Burning fat vs. burning sugar


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Just my experience so far:

I am seriously into endurance training since mid August. With seriously I mean, to build an aerobic base, Maffetone talks frequently about.

To build an aerobic base, I have to get in tune to myself, to get to know, where I have to go to with my breathing and breath rate, cadence of strides while running or strokes when rowing, all around relaxed feeling while moving which result in a frame of heart rate that yields benefits that seem not to be attainable otherwise.

I remember @aciampa said somewhere the magic of the Maffetone formula lies in the adjustment. I totally agree with it.

In this four months I lost 10kg/22pounds of bodyweight, lots of fat around the waist. I move better and regained lots of mobility/flexibility. Good aerobic training seems to make me more modest.
Harald, that is remarkable progress. Did you change your diet at all or is this a product of just the increased endurance work. I'm figuring the latter as I suppose your diet was already dialed in.

Al Ciampa

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Certified Instructor
I only brought this up as a question and wanted some knowledgable feedback.
This is just not true.

I am surprised that so many disbelieved that it has been thought that aerobic exercise lowers testosterone and GH levels.
I did not disbelieve that this was thought; I simply do not agree with the conclusions of most of the literature that states this. To be clear in my meaning, I don't believe the conclusions of many authors as being applicable to anyone other than the sample population that they used in the study, especially if it narrow.

This is from your post:

"With regards to aerobic training, studies have demonstrated that endurance athletes have lower testosterone levels when compared to sedentary individuals (Strüder et al., 1998; Maïmoun et al., 2003)."

Did the original paper look at the diet and lifestyle of the sample pop? I doubt it. Also, did they look at the actual intensities and volumes of the subjects? I doubt that too. Considering the dates on these are at the turn of the century when endurance training was still lots of volume at high intensities with lots of grains and carbs, I suspect that the hormone values of those subjects do not match your typical athlete or trainee who runs at a moderate intensity 3x/wk for 60min.

"However, Strüder et al. (1998) showed that although testosterone levels were indeed lower in elderly male runners compared to age-matched sedentary subjects, the same was not true for previously sedentary subjects who performed aerobic training for 20 weeks 3 times per week with an intensity of 50 to 65% of aerobic power."

Notice that word "elderly." My uneducated guess is that the results likely do not apply to most of the population. However, sedentary subjects who performed aerobic training for 20 weeks 3 times per week at an intensity of 50-65% of aerobic power did not have lower T values than a comparable population.

"Even though testosterone reduction during aerobic training has not been clearly demonstrated, it is possible that a certain amount of time is necessary for the endocrine system to adapt to the volume and intensity of training when these factors exceed a certain stimulus threshold"

I wonder what that threshold is? Perhaps this is the critical factor.

It was also my understanding that when these levels drop, cortisol levels rise.
But the research you are reading states something different:

"this does not completely explain the occurrence of testosterone reduction with aerobic training, given that increases in basal cortisol levels and the consequent testicular suppression are most commonly related to overtraining. In fact, testosterone levels have been shown to be reduced in endurance athletes with no alterations in cortisol levels (Maïmoun et al., 2003) as well as in non-athletes subjected to aerobic training (Cadore et al. 2010)."

LSD is aerobics exercise therefore also lowers these levels.
The bottom line, Carl, and why I initially responded to your question how I did is this: this just does not play out in many clinical experiences. Plenty of athletes use LSD/aerobic training to get into shape for whatever, and obviously do not suffer from low T or GH.

That "scientists" make claims about a small group of people doesn't make it so. You have to read the details of the study. I will agree that high volume endurance training, which is usually trained to hard by those cats, combined with a high grain diet will tank T and GH.

Anna C

More than 5000 posts
Elite Certified Instructor
I remember @aciampa said somewhere the magic of the Maffetone formula lies in the adjustment. I totally agree with it.
I agree too; not only because the adjustments are smart, but because when you're talking about steady state aerobics (running, cycling, rowing, etc.) as we are, 5 or 10 BPM is a very large difference in what is happening physiologically, and how the body responds and adapts to the training.

In this four months I lost 10kg/22pounds of bodyweight, lots of fat around the waist. I move better and regained lots of mobility/flexibility. Good aerobic training seems to make me more modest.
Many of us that are doing the LSD training along with kettlebell training are seeing these changes. I got a Bod Pod measure today that shows a lean mass increase of 3.5 pounds along with a 4.5 pound weight decrease since 8/23/16. That's 8 pounds of fat melted away from all my hours of cycling that I've been doing these last 8 weeks! It is a wonderful thing, especially this time of year when things often tend to go the opposite direction.

Edit: @banzaiengr Seeing your question to Harald, I'll add that I have not changed my diet in the 3 months since my last Bod Pod measure, but I do seem to be a little less hungry overall.
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Harald Motz

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Certified Instructor
Harald, that is remarkable progress. Did you change your diet at all or is this a product of just the increased endurance work. I'm figuring the latter as I suppose your diet was already dialed in.
I did not change my diet, and it is anything but dialed in. Fat, carbs and protein, I have them all and am not overly obsessed with it. I am just a bit more cautios, about what westernized children like. My craving for caffeine is reduced.

I seem not want to replenish, what I "burned" through my endurance activity. Weight loss is not a goal, but when it happens, so be it. When easy endurance is the cause, than it has its effects, I have no problem with.


More than 5000 posts

Kind of "optimization" is: eating sugar just before and just after training. This will help to muscle recovery. Protein intakes throughout the day.

From my experience, I gain weight if I eat simulaneously sugar and fat. I maintain my weight if I eat either sugar or fat.

If you preferentially eat fat (or "only" fat), you will burn this one first. The same for sugar.

When you eat both of them, body use sugar first. If it is enough to get energy it needs, it will store fat. If it is not enough, it will consume a little in its "fat storage".

"Eat sugar and burn sugar. Eat fat and burn fat."

Kind regards,



Triple-Digit Post Count
Two thoughts here, one is that many people (even doctors) fail to realize that the blood level of a hormone, to some degree, indicates the amount that's NOT being used. The article points this out ("increased utilisation of the hormone by muscle tissue and increased hepatic degradation of the hormone, may be responsible for the decrease"). So a higher level may indicate poor utilization, a lower level indicate good utilization.
that is an EXCELLENT observation! I am not qualified to comment on the veracity of that statement, but it sounds intuitively right... blood is a transport mechanism, so whatever is NOT present in it tells a story too... so simple and intuitive it probably gets overlooked all the time. Science has to be complex or it doesn't count ;)


Triple-Digit Post Count
I seem not want to replenish, what I "burned" through my endurance activity
I would tend to think you're doing it exactly right!
At least by StrongFirst standards, where exercise is a recharge, and exactly the way I am doing my LSD work, and have been taught to do it!

Can't argue with actual results


More than 5000 posts

I think I read a study a while ago which argued that the more you are thinking about your weight (then, thinking about losing weight), the less you are able to do it, due to hormonal secretion, even if you are doing physical activities. This hormonal secretion prevents from weight loss.

It seems that the "psychological dimension" of the problem is critical: weight is not the problem in itself. The most important is having a healthy way of life (or at least as much as possible).

From what I noticed with friends, it tends to be true. They eat better, use stairs, walk, and do not necesarily do sport...and lose weight.

Kind regards,



Quadruple-Digit Post Count
When you eat both of them, body use sugar first. If it is enough to get energy it needs, it will store fat. If it is not enough, it will consume a little in its "fat storage".
Can you elaborate a little? As I understood it what you are saying is, if one is eating sugar (and this includes carbs) and (dietary) fat together, body uses up the sugar intake first, and if that was enough for the body, it will store the dietary fat intake as body fat.

If it is not enough, it will consume a little in its "fat storage".
If it is not enough meaning, if both sugar and fat together is not enough?


More than 5000 posts

@Abdul Rasheed
If it is not enough meaning, if both sugar and fat together is not enough?
We assume that one consumes both sugar and fat and then, has an activity:
if sugar amount is enough (to do the activity) => fat storage (because there is no need of this energy)
if sugar amount is not enough (then, it has been entirely consumed) => use of fat (because there is a additional need of energy).

For the body, sugar is easier to use than fat (excepted in ketonic diet, and to some extents, paleo diet)

You are right, may be I was not very clear ;)

Kind regards,



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Prior to my inquiry on the forum I had sent an email to Dr. Maffetone's web site. As many of you responded, especially @aciampa and @Steve Freides the trick here is of course training at MAF to avoid all the unwanted hormonal changes that training above the aerobic threshold causes. My first question was in regard to is it the low carb diet or the training, in which Ivan, one of Dr. Maffetone's associates answered it is a chicken egg situation. I have pasted the email below;


It is a chicken/egg issue. Nutrition is a very powerful potentiator of aerobic function in the body.

However, the reason LSD lowers testosterone and GH is that most people do their LSD at above their aerobic threshold. In other words, they have some amount of anaerobic function for long periods of time, which shouldn't be happening when you train aerobically. Effectively, one of the main purposes of training via the MAF Method is to train at a physiological intensity where sugar-burning does not increase. The MAF Heart rate points to the physiological intensity at which the body is at its maximum rate of fat-burning. Because cortisol increases in order to promote sugar release and availability, staying at an intensity where fat-burning takes precedence (the MAF HR/aerobic threshold) effectively means that your cortisol levels do not rise chronically (and neither do your GH levels drop), contrary to the effects sometimes seen in LSD.

Put another way, if we define "LSD" as "training which often raises cortisol and lowers GH" then MAF Training is not a form of LSD. You'll find that an abundance of our materials, especially our white papers, delve into this topic.

Some people are genetically geared towards fat-burning in the sense that they have a much greater percentage of Type I fibers than others. But in all people, the MAF Method does serve to optimize your existing Type I fibers.

Ivan Rivera

Steve Freides

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Staff member
Senior Certified Instructor
I'm glad to hear it sounds like we're all saying the same thing, and thanks for posting that.



More than 500 posts
To provide some perspective. I am an exercise physiologist with lots of experience in testing athletes. Most people are going to reach a respiratory quotient (RQ) of about .85 at a zone 2 (marathon race pace) effort, which is in the ballpark of the MAF pace. At this RQ, they are burning about 50% fat, 50% carbohydrates. That is when running at a pace that they can maintain for 26.2 miles! If you think about any gym effort, or the fuel mix used in most fitness tests, it is going to be nearly 100% carbohydrates. Ketogenic diets change most of this. I have seen people at 90% of VO2 max still burning mostly fat.

A low carbohydrate diet or a high volume of zone 1-2 training (MAF pace or slower) will greatly enhance the body's ability to burn fat and will increase intramuscular fat stores. I have seen cross country runners (who do plenty of hard intervals) who are burning 50% fat at faster than a 6:00 min mile pace (>10 mph), but they were running 120 miles per week. In this case, it was not about keeping their heart rate low (i.e., MAF training) but rather about a high volume of training.

But I would not consider becoming a better fat burner to be an important consideration for training programs of anyone but ultra endurance athletes. For everybody else, it just does not matter much.


My Third Post
Hi, All -

I've enjoyed this thread and have been doing some research of my own and wanted to contribute to the discussion.

I have to agree with original initiator of this thread, "banzaiengr" regarding LSD and increased cortisol, lower testosterone.

This was a well designed study that looked at cortisol levels at varying aerobic intensities (rest-control, 40%, 60%, and 80%) for 30 minutes of aerobic duration with 12 moderately trained subjects (n=12) at a median age of 26 years old.

Study results show that subjects exercising at 60% VO2 max (HR ~ 150bpm, these are young kids). Using the MAF formula (180-age), shows that this cohort was training below their aerobic threshold (MAF = 154 bpm), yet still showed a 40% (+/-) 12% increase in cortisol levels. Keep in mind this training was for only 30 minutes, rather brief.

Cortisol is the antithesis of testosterone. Consequently, one could conclude from this study that athletes performing aerobic exercise (LSD) using MAF will exhibit increased cortisol / reduced T levels.

It was interesting to note that the cohort who trained aerobically at 40% of VO2 max (60% MHR ~ 115 bpm) were able to slightly lower cortisol levels, although not statistically significant.

Guess this means for those trying to lower stress levels, it's best to stick with walking, preferably outdoors in the woods or some other natural setting.

Thanks everyone for sharing on this discussion. Always enjoy the contributions from all the members at Strongfirst.

Please see attached for full study

Cheers, Jason


North Coast Miller

More than 2500 posts
Maybe I'm missing something here.

As I understand the literature, exercise induced increases in cortisol result in lower total testosterone in the post exercise period (bad?). It also increases free testosterone in the post exercise period (good/better?). It temporarily impedes protein synthesis (bad?).

- Endurance training increases mitochondrial density.

- Higher intensity endurance training improves mitochondrial efficiency processing pyruvate and improves acid clearance rate.

- Chronic increases in cortisol induced by stress or medical complications are associated with drops in protein synthesis and presumably loss of muscle mass but...

- while this has been theorized/extrapolated to physical activity, it has never really been demonstrated due to temporary exercise induced increases in cortisol.

Over time, exercise adapted people seem to have a reduced increase in post exercise costisol levels. Consuming carbs post exercise also seems to significantly improve cortisol clearance rates. Exercise reduces chronic stress levels somewhat.

Putting too much emphasis on exercise induced cortisol levels (similar to fretting over ROS levels) might be overthinking things a bit.


More than 500 posts
It is well known that cortisol increases with exercise intensity, see below:
Of course cortisol is catabolic. However, another, related mechanism is thought to be acting here.

In the figure above, endurance exercise results in a signaling cascade in the muscle driven by the depletion of ATP among other things. ADP and AMP accumulation cause the increase in AMP Kinase, and then TSC1/2 downstream. TSC1/2 inhibits mTOR. mTOR is part of the anabolic signaling cascade in muscle following strength training. This is presumably how endurance exercise training can interfere with muscle hypertrophy and why marathon runners are so skinny (continually supressing mTOR).

The real question becomes how much and at what intensity is required to inhibit mTOR? This is still up for debate and to some extent it is probably an individual response kind of thing. Some people seem to be able to handle lots of endurance exercise without losing muscle.

During really easy exercise (i.e., walking) the AMPK response would not be very high. During brief, but intense exercise, the same is true. It is the middle ground, moderately long, moderately intense, that probably produces the biggest AMPK response (i.e., tempo run intervals or prolonged zone 3 pace efforts, or half marathon pace).


More than 500 posts
Note also in the image I supplied above, that Akt, which is part of the mTOR - hypertrophy signaling cascade, is also part of the insulin signaling cascade (see below)


Bill Been

More than 500 posts
Well......that seems to have sent everyone to their corners to have a good think!

Let me spur further discussion:
How can the information from Dr. Prevost inform our training?
Does it help to explain the phenotypic expressions of different athletes?
What would be the likely outcomes from continued stimulation of one or the other of those signalling pathways?
What is the significance of insulin in the context of these pathways and does that inform dietary considerations?
Which signalling pathway best reflects YOUR training goals? If you wish to be stronger? If you wish to compete in a marathon? If you wish to train for general health and functionality?
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