Fasted Workouts and Fasted Cardio vs EPOC – For Fat Loss

January 30, 2009

There are two schools of thought when it comes to losing body fat. The first approach is to focus on utilizing as much fat as possible during your workout, by going into your workout in a fasted state. The other approach is to not worry about fasting and focus on intensity to burn more calories around the clock after the workout is finished (EPOC). Let’s talk about the benefits of both, as well as something significant that rarely gets mentioned.

mountain lion hunting
[When an animal is in a fasted state, something interesting happens to give that animal an energy boost. This boost of energy gives the animal the ability to reach peak performance even when it hasn’t consumed a calorie for long periods of time. We will talk about how and why this is significant later in the post.]

The Argument For Working Out in a Fasted State

Anyone who has read my blog for any period of time, knows I recommend to do your workouts in a fasted state. The problem with eating before working out is that you are simply burning food energy vs body fat for energy. Plus…eating releases insulin, which interferes with your body’s ability to burn body fat. Basically, eating before your workout gets in the way of burning body fat during your workout.

The Argument Against Working Out in a Fasted State

It seems like “a no brainer” to workout in a fasted state…but it isn’t that simple! Intense training has been shown to increase the calories burned long after to workout is over. In fact, it is possible to burn an extra couple hundred calories after an intense workout. Those who argue against working out in a fasted state, claim that you will not have enough energy to have an intense workout. This seems logical on the surface, but the body is smarter than that…

sympathetic nervous system SNS

[An exciting picture of neurons! Actually, it is a pretty cool picture of the nervous system. Who would have thought that was possible?]

Your Sympathetic Nervous System = Energy in A Fasted State

For the longest time, I didn’t understand why I had more energy after fasting. I have my most productive hardcore workouts after fasting for 5-18 hours. If I ate anything in that 4-5 hour window before training, the workouts just weren’t as intense. Ori Hofmekler explained where this “hidden” energy source came from…the Sympathetic Nervous System (SNS).

Why Does The SNS Kick In When in A Fasted State?

Ori explains it best…

“When fasting, a primal survival mechanism known as the fight-or-flight reaction to stress is triggered, maximizing your body’s capacity for generating energy, being alert, resisting fatigue and resisting stress. The survival mode is primarily controlled by a part of the autonomic nervous system known as the sympathetic nervous system, or SNS. When it’s in gear, the body is in its most energy-producing phase, and that’s when the most energy comes from fat burning.”

This makes sense, because as hunters and gatherers our ancestors needed to be at our peak performance when hungry in order to catch the next meal (kind of like the mountain lion pictured above).

Eating Before Working Out Interrupts This Surge of Energy

Ori explains how the Parasympathetic Nervous System slows you down after a meal. Note: In the article I’m quoting he is talking about morning meals and not eating before your morning workout…

“If you do eat a breakfast of, say, bagel, cereal, egg and bacon, you’ll most likely shut down this energy-producing system. The SNS and its fight-or-flight mechanism will be substantially suppressed, and your morning meal will trigger an antagonistic part of the autonomic nervous system known as the para sympathetic nervous system, or PSNS. The PSNS will make you sleepy, slow and less resistant to fatigue and stress. Instead of spending energy and burning fat, your body will be more geared toward storing energy and gaining fat.”

Ori, recommends mainly eating at night after your physical activities are done for the day. He claims that food makes your body relax and prepares the body for sleep.

You Can Have an Intense Workout While Fasting

As I stated earlier, I have a better workout in a fasted state. Not only do I have more energy, I don’t burp up a meal when doing an intense interval or circuit. So, my argument is that working out while fasting allows the body to burn more calories during AND after your workout.

Note: Just like the rest of my site, there are no “absolutes” here. There are a lot of approaches to get lean, this approach just makes sense to me (and it flat out works). The majority of you have already read my approach to cardio, but if you haven’t…here is a little mini-course I threw together: Low Body Fat Cardio

Important Message: Although this site has received 25+ million visitors, I am starting from scratch and abandoning it. This site is dated and old school looking, terrible to read on mobile, etc.

It's like a Ford Pinto compared to my new site...which is like a Ferrari. Click the link to head over to my new site.

Starting Over...R.I.P. Fitness Black Book!

Thanks for reading all these years!


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{ 23 comments… read them below or add one }

Ted February 21, 2009 at 2:18 pm

I read in Men’s Health that eating carbs after 6/7:00 p.m. makes them turn into fat. If I’m fasting during the day as you recommend, then why don’t the carbs I eat at night on carb days turn into fat? Or do they? I’m getting more defined pretty rapidly, but I’m wondering if there’s a better way to distribute my carb calories on my carb days?

Note: I do HIIT 4x per week, steady state 2x per day for 30 minutes, and I lift weights 5x per week. I alternate 2 days high protein/fat and 1 day high protein/carbs.

Also, are there times of the day when different types of carbs are better than others?

Also (sorry for so many questions) I heard that if I drink my post-lifting protein shake along with gatorade or fruit juice, the protein gets to the muscles faster and builds them faster. (I am trying to gain a LITTLE muscle–5 lbs or so. I’m 6’2″, 184 lbs, 12% bodyfat.

Thanks Rusty!
Your blog is a great resource and so much easier to follow than any of the other sources. I personally only enjoy eating if I get to eat as much as I want (which is a lot) and eating 6 small meals per day is absolutely miserable for me. I used to get hungry during the day…but I realize now that that was because I ate breakfast! My body doesn’t need that. I have a few veggies, nuts and fruits throughout the day if i get REALLY hungry, but usually there’s no issue. I feast at night! Lost 4 lbs in 2 weeks. 🙂
Keep writing!

CaRtz February 22, 2009 at 2:37 am

Hi Rusty/Everyone,

I’m trying to follow the fasted state approach before hitting the gym but there are times where I burp while doing cardio. Why is that? Is it because I sometimes eat a cookie before working out? =)

Thanks in advance to whoever can answer.


admin February 22, 2009 at 3:18 pm


There are simple carb strategies that work well…mainly this…eat the majority of your daily carbs 1-2 hours after your workout and go low carb the rest of the day (this is when you are tying to get extra lean). I wouldn’t drink gatorade or go out of your way to add in any extra carbs with your protein. Just drink the normal amount of carbs that the shake has.


Yep…it is that cookie that you are eating. If I burb while doing cardio, it is a sure sign that I have food lingering in my stomach and I ate too close to workout time.


CaRtz February 24, 2009 at 12:53 am

so that’s why! =)

Last question on this topic, Rusty: I don’t need to lose weight since I’m already thin (thanks to your guidance and all that cardio last year), do I still need to go to the gym on an empty stomache or am I allowed to eat 2-3 hours before? I did some back-reading in this site and I’ve learned that I can drink a protein shake before working out, is that the only thing I can take in?

I just don’t want to be too thin and look like an anorexic. Lol.

Thanks again for all your help!


Dennis February 25, 2009 at 7:48 pm

Dr. Ronald Klatz’ book, Growing Young with HGH, presents three graphs (p. 230) showing the relationships among blood glucose, plasma insulin, and plasma HGH. This is of particular interest to me because I am old enough to be very low in HGH and yet not accepting Mother Nature’s prescription for my age-related demise. I believe this information is of value to readers here, regardless of age. The research the Klatz cites was published in 1963. It describes a three stage feast-fast cycle with every meal. In the first stage, within the first hour after eating, blood sugar rises and insulin is released, which encourages the storage of excess carbs and fat. After the second hour (stage 2), GH is released and the levels of insulin and blood sugar start to fall. At this stage, GH acts to build up muscle protein, which is enhanced by insulin. In stage 3, more than 4 hours after eating (i.e., the fasting stage), GH levels remain high as insulin almost disappears. Stage 3 is when GH acts solely to mobilize the body’s fat stores for burning as fuel.
Fast forward to the present. An epub ahead of print, in the Journal of Strength and Conditioning Research, shows the effects of fasting on several performance categories in cyclists. To quote some of the main results, “The cyclists’ PWR (power to weight ratio) and body composition improved significantly, and their overall weight, fat weight, and body fat percentage decreased. Lean mass was maintained.” Furthermore, “Caloric restriction (up to 40% for 3 weeks) and exercising after fasting overnight can improve a cyclist’s PWR without compromising endurance cycling performance.”
I think this is pretty cool stuff that lends scientific credence to Rusty’s approach. These are just a couple of the items that I wanted to call to your attention. There is a LOT more to learn from scientific research on this subject. Indeed, a PubMed search today came up with 2,722 research references on “exercise AND fasting.” Whew!

admin February 27, 2009 at 11:30 pm


I still think you should go in fasted if it doesn’t bother you too much, just increase you caloric intake a bit the rest of the time to insure you aren’t too skinny.


Comments like yours are the “true gold” in this site! I love it when people add in great content into the comment section. I can’t encourage this enough. I am going to dig in to your site, because I can tell you really dig in to the subject.

Great Comments!


Emma March 17, 2009 at 3:32 pm

Wow, its so good to finally see someone writing about this! This is what I have been following, but I always felt kind of guilty, like I was doing something wrong whenever I exercised in a fasted state. Society drills in our heads that we need to eat before we exercise, but I always felt that my workouts were much more intense and enjoyable in a fasted state, and now I know why! Thanks for writing about this! I also had a question about pure brown rice protein powder. Is it a good protein source? I am vegan, so I am looking for something that can give me protein without giving me any carbs or fat. I am allergic to soy, so I can’t have any soy-based stuff.

Thanks for any help you can give me regarding this!

Johny April 1, 2009 at 2:06 pm

Will this fasting technique work with a swimming workout?

Boss Lady May 27, 2009 at 7:30 pm

Can I fast for 3 days and workout at the same time?

Rafi Bar-Lev September 27, 2009 at 7:52 am


Do you think the fasted state “boost” you’re talking about here is because when in a fasted state, our bodies are programmed to give that extra boost so we can acquire food for ourselves? That’s the first thing that came to my mind when I thought about why we would have energy despite fasting.

Great post!


alex silva November 4, 2009 at 8:28 pm

First, I’m not against fasting (if done correctly) since I do it (on controlled “environment”, in the morning and low intensity/not more than 2hrs). But a lot of what it is said here in favor of feasting is not accurate. Very careful with fast training. If your goal is to loose fat, that could work but remember one of the biggest truths in fitness/nutrition: the fat burns in the carb’s pyre, i.e. if you don’t have enough carb’s your body won’t have energy to lipolysis (turn fat into nrg). Also, if you don’t eat, your l-carnitine levels are low and fat won’t be carried into the cells to be turned into nrg (you can always take l-carnitine as suplement).
When you work out fasting, after 30 or 45 minutes (depending on the individual and/or the workout) your muscular glycogen ends and your body will use fat (on low intensity workout, aerobic) but also protein as an nrg source, i.e. will start a catabolic process. You can see the dilema/irony here: you build up some muscles but others are being destroyed to feed them…
you can work out fasting but not for a long period/high intensity or your output will decrease and acidosis will occur, leading to cramps and other (more) serious fx. A single fasting workout can’t produce two results (fat burn and lean muscle gain). Talk with someone credited, even better if it’s someone working with athletes. If you feel sick eating before workout, take 1 or 2 pcs of fruit one hour before – no burp or throwing guaranteed

nicole January 26, 2010 at 3:04 pm

Hey rusty,
so more to clarify than anything. i instruct back to back spin classes from 5-7pm on a wed night.
that day on waking i do 1,000 skips, then 1/2hr pilates before eating half a cup of oatmeal with 1 scoop protein powder (1/3 serve-30 cals) if i then go 5 hours and eat a 180cal protein bar or 85g tin tuna and some baby greens for lunch will i be ok to be up the front of 40people whilst doing so much high intensity cardio without crashing and burning? typical diet at the moment never goes over 1000 cals so i don’t have that many stores so will prob be reasonably depleted of glycogen.mentally i can do it tho so is the slight calorie decrease in performance worth it for the pay off of cardio in a fasting state?
thanks so very much!

jason May 18, 2010 at 5:45 pm

I have to agree on the intense workouts that can be performed in a fasted state. The way I have my IF set up, I’m fasted for 15-16 hours(aside from a pre workout shake) before I workout. My energy levels are surprisingly high. Although the promise of carb goodness right around the corner is definite motivation.

Chris June 10, 2010 at 11:19 am

hi i am a personal martial artist/trainer/nutritionist standing at 6’2″ 180 lbs, 7% bodyfat, so you can picture that i am lean and packin muscle >=] i am a strong believer of this, i have gone days fasting and still do strength training to a high intensity, and have seen amazing results from this. I get such an energy boost that i dont need as much sleep as before. 4 months back I was 215, with a little extra muscle but my body fat was 23% thats when i decided to lose some weight…after jogging like a marathon runner and lifting and eating wisely, i only went down to 205lbs…for some reason i was stuck at 200 to 205lbs and couldnt drop anymore weight! I got so dissapointed I went back up to 212lbs…that’s when my nutritionist co worker advised I should fast! It was the best thing I could have done…my abs and even my serratus anterior muscles are cut up! I am shocked because I would work so hard to see those mucles show and never seen them until i fasted! Its clear to me that this method clears the body of toxins and bodily pollution so the stomach shrinks allowing me to see endless definition on my core and even chests!
here is a link of a video of how i like to train while fasting!
One hand pushups and even finger pushups!
I feel so light on my feet and hands!

Rob January 18, 2011 at 5:50 pm


I was wondering what your thoughts are on using BCAAs pre-workout after going through a 10-20 hours fast?

Ryan lilliard June 25, 2011 at 8:39 pm

Say if i try in a fasted state everyday 5 times a week, on the 5th day i usually do abs, could i maybe do abs and say a 20minute cycle on the bike, or would that lead to muscle breakdown due to not eating for say 12hours?

Thanks in advance

Niko - noeXcusefitness December 5, 2011 at 4:41 pm

I agree with the principle, my only issue is my lifestyle dictates that I train at about 8:00pm each night, so I can’t train in a fasted state (otherwise I would never eat at all). As an alternative I am trialling carb back loading, where basically I only eat about 30grams of carbs during the day. I only consume carbs after my training session (in large amounts). I am trialling this process to see how it affects my insulin levels and in turn my ability to gain muscle whilst loosing fat. I will let you know how it goes.

Chastina July 13, 2012 at 10:03 am

Greetings Mr. Moore,

I am so happy I found your blog. I have been criticized all my life for eating the way I do (I only eat when I am hungry and I hardly ever need food before workouts) and, even though I have always been very fit, some have even said I have an eating disorder…5’9 and 155lb, I do not have an eating disorder.

I find it a little funny that friends and gym patrons will ask me about my eating habits (stating that they are lost and confused about nutrition) but as soon as I start to go over how I eat they become instantly dismissive, and some even flip from inquisitive listener to disapproving nutrition experts; “No wonder you are so thin, you are starving yourself!”

I recently started training again and I love my gym but the trainers there are…well, they do not have the same views. I work with a trainer (and even though I explained my way of life and eating, he still pressed that I should stick to his plan) and the eating regiment he put me on was making me sick, as well as made me incredibly lethargic during my workouts (not to mention it felt like I had a rock in my stomach), and worst of all I gained 10lbs in the three months of training. I sat down with my trainer and we agreed that I was getting stronger (can easily pull a sled with 500lbs on it) but I was not slimming down, I was bulking up.

I have been trainer free for 5 weeks now and I dropped the 10lbs, my energy is sky high, and my skin is glowing. My boyfriend told me that I was being too patient with the trainers and should have dropped them right away…should have listened to him.

I like my gym and I really do love my the employees there (great people) and because they are great people communicating that my style of fitness is different but not wrong is easily accepted by them…if only because of the speedy change they have witnessed first-hand.

It is refreshing to read that there are others like me and to see how fit they look as well. Thank you for posting such an interesting blog on a subject most choose to ignore or dismiss. I also love all the responses, great questions.


stacy August 6, 2012 at 3:45 am

In theory I love the idea of working out in a fasted state/first thing in the morning. However, in practice I’ve found my performance is terrible, I get dizzy, see stars, and generally have a horrible workout.

If I exercise around sunset, I’m terrific.

My question is if it’s been 5-6 hours since you’ve eaten, is that still a ‘fasted state,’ or must it be a full 12 or so?

I am only going by anecdotal evidence, but I find men in general have a much easier time with surviving hunger. Most women I know need to eat frequently.

Jason August 26, 2012 at 2:30 pm

Stacy, how much are you eating during your window the day before? If you do not consume enough healthy calories your body will most definitely shut down mid workout. Also, what are you eating during your window? (window being the time between fasting where you consume your food for the day.) Also, how much water are you taking in daily? I have not heard of anyone having the same issues you describe.
If your already at a healthy body weight.

To awnser your question, from my research I am finding most people describe thier “fasting time” as anywhere from 8-24 hours pre workout. 5-6 hours is most likely not enough time, try timing your fasting time so that you can sleep during the majority of it. Remember water is ok during your fasting, a big gulp will curb any hunger pains temporarily before bed. In some extreme cases I will also chew gum to help.

Jason August 26, 2012 at 2:39 pm


Thank you so much for this post. As someone with a very busy schedule (new baby, 2 jobs, student) eating HEALTHY snacks every 2-3 hours is nearly impossible. I really like the idea of IF and started it yesterday after a few hours of research. I found this blog post to be the most effective and to the point for information.

I stopped eating last night at around 9pm, and woke up today and left for a long hike and bike at around 10:30. I must say, I was shocked at the results. I felt as though I had endless stamina and energy. I did not feel sick or hungry at all. And for some reason even found myself rarely reaching for my water bottle. It blew me away. I really like the idea of this approach and plan on sticking with it for the next 4 weeks to see how it turns out. I just have a few questions for you, I will try to keep them short and to the point. My goal is to shed this horrible spare tire ive been carrying for the last 8 years. I have lost a total of 65 poounds, but cant seem to shake off this stored fat. Im hoping IF will help.

Is it ok to plan my daily eating around IF? if so, should I take one day a week where I attempt to eat regularly?

Is a small amount of caffiene ok pre workout? I find that it makes a world of difference for me in my morning workout, as I am not a regular caffiene user.

And finally, what is the deal with these “sugar substitutes” are any of them “healthy” in the sense that they dont trigger insulin response the same as normal sugar?

Thank you for your time, I look forward to reading more of your posts! keep it up!

Jason August 26, 2012 at 3:02 pm

Thank you Mark Sisson, found the awnser to my question regarding artificial sweeteners.

Fitness Wayne | Paleo and Strength Training November 20, 2012 at 8:34 am

I have been paying more attention to this lately because I have been doing a lot of fasting to get lean. I have noticed a decrease in performance when I fast but I think it might be a mental barrier holding me back.

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