Fasted Cardio Roundtable

Featuring Christian Thibaudeau, Lonnie Lowery, PhD, David Barr, and Dr. John Berardi

It's a subject that always leads to a heated debate: cardio performed in the morning on an empty stomach. Is this the fastest way to lose fat, or is it a sure way to "eat up" all that hard-earned muscle? We sat down with four T-Nation experts and decided to find out.

T-Nation: Several years ago, fasted cardio was touted as being the quickest way to drop excess body fat. The general suggestion was to wake up, drink some water, then do your cardio before eating.

But then many experts started harping about muscle loss in this state. They said that fasted morning cardio was just too catabolic. So, fasted energy systems work: good or bad? Lead us off, Lonnie!

Dr. Lonnie Lowery: From a biological perspective, fasting for a few hours or overnight does result in much lower insulin concentrations in the blood. This facilitates fat oxidation because insulin, as a necessary storage hormone, indirectly degrades the secondary messenger "cyclic AMP" within adipocytes or fat cells.

Cyclic AMP is a signal to break things down within a cell such as glycogen (stored carbohydrate in muscle tissue) and yes, triacylglycerols (stored fat in muscle and fat tissue). So in weight loss situations, well-timed lower insulin concentrations can be helpful.

There are even data suggesting that its effects linger for many hours, making the first few waking hours an advantageous target. That is, we don't always want cAMP being degraded, and prior to breakfast it won't be. This isn't to say insulin is bad by any means; we need it to preserve protein balance and maintain muscle mass, as well as for other critical bodily functions. We just don't need it elevated at certain times.

Conversely, cAMP can indeed be preserved by methylxanthines in coffee and tea, as they interfere with a cAMP destroyer called phosphodiesterase. So why aren't heavy coffee/tea drinkers all extremely lean? Because much of the fat that's broken down and mobilized circulates throughout the bloodstream of a sedentary person and eventually gets re-esterified or rebuilt into stored fat. It doesn't get taken up by contracting skeletal muscle and burned on its trip through the blood.

T-Nation: So mobilizing the fatty acids from adipose tissue isn't enough?

Dr. Lowery: No, moderate intensity exercise (muscle contractions to take up the circulating fatty acids) is necessary.

It should also be noted that exercise itself, particularly after fasting for a couple of hours, stimulates cAMP naturally by way of hormones such as epinephrine (adrenalin). This is a better long term approach to fat loss because excessive, ongoing coffee/caffeine intake can lead to higher cortisol concentrations over time, which ironically could worsen central body fat gain according to relatively new research. Not to mention cardiac arrhythmias (skipped beats), sleeplessness, anxiety, and the other classic side effects of excess caffeine.

Lastly, the intensity of the exercise bout affects whether fat or carbohydrate is used as a fuel source. This is the well-known crossover effect. Intense exercise is too rapid/demanding to allow for fat breakdown/oxidation. Carbohydrate (glycogen) must be used. Hence, fasting or drinking a cup of coffee prior to intense exercise isn't as helpful.

There's a school of thought that moderate, non-panting exercise in a mostly-fasted state can be done frequently and effectively for direct fat burning and subsequent body composition improvements. A cup of coffee or green tea would be helpful in such a situation biochemically, although there's no research to my knowledge directly investigating the all-important end result of better fat loss over time.

And there's an opposing and equally valid school of thought that more intense exercise also leads to leanness over time, as well as cardiovascular benefits. The choice becomes situation specific.

Now, when physique is paramount, I prefer fasted or mostly-fasted (half a scoop protein in water or coffee), non-panting AM cardio for 45-75 minutes that facilitates rather than harms recovery. (About 60% of VO2max keeps one below neuro-endocrine thresholds.)

It doesn't feel like a workout because it's not meant to be one. It doesn't add to training volume or risk overtraining and staleness, which, by the way, hits about half of individual sport athletes.

This approach also directly mobilizes and burns fat stores without draining biological resources toward cardiovascular adaptations. I don't want to be a runner. (Many bodybuilders don't care about much other than highly visible muscle mass.)

T-Nation: Holy crap, Lowery, leave something for the others to talk about! Okay, Barr, let's hear your opinion. Is fasted cardio good or bad?

David Barr: It's horrible! We should never be completely fasted for any reason. As soon as you're protein starved, you start breaking down muscle, which directly contradicts our goals, whether they be fat loss, muscle growth, or athletic performance.

Throw a catabolic activity like cardio on top of that and you're practically begging to waste away. Fortunately, it's not too difficult to prevent this muscle catabolism, because all we have to do is eat a little protein.

When it comes to cardio, eating protein before the session will preserve muscle tissue without impacting on fat loss. While some of the protein will be "burned off" as energy, the amount of muscle saved will more than make up for any minor alterations in fat calorie expenditure. Metabloic Drive® Protein is the perfect protein for this, because its slow entry into the blood limits the amount of amino acids that'll be used for energy (i.e. oxidized).

As for the other macronutrients, it's fine to be fasted as long as you're strictly going for fat loss. Understand that at first you'll feel the energy depravation, and may even want to prematurely cut your cardio short. If this occurs, then using something like Spike® or especially Hot-Rox® will not only enhance energy levels, but directly increase fat loss.

T-Nation: Thank you, you Biotest whore. What are your thoughts on morning cardio, Thib?

Christian Thibaudeau: Well, I'd first like to say that nothing is 100% good or bad. Morning cardio is no exception. When faced with such a subject, I always end up doing a pros and cons list and go from there. This way I can better organize my own opinion and give the readers a chance to make up their own minds.

First, let's look at the pros of fasted morning cardio:

Pro #1:

Morning cardio could potentially increase the amount of free fatty acids (FFA) used up as fuel. This is not due to performing cardio in a glycogen depleted state though, since this isn't happening here. Unless you go to sleep in an already depleted state, you won't wake up in such a state.

During sleep almost 100% of the energy expended comes from fatty acids because of the extremely low intensity of the activity and because of the natural hGH burst which occurs 30 minutes or so after you enter the deep sleep phase (hGH increases fatty acid mobilization).

So you really aren't depleting your intramuscular glycogen stores during the night. You might be tapping your hepatic glycogen stores slightly, but even then that can't account for much since at best this contains maybe 200-300kcals of stored energy. So it's a fallacy to believe that when you wake up your muscles are emptied of their glycogen.

However, since fat is the primary energy source during your sleeping period, chances are that upon waking you have a greater amount of free fatty acids available. Since you don't have to mobilize them (they're already freed up) they become easier to oxidize for fuel and are thus more readily used up during morning cardio.

Pro #2:

Fasted morning cardio could also potentially be glycogen-sparing for the same reason as stated above: the greater availability of FFAs reduces the reliance of glycogen for fuel during low-intensity energy systems work.

Pro #3:

Fasted morning cardio could lead to an improved fatty acid mobilization during exercise and increase insulin sensitivity afterwards. This might be true of exercise at a low level of intensity (50-75% of max VO2) since this decreases insulin levels via the stimulation of adrenergic receptors. A lower insulin level can increase fatty acid mobilization.

However, a higher intensity of work (above 75% of max VO2) can actually have the opposite effect. So in that regard a moderate or even low intensity of work would seem to be superior in the morning as far as fat mobilization goes. (Galbo, 1983, Poortmans et Boiseau, 2003)

To counterbalance the reduction in insulin production during exercise at a moderate intensity, insulin sensitivity is increased, especially in the muscle. Since insulin sensitivity is already high in the fasted state, morning cardio could allow you to significantly increase glycogen storage and reduce the storage of carbohydrates as body fat.

So in that regard, morning cardio in a fasted state could increase fat loss during a cutting period and allow a bodybuilder in a bulking phase to significantly increase his carb intake without gaining more fat.

T-Nation: Okay, all that sounds good, so what are the cons?

Thibaudeau: If fasted state cardio could potentially increase fat mobilization, it's also potentially more catabolic to muscle tissue. This is due to an increase in cortisol production during fasted exercise. Since cortisol levels are already high in the morning, this could lead to more muscle wasting than during non-fasted cardio.

In fact, cortisol levels could increase muscle breakdown and the use of amino acids as an energy source. This is especially true if high-intensity energy systems work is performed. If an individual uses lower intensity (around 60-65% of maximum heart rate), the need for glucose and cortisol release are both reduced and thus the situation becomes less catabolic.

I personally do believe in the efficacy of morning cardio, but not in a completely fasted state. For optimal results I prefer to ingest a small amount of amino acids approximately 15-30 minutes before the cardio session. A mix of 5g of BCAA, 5g of glutamine (yeah, I know that Dave Barr won't agree with me on this!), and 5g of essential amino acids would do the trick in preventing any unwanted muscle breakdown.

However, I'll also play devil's advocate and say that morning cardio won't be drastically more effective than post-workout or afternoon cardio work when it comes to fat loss. Personally, I prefer to split up my cardio into two shorter sessions (morning and post-workout).

T-Nation: Interesting. Now let's hear what Berardi has to say.

Dr. John Berardi: Geez, is there much left to say? These guys hogged all the sciency sounding arguments so I'll just shoot straight and to the point.

I wish there were a simple "good or bad" answer to this question, but there isn't. Things are never this simple. After all, I believe that AM cardio performed on an empty stomach is incredibly awesome for fat loss in certain situations and should be avoided at all costs in others. How's that for an answer?

Here are the circumstances in which I think fasted cardio is awesome and in which I think fasted cardio isn't so awesome:

  • AM fasted cardio should be done when you're only interested in body comp and you have either a mesomorphic or endomorphic body type.
  • AM fasted cardio should never be done when you're an anaerobic athlete requiring strength and power or you simply have an ectomorphic (naturally skinny) body type.

To make it even simpler, here's a chart to determine if AM fasted cardio is for you:

Is AM fasted cardio for you?    
You're an ectomorph No  
You're a mesomorphic strength/power athlete No  
You're an endomorphic strength/power athlete No  
You're a mesomorphic bodybuilder/exerciser Yes  
You're an endomorphic bodybuilder/exerciser Yes  

T-Nation: Good points, JB. Okay, that was a lot to absorb. Does anyone have any comments or brutal attacks on the other experts' answers?

Dr. Lowery: First a brutal attack: Dave Barr is an insulin-oholic. Forget Alcoholics Anonymous (AA), he should start IA for size-crazed bodybuilders who can't get away from their obsession to take up more space at any cost. But what do you expect from a guy who lives on Pop Tarts?

Okay, enough slamming. Actually, David is a very bright, very cool guy and I identify with his need for size. I'd personally be hesitant though to indulge in large amounts of protein while attempting to perform mild cardio in a mostly-fasted state.

Proteins are certainly insulinogenic, even if there's co-stimulation of glucagon. That creates the risk of body fat protection prior to our uphill walking. But David wants to spare muscle at all costs (even if it's potentially slowing fat loss) so I do know where he's coming from! It's just interesting to see our individual perspectives and how they affect our reasoning.

Christian and I are on the same page, I think. I admit that I too have turned to 5g glutamine and/or a few grams of protein out of muscle preservation paranoia. Can I prove that it helps? Nope. But the underlying physiology is convincing. It's like the argument as to whether early AM cardio (or longer duration cardio) is really superior to other types. You won't find it in the literature, but biochemically it's compelling. I want to torch fat directly.

Lastly, I think John summarized pretty well what we've all been saying. The choice of fasted cardio is relative to goals, intensity, and even how we define "fasted" (i.e. a few grams of protein looks helpful in the early waking hours). I agree that no bodybuilding-oriented ectomorph in his right mind should be prioritizing fat loss over muscle preservation!

I'd reiterate though that there are indeed performance athletes (e.g. football linemen) who could use fat-specific weight loss but are nonetheless power athletes of a sort. These guys could use light to moderate aerobic work/fat loss that doesn't add to their existing load of two-a-days with the team, with concomitant weight room efforts.

Thibaudeau: Good points, Lonman. In regard to the adequacy of morning, semi-fasted cardio for different types of individuals and situations, I think JB brings up an interesting point. While I do agree with his general overview, I'll side with Lonnie's opinion that some performance oriented athletes can indeed perform AM fasted energy systems work.

Endomorphs can indeed thrive on morning cardio provided that the intensity and duration are both reasonable. Performing a low-intensity activity (for example, walking on the treadmill at 3.0mph with a 10 degree incline at around 65% of your max heart rate for 30 minutes) will hardly have any negative impact on subsequent performance and muscle mass.

This is especially true if a proper pre and post-cardio nutrition approach is used. Obviously, if the intensity and/or duration are much higher, then yes, morning cardio can be destructive to performance and muscle mass.

I personally found that athletes actually perform better a few hours after a low-intensity/short-duration morning cardio workout. It could be psychosomatic or due to a "loosening up" of the body, I don't know. But I've seen it time and time again with my athletes.

I'm currently training a bodybuilder who's four weeks out as we're doing this roundtable and he's right at 30 minutes of morning cardio at 65%. He trains four hours later and he's constantly increasing his front squat and several other lifts.

I'd like to bring up one other point: energy systems work can be detrimental to muscle mass and performance regardless of the time it's performed if intensity or duration is excessive. This is why I always prefer to use a split cardio approach. If an athlete is scheduled for 60 minutes of low-intensity cardio on a day, I'd rather have him perform two daily sessions of 30 minutes. Morning cardio allows me to do that without messing up the individual's schedule too much.

In any case, if body composition is the goal, I don't recommend ever going over 45 minutes per session unless we're well below the 65-70% intensity mark (for example taking a long, slow walk in the woods).

Barr: If the insulin-oholic whore may have a word... Lonman, I see what you're saying about proteins stimulating insulin, but there's another reason why I opted for Low-Carb Grow! before the cardio. That's because it's very unlikely that the prolonged trickle of amino acids, from the casein into our blood, will increase insulin levels. Subsequently, it won't inhibit fat loss! Sweet deal.

As far as glutamine supplementation goes, it's been shown that 35g of glutamine a day had no effect on fat loss or muscle mass in athletes during dramatic short term calorie restriction (Finn et al., 2003). This study period wasn't very long and didn't involve morning cardio, but importantly shows that there are no major anti-catabolic effects of glutamine. The fact that wrestlers were used lends credence to this study, because they're often the most catabolic dieters around!

More importantly, I'm still uneasy about the effects of pre-workout glutamine on fat burning and glucose utilization. After all, glutamine is readily converted to glucose and could therefore provide energy with which to hinder fat burning.

Supporting this idea, a brand new study showed that aside from the differential effects on insulin stimulation, we might as well use glucose pre-workout if we're going to use glutamine (Iwashita et al., 2005). Sadly, this study used a huge dose of glutamine administered via IV, so the data aren't directly transferable, but it reinforces the gluconeogenic role of glutamine. In other words, glutamine acts like glucose calories when consumed prior to morning cardio, and could subsequently inhibit morning fat burning.

If you're on Fear Factor and you need to drink a nasty amino acid shake to defeat your large-breasted opponents, then you should consume glutamine. Otherwise it doesn't look good for glutamine and morning cardio.

Okay, that wasn't very PC of me, but Mr. Hyde tends to come out when the topic of glutamine comes up. As far as the other amino acids acting as gluconeogenic precursors, I believe that the slow GI delivery will limit this.

Dr. Lowery: Barr makes a good point about the gluconeogenic nature of glutamine: it can raise blood glucose. But then the vast majority of amino acids are glucogenic ultimately, so we're back to the total dose thing. Hence taking a few grams of glutamine prior to AM cardio doesn't seem "insulin risky" when getting serious for a competition. (Not everyone goes this deep into a diet with concomitant over-reaching in the gym, I concur.)

I've been reviewing a fair amount literature lately on amino acid intake (including glutamine) and body comp changes, so I'm glad you pointed out the short duration thing. It's a real difference between much research and free-living athletes that may not benefit for months. Heck, if we do go with acute data, there's even the one glutamine study suggesting a GH boost which would be helpful to lipolysis. (Interpret as you wish.)

And as for Grow!, I haven't seen time course data on that trickle effect (e.g. slow-acting casein in the blend) but if there's no initial rush from the whey isolate, it'd be helpful here. Of course, I like the idea that there is an initial rush of amino acids, followed by the lingering casein effect.

Thibaudeau: As Dr. L. mentioned, glutamine is glucogenic (it can be used to produce glucose). However, it comes to a matter of glycemic load. If you're ingesting 5g of glutamine pre-cardio, at the most this means that 5g of glucose will be produced (it more likely closer to 2-3g). This is a very small quantity which shouldn't affect insulin release significantly. And it certainly won't interfere with body fat mobilization and utilization.

As I see it, it's just enough to maintain stable blood sugar levels when exercising, so it should help protect muscle glycogen stores. This is beneficial, especially if you have a strength training session planned later that day.

Anyway, in the morning I recommend low-intensity energy systems work (around 65-75% of max heart rate) which should predominantly use fat for fuel. So in that case, any glucose formed from glutamine shouldn't interfere with fat loss.

Dr. Berardi: Okay boys, I've gotta elbow in now since you're all wrong! Okay, I'm just kidding. In all seriousness, I've got four points to make.

1 – It's always about body comp.

There are few - nay, very few - individuals out there that are interested in either muscle gain or fat loss at all costs. Remember, not even the NFL lineman wants to sacrifice muscle mass or strength and power to lose some fat. Nor does the skinny bastard want to lose his cuts in the name of raw, flabby bulk.

So, with this said, it's important to conduct any discussion of fat loss or muscle gain with the caveat that, ultimately, it's optimal body comp that everyone's after.

  • The NFL lineman wants to be a bit leaner without sacrificing muscle size, strength, and power. (But, remember, in some cases, he doesn't want to be leaner. His bulk helps plug up the line and create a pretty big barrier to getting to his quarterback.)
  • The O-lifter wants to be lighter while maintaining or increasing muscle power (and although the CNS drives the muscle, muscle mass is still correlated with power).
  • The pre-contest bodybuilder wants to drop fat while preserving muscle fullness (and this includes contractile protein as well as muscle glycogen, intramuscular triglycerides, and intracellular water).
  • The skinny bastard wants to be bigger while still retaining some degree of leanness - creating a muscular appearance.

The point? Rarely does a person strive for extreme muscle gain or fat loss at all costs. He's usually looking for a balance of muscle and fat, a balance ideal for his sport or aesthetic desires.

In fact, it's for this reason that we actually measure the muscle:fat ratios of each of my Olympic athletes and that we put more stock in these data than the percentage of body fat data. But remember, this stuff isn't just for elite athletes. The recreational lifter or bodybuilder is probably more interested in the muscle:fat ratio than most of my Olympic athletes.

2 – Athletes need to use nutrition to drive body comp, not training.

Here's an important lesson. I teach all my Olympic coaches and athletes that nutrition needs to be the body comp control variable - not training. Look at how typical athletes look at body comp. They're out of shape in the off-season and then they "train their way into shape." Oops, there's a knee injury. They get fat. Oops, they're tapering. They get soft. Whew, they can train with high volume/intensity again. They get lean.

Notice the pattern? Most people use training specifically to dictate their body comp. This is a mistake. If they'd learn good nutritional habits and follow them year-round, adjusting based on training volume/intensity, they'd always be in the driver's seat of their physiques and would always be able to maintain a respectable body comp.

So, when it comes to athletes, I prefer that they train their skill set and sport-specific energy systems and then recover the rest of the time. Now, recovery doesn't only mean sit on their asses or sleep. Light exercise can be considered active recovery. And maybe that's what Lonnie and Christian mean by low intensity cardio. But we have to be clear - it's gotta be very low intensity cardio.

Yet I still don't prescribe it for fat loss in my athletes. If my athletes do this type of low intensity cardio, it's for recovery - if they need it. If not, they do sit on their asses or sleep. And they control their body composition with nutrition.

T-Nation: This is a great point. Applying it to the average guy, I see way too many people treadmilling their asses off instead of just tightening their diets. I'd rather choose better foods that live in the hamster wheel, you know? Okay, JB, lay your next point on us.

3 – What if it's an elite strength/power athlete with a very sluggish metabolism?

In this situation, we find the balance between eating enough for recovery and eating enough of a deficit for fat loss. Most often we can find that balance point with no problem. And still, I don't have to force any unnecessary physical activity on them - physical activity that might compromise their performance or recovery.

However, once in a while, this approach doesn't work. So what do we do? Well, we focus on increasing what's called "energy flux." As flux is the relationship between intake and expenditure, we're talking about boosting both energy intake and energy expenditure to create a new metabolic situation in the body.

4 – Recreational exercisers and bodybuilders can and should do things differently than athletes.

As recreational exercisers and bodybuilders are mostly concerned with aesthetics, they want to use whatever exercise and nutrition variables are at their disposal to achieve that optimal relationship between muscle and fat.

Of course, it bears repeating that said optimal point will be different for different folks. The typical recreational exerciser wants to look like Brad Pitt from Fight Club: moderate muscle, low fat. And the typical bodybuilder wants to look like Ronnie Coleman: sick amounts of muscle, sick absence of fat.


The first type of individual, because he doesn't need a crazy amount of muscle, can afford to do some strength/power stuff, energy system stuff, and cardio stuff. And as long as he does a certain amount per week (I typically recommend between five and seven hours of exercise per week to achieve this look), he can achieve that Brad Pitt look by eating clean and training with a constantly changing mixture of those exercise modalities.

The second type of individual, now that's something else. Because he wants lots of freaky muscle and less than 3% body fat, he can only focus on strength/power stuff and low intensity cardio stuff. (The energy system work just always seems to flatten those big puffy muscles right out). This individual needs to be super strict with the diet, counting calories, cycling macros, the whole nine yards. And, of course, it's likely that drugs will have to play into this situation as well.

So let me get to the point of this long ramble. The point is that there are so many sets of goals out there. And for each goal there has to be a comprehensive nutrition and exercise approach that targets that goal with the right set of strategies.

Any discussion of "protein" alone to get a great body is just stupid. And discussion of "fasted cardio" alone to get a great body is just stupid. Any discussion of "carbs" alone to get a great body is just stupid. Any discussion of "heavy lifting" alone to get a great body is just stupid. It's how all these things fit together that makes or breaks your progress!

T-Nation: Okay guys, it looks like the answer here is going to depend on the person's primary goal and his genetics or natural body type to an extent. But you've given everyone a lot to think about. The following discussions and pissing matches should be interesting. Thanks!

Chris Shugart is T Nation's Chief Content Officer and the creator of the Velocity Diet. As part of his investigative journalism for T Nation, Chris was featured on HBO’s "Real Sports with Bryant Gumble." Follow on Instagram