting differently than the person next to you.

My best advice?  Give it a shot, track your results, and see how things go!

Questions about intermittent fasting

kiwi

“Won’t I get really hungry?”  

As explained above, this is generally a result of the habits you have built for your body.  If you are constantly eating or always eat the same time of day, your body can actually learn to prepare itself for food by beginning the process of insulin production and preparation for food.  After a brief adjustment period, your body can adapt to the fact that it’s only eating a few times a day.

Remember, your body’s physical and cognitive abilities aren’t diminished as a result of fasting.

“Where will I get my energy for my workouts?  Won’t I be exhausted and not be able to complete my workouts if fasting?” 

This was a major concern of mine as well.  And for my first workout or two, it was very weird to not eat a heavy carb meal before training.  However, after a few sessions, I learned that my body could certainly function (and even thrive) during my training sessions despite not eating a pre-workout meal.

As Mark’s Daily Apple states:

Fasted training can actually result in better metabolic adaptations (which mean better performance down the line), improved muscle protein synthesis, and a higher anabolic response to post-workout feeding (you’ll earn your meal and make more muscle out of it if you train on an empty stomach).

That being said, I’m currently experimenting with a pre-workout BCAA supplement to see the effect it has on muscle creation.  So far, so good, though I’m not sold on the necessity of the supplement yet.  I’ll keep you posted :)

“I like the idea of fasted training, but I work a regular 9-5 and can’t train at 11AM. What am I supposed to do?”

Martin from LeanGains lays out a few different options for you, depending on your training schedule.  The best advice is to not freak out and overanalyze unless you are an elite athlete concerned with the absolute optimal performance at all time.

If you’re just a normal guy or gal looking to drop a few pounds and get stronger, do the best you can.

“Won’t fasting cause muscle loss?”  

Another big concern of mine, but it turns out…it was unfounded.  We’ve been told by the supplement industry that we need to consume 30 g of protein every few hours, as that’s the most amount of protein our body can process at a time.  Along with that, we’ve been told that if we don’t eat protein every few hours, our body’s muscle will start to break down to be burned as energy.

Again, NOT TRUE!  This study shows that our bodies are quite adept at preserving muscle even when fasting, and it turns out that protein absorption by our body can take place over many many many hours. Protein consumed in a shorter period of time has no difference on the body compared to protein spread throughout the day.    

“What about my body going into starvation mode from not eating?” 

Now, the thought process here is that when we don’t feed ourselves, our bodies assume calories aren’t available and thus choose to store more calories than burning them, eliminating the benefits of weight loss with fasting. Fortunately, this is NOT true.

As Martin from LeanGains so eloquently explains (as you can tell, he’s good at this stuff):

“The earliest evidence for lowered metabolic rate in response to fasting occurred after 60 hours (-8% in resting metabolic rate). Other studies show metabolic rate is not impacted until 72-96 hours have passed.

Seemingly paradoxical, metabolic rate is actually increased in short-term fasting. For some concrete numbers, studies have shown an increase of 3.6% – 10% after 36-48 hours (Mansell PI, et al, and Zauner C, et al).  Epinephrine and norepinephrine (adrenaline/noradrenaline) sharpens the mind and makes us want to move around. Desirable traits that encouraged us to seek for food, or for the hunter to kill his prey, increasing survival. At some point, after several days of no eating, this benefit would confer no benefit to survival and probably would have done more harm than good; instead, an adaptation that favored conservation of energy turned out to be advantageous.”

“This sounds crazy, I’m not gonna do it.”

That’s cool.  Are you losing body fat, building muscle, and getting a clean bill of health from your doctor?  If you can say yes to those things, AWESOME. Keep doing what you’re doing, because it’s working.   

However, if what you’re doing ISN’T working, or you’re not getting the results you were hoping for, why not give it a chance?  Hopefully the dozens of studies at least peak your curiosity.  Self-experimentation is the best way to determine WHAT methods work for you.

Tips and tricks about Fasting 

hungry ant

Don’t freak out.  Stop wondering: “can I fast 15 hours instead of 16?” or “what if I eat an apple during my fasted period, will that ruin everything?”  Relax.  Your body is a finely tuned piece of machinery and learns to adapt.  Everything is not as cut and dry as you think.

If you want to eat breakfast one day but not another, that’s okay.  If you are going for optimal aesthetic or athletic performance, I can see the need to be more rigid in your discipline, but otherwise…freaking chill out and don’t stress over minutiae.

Expect funny looks.  A few weeks back I had a number of friends staying with me, and they were all completely dumbfounded when I told them I didn’t eat breakfast anymore.  I tried to explain it to them but received a bunch of blank stares.  Breakfast has become so engrained in our culture that NOT eating it sounds crazy.  You will get weird looks from those around you…embrace it.

Stay busy.  If you are just sitting around thinking about how hungry you are, you’ll be more likely to struggle with this.  For that reason, I time my fasting periods for maximum efficiency and minimal discomfort:

  • My first few hours of fasting come after consuming a MONSTER meal, where the last thing I want to think about is eating.
  • When I’m sleeping: 8 of my 16 hours are occupied by sleeping.  Tough to feel hungry when I’m dreaming about becoming a Jedi.
  • When I’m busy: After waking up, 12 hours of my fasting is already done.  I spend three hours doing my best work (drinking green tea and listening to PM, which is exactly what I’m doing while writing this article!), and then comes my final hour of fasting: training.

I don’t have time to think about how hungry I am, because I keep my brain constantly occupied!

Zero-calorie beverages are okay.  As previously stated, I drink green tea in the morning for my caffeine kick while writing.  If you want to drink water, black coffee, or tea during your fasted period, that’s okay.  Remember, don’t overthink it – keep things simple!

Track your results, listen to your body:  

  • Concerned about losing muscle mass?  Keep track of your strength training routines and see if you are getting stronger.
  • Buy a cheap set of body fat calipers and keep track of your body fat composition.
  • Track your calories, and see how your body changes when eating the same amount of food, but condensed into a certain window.

Everybody will react to intermittent fasting differently; I can’t tell you how your body will react.  It’s up to you to listen to your body and see how making these adjustments change your body.

Don’t expect miracles.  Yes, intermittent fasting can potentially help you lose weight, increase insulin sensitivity and growth hormone secretion (all good things), but it is only ONE factor in hundreds that will determine your body composition and overall health.  Don’t expect to drop to 8% body fat and get ripped just by skipping breakfast. You need to focus on building healthy habits, eating better foods, and getting stronger.

This is just one tool that can contribute to your success…

To sum it all up

Grass

Intermittent fasting can potentially have some very positive benefits for somebody trying to lose weight or gain lean body mass.

Men and women will tend to have different results, just like each individual person will have different results.  The ONLY way to find out is with self-experimentation.

There are multiple ways to “do” intermittent fasting:

  • Fast and feast regularly: Fast for a certain number of hours, then consume all calories within a certain number of hours.
  • Eat normally, then fast 1-2x a week: Consume your normal meals every day, then pick one or two days a week where you fast for 24 hours.  Eat your last meal Sunday night, and then don’t eat again until dinner the following day.
  • Fast occasionally: probably the easiest method for the person who wants to do the least amount of work.  Simply skip a meal whenever it’s convenient. On the road? Skip breakfast.  Busy day at work? Skip lunch.  Eat poorly all day Saturday?  Make your first meal of the day dinner on Sunday.

Remember: One of the Rules of the Rebellion is to QUESTION EVERYTHING.  If this seems like something you’d like to try, give it a shot. If it sounds crazy to you, ask yourself why you think it sounds crazy, and do your own research and experimentation before condoning/condemning it.

I’d love to hear from you:

  • What are your questions with intermittent fasting?  
  • What are your concerns?
  • Have you tried intermittent fasting?
  • Have you had success with it, either with muscle gain or weight loss?

Thanks for leaving your comment, I’m excited to get the conversation started.

-Steve

PS: Added an important caveat:  If you are somebody who has blood sugar regulation issues (diabetes, hypoglycemia, etc.), I strongly recommend you discuss with your doctor or medical professional before making changes to your diet.  Remember, question everything!  

Today’s Rebel Hero: My friend Reece from Shelby.TV:

Reece

From Reece: “Falmouth Sprint Triathlon 2013: I finished 91st overall (out of ~800). Not bad considering I didn’t get to train as much as I would have liked, but shooting to break an hour on the next one!”

WOO! Cape Cod represent!

Congrats Reece on your success man, and I look forward to that email where you tell me you broke an hour.

Want to be the next Rebel Hero? Take a photo of you doing something epic in your Nerd Fitness gear and send it to [email protected] so we can feature you on the site!

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Photo Source: seal mouth, tony the tiger, anatomy, cog, small plates, apples, fridge, ant, boy girl, kiwi

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  • Julianna

    Hey, my sister did this. I want to do it now, and I want to know, should I add my workout right before I begin eating or is it alright to exercise and then wait 3 hours before I begin?

  • mina

    How do i know how much calories I should consume during the certain time frame when i can eat? Im 5’1 female 130. I gained weight the past two years 30 pounds to be exact and would like to be back to my normal size other diets I’ve tired make me feel more hungry than normal . I tend to skip meals anyways so i think ill try this out.

  • susanmcg

    There’s a website/ / app that gives calories for every food in the world! My Fitness Pal can help you count the 500 calories you should have on your fasting days. Be sure to leave 16 hours before eating to gain the best health benefits.. dont be afraid of a little hunger. ignore and and go get a massage!

  • Toks

    Nice article…thought skipping breakfast causes ulcer. Please can use blighted me on that?

  • Tom

    Fun to read your article…I’ve been doing 19 hr. I.F. for 15 months now. I was nervous in the beginning since I train hard (running, cycling, rock climbing and yoga) everyday for 1-3hrs. and thought I would bonk doing hill repeats on my bike, or at the end of a long multi-pitch climb. It never happened and my friends, who love their breakfast; were amazed at my results. Food preparation and food digestion slow the body and life down. My thinking is much clearer now and my physical body is leaner, stronger and more energetic that I’ve ever been (now 43 yrs old). Who knew!? Americans are programmed to follow the 4 food groups, drink milk for strong bones, eat a solid breakfast, etc., I think we’ve fallen for a bunch of propaganda at the hands of corporate greed. I wish more people would try IF, but I’m confident, over time, people will see the huge benefits and take that wise step forward, or backwards, depending on how you see it:)

  • Dale

    Great article!

    I’m 68 and have been into cleansing and fasting since my 30′s, and though the biochemistry of IF has until recently been unknown to me, nonetheless I am aging very gracefully (thank you very much) without being exactly sure why. But hey, I’ll take it, right!

    Seriously you get to my age and it’s really a shame to observe how the vast majority of my contemporaries are, well, looking like sad, wrinkle-faced, old farts who are clearly “digging their graves with their forks”.

    I’d like to reference the comment below where eating “avocado and hard boiled egg” is suggested. In “Sports Speed” by Dintman/Ward/Tellez maximizing HGH secretion is king/queen when it comes to maximizing muscle growth. They recommend a small, protein/carb-balanced snack of 100 calories (1 oz. turkey breast and half a fruit is their example) 30-45 minutes prior to workout or competition to “lower insulin and therefore tap into your stored body fat more efficiently”. And then there is another window 10-15 minutes post activity for a similar 100 calorie snack “to set the appropriate hormonal balance between insulin and glucagon for the maximum release of HGH”.

    However, a la yourself and Dr. Mercola, I skip the first window so I’m still “belly-empty” while working out to get the IF advantage you describe. But I do eat the balanced snack post workout to max my HGH output. Then as Dintman et al. likewise recommend I eat a good-sized meal within 2 hours.

    For my “HGH snack” along with egg or meat I just swallow a spoonful or 2 of coconut oil if I have no avocado. This I do to train my body to derive calories from fat rather than carbs (avocado serves this same purpose) which I believe is in alignment with the Paleo Diet, and really does make sense when you consider what energy sources were actually available to our ancient ancestors who realistically had to be “monovores” at any particular feeding opportunity. I mean, “Ok, children, now that we’ve gorged on antelope we need to find some nice fresh fruit to balance our meal with sufficient calories”, is patently ludicrous.

    Thanks for your research. And take it from an “old guy”, if you eat right; train right and put your macho/macha ego aside to avoid injury, decades from now, my friend, you will be oh so very, very glad that you did!

    To a life well-lived!

  • Guest

    FINALLY! This is working for me when nothing else would! I was on a PSMF for two weeks and the scale didn’t budge. I was insulin resistant, metabolic syndrome. This did the trick, down 10 lbs in 7 days, finally have my sex drive back, feeling awesome, and feel like the window of feast is the guide I need to stay on track with my life. Come to think of it my grandma was diabetic and my mom ate probably only in a 6 hour window. Thanks so much for this article. Its changed my life. Now even if I have a carby meals, I had a protein meal first and I am going to burn it off with the next daily fast. Thanks so much!

    I literally can’t wait to get on the scale each day. A long way to go but finally things are moving in the right direction!
    XOXOXOXOXOXOXO

  • http://www.nicoleunderhill.com/ Catch The Islands

    This is the only thing that worked for me. I was insulin resistant/metabolic syndrome and my body would not let go of fat until I added intermittent fasting. Thank you.

  • https://twitter.com/Jameesssss James Roberts

    I’ve been doing this for nearly a week now, and I have lost 12lbs. No doubt that some of that is water which I have retained. My question is, I am consuming around 1200-1500 calories in about a 4-5 hour eating window, is this wise? I haven’t noticed a decrease in muscle mass or strength, If any thing I feel noticeable stronger. My main priority is to lose body fat as I have recently taken a 4 month break and feel all fat and miserable because of it. By increasing my Insulin sensitivity my reasoning is that; because my body is entering a catabolic state after a 19 hour fast with training, then my current 1500 calories will be used more efficiently than say maintenance at 2500? So therefore I could still gain some lean mass as well as reducing my body fat percentage? I’m relatively new to the concept of IF but I do appreciate the science behind it, I was looking if anyone could confirm my theory and or give me some advice for my current goals?

  • Matias

    Nice post dude! I used to be a ketogenic diet doer on the past years, but I can’t do it anymore for practical reasons (having to eat out of house too often). One of the best things about ketogenic diet was that I could feel satisfied (as well as losing fat/getting some muscles) without eating too many times throughout the day.
    I feel that intermittent fasting could be a new practical solution for my dilemma as I need to drop some pounds. I just hate losing too much time of my day with multiple meals.
    Could you give me some advice? If I try intermittent fasting, which meal timing would be the best?
    I exercise 5 times a week, gym on mon/wed/fri and boxing on tues/thurs, always on 7pm. The earliest I can eat before my training time is 5:30pm.
    I though about starting my eating period at 5:30pm (around 25% of total calories), with a nice meal, exercise 7pm, then a post workout meal with 50% of total calories and eating the other 25% around mid night. I usually sleep around 1 or 2am. Does it sound good?

  • cremo

    can i fast for 12 hours instead of 16

  • Adriana Castro

    Loved your article. I am a 28 year old woman and I am on my third week of this diet pattern, and honestly I love it. I drink my coffee or green tea in the morning and I get going. I fast between 7:30 and 11:30 EVERYDAY and I can honestly say I have so much energy and my first week I lost 3 lbs. I don’t know if that is normal for all intermittent “dieters” but it worked for me. I was so caught up in making sure that I was eating all the time and now I don’t have to. It’s the easiest thing ever! My energy level is much higher than before I started the diet that’s for sure. So, in case you are a woman and you are tempted on trying this, I say go for it! I love it!

  • cactus

    This has been up for a while, but I just saw this. A few days ago, after he asked, I described to a friend what I have been doing for the past year or so to lose 33 lbs (206 down to 173 lbs) and he said, “Oh, that’s intermittent fasting.” So, I searched the term and ended up here. I am 63; I eat once a day SUN – TH at about 6p and then have 1500 calories, mostly salads. I try to avoid sugars. Technically, it’s not a fast, as I have coffee with half and half (dollops not gallons) in the AM. Other than that I don’t drink anything but water or sparkling water flavored with a fruit essence EVER. No sugared drinks; no diet drinks, no ETOH, EVER. I like being full once a day, so I just chose this pattern without knowing about the technique per se. I work out at the gym 3 days and run four days. I have no energy issues. I don’t necessarily recommend this for anyone else, but it worked for me and I thought it might help somebody else. OH, I eat a very nice meal Friday eve, including desserts, and Saturday is a free day, including desserts, and I pack it in good. Good luck with whatever path you choose.

  • greg

    does anyone have any advice on how to incorporate this lifestyle change while on a bike tour? i have a few more months on the road. would it be the wrong time to start since i am in the saddle sometimes 10 hours a day a burning through a lot of calories. im not so much looking for the fat burning benefits obviously.

  • blonde_apocalypse

    I’ve done fairly extensive fasting for spiritual purposes, and the main reason I gave it up is because of the headaches. 20 hours into a sundown-to-sundown fast, and my friggin head hurts so bad I can’t remember why I even cared about whatever it was I cared about so much to start a fast, forget being productive at work or getting in a workout at night. Any suggestions?

  • Anne Marcon

    So with very little time right now , I have a couple of quick questions. Whilst fasting (whichever way) can you still have
    Supplements
    Vege juice
    Tea green/herbal
    Coconut water
    Coconut oil
    Lemon juice

  • justsomeone

    Doctors advise that this should only run for a max of 3 months… esp. when it’s the 24 hr type.

  • Annie

    I am very interested in possibly starting this intermittent fasting, however I am a little concerned about loosing fat in areas I would not like to. Breast for example. Does any one have any experience on this or can help me out? I do not want to lose my boobs.

  • Justsomeoneelse

    Which doctors please?

  • josh

    This sounds like something that would jive with my own comfort level regarding calorie counting and structured eating. I am confused about this though–how are we buying/preparing/eating less food while fasting if we’re consuming the same amount of calories? We are consuming the same amount, right–just during the 8-hour window instead of all day? I may have missed something..

  • Chrissisbliss

    I’ll stick to breakfast simply because if I don’t I get wicked headaches that I can only sleep off (I have no idea why) then workout. So I’ll eat between 8am and 4pm. Which means my fasting period will be from 4pm to 8am the next morning. Starting today. I’m ecstatic!

  • Rachel Turluck

    Would intermittent fasting be ok during pregnancy or is it not recommended?

  • Rachel Turluck

    And what is ok during fasting time? Just water or any liquid or alcohol or what?

  • Shaun

    If you are to consume 1/2 your calories post workout, does that include fat? I was under the impression you’re only suppose to consume a light meal or shake containing only protein and fast digesting sugars. Does that rule not apply with the IF diet?

  • Rachel Turluck

    What about during the fast? Just water? Alcohol allowed? Coffee?

  • Digitalsoju

    The “Fast and feast regularly” doesn’t work for me unfortunately. I haven’t been eating breakfast since middle school, yet once I stopped working out in college my body found it’s way to store fat in my stomach.

    I still don’t eat breakfast these days, yet don’t seem to reap much of the benefits listed here by eating within a certain window (6 hours for me, 12 pm and 6pm). I didn’t even know this was considered a diet, I thought it was just called “not eating breakfast.”

  • lynette Rall

    I am now TOTALLY confused – above you state that the growth hormone is increased during fasted states (both during sleep and after a period of fasting).  I have JUST watched an excellent BBC Knowedge proramme hosted by Michael Mosley (EAT, FAST AND LIVE LONGER) available on YouTube. The scientists in this programme enphatically state that fasting DECREASES the growth hormone, by significant amounts!! And this growth hormone is for sure linked to AGEING.

  • lynette Rall

    Sorry about the spelling, BBC KNOWLEDGE PROGRAMME…

  • MCL

    As the article itself explains: no caloric drink is allowed. That means: sugarless coffee is ok. Alcoholic beverage is not allowed (highly caloric). Plus don’t try fasting while pregnant, please.
    Summarizing: sugarless coffee and tea is ok. Diet drinks too. Some dieters say you could drink a Whey Protein dose (with water) once in a while, this is not generally recommended though. BCAA could be a less caloric alternative.

  • Pro_Magnon

    Great article. Thank you! I’ve had great results with bulletproof intermittent fasting(only fat in morning) and I feel and look great. What is your take on allowing fat in the am?

  • Alexandra Peek

    Is the author still doing this? I notice it’s a year old and want to know if he still believes this is a good method since I really want to try it!

  • Ella

    I have been practicing intermittent fasting for over a year now with great results. My variation on it is that I skip dinners. I eat between 8-9 AM and 2-3PM in 6-7hr interval. My cholesterol dropped from 245 to 173, I look better, I got my high school weight finally. And I am a woman. Also, I eat a high raw diet. I believe quality of food is very important.

  • madmark

    I just found this. I think I’ll give it a shot. I usually work out around 1100-1130 anyway. Would taking any type of pre-workout supp, cause any type of negative effect on fasting? I assume not, but thought I’d ask. The types I’m thinking of would be Mr. Hyde, C4 Extreme or No-Xplode…

  • Rosie

    I would like to thank the author for such a great article! The intermittent fasting works miracles! i do the 16 hours except i start in afternoon so i can eat in the next morning. I dont restrict what i eat i eat whatever i want usually, i allow myself some chocolate and i ofcourse make sure i get enough protein since i workout frequently and i am losing weight and toning up.