While I’m waiting for more than three whole people to step up and prove that they can train harder than me I wanted to run a piece I wrote a while back and never got around to finishing. And don’t worry, I’m not done thumping on about the failure thing, or the inability of so many supposed fitness professionals of knowing what failure actually is.
The Instagrammatization of Fitness
I’ve watched the online fitness industry develop for nearly 25 years now. And in recent years, it’s gotten funny in a lot of ways. Among these is the Instagrammatization where people only seem capable of communicating or reading pretty Infographics. Said Infographics placing a primacy on being short. Which means that they cannot convey nuance. Rather, people tend to make singular (and often trite) absolutist statements because that’s all there is space for.
Add to this the trend where something becomes “true” by repetition. Someone makes up one of these infographics with a bunch of repeated statements (some of which are right and many of which are wrong). Someone else assumes it’s true and reposts it to tell their friends. And they tell two friends and they tell two friends….
Soon the ideas, whether correct are not become “true” by repetition. Or rather they are accepted as true by repetition. And in so many cases, like the idea that we need 8 glasses of water per day, that truth by repetition is incorrect. Or at least contextually incorrect.
The Role of Anecdotes
Add to this another trend. In one particular “evidence based” group, anecdotes have now been declared to be evidence. Well, their anecdotes anyhow. We all know full well that they would never accept anecdotes from anyone THEY disagreed with.
But even this is context specific and apparently all it takes is a single paper (a single paper by a member of that particular group generally speaking) to cause everyone to throw a decades old anecdotal idea out like the proverbial baby with the bathwater. So long as they dislike the idea that is. And can get an infographic out of it.
It’s a really cute game they play. Anecdotes (well their anecdotes) count until they don’t count anymore and science counts until it doesn’t support what they are selling. It’s convenient and sure makes it tough to lose an argument when you can shift the goalposts at will.
Don’t like the science? Use an anecdote (even better when it represents you and only you so that you can sell a new high frequency ebook). Don’t like someone else’s anecdote? Use science instead. Around and around it goes.
Note: The above will be easy for people to misread. I am not saying that I am either for or against anecdotes. Clearly it would be nonsensical to throw out ideas that have been maintained for decades or longer. In some cases (i.e. feed a cold, starve a fever), they have turned out to be true. In others (take your pick from astrology, homeopathy, Traditional Chinese Medicine) they have absolutely not.
Even in the realm of bodybuilding, many of the things that the “bros” figured out over decades of trial and error have turned out to be true. And many have not (i.e. clean eating, rigid eating, eating 6 meals/day, starvation mode).
But ultimately anecdotes are just that (and the plural of anecdote is not science). That’s why we do controlled science. Because “Well this worked for me” doesn’t get it done.
What I am saying is that I find the cute game of a supposed “evidence based” crew to be palpably hypocritical. Somehow THEIR anecdotes are valid until THEIR science is the final word when there is anecdote they dislike. Or science is the final word until it doesn’t support what they are selling at which point you “have to think outside the box”. It’s just a bunch of bullshit guru goal shifting.
Anyhow, today I want to address an example of this. A decades old anecdotal practice that was thrown out based on the findings of one (but not really just one) direct study on the topic. And which has now been immortalized by the trite Instagram statement that:
FASTED CARDIO HAS NO BENEFIT FOR FAT LOSS.
One sentence. No context, no nuance. Generally included with 7 other “TRUTHS” or whatever. Being reposted by people who I am 1000% sure have not read the singular paper this is being based on. They saw it posted by someone they take to be an expert, assume it must be correct and reposted it and reposted it and reposted and now it’s considered true by repetition.
But is it?
A Very Brief History of Fasted Cardio
Fasted cardio refers to the idea of doing aerobic activity first thing in the morning after an overnight “fast” (i.e. not having eaten for some period of time, perhaps 10-12 hours). Hence fasted cardio. This is not a new idea although I couldn’t tell you when it really came into vogue in the fitness realm. When I first got interested in fitness and training in the mid 80’s or so it was already an accepted part of contest prep and I suspect the idea was around long before that.
I know John Parillo recommended it widely in the 1980’s and there may have been some before him advocating it. In the big picture, it doesn’t really matter when it started to be recommended The point is that it’s been around for decades, used by god knows how many physique athletes to reach the lowest levels of leanness for their contest.
Throughout the 1990’s and into the 2000’s, the idea of performing your morning hour of fasted cardio as part of your physique show contest prep was basically set in stone. It was simply done as a matter of course and nobody really questioned it.
Of course, in the late 2000’s the HIIT craze took off (I’d note that I was one of the first to write about HIIT and fat loss back in 1998 in my first book The Ketogenic Diet) and everybody started doing intervals every day and burning out completely.
But up until that point, if you were contest dieting for a physique show of some sort, you got up, took your stimulants or fat burners and did your morning hour of cardio. Sometimes you did another hour in the evening towards the end of prep although that wasn’t fasted so it’s not really relevant here. But it was just another accepted part of contest prep.
Note: On that note, another one of those trite Instagram ideas is that IF YOU ARE DOING TWO HOURS OF CARDIO PER DAY, IT’S WRONG. Which ignores smaller women who often reach a point with their calorie intake that they may have to do two cardio sessions to maintain a deficit and get contest lean. But these stupid fucking Infographics can’t provide even that level of context because then they couldn’t put 8-10 stupid statements in a row to seem edgy. Anyhow.
From memory Dante Trudell advocated it even during bulking phases (Parillo probably did too) to try to limit fat gains although I doubt it had much effect in this regard (it’s easier to just keep calories under control). Regardless, literally nobody questioned any of this for decades. It was simply part of the culture and part of prep: when you were dieting, you did your morning cardio.
At some point, I’d say the early 90’s, the idea of fasted cardio trickled out into the general public. I couldn’t tell you exactly when or by whom although I want to say it was Muscle Media 2000 driving that bus. I’m 99.9% sure it was in Bill Phillips Body For Life book but do not swear me to that. But inasmuch as bodybuilder methods are often held up as THE BEST WAY TO LOSE FAT, there was some logic to adopting a practice that sure seemed to have been beneficial for getting lean for literally decades.
And then seemingly overnight that changed. Well maybe not overnight. But at some point in the mid 2010’s. Suddenly fasted cardio had no benefits. Not even potential benefits. And 8-10 item lists of new fitness “truths” stated without context or nuance that that was the case.
But is it true?
A quick note: I am ONLY talking about the impact of morning fasted cardio on fat loss. Issues such as adherence or what have you, while important, are not the focus. The issue here is whether fasted cardio has any benefits, or potential benefit, for fat loss.
As usual, a little background physiology.
How We Lose/Burn Fat?
Although there are more steps in the process, you can break down the important steps in fat loss to the following three:
Mobilization is getting the actual fatty acid out of the fat cell and, really, it’s the most important one of the three. This is hormonally based with insulin and the catecholamines playing the major roles. Very simply, insulin inhibits fat mobilization and the catecholamines increase it (kind of, it’s complicated).
I’ll spare you the details involving cAMP, ATGL, HSL and and all the rest. Other hormones such as testosterone, estrogen, progesterone and Growth Hormone play secondary roles. There is also Atrial Natriuretic Peptide (ANP), a fat mobilizing hormone that works outside of the normal catecholamine pathway.
In a very real way, mobilization is the key step. Short of surgery or Cryolipolysis or something, if you can’t get the fatty acid out of the fat cell, you can’t get rid of it or lose the fat.
Once the fatty acid is in the bloodstream, it has to be transported away from the fat cell. If it doesn’t it will simply be stored back in the fat cell, a process called re-esterification (fun fact: women are more efficient than men at re-esterifying mobilized fatty acids). Transport primarily has to do with blood flow through the area. If blood flow is good, mobilized fatty acids will be more readily transported away from the fat cell than if it is bad/poor. I’ll come back to this below.
Once in the bloodstream, the fatty acids has to be burned (oxidized) for energy in a tissue such as skeletal muscle, the heart, etc. A whole bunch more steps are involved here having to do with Fatty Acid Transport Proteins (FATP) but eventually the fatty acid gets into the mitochondria (THE POWERHOUSE OF THE CELL) where it is oxidized producing energy in the form of ATP (along with CO2 and water which are excreted).
Now you have burned fat: the fatty acid previously stored in your fat cell is gone.
I’d note that it is possible for fat mobilized from one area to be stored in fat cells in a different area. Women’s bodies are better at this too, mobilizing fat from upper body areas and storing them down in the lower body.
Mind you, to actually lose fat in the long term requires being in negative energy balance, or more specifically negative fat balance, such that you burn more fat than you store in the long-term. The above is just the physiology of how fat is taken from inside the fat cell and ultimately “destroyed” (for lack of a better term). So long as fat that has been mobilized and burned is not stored back in that same fat cell, it will become smaller over time.
Related:What is Energy Balance?
So that’s the process of fat loss, why does this matter?
The Rationale for Fasted Cardio
The general idea behind doing fasted cardio is that more fat will be used for fuel during exercise, hence it will hasten fat loss. I’d note that this is based on the premise that what you use during exercise is most relevant for long-term fat loss. And, contextually at least, this idea is false.
HIIT studies and other work show that if you use more glycogen during exercise, you tend to burn more fat the rest of the day. Clearly how much fat you burn over the 23 non-exercise hours is likely to be more relevant than what you burn during that one hour. This alone would seem to argue against fasted cardio but bear with me, I’ll get to it.
Several rationales for how fasted cardio does this have been given and one of them is totally bogus.
Specifically it is often claimed that fasted morning cardio burns more fat because you have depleted muscle glycogen. But this is untrue, the amount of muscle glycogen depleted overnight will be very small. It takes 3 days of complete carbohydrate restriction, even without exercise, to deplete muscle glycogen by 30-40%. Overnight the effect is inconsequential.
However, liver glycogen will be depleted overnight as its glycogen will be broken down to maintain blood glucose. After an overnight fast, what you usually see is a metabolic state where blood glucose is at the low normal range, insulin levels are low, glucagon levels are up (meaning nothing since glucagon does not impact human fat cells), and GH levels are increased.
Due to the lowered insulin levels, the normal block on fat mobilization is reduced or removed (even at basal levels, insulin inhibits fat mobilization by 50% of maximum but this is to protect the body from excessive fatty acid release). So you have more fatty acids in the bloodstream first thing in the morning in the face of decreased blood glucose and insulin. The morning cortisol pulse even helps to mobilize fatty acids for energy. See, cortisol isn’t all bad.
And in that situation, we know that there can be an increase in fatty acid oxidation due simply to availability. Studies regularly show that the percentage of fat used for fuel during cardio is higher under fasted conditions than when the person has eaten. This is really not debatable.
But the question still becomes whether or not this matters in the big picture in terms of fat loss. Or whether or not it even has the potential to enhance fat loss. And the answer to that is a matter of context.
The Importance of Context
As I said in the introduction, one big problem with the Instagrammatization of fitness is that nuance and context can’t be presented. It’s just one absolute statement most of the time. Because how else do you fit 8 of those fucking things in an image without running out of space?
But whether or not fasted cardio might be beneficial depends on context and the individual. And a big aspect of whether or not it even has the potential to be of benefit depends on initial body fat percentage (BF%). Anyone who has read my books knows that I set up diets according to categories based on the dieter’s initial BF%.
Please note: These are non-DEXA values, based on older methods such as calipers. DEXA measures systematically higher than those other methods (I don’t know why) and the values should be adjusted up by roughly 3+% or a little bit more. So a male DEXA’ed at 18%, roughly equivalent to 15% by older methods, is in Category 1.
So Category 1 is the lean dieter trying to get to extremely lean. Category 2 is kind of the “average” individual. And Category 3 is the individual carrying a significant amount of bodyfat.
And I set things up according to this as initial BF% determines a huge amount of physiology. For example, leaner individuals are more likely to lose muscle mass when they diet. Heavy resistance training becomes that much more critical as does sufficient protein intake with lean dieters needing more dietary protein than those carrying more fat.
Fun fact: This is at least part of why women lose less LBM when they diet than men. They are starting at a higher BF% than men on average. So you would mostly expect a female at 21% body fat and a male at 21% body fat to lose relatively similar proportions of fat and muscle. But a female at 21% will lose less than a male at 10%. And this is true to a first approximation. There are other physiological differences at play. For example, estrogen enhances fat oxidation which spares protein.
Let me state what should be obvious but I’m sure someone will pedantically nitpick: the values above are not hard cutoffs and this should all be thought of as a continuum. It’s not as if male physiology changes completely when someone goes from 15% to 16% body fat (or female from the equivalent numbers). It’s a gradual change from high to low or vice versa. But, in a practical sense, I have to use some sort of cutoff. And those are the ones I use.
The point of all of this being that initial BF% plays a huge role most aspects of human physiology. Which means that the potential usefulness or benefit of any given dietary or training strategy might be impacted by that. In fact, it will be impacted by that. So as an example, whether or not fasted cardio might have any potential benefit for fat loss might depend on their initial BF%.
In that vein let me reiterate that it was physique dieters, who would have been in my Category 1 who were promoting the idea of fasted cardio to enhance fat loss, in the first place. It only got out into the general public consciousness much later.
Dieting Category and Fat Loss
Building on that idea is the following issue: at the extremes of BF%, you often see two different potential “bottlenecks” (for lack of a better word) in that three stage process of fat loss. Basically, the potential limiting factor in fat loss is different at the two extremes.
In Category 3, due to the development of insulin resistance there are generally tons of fatty acids available in the bloodstream, I’ll spare you the details why. The problem here is that carrying excess body fat is generally associated with becoming metabolically inflexible. By this I mean that tissues in their body such as skeletal muscle are no longer able to switch from using glucose to fatty acids for fuel, something that happens readily in leaner individuals.
You often see mitochondrial dysfunction along with a high rate of carbohydrate burning (indicated by a high resting RER/RQ). Basically their bodies have sort of “lost” the ability to use fat for fuel even though there’s tons floating around in the bloodstream.
And as I discussed in my Training the Obese Beginner series, you can “fix” this by changing diet training to deplete their muscles of glycogen and IMTG. You lower their carbohydrate intake, do glycogen depleting exercise and boom: you enhance whole-body fat oxidation. Building aerobic capacity to improve mitochondrial function also helps. All of those fatty acids that are floating around can now be burned effectively for energy
In Category 2, everything sort of works fine. Fat oxidation in muscle is fine and fat mobilization from fat cells is fine. It’s a wash here and there is no real “bottleneck” to speak of in anything really. Basic diet, basic training and fat is lost until folks get to the top end of Category 1.
The main thing to remember is that Category 2 is more or less an “average” bodyfat percentage. For men it’s ~16-25% bodyfat, for women 25-34% or so. Just keep those vague values in line.
And in Category 1, you see a situation essentially reversed from the Category 3 dieter. Here metabolic flexibility is generally good and the ability to use fat for fuel is just fine. Sure, the body still prefers carbohydrates if they are available, but it can switch back and forth easily (note this isn’t universally true and lean individuals can be genetically insulin resistant). If carbs are available, their bodies burn carbs. If carbs aren’t available, they switch to using fat for fuel.
So where is the bottleneck here? Well in a sense there are several.
The primary one is mobilization: as you get leaner it becomes more difficult to mobilize fatty acids. There are a bunch of reasons for this. One is that fat cells become more insulin sensitive. So lower levels of insulin can either store fat or inhibit mobilization. I’m not saying go zero carbs, here. What I am saying is that exercising under low insulin conditions might be valuable at this level since mobilization has become so much easier to inhibit.
There are even more adaptations. As fat cells get smaller, it gets harder to mobilize fatty acids. Different types of fatty acids are also relatively harder or easier to mobilize (saturated is harder than unsaturated) and the last fat cells tend to be higher in the fatty acids that are more difficult to get out.
That’s in addition to all of the general adaptations to dieting such as reductions in thyroid hormone, catecholamines, leptin, etc. which impacts on fat cell metabolism. Along with that is an overall decrease in metabolic rate which reduces the burning of everything. By the time a lean dieter is getting very lean, the body is fighting back on all fronts.
As well, by the time dieters get this lean, they have lost most of the easy to lose fat. The fat that mobilizes easily, that has good blood flow for transport.
What’s left is the “stubborn fat“, the body fat that is harder to mobilize and get rid of. For men it’s the abs/low abs and low back fat that is the last to go. For women it’s the hips and thighs. Stubborn fat is stubborn for many reasons. I listed some of them above, general dieting adaptations, smaller fat cells. But there’s a lot more to it.
I wrote an entire book about stubborn fat, too.
There are other differences having to with adrenoceptors, the receptors where the catecholamines bind. The two important types here are beta-2 receptors which mobilize fat and alpha-2 receptors which inhibit fat mobilization. As you might guess, stubborn fat has more alpha-2 receptors than beta-2 receptors. In fact, women’s hip and thigh fat may have 9 times as many alpha-2 as beta-2 receptors. This makes fat mobilization from that area much more difficult.
Blood flow is also usually worse in stubborn fat areas. Put your hand on a stubborn fat area and it’s usually cold to the touch. That’s due to poor blood flow through the area. That means that even if the fatty acids are mobilized, they may not be transported elsewhere in the body for oxidation. They simply get re-esterified and stored back in the fat cells which means they can’t be burned off.
Note: adipose tissue blood flow is also controlled by beta and alpha-adrenoceptors with the same effect. Beta-receptor simulation causes vasodilation and alpha-receptor stimulation causes vasoconstriction.
This all adds up to a situation where mobilizing and/or transporting fatty acids out of fat cells can become limiting. But once they are out, burning them for energy is relatively trivial.
Like I said, this is effective the opposite situation of the Category 3 individual. For lean dieters, fat oxidation is basically never the limiting factor. Rather, mobilization, along with transport, tend to be the problems. And as I said above, without surgical means, if you can’t mobilize the fatty acid out of the cell or transport it to where it can be burned, you can’t lose fat from the area.
A Quick Summary
So let’s sum up:
- The idea behind fasted cardio is that, for primarily hormonal reasons, there will be more fatty acids in the bloodstream after an overnight fast.
- Elevated levels of fatty acids in the bloodstream will tend to promote the use of fat for fuel.
- Whether or not using more fat for fuel matters in terms of fat loss is debatable.
- The initial bodyfat percentage of the dieter determines a ton of physiology.
- In this context, it determines where any potential bottleneck in the 3-step fat loss process might occur.
- For the dieter carrying excess body fat, there are plenty of fatty acids already available. Oxidation is the problem.
- For the average dieter, everything is fine.
- For the lean dieter, mobilization and/or transport may be limited but oxidation is no problem.
And hopefully the implications of the above are clear. If not, here they are.
For the Category 3 dieter carrying excess bodyfat, there is no reason to think that morning fasted cardio would help. There are plenty of fatty acids around. Having more doesn’t matter since oxidation in the muscle is the issue.
For the Category 2 dieter with average bodyfat, fasted morning cardio is unlikely to have any benefit. Mobilization is fine, transport is fine, oxidation is fine.
And then there is the Category 1 dieter who is already lean and trying to get very lean. For whom fatty acid mobilization and transport may be limiting. For whom even low levels of insulin will inhibit fatty acid mobilization. And this is the group where fasted morning cardio MIGHT have the POTENTIAL to enhance fat loss.
Please note bolded words: MIGHT and POTENTIAL.
I’m not saying it does or it doesn’t at this point. I’m saying it might.
Is Fasted Cardio Useless for Fat Loss?
Which brings me in an interminably long way to address the actual question stated without nuance or context in oh so many fitness Infographics: Is Fasted Cardio Useless for Fat Loss?
Now the idea for this current article came from an article titled Fasted Versus Nonfasted Aerobic Exercise on Body Composition: Considerations for Physique Athletes by Guillermo Escalante and Christopher Barakat which I will look at in some detail.
This specific article wanted to re-address the issue of fasted cardio and fat loss, stating that:
Although there are many ways in which physique athletes may perform aerobic exercise (i.e., type, intensity, duration, frequency, etc.), performing aerobic exercise, or “cardio,” as the first thing in the morning after an overnight fast is a common strategy used by some competitors (17, 25, 49).
The theory behind performing fasted cardio is that low glycogen levels after an overnight fast allow for greater mobilization of stored fat to be used for fuel because carbohydrates are not readily available to produce energy. Although in theory this may seem promising, the purpose of this article is to examine the existing literature on the effect of fasted versus fed cardio on improving body composition for physique athletes.
Now in the article they look at a ton of topics most of which I will only touch upon. Go read the full thing if you want the details.
The first deals with acute studies of fuel use during fed and fasted cardio. The short version is what I wrote above: fasted cardio done at moderate intensities (think LISS or MISS) burns a larger percentage of fat for fuel than when the same cardio is done after eating. Interestingly, they reference one study which found an increase in muscle glycogen during fasted cardio (fed cardio tends to promote carbohydrate burning for fuel). They write:
Hypothetically, the acute increases in fat oxidation and the effects fasted exercise has demonstrated regarding the increase in muscle glycogen are beneficial for a physique athlete. Because a physique athlete’s primary concern is body composition and aesthetics, these adaptations may translate to a leaner physique with more muscle fullness over time.
In addition, this increase in basal glycogen content may improve the physique athlete’s performance during their resistance training exercise regimen, which is crucial for their ability to build and/or preserve muscle during a caloric deficit.
Do note that almost all studies on this topic are done in untrained and/or obese individuals. So there is no guarantee that it applies to lean trained athletes. Remember, folks, context.
They also note other data showing changes in the activity of enzymes such as adipose triglyceride lipase and hormone sensitive lipase (both involved in fat mobilization) that are only upregulated during fasted cardio. They conclude:
Additional evidence regarding acute hormonal changes have also favored fasted exercise. For example, increases in adrenaline, noradrenaline, and growth hormone were greater in fasted conditions compared to fed. Moreover, higher levels of growth hormone have been shown to increase catecholamines (9) which may further increase fasting-induced lipolysis (16).
When taking all the aforementioned acute effects of fasted aerobic exercise into consideration, it is possible that physique athletes may benefit from this mode of exercise to improve their body composition; however, longer training studies in this population are necessary to investigate whether significant differences are observed between the 2 modes of exercise.
Basically, there are indirect suggestions that there might be benefits to fasted cardio but we can’t conclude anything until we do longer term studies and actually measure the changes over time. Fair enough and note the guarded language that they use which is how real scientists actually write.
Given the above, the next logical step is to look at what chronic studies have been done. And there aren’t many.
The first was a study of fed and fasted cardio during Ramadan. In it, 19 males performed 40-60 minutes of aerobic training three times per week at 60-80% of their maximum heart rate either fed or fasted for 30 days. Both groups lost bodyweight but ONLY the fasted group lost a statistically significant amount of body fat.
AHA, fasted cardio works! But not so fast (har har har). The subject’s diets were tracked but not controlled and the fed group ended up eating more so of course their fat loss was less. Well, they ate more within the known limitations of food reporting (which is crap). The exercise sessions were only loosely controlled and subjects did different types of exercise. Body fat was measured by skinfolds which are poor at best and you can’t really conclude much from this.
A second study, not included in Escalante’s paper compared fed or fasted HIIT on fat loss in obese women who were not dieting. No difference in fat loss was seen but, as I discussed above, I would not have expected there to be a difference based on physiology alone.
Next Escalante examined a meta-analysis by Hackett and Hagstrom that included a whopping 5 papers including 96 total participants with both randomized and non-randomized studies that either examined changes in body mass or body fat. The article states:
Although the authors stated caution is warranted when interpreting their findings due to the limited number of studies available on the topic, they reported trivial to small intragroup and intergroup effect sizes for the effect of fasted versus fed aerobic exercise on body mass, % body fat, and lean mass (21).
Of those 5 studies, only 2 examined changes in BF% so it seems a reach to draw very strong conclusions from that. Both of those were in females and there are factually differences in the physiology of all of this for women versus men. Or so I’ve heard.
But one of those two studies is worth examining in more detail because it seems to be the ONE study that most of the “evidence based” people are using to support the idea that fasted cardio is useless. Reading this Escalante article was the first I’d even heard of the Ramadan paper and I daresay most in the field haven’t heard of it either. I certainly can’t recall anybody talking about it.
Rather, all of the trite Infographics stating that fasted cardio has no benefits in absolute terms seems to come from the findings of a single study.
So what is it? Or rather who is it by?
I’ll give you ONE guess.