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A.M. Cardio Myth Exposed

Performing Cardio Before Breakfast
Is said to burn fat fast, but is it true?

The Myth Of Cardio Before Breakfast—Debunked!

We've all heard it before, the theory that doing cardio on an empty stomach after an overnight fast sends fat burning into overdrive. If only it were true.

In 1999, Bill Phillips published his bestselling fitness book, Body-for-LIFE, which promised a body transformation in 12 weeks.

In his cardio chapter, Phillips put forth the theory that performing aerobic exercise first thing in the morning on an empty stomach maximizes fat loss.

The rest, as they say, is history. Ever since, every Tom, Dick, and Harriett has been shuffling off to the treadmill each morning before raising so much as a spoonful of oatmeal to his or her lips.

His rationale was as follows: A prolonged absence of food brings about a reduction in circulating blood sugar, causing glycogen (stored carbohydrate) levels to fall. That leaves your body no choice but to rely more on fat, rather than glucose, to fuel workouts.

Moreover, the low insulin levels associated with fasting are conducive to fat breakdown, increasing the availability of fatty acids to be used as energy during the exercise session.

The strategy became popular with bodybuilders and other physique athletes striving to get as lean as possible. After all, who wouldn't want to burn more fat while expending the same amount of effort?

After all, who wouldn't want to burn more fat while expending the same amount of effort?
After all, who wouldn't want to burn more fat while expending the same amount of effort?

I'm sorry to say it, but the whole zombie-before-dawn-at-the-gym thing was a big mistake.

Here's why:

Measuring Your Morning Cardio And Metabolism

First and foremost, it's shortsighted to simply look at the number of fat calories burned during an exercise session. Your metabolism doesn't operate in a vacuum.

Rather, the body continually adjusts its use of fat and carbohydrate for fuel depending on a variety of factors.

As a general rule, if you burn more carbohydrate while exercising, you'll ultimately burn more fat in the post-workout period and vice versa (1).

Which Begs the Question:

"Who Cares if you burn a few extra fat calories while exercising, if an hour later, the ratio shifts to a greater carbohydrate utilization?"

In the end, it doesn't make a bit of difference. You need to evaluate fat burning over the course of days -- not hour to hour basis -- to gain a meaningful perspective on its impact on body comp.

Let's say you're a skeptic, though, and figure it's better to burn more fat now rather than later. A bird in the hand is better than two in the bush, right? Well, not in this case.

True, the research does show that fasted cardio can increase fat utilization during exercise compared to performing cardio in the fed state. Except this only occurs at very low levels of training intensity.

During moderate-to-high intensity levels, the body continues to break down significantly more fat when fasted compared to after you've eaten.

So far, so good. Unfortunately, the rate of breakdown exceeds your body's ability to use the extra fatty acids for fuel. In other words, you have a lot of extra fatty acids floating around in the blood that can't be used by working muscles.

Ultimately, these fatty acids are repackaged into triglycerides post-workout, and then shuttled back into fat cells. So you've gone to excessive lengths…only to wind up at the same place.

During moderate-to-high intensity levels, the body continues to break down significantly more fat when fasted compared to after you've eaten.
During moderate-to-high intensity levels, the body continues to break down significantly more fat when fasted compared to after you've eaten.

Fasted Cardio Doesn't Mean Fast Results

Okay, so perhaps you're thinking that you'll just perform fasted low-intensity cardio to burn those few extra fat calories. Nice try, hot shot. You see, training status also has an effect on the fasted cardio strategy.

Namely, if you exercise on a regular basis -- and if you're reading this article, that likely includes you -- the benefits of fasted cardio on fat utilization are negligible even at low levels of intensity.

Horowitz and colleagues (2) found that when trained subjects exercised at 50 percent of their max heart rate, an intensity that equates to a slow walk, there was no difference in the amount of fat burned--regardless of whether the subjects had eaten.

These results held true for the first 90 minutes of exercise; only after this period did fasted cardio begin producing a favorable shift in the amount of fat burned.

So unless you're willing and able to slave away on the treadmill for a couple of hours or more, fasted cardio provides no additional fat-burning benefits, irrespective of training intensity.

Fasted cardio makes even less sense when you take into account the impact of excess post-exercise oxygen consumption. EPOC, commonly referred to as the "afterburn," represents the number of calories expended after training. Guess what? Eating before exercise promotes substantial increases in EPOC (3).

And guess where the vast majority of calories expended in the post-exercise period come from? You got it, fat!

Take Home Message:

"More epoc equals more fat burned. This favors eating prior to performing cardio."

There's also the intensity factor to consider. Research indicates that high-intensity interval training is more effective than steady-state cardio for fat loss (Bill Phillips actually recommended HIIT as the preferred type of cardio in his book).

Ever try to engage in HIIT session on an empty stomach? Bet you hit the wall pretty quick. In order to perform at a high level, your body needs a ready source of glycogen; deplete those stores and say goodbye to elevated training intensity.

The net result is that fewer calories are burned both during and after exercise, thereby diminishing total fat loss.

On top of everything, fasted cardio can have a catabolic effect on muscle. Studies show that training in a glycogen-depleted state substantially increases the amount of tissue proteins burned for energy during exercise (4).

Protein losses can exceed 10 percent of the total calories burned over the course of a one-hour cardio session -- more than double that of training in the fed state (5).

Any way you slice it, sacrificing hard-earned muscle in a futile attempt to burn a few extra calories from fat doesn't make a lick lot of sense--especially if you're a bodybuilder!

To Cardio or Not to Cardio Before Breakfast

Summing up, the strategy to perform cardio on an empty stomach is misguided, particularly for physique athletes.

At best, the effects on body composition won't be any better than if you trained in a fed state; at worst, you'll lose muscle and reduce total fat loss. So if you should eat…what should you eat prior to cardio?

The answer depends on several factors, including the duration and intensity of training, the timing of previous meals before the cardio session, and individual genetics.

A good rule of thumb is to consume approximately 1/4 gram of carbohydrate and 1/8 gram of protein per pound of your ideal bodyweight (which may differ from your actual weight).

For example, if your ideal bodyweight is 200 pounds, then your pre-workout meal should consist of approximately 50 grams of carbs and 25 grams of protein. A shake made of natural fruit juice and whey protein is a good option, particularly if cardio is done early in the morning before breakfast.

Of course, individual response to macronutrient intake will vary, so use this recommendation as a starting point, and adjust accordingly.

References
  1. Hansen K, Shriver T, and Schoeller D. The effects of exercise on the storage and oxidation of dietary fat. Sports Med 35: 363-373, 2005.
  2. Horowitz JF, Mora-Rodriguez R, Byerley LO,and Coyle EF. Substrate metabolism when subjects are fed carbohydrate during exercise. Am J Physiol 276(5 Pt 1): E828-E835, 1999.
  3. Lee YS, Ha MS, and Lee YJ. The effects of various intensities and durations of exercise with and without glucose in milk ingestion on postexercise oxygen consumption. J Sports Med Physical Fitness 39: 341-347, 1999
  4. Blomstrand E, Saltin B. Effect of muscle glycogen on glucose, lactate and amino acid metabolism during exercise and recovery in human subjects. Journal of Physiology. 514:293-302, 1999
  5. Lemon PW and Mullin JP. Effect of initial muscle glycogen levels on protein catabolism during exercise. J Appl Physiol 48: 624-629, 1980.

Related Articles

About The Author

Brad Schoenfeld, M.Sc., C.S.C.S., is an internationally renowned fitness expert and widely regarded as a leading authority on body composition.

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AST88

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AST88

****, i know loads of fitness models that live by fasted cardio. I have also seen great results from it. Not really sure what to think now though.

Feb 18, 2012 7:15am | report
theodorusrex

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theodorusrex

If it works for you, keep doing it.

Sep 5, 2013 3:16pm | report
ashokrudraraju

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ashokrudraraju

i found another article here on bb.com ....(http://www.bodybuilding.com/fun/topicoftheweek20.htm) ...which says otherwise
.....

if u guys are confusing me..... these two articles totally contradict each other ....

Mar 12, 2012 4:31am | report
muratjohn

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muratjohn

well, this article is from 2011 and the one you found is from 2005. so i would say newer is better :)

Mar 28, 2012 5:57pm | report
m.keetonma

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m.keetonma

I am astounded, but glad to hear it, because I can't do cardio on an empty stomach anyway. I need at least a breakfast bar or a banana before running in the morning.

Mar 12, 2012 4:56pm | report
DobieQueen

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DobieQueen

stick to more protein if you do cardio in the mornings and have it as your last meal at night before bed... banana and bars are usually high in sugar... good quality protein and water work wonders... add a potassium and taurine supplement to the shake and you have even better benefits of a banana in your shake. :)

Jan 23, 2013 6:15am | report
snarvekar20

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snarvekar20

I would say this is not true. It is a general principle in biochemistry that the liver, when low on glycogen will use adipose tissue as an energy source. Therefore in the morning when you have fasted for some amount of hours, levels of glycogen are low. Meaning the liver, will use adipose tissue as a source of energy to put in glucose to the bloodstream for muscle tissues to uptake.

Jun 3, 2012 3:50am | report
snarvekar20

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snarvekar20

unless you have minimal bodyfat, then yes you should probably eat something. But if you are trying to lose weight/fat like many people who do cardio in the morning on an empty stomach are-- then doing cardio on an empty stomach is beneficial because then you will burn adipose tissue for energy

I am waiting for your rebuttal to this.

Jun 3, 2012 3:52am | report
fdashty

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fdashty

I see where you are going with this and you are basically right but, think simpler than this...it doesn't matter how the energy is stored and what form it is in. once that energy is in your body, IT IS IN YOUR BODY. One of the points of this article is to explain that our bodies are so efficient at converting fat (glycerol) into glycogen/glucose and putting it into our bloodstream, resulting in high levels in the blood glucose during cardiovascular exertion that exceed that actual need. The remainder of glucose/glycogen is then repackaged back into fats and the cycle continues. The article explains the rest...

Apr 23, 2014 3:44pm | report
Kerriak

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Kerriak

I'm glad to see that something I was't a fan of was debunked.
Not eating before cardio, No Bueno!

Jul 31, 2012 9:34am | report
EbwinLeon

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EbwinLeon

**** , Fasted Cardio , Carb cycling , Intermittent Fast works and i even gained lean muscle of it

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Aug 1, 2012 8:11pm | report
adrianrome

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adrianrome

nice article... I am not used to do those type of cardio exercices... but I will make them, in this way I will loose a lot of my BF percentage :D

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Sep 7, 2012 4:22am | report
Sheishmustache

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Sheishmustache

What if I have two breakfasts? one very light and the "main" one, if you will. The very light is fruit and a protein shake, then I do the cardio, not enough to have me satisfied for a long time, but I don't go there starving. Is it better this way than a "full" breakfast then cardio? is it the same? is it just as the cardio on empty stomach?

Oct 5, 2012 8:15pm | report
ConanOB911

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ConanOB911

I do HIIT on an empty stomach and don't hit the wall pretty quick.
I actually deadlift, squat and press on an empty stomach and feel better than ever.

Oct 10, 2012 9:24am | report
admdc01

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admdc01

If you have a breakfast (150gr broccoli 100gr turkey) at 06:30am and you work out at 11:30am, is it on an empty stomach ? Because if it's the case, my experience and body transformation will tend to proof the contrary ;-)

Oct 13, 2012 2:42am | report
twdowney

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twdowney

Why're you going that long without eating?

Feb 13, 2013 1:02pm | report
Babakg

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Babakg

hmmm i dont like this. i see many bodybuilders and i myself have seen results from fasted cardio.

who's to say that in a few years another article will come out debunking this??

Oct 17, 2012 11:34am | report
bigboi86

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bigboi86

Dr.Oz was talking about on one of his shows based on a study- If you do cardio in the morning after eating breakfast then you will keep muscle but burn fat. If you do fasted cardio then you will lose both muscle and fat.

Oct 26, 2012 12:00pm | report
imthepsychic

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imthepsychic

i read on t nation that people have a carb cut off time plus fasted steady state cardio to get good results. and i think from another site to take a no carb iso to preserve the muscle from catabolic effects.

Nov 1, 2012 7:35pm | report
glenndrei

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glenndrei

I recently have been given a CLA supplement,and been using it for a couple of weeks now, can't afford pricey whey, casein and other fat burning supplements: cut to the chase( and 'nuff bout my meager financial resources and prob's) i definitely eat 3 times per day, if this is my lifestyle pattern along with CLA alone as a fat loss supplement, what should I modify in terms of what should I eat and some tips on how to speed up my "shredding process"??
Look forward to hear from you guys!

Nov 4, 2012 10:55pm | report
mulletboy1

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mulletboy1

I think some people are missing the point. It's the EPOC that is most effective on a fed Session. The one thing to realize is that not jump starting your metabolism first thing induces the body to store more when you do eat. Yes it is done all the time where people are loosing weight from a fasted session, but over time you will feel run down and your intensity will diminish compromising your intensity and your metabolic rate. Conclusion, have your body running at optimum level to burn more through out the day and have more bounce in your step by not depriving it.

Nov 8, 2012 5:36am | report
Raymitch7410

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Raymitch7410

Light intensity pre-breakfast cardio works. Period. It also easily lets you do an additional workout later in the day. I've personally seen great results, and have seen others get great results.

Light Cardio in a fasted state is easy to do, an easy habit to get into and an easy routine to sustain, all while being effective.

Nothing in this article "debunked" the fact that it works and has multiple health benefits including but not limited to weight loss.

The National Center for Biotechnology Information
J Physiol. 2010 Nov 1;588(Pt 21):4289-302.

http://www.ncbi.nlm.nih.gov/pubmed/20837645

**Here is a plain language article covering the study**

http://well.blogs.nytimes.com/2010/12/15/phys-ed-the-benefits-of-exercising-before-breakfast/

Nov 8, 2012 6:54pm | report
SvenErik73

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SvenErik73

Ray, you may be mis-quoting the first reference from the National Center for Biotechnology Information.

This article is testing fast versus fed cardio with the specific aim of determining which on has a more positive effect on insulin sensitivity and whole body glucose tolerance.

I quote from their conclusion.

"In this study we administered a hyper-caloric HFD to healthy subjects and demonstrated for the first time that early morning exercise in the fasted state is more potent than an identical amount of exercise in the fed state to improve whole-body glucose tolerance, as well as to induce beneficial adaptations in muscle cells that eventually may contribute to improved peripheral insulin sensitivity."

As for the NY Times article, it becomes a case of whom to believe. The Glasgow University Institute of Cardiovascular and Medical Sciences conducted a similar study between fasted and fed and their results came back as negligible.

Mind you the Glasgow study was interesting as their subjects (male) had BMI's over 25 whilst most other studies admit to using young, healthy, physically active subjects.

Personally I eat a small amount prior to my workout as working out on a totally empty stomach leaves me felling flat before I even lift the first weight.

Jan 28, 2013 7:41pm | report
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dogfight

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dogfight

I have also had luck with IF eating and fasted cardio. Not sure why they think its a myth? if you do intense cardio for 15 mins 4 times a week and dont eat for 2-3hrs afterward you will see results combines with a weight program. And you will not lose muscle mass if your lifting heavy. 5x5 with a few high rep sessions will balance this out.

Nov 17, 2012 1:33pm | report
Zeuli312

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Zeuli312

Did anyone else realize on the previous page where you clicked on this article to read, the article right next to it states the complete opposite. So they wrote how fasted cardio was the way to go, then someone else wrote an article saying its not true, all published by bodybuilding.com, make up your mind, WTF

Dec 2, 2012 4:42pm | report
Showing 1 - 25 of 36 Comments

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