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Is Fasted Cardio Useless for Fat Loss: Part 2

Continuing from Part 1, I want to finish up looking at the oft stated, oft repeated, oft reshared statement that “FASTED CARDIO HAS NO BENEFITS FOR FAT LOSS.”    Last time I looked at some of the basic biology of fat loss along with how initial bodyfat percentage might impact on where a “bottleneck” might show up.

Following that I started to examine a paper by Escalante and colleague(s?) that also looked at the topic.  They started by looking at the acute studies which I don’t find terribly relevant.  Then they moved onto the chronic studies which are few and far between.

One was the Ramadan study that was poorly controlled and from which I don’t think you can draw many conclusions.  They next looked at meta-analysis of 5 papers pointing out that only 2 of them had BF% as an end goal.  Then they began looking at some detail at a single paper, the one that seems to be driving the idea that fasted cardio is useless.

I finished last week by asking if anybody knew what the paper was.

Or more importantly…who it was by?

Did you guess?

Schoenfeld et al (2014)

In 2014, Brad Schoenfeld and colleagues published a paper titled: Body composition changes associated with fasted versus non-fasted aerobic exercise.  J Int Soc Sports Nutr (2014) 11:54.

And so far as I can tell more or less the ENTIRETY of the belief that “fasted cardio has no benefit for fat loss” came from the results of THIS ONE STUDY.   Because even the authors didn’t seem to be aware of the Ramadan study (published in 2012), writing in the discussion:

To the authors’ knowledge, this is the first study to investigate body composition changes associated with aerobic exercise performed in the fasted versus fed state while subjects maintained a caloric deficit.

Which was clearly not the case.

The One Paper Problem

In the original draft of this article, I went off on one of my long-ass patented rants about what I call the “just one paper” issue.  Where a single paper that a certain evidence based crew doesn’t like must be replicated (or will be dismissed as just one paper) but when just one paper by one of their own is somehow the final word on the topic that will then be stated in absolute terms.

Well this is an example of that.  How just one paper, that happens to be by the leader of the evidence based circle jerk, has now become absolute truth because hundreds of people have shared the same fucking wrong Instagram meme.  Cute isn’t it?

Fasted vs. Non-Fasted Cardio

The study took 20 women who reported performing aerobic activity several times per week. The paper states that “several were off-season track and field athletes” but no indication is given of how many it was.  I mean, I take several to mean more than one but less than a few.  Maybe 3?   Four?  I have no idea and it seems like saying “three were off-season…” would have been easy in the text.

For the duration of the study, the women performed 50 minutes on a treadmill at 70% of maximum heart rate three days per week and they were supervised.  Half did the cardio fasted and the other half did it after eating.

The subjects were instructed to not perform extra activity.  We might raise the question of whether or not highly active women did or did not adhere to this (and it’s interesting that Brad raised the criticism of a volume paper he didn’t like by bringing this very issue up that we can’t know if they did extra arm work) but…..what’s good for the goose is clearly not good for the gander anymore.

Anyhow.  The women were given a specific hypocaloric diet (designed by Alan Aragon) to put them in a 500 calorie/day deficit.  Protein was sufficient at 1.8 g/kg, dietary fat was 25-30% and I wouldn’t expect this to be stupid coming from Alan.  The women also received a standardized protein/carb shake which the fed group consumed before cardio and the fasted after which is a better control that most papers use with stuff like this.  So far so good.

Dietary adherence was tracked through Myfitnesspal and well, I realize that this is the best that can be done.  Controlling food intake for even short periods of time is insanely expensive and simply isn’t realistic under most conditions.  But we also know that food records are rough at best.

But it is just the reality of the situation and I’m not going to dismiss this out of hand.  Few studies can truly control diet and to dismiss any paper on these grounds would mean dismissing about 99% of them. It’s simply a major limitation of most research in the field that has to be taken into consideration.

Measurements were made via tape measure for circumferences and to calculate BMI and body fat was measured by BodPod.  They state that it shows good consistency with DEXA in this population and this does seem to be the case.

The women reported essentially identical nutrient intakes over the length of the study and this didn’t differ between groups.  Within the limitations of food records, we can take this at face value I guess.  There’s really no other option.


Here were the body composition results.

Body Composition Changes for Fed vs. Fasted Cardio

You might note that the average BF% for the women was 26.3% for the fasted group 24.8% in the non-fasted, both at the low end of my Category 2.    Obviously there was some variance in this based on the standard deviations.

Based on the average data and standard deviations, and assuming a normal distribution, we can conclude that it’s very likely more than half of the women had a body fat between 18.4% and 34.2%.  Yes, this is a weird vague statement but without having the actual range of lowest and highest provided, it’s the best that can be done.  But that’s a pretty wide range, anywhere from my Category 1 to the high end of my Category 2.

This also means that only a handful (I’d speculate the off season track and field) athletes were towards the leaner end.  Which, if you recall from Part 1 means only a handful were in the BF% range where I argued that fasted cardio might be beneficial to begin with.

In any case, both groups showed a significant drop in body weight from start to finish although both groups were identical.  Neither group showed a significance in differences in changes in BF%.  The study states

There was a trend for an effect of time (P = 0.06), with a trend for a decrease in percent body fat from pre- to post.

Ah, the good old trend, the less said about which the better.

Because whether folks like it or not, P<0.05 is the cutoff for statistical significance and this study didn’t reach it.   In that sense we can not only say that the change in BF% wasn’t different for fasted cardio vs. fed cardio but that it wasn’t significant for either group.

So the fasted cardio’s non-significant change in BF% was equivalent to the fed group’s non-significant change in BF%.  Which doesn’t seem to say much to begin with.

That said, there was a statistically significant difference in the change in fat mass that was significant in both groups.    But there was no significant difference between the two groups which is the important bit here.

If you’re wondering how changes in fat mass can be statistically significant and changes in BF% not be well…statistics.  It’s just the way the math works sometimes.   I’d mention that the average change in fat mass was 0.7 kg (1.54 lbs) in the fed group and 0.9 kg (~2 lbs) in the fasted group, just under a 0.5 lb (a little less than 0.25 kg) difference over the length of the study.  Keep in mind that only 3 aerobic sessions per week were done.  Would it have been a larger differential with more sessions?  Maybe, maybe not.

Their Discussion

In the discussion, the paper looks at some of the same science I described above, lists the limitations including the issue of food self-reporting.  They mention that both groups lost less fat than predicted so they probably did under-report their true calorie intake.  It’s impossible to say if one group underreported by more than another.  They also acknowledge that the women might have done extra cardio outside of the study.

They write:

In conclusion, our findings indicate that body composition changes associated with aerobic exercise in conjunction with a hypocaloric diet are similar regardless of whether or not an individual is fasted prior to training. Hence, those seeking to lose body fat conceivably can choose to train either before or after eating based on preference.

It should be noted that given the small sample size and short study duration, we cannot rule out the possibility that either condition might confer a small benefit over the other with respect to fat loss. Further study is warranted in a longer term trial with a greater number of participants.

My Comments

Ok, so this study isn’t terrible, even by Brad’s low standards for scientific rigor (you don’t have to blind the BodPod which is why I didn’t bring it up).  Food wasn’t controlled but it never is in this population or in most studies.   Bodpod isn’t the best method for measuring BF% but it’s cheaper than DEXA.

We might consider that error in measurement for the BodPod is listed as 1-2.7% which is larger than the average change in BF% during this study which were 0.7% in the fed group and 1.3% in the fasted group).  Especially within the context of the average fat loss which was just about 2 pounds.  When the measurement error exceeds the apparent change, it’s honestly hard to conclude much of anything.

So there ya’ go.   We’ve got one study, fairly well done that found no significant difference in fat loss between a group of women who did fasted versus non-fasted cardio.

That said, the conclusion above is interesting to me since it clearly acknowledges the limitations of the study and the possibility that a small benefit might occur in terms of fat loss.  Mind you, it doensn’t say which way.  Maybe fed would be superior to fasted.  And that further study is warranted.

And yet somehow this one paper seemingly has led the online fitness space to conclude that fasted cardio not only does not have any benefit but can’t possibly have any benefit.   I can’t recall ever seeing the statement about fasted cardio being qualified in any form or fashion on the trite memes that get shared.

It’s almost like nobody read past the abstract or even attempted to read the actual paper, preferring to just repeat/repost some trite Instagram meme they saw without thinking about it.


Back to Escalante’s Comments

So what did the paper that started this have to say about this singular research study?  First they acknowledge that it was the only one that used a hypocaloric diet that was tracked using an online diary and which was geared towards weight/fat loss.   As they write:

Hence, out of the 5 studies included in the [Hackett] review article, only one study’s design would be similar and parallel to how physique competitors approach their diet when attempting to lose body fat.

However, that’s where the similarities start and stop and the mention these differences.

They point out that while the women in Schoenfeld et al. were given 1.8 g/kg protein, physique competitors are often recommended to and/or consume more than that.  While the women in Schoenfeld performed 3 supervised aerobic sessions per week, physique competitors perform aerobic activity at various frequencies, intensities and durations.

Related: How Much Protein Do Athletes Need?

As well, while the average BF% in Schoenfeld et al. was 24-26% (with the range mentioned above), the typical physique competitor may start at 10.5-14% for men and 20.3-22.7% for women, both well within my Category 1.

Which, as I mentioned, is the place I would consider fasted cardio to have potential benefits.

So already we see differences between the single study and what might apply to a lean dieter/physique athlete: they eat more protein, may do more/longer/different intensity aerobic activity (in addition to weight training and possibly HIIT) and usually start out leaner (my Category 1 which is a lot of why I define it that way).

To that we might consider the difference in the study group in Schoenfeld et al. that was certainly dieting and tracking (although possibly undereporting) to hardcore dieters who may be controlling their food intake to the gram.

I could probably even get way up my ass about the potential impact of exercise on appetite and hunger intake but I won’t.  The point being that if there were even a small systematic difference in true calorie intake between the fasted and fed groups would easily eliminate even small potential changes in BF% in either direction.

I’m not saying they did or they didn’t.  I’m simply saying that it’s another difference to consider in terms of drawing conclusions about fasted versus fed cardio in terms of the results of this singular study.  Especially as it might apply to very lean hardcore dieters.

The Important Bit: The Study Duration

But perhaps most importantly, and this speaks to the bit I left out of the above, was the length of the Schoenfeld et al. study which was a mere 4 weeks.  In contrast, a typical contest prep diet is easily double or more that.

In the modern era, a 6 month/24 week long contest diet is fairly common.  Even the relatively lean female or male looking to get significantly leaner (i.e. 15% to 8% for men or 24-16% for women) is easily looking at an 8+ week diet under most circumstances. And usually longer.

And this is important.  As the Escalante paper states:

Because preparation for a competition requires time, the longer the prep, the more important “small” changes can compound to yield greater final results.

Let me make it very clear that this specific limitation is mentioned by Schoenfeld et al. writing:

First, the duration of the testing period was fairly short, lasting just four weeks. While this period is certainly sufficient to attain significant fat loss, it remains possible that subtle changes between protocols would take more time to manifest.

Which once again is a well phrased and guarded conclusion.  One that seems to have been missed in its totality when the Instagram meme gets shared.   Though I do wonder if Brad presented this study’s conclusion in quite as nuanced a way….

Small Changes Over Long Time Periods Equal Big Changes

The issue here is that small changes over short periods of time can become big changes over longer periods of time.  So let’s do some hypothetical math.  Let’s assume that under a specific set of conditions, fasted cardio netted an extra 0.25 lb fat loss/per week.

I’m not saying it does or doesn’t.  Let’s assume.  Now across 4 weeks that’s only one pound difference in fat loss.  This is unlikely to be statistically significant.  We might also question it’s real world significance in the big picture.  But bear with me.

In the Schoenfeld et al. study, the average difference in fat loss was only 0.5 lbs, a value too small to possibly reach statistical significance.  I’d note that that 0.5 lbs was based on an assumed three sessions per week.  Many if not most physique athletes do more than this and you’d expect any small differences in fat loss to be greater under those conditions.

So let’s assume someone is doing 6 sessions of fasted cardio per week and this is netting them an extra 0.25 lbs fat loss per week.  Again, I’m not saying it does or it doesn’t.  Assume.  Across 8-24 weeks, this potentially adds up to 2-6 lbs fat loss difference.

For a physique competitor, a 6 lb greater fat loss is absolutely enormous, the difference between placing/winning and losing.  Or even reaching stage condition.  Even for the lean dieter looking to get very lean, it can matter.  A 2 lb extra fat loss over 8 weeks is 2-4 weeks less dieting to reach a specific BF% goal.    This is even more true if that increased fat loss means that less muscle loss is occurring.

Let me state it again: I am not saying that fasted cardio does or does not cause this to happen.   I’m simply expanding on what Escalante and his co-author wrote in their article/paper.

Following their own train of thought, they offer this analysis:

The fasted group went from 26.3 ± 7.9% body fat to 25.0 ± 7.7% body fat and from 16.5±5.5kg to 15.4±5.5kg of fat mass, whereas the fed group went from 24.8 6 8.4% body fat to 24.1 6 8.5% body fat and from 15.7 6 6.3 kg to 15.0 6 6.1 kg of fat mass (52).


Although the differences between the 2 groups did not reach statistical significance, failing to reach statistical significance does not always mean it is not practically relevant.

Now, let me make it clear that these are their words not mine.   In a sense they are correct, mind you.  In the real world of sport, where 1% or less might separate first and last, microscopic differences in improvements or performance can matter.  But in the average 8 week exercise physiology study with limited subject numbers, such a small difference may not reach statistical significance.

I’d note that it works in reverse too.  A result can be statistically significant but utterly real-world meaningless.  I’ve read diet papers that used some intervention and found a statistically significant increase in weight loss over 12 weeks.   But the actual difference was like 1 lb or 0.08 lb/week difference.    Statistically significant?  Sure.  Real-world significant for someone carrying a lot of excess weight?  No, not really.

Tl;dr: a study result can be statistically significant but irrelevant in the real world or non-statistically significant but still relevant (usually under extreme conditions such as elite sport).

How to Lie With Statistics

At the same time, there is a slight issue with this line of thought which gets into the weeds about statistical significance and what it represents.  Essentially, based on the data as presented, it is correct to conclude that the fasted group lost (slightly) more fat on average.

How to Lie with Statistics by Darrell Huff | Audiobook | 

However, without getting into the controversy over hard P-value cutoffs and all that shit, the fact is that the result didn’t reach statistical significance.  So those results are also compatible with the null hypothesis that there is no difference between the groups.

More accurately, since P didn’t reach statistical significance, you can’t exclude the null or conclude that the apparent difference in fat loss occurred due to the intervention.   So yeah, maybe the fasted group did lose a bit more fat than the non-fasted group but without reaching a P<0.05 you can’t say that it was due to the fasted cardio per se.  Any difference might have been due to nothing more than chance.

In that sense the effect sizes (essentially a measure of the magnitude of the change) are worth considering I guess.  They were 0.20 for the fasted group and 0.11 for the fed group.  Certainly the fasted group’s effect size was “double” but both values are considered small.

Of course, James Krieger would phrase that as “Is a doubling of effect size not worth considering?” like he did with the meaningless BF10 values.  And no, it’s not worth considering when it’s from small to a little bit less small.  Anymore than it was worth considering going from a BF10<1 to <3 or whatever.  A little less meaningless is still meaningless, James.

Mind you, what is small over 4 weeks might become large over a longer time interval but we don’t have that data.

A Short Side Rant

Something I find interesting.  Whenever Brad (or James Krieger) do a statistical analysis and the effect sizes are small like this, they conclude that there is no effect of the intervention.  Which is not incorrect.     A trivial or small effect size doesn’t mean much and I’m not saying it does.

But the statistics in their own volume paper were equally weak.   For all four muscles, P<0.05 was not reached.   By throwing a different statistical analysis (one they haven’t used before or since), two muscles were still not significant (BF10<1.0).  The other two muscles reached a BF10<3 which is considered “meaningless”

Yet somehow their conclusion was that


It’s almost like they just change the rules depending on whether they agree or disagree with the research.  I mean it’s not almost like that’s what they do.  That’s EXACTLY what the fuck they do.  Anyhow.

Oh yeah, I am STILL waiting for James Krieger to provide the supposed statistical reference showing that BF10<3 isn’t meaningless.  It’s been 1.5 years and it’s time for James to admit he was FUCKING LYING about it.

The Initial BF% Issue

Let’s return to the starting BF% issue.  As above, the average body fat of both groups was in my Category 2 although there was some variability.  Clearly some were leaner and some were fatter.  I would suspect that the track athletes were in the leaner group but that’s just a guess.

Related: What is Body Composition?

But this brings up another issue endemic to studies like this: when you collapse all of the subject data together, you often end up missing the details.  Many recent studies, which have started to provide individual data, are demonstrating this in my mind.

Because the picture that emerges is that some subjects get a staggering response but others not so much.  In hypertrophy studies you often see a situation where nearly half the subjects lose size.  Or you see a situation where a single outlier in one group pulls the average of that one group up making it look superior overall when it was only superior for the one outlier.

Addressing, this Escalante writes:

In addition, because the individual results of the participants were not reported in this study, it is not possible to determine the individual variability of fat mass and fat-free mass over the course of the intervention.

Perhaps the women who started out leaner did in fact get different results.  Perhaps they didn’t.  I don’t know and you don’t either.    When all you see is an average, with its own variability, you can’t know one way or the other.

When you consider that, statistically, only a handful of the women were likely be in my Category 1 in terms of their BF%, it would be hard to show a benefit of one type of cardio over the other when all of the data was collapsed and averaged out.

Making More Assumptions About Lean Dieters

That is, let’s assume that only lean dieters will see any benefit from fasted cardio.  Again, assuming. If only a few of the total subject number were that lean, any benefit they might have gotten will be completely overshadowed by the rest of the subjects when you average everything out.

One way to address this would be to provide individual data to see if the leaner women saw a difference for fasted versus fed cardio.  Another would be to do a sub-analysis of the very lean women for comparison purposes.  Given the small number of study subjects, and the realistically small number of very lean women, this would probably have been statistically meaningless and/or impossible to do.

Of course, having all of the women in both groups be at a sufficiently low BF% would have provided more data in this regard.  But that’s not what happened.  All we have is the data which was the data (which is the data).

To this Escalante add:

Finally, the hormonal and metabolic changes that a lean physique competitor will encounter to get to extremely low levels of body fat will be more drastic as they get closer to competition compared to an individual who starts a fat loss program at higher levels of body fat and is only looking to get to “healthy” levels of body fat (59).

Which gets into my discussion above about fat loss physiology and categories.  I’ll be the first to concede that women and men in the average to high BF% levels won’t see any benefit in terms of fat loss from fasted cardio.  There’s simply no physiological reason to think that they would.   And I’ve said that since at least 2010 and probably earlier than that.

It’s when you’re looking at men at 12-15% going lower or women at 20-24% that fasted cardio might have a benefit.  I SAID MIGHT.

And the Schoenfeld et al. study simply can’t speak to that population exclusively.  Even if some of the females were that lean, any advantage they might have gotten would have been overwhelmed by the non-results in women carrying more fat when it was all averaged out.  That’s on top of other differences in terms of protein intake, most likely underreporting calorie intakes, etc.

Towards that Escalante conclude:

Hence, any minor benefit that may be derived from fasted cardio should be considered and further investigated with physique competitors undergoing conditions that more closely represent how they may perform fasted and fed cardio before definitive conclusions can be drawn about the effectiveness of the 2 modes of cardio to improve body composition.

Basically, we need more research.  But we always do.

Protein Enhanced Aerobic Exercise

The final topic discussed by Escalante is the idea of protein enhanced aerobic exercise.   That is, consuming protein prior to or during aerobic exercise.  Now they don’t really define this term but I take it to mean consuming protein alone prior to cardio.  Based on the literature they cite, they may simply be considering higher protein mixed meals.

As they state

Maximizing fat loss while minimizing lean body mass loss is a key aspect of physique preparation.  A concern often raised about fasted cardio is the potential for muscle loss.

Now it is true that amino acids are used for energy during aerobic exercise but the impact is generally fairly small.  Under most conditions, about 5% of the total calorie expenditure may come from protein although this can be doubled to 10% if glycogen has been depleted.

This is still a relatively small amount: if someone were to burn 450 calories during an aerobic session 5-10% is 22-45 calories or 5-10 grams of protein.  At a typical brisk walking pace, an hour might burn 300 calories and 5-10% from protein is at most 30 calories, about 8 grams of protein. Which isn’t to say that every bit doesn’t matter at the extremes.

Now one pound of muscle contains ~120 grams of protein so assuming this all came from protein, it would represent 1/24th to 1/12th of a pound of muscle.   Mind you, if you’re doing aerobic activity 6 days/week that means you’d theoretically lose one pound of muscle every 1-2 weeks.

But realistically these amino acids are coming from the free amino acid pool to begin with rather than actual muscle tissue breakdown.  At least that’s what I’ve heard.

The Protein Book: A Complete Guide for Coaches and Athletes 

So I don’t see muscle loss as a real concern: the small amount of burned amino acids, again from the free  amino acid pool, can be readily replaced with even a small amount of protein consumed during or after training.

Other Benefits of Protein Enhanced Cardio

But Escalante suggests that there may be further benefits of “protein enhanced” cardio even if I find most of their references fairly weak.   Looking at the Thermic Effect of Food (TEF), they cite two papers which fed either 900 or 750 calories before cardio and found a microscopic increase in calorie expenditure (12-36 calories over 3 hours which is irrelevant against eating 750-900 calories).

But TEF studies never find results that are quantitatively relevant.  On top of that, a physique athlete on lowered calories wouldn’t have the “room” to eat that much before cardio.  So it’s a non-starter.

They also claim that protein during aerobic activity may prevent muscle breakdown but the paper cited, a position stand, only mentions one study where protein was added to carbohydrate during endurance activity.

They next contend that protein prior to exercise increases energy expenditure.  Their first paper cited is on resistance training and is thus of no relevance here.  The second compared 24 grams of carbs or protein before aerobic, HIIT or resistance exercise in women.   It found a roughly 60 calorie greater expenditure in the protein group compared to the carbohydrate group.  However, there was no control group to compare to and the women had an average of 28% body fat, questioning its relevance to lean physique athletes or dieters.

They also argue that higher protein in the morning can impact on food intake and appetite later in the day.  But three of the four studies were simply looking at high protein mixed breakfasts.  The fourth looked an egg based breakfast versus a bagel breakfast.  None involved exercise and there’s nothing to say that protein immediately after morning fasted cardio wouldn’t have an identical effect.  So I don’t see this as relevant.

Only a single study they cite would seem to have much relevance.  In it, men were given 25 grams of whey, casein, maltodextrin or nothing (control) prior to 30 minutes of relatively moderate aerobic activity.    During the exercise, the casein group burned a whopping 1 g extra fat between minutes 10-15 and 25-30.  Energy expenditure measured 15 minutes after the exercise bout was also slightly higher.  Certainly every bit counts but these effects tend to be staggeringly short lived.

Of perhaps the most interest, fat oxidation was not impaired in any group.  In fact, both the casein and maltodetrin group burned MORE fat than the whey protein group.  To be honest, I find this bizarre as the insulin response from the carbohydrates should have impaired fat oxidation.    Of course, the average BF% in the men was 19%, in my Category 2.  So again I’d question the relevance of this.

Is Protein Enhanced Cardio Useful?

So overall I don’t find their argument for protein enhanced cardio, at least as they seem to be describing it to be that well supported.    Certainly not based on the literature they cited anyhow as only one was really that relevant to the issue here.

As well, there is a separate issue that they didn’t consider which is that eating before cardio will reduce blood FFA levels (due to increased insulin), semi-defeating the purpose of doing fasted cardio to begin with.    This is going to be especially true in the very lean for the reasons I described above: fat mobilization is the limiting factor at play.  Raising insulin prior to cardio negates the potential benefit.

No, it didn’t in the final study they cited which is very strange.  But again it wasn’t in very lean individuals where insulin can have a much more potent effect in this regard. So overall whether it’s a high protein mixed meal or protein alone, I don’t find the data terribly convincing that it has a benefit within the context being described: very lean dieters or physique athletes.

Which isn’t to say that I don’t see a possible benefit of consuming a small amount of protein DURING morning fasted cardio.   A mere 6-10 grams of protein in water would more than offset any potential burning of amino acids and by waiting until the cardio is started to consume it insulin release is blunted and the fatty acids already in the bloodstream won’t be cleared during cardio. This seems like the best of all worlds to me.

Escalante et al’s Conclusion

So let me wrap up by looking at some of Escalante’s conclusions.    First they state that fat loss must always be caused by a long term energy imbalance between food intake and activity.  And that over time, as people get leaner, fat loss becomes more and more difficult.   This leads them to mention that physique competitors are attempting to reach the extremes of low body fat and may encounter fat loss plateaus; plateaus that may not occur in the general dieter.

They state correctly that studies have not been done on physique competitors (or I’d add my Category 1 dieters) and that differences in initial BF%, protein intake, resistance training, etc. may make studies done on other populations of less relevance.  Further, small changes in fat loss here may not only add up over long times but be critical at the extremes.

They also bring up an unaddressed issue which is the use of thermogenics or fat burners which might also impact on this.  In this vein I’d mention that yohimbine HCL, a compound that inhibits alpha-2 receptors only works if insulin is low.  That is, it can only be used under fasted conditions.

They comment on a bunch of other stuff that doesn’t really matter (i.e. chronic adaptations to fasted cardio) and conclude that protein enhanced cardio may of some benefit.

So that’s their conclusion.  What’s mine?

Oh You…The Fitness Industry

After posting Part 1 of this article, someone showed me the following image, a perfect example of the bullshit Instagrammed direction this industry has gone.

Rest in Peace Fasted Cardio

First off, 2006?  How young was the person who made this?  This idea goes back to the 1980’s if not earlier.  Kids today, don’t know nothing about nothing.   And “debunked one too many times?”  Really?  How so?  By acute studies on fat oxidation during cardio?  By something else?

Because factually, there is ONE FUCKING PAPER, limited in duration and scope directly addressing the issue.   ONE FUCKING PAPER.

Yet somehow that’s sufficient in this case to throw out the idea completely.   For fuck’s sake, people.  For fuck’s sake.

Is Fasted Cardio Useless?

So is the case closed, is fasted cardio useless in terms of potentially enhancing fat loss?  Well, as I have said for years, said above and will repeat here, in a majority of cases, it has no real benefits over non-fasted cardio.  For those carrying excess body fat or even in a moderate body fat range, there is not only no seeming benefit but no reason to expect one on a physiological level.

As a reminder:

In the case of someone carrying excess body fat, there are already plenty of fatty acids available.  The bottleneck here is fat oxidation due to a loss of metabolic flexibility.  Doing cardio fasted to take advantage of increased blood fatty acid levels wouldn’t be expected to have an impact.  Cardio can and should be done whenever the person will do it.

For the individual in a moderate body fat range, there is no real reason to expect a benefit either.  Pretty much everything works ok at this point.  Fatty acid mobilization is fine, transport is fine, the person isn’t down to stubborn fat yet, and fat oxidation is fine.  Cardio can and should be done whenever the person will do it.

But what about for the very lean dieter, the male at 12-15% attempting to get lower or the female at 20-24% wanting to get very lean.  Here the physiology changes.   Issues of fat mobilization, especially for women’s lower body fat, become an issue.  That’s on top of all of the other adaptation occurring.  Of course, this includes the physique athlete or some performance athletes going to the extreme which, admittedly, is a fairly small percentage of the dieting public.

But has it been conclusively shown that fasted cardio is useless?  Clearly I don’t think so.  Because at this point, the data is simply too limited to draw that conclusion.  The one study nobody seems to know about on athletes during Ramadan was too poorly controlled to draw any conclusion.

That leaves us with the single paper which, while certainly more relevant to dieters, cannot be automatically extrapolated to all situations.  The women’s body fat percentage was, on average, out of the range that you might expect a benefit.  Even the inclusion of some very lean women doesn’t change that without having access to individual data.

Couple that with the short duration (4 weeks), only 3 sessions of exercise, uncontrolled food intake (relative to psycho dieters), etc. and we have a situation far removed from what would be seen in the extremely lean dieter and especially the competitive physique or performance athlete.

Any small benefit from fasted cardio would be unlikely to show up over a duration that short .  And when physique athlete or even very lean dieters are doing 3-6 months of straight dieting, small changes can add up to big differences.  The paper in question even made that point in their discussion.    A point that has been completely lost in all the Instagram memes people keep fucking sharing.

Does that mean I am saying that fasted cardio does or will have a benefit in those situations?  No, that’s not what I’m saying (although I will assuredly be accused of such).

Rather, what I’m saying is that I think it’s a little bit too early to throw the baby out with the bathwater on this one.  In at least one very specific context, that of the very lean dieter or physique/performance athlete trying to get extremely lean, it seems possible that fasted cardio could still have benefits.   It’s also possible that it doesn’t.     If the research is done and it says I’m wrong, I’ll be wrong.

My point is that, based on the data of a SINGLE PAPER (even if it is by the leader of a certain “evidence based” circle jerk), certainly that conclusion seems preliminary.  Especially when it is presented without context or nuance.

And just putting it as #3 in a list of 8 absolutist statements for your Instagram doesn’t make it true by repetition because a bunch of other people shared it.

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