Fat burning beast!

(Erin Macfarland ) #1

Ok I am very excited to report the results from my active metabolic assessment. I am a runner (mostly 5k and 10k distance racing) and lift weights. I’m in my second go round with keto (first time was beginning 2015 to spring 2016) and started back again in Sept 2016. Body fat is 12%, vo 2 max is “optimal” which is the highest possible score. Here’s the drum roll part…as demonstrated by Phinney and Volek, fat adaptated athletes continue to utilize fat as fuel in higher heart rate zones at a dramatically higher rate than carb burners. My fat utilization rate in zones 1 and 2 is nearly 100%. My rate at zone 5 (highest heart rate zone) is…between 60 and 70%! That is incredible. That means my body is experiencing less stress and oxidation than if I were burning carbs. Keto on ! It’s amazing

Fat adapted zone 2 heart rate?
KETO Bonking
Heart Rate Zones - Fat Burn
Endurance athletic performance via anaerobic glycolysis issue?

Fantastic! I’m so happy you got these tests done and shared the results with everyone. :bacon:

(Erin Macfarland ) #3

There is so little info out there it’s important to share !

(ianrobo) #4

would love a metabolic assessment like this but bet it is expensive ?

(Erin Macfarland ) #5

I’m not sure where you are located geographically, but many upscale gyms offer such a service as well as some specialty metabolic/weight loss type clinics located in hospitals or universities. We live in Colorado and go to Lifetime fitness, which is a national chain of huge fitness centers. I believe the typical cost of this test is around $200, but my husband works for them part time so I used one of the tests he had available to him. If you are an athlete and fat adapted it is very much worth knowing your HR zones and where you’re at with your fat utilization!

(ianrobo) #6

UK here but just checked and could not find anything, having a lactate threshold test next week so will be fascinating to compare to last June when I was a fat burner and fitness wise about the same.

(Erin Macfarland ) #7

Share your results!

(ianrobo) #8

I will !! with Lactate I expect a much higher power level obviously !


That is amazing. The fat burning at high intensity seems very high. Are you able to post the graph or table from your assessment?

Should look something like this (but with speed rather than watts)

(Erin Macfarland ) #10


A university with a sports physiology department, or a technical institute of sport (or local equivalent) should offer this assessment.

Just figure out where elite athletes are going for their testing and it is very likely that you can pay for a private assessment.

(Erin Macfarland ) #12

One caveat, the zone 4 and zone 5 would not register because of the percentage of fat oxidation, my trainer graphed out those zones for me based on the previous numbers. Notice in zone 1 I hit 100% fat utilization!


Hi Emma,

Those are great results, (and I don’t want to take anything away from them), but I would request the test again. Looks like their machine simply stopped reading,

Also, looks like your trainer has just taken your previous zones and taken a straight line approach to give you your % estimates. Every substrate utilisation test I’ve seen (and that’s a few) shows a crossover and rapid dive at high intensity.

If you look at the graph above, you will see that it essentially mirrors yours until high intensity. The same for the below graph. If you stop the reading at 11km/hr, which might roughly equate to zone 3, you get this:

It looks like that person can sustain those levels right through, but as soon as intensity ramps up, the body switches over to carbs to provide power…

Again, your test looks great, and VO2 is great, but your trainer/tester can’t make an assesment on fat utilisation at high intensities based on the prior zones.

But, your test results definitely are the result of a Ketogenic diet. Here is an interesting article from a Junior World Ironman champ and his changes after shifting to a LCHF diet.

(Erin Macfarland ) #14

He had never seen anyone who was fat adapted and had readings in the higher zones as I was running that some how didn’t translate to the graphs. I may request a redo of the higher zones for accuracy, but I went on his interpretation of my percentages, which at least I know are still very high compared to a carb burner. I’m not sure if the issue was the equipment, it seemed to work ok to gauge my vo 2 max. Maybe a bike test would give me a better reading?


Running on a treadmill is fine for substrate metabolism utilisation testing. But my guess is that the mouthpiece or machine measuring your CO2 exhalations stopped working/reading. This is not required to measure your VO2 max (that is just heartrate and treadmill speed).

But to give you an estimate of 60% at high intensity, your tester has just taken a trend estimate and drawn it forward. That actually makes sense once you say that the’ve never seen a fat adapted athlete. Because a non fat adapted athlete graph looks a lot like this:

So, they assumed that the prior trend continues. But what actually happens in fat adapted athletes is this:

You always see the carb line rocket up (in your case, the fat utilisation line rocket down) at high intensity. Basically, we can’t sprint on fat.

Knowing what your fat ulitilsation at a very high intensity might not be useful for training, but if you are in a 5k race you will almost certainly be burning more carbs than fat (above threshold).

Again, I don’t want to take anything away from your results - they are very impressive, and I would be happy to have them, but your tester has done you (and themselves) a disservice by estimating out the last two zones, because it all goes crazy in those two zones (for fat adapted athletes)


Good article here on the subject.

And yes! you are correct, the best part of those results is the far far lower oxidative stress that you put on your body during exercise. For me, my inflammation is much less and my recovery is much quicker.

(Erin Macfarland ) #17

I race mostly 5 and 10ks and generally don’t hit my threshold during those efforts so I can assume I’m in a predominantly fat burning state even when I race. Interesting in those graphs from other fat adapted athletes that they never hit 100% fat utilization in zone 1.


They are averaged, which generally provides a more accurate/replicable result.

(Erin Macfarland ) #19

I checked in with the trainer about the readings, apparently their software does not register fat utilization in the higher zones, which is why the report I received said I was buring 100% carbs in z4 and 5, which is obviously not correct. So it’s an issue with the software. I will keep in touch with him and see if there are improvements that give accurate readings


Hmmm, doesn’t make much sense to me. As long as they can measure CO2 and O2, they can measure fat and carb utilisation. i.e The method, measurements, calculations and system requirements to get readings at z1 are no different to those required to get readings at z5.

Perhaps because they are a gym, they don’t want to put people through a maximal test, for liability reasons or something.

They do show pictures on the web of their software producing information on Z4 + Z5 though, so who knows.