How much fat was I burning?

It took some maths for me to figure out my own fat oxidation rate from my VO2max testing. Here’s the math (REE from VO2max).

At one point I got over 1.2 g/min of fat oxidation. Not bad considering that high numbers are often 1.6 g/min sort of numbers. Here’s the classical curve – an inverted parabola – of heart rate (x-axis) vs fat oxidation in g/min (y-axis).

The R^2 is 0.87 which is a pretty decent fit.

My sweet spot for maximum fat burning is about 120 bpm. My MAF range is 112-122 which nicely straddles this sweet spot of fat burning found during VO2max testing.

If you do the same maths on VO2max data you can find your sweet spot. But it won’t work well for fat burning if you are not fat adapted already. Or just use the MAF 180 formula.


Another Look at the Lambert Endurance Study

In this post I looked at a study on (Fat Adapted Athletes). I wrote the original post well before I had my own VO2max tests so I didn’t have a way to apply it to my own situation.

I found a link to a paper which is critical of the study (Asker E. Jeukendrup. High-carbohydrate versus high-fat diets in endurance sports.  Schweizerische Zeitschrift für «Sportmedizin und Sporttraumatologie 51 (1), 17–23, 2003).

The practical relevance of the improved endurance capacity at 62% VO2max reported by Lambert et al. [Lambert et al. 1994], however, is questionable since no endurance events are completed at these low exercise intensities.

I think this is a valid criticism of the work capacity of Low Carbohydrate athletes. There is a sweet spot where the diet is the most efficient.

However, in its favor the Low Carb diet lowers the RER and increases the VO2max point where carbs are oxidized. In my own VO2max testing, my RER crossed over the 0.7 line (From 100% fat burning just starting into burning carbs).

My own crossover point was about 59% of my VO2max which is quite close to the point noted above. That is a sweet spot since it has as high of possible fat oxidation with zero carbohydrate oxidation.

It is probably true that there are few competitive sports where operating at this point offers an advantage. Endurance activities of the Long/Slow sort may be an exception, particularly in long ultra-marathons.

In theory, a fat adapted person could perform very long activities at this level. This number is essentially the MAF number in my case. But that’s partly because I am already fat adapted.

What does this look like for the vegan FASTER study participant? His VO2max was an impressive 63.4. So, 63% of that is 39.9. At that value Damian’s %CHO was 88%.  That means 88% of Damian’s energy was coming from carbohydrates. That puts him at a performance advantage if the activity is within his carbohydrate stores but a disadvantage if the activity for a longer time where he needs to access his fat stores.

It’s also an interesting discontinuity in his data at the next point. There his VO2max dropped and his carbohydrate oxidation went way up. Not sure if this was a walk/run transition. Perhaps Damian is a much more efficient runner than fast walker?

I would say that it seems pretty clear to me Damian is not very good at burning fat. His RER never gets below 0.85 which is a mixed fuel mixture. Not sure how low a dietary fat level he is normally at?

Damian’s MAF Number

Damian was 32 years old. His MAF is 180-32 = 148. Unfortunately, there is no Heart Rate column in his data and I can’t figure out what the correlation to the RR BPM column means.

FASTER Subject 43

Damian Stoy was also a participant in the FASTER study (Jeff S. Volek, Daniel J. Freidenreich, Catherine Saenz, Laura J. Kunces, Brent C. Creighton, Jenna M. Bartley, Patrick M. Davitt, Colleen X. Munoz, Jeffrey M. Anderson, Carl M. Maresh, Elaine C. Lee, Mark D. Schuenke, Giselle Aerni, William J. Kraemer, Stephen D. Phinney. Metabolic characteristics of keto-adapted ultra-endurance runners. Metabolism, Volume 65, Issue 3, March 2016, Pages 100-110.).

put up his VO2max test results (UConn FASTER study and blood test results) and it is really interesting.

Damian is a male, 32 yrs old, 66″ tall vegan who weighs 128.6 lbs. Damian had a VO2max (of 63.4) which exceeded Ben Greenfield’s VO2max (61.1)  (Rewriting The Fat Burning Textbook – Part 2: Why You’ve Been Lied To About Carbs And How To Turn Yourself Into A Fat Burning Machine.). I don’t see what the termination conditions were for either test. Damian’s VO2max had not flattened out as far a I can see and neither had Ben’s. In fact Damian’s RER of 1.21 is supposedly past the RER of 1.15 that I was told was a termination co-condition.

Ben did cross over the 1.0 RER number at 10:31 into the test and Damian crossed over at 8:02. It could be said that Ben is a great fat burner but it must also be admitted that Damian is a darned good carb burner.

They may have both dropped out due to RPE (Rate of Perceived Exertion). Again, there’s nothing here that account for what ended their test.

RER vs Ben Greenfield

What is fascinating is the RER numbers. The lowest RER value Damian ever got was 0.85 and it happened at a very early point in the test (26.5 or 43% of VO2max). That indicates to me that Damian is very adept at burning carbohydrates but not at all adapted to fat burning.

I wonder if his very low body weight affected the result? Now an “advantage” that Damian had was that he weighed quite a bit less than Ben Greenfield (128.6 lbs vs 173.9). The VO2max number is divided by body weight. Ben’s Max VO2 (not adjusted for weight) was 4.75 and Damian’s was 3.71 so Ben is using a lot more air volume but he’s larger so he has to.

Damian is also a professional runner (What is Wholistic Running?). Ben is an all-round athlete.

His Other Vegan Bloodwork

Damian posted his Fasting Glucose number and it was 94 which is in the reference range of 65-99 but somewhat high for an athlete. Not unexpected given his high carbohydrate diet.

His platelet count is also low at 137 (reference range 140-400).

Fat Adapted Athletes

Fat adaptation is the shift from carbohydrates as the primary fuel source to fat as the primary fuel source. Here’s a study of fat adaptation (Helge JW, Watt PW, Richter EA, Rennie MJ, Kiens B. Fat utilization during exercise: adaptation to a fat-rich diet increases utilization of plasma fatty acids and very low density lipoprotein-triacylglycerol in humans. J Physiol. 2001 Dec 15;537(Pt 3):1009-20.). The study:

was carried out to test the hypothesis that the greater fat oxidation observed during exercise after adaptation to a high-fat diet is due to an increased uptake of fat originating from the bloodstream.

The study had 13 male untrained subjects, seven consumed a fat-rich diet (62 % fat, 21 % carbohydrate) and six consumed a carbohydrate-rich diet (20 % fat, 65 % carbohydrate). Note that this was not a low carbohydrate diet (at 21%). The length was 7 weeks of training and diet.

The performance test was 60 min of bicycle exercise performed at 68 +/- 1 % of maximum oxygen uptake. This rate is the maximum rate of fat oxidation from this study (Nutrition. 2004 Jul-Aug;20(7-8):716-727. Optimizing fat oxidation through exercise and diet. Achten J, Jeukendrup AE.). The test measured the RER and found that the high fat group used significantly more fat as fuel:

During exercise, the respiratory exchange ratio was significantly lower in subjects consuming the fat-rich diet (0.86 +/- 0.01, mean +/- S.E.M.) than in those consuming the carbohydrate-rich diet (0.93 +/- 0.02).

An RER of 0.85 indicates that the subject were taking energy equally from fat and carbohydrates so the high fat group was getting about half of their energy from fat and half from carbohydrates. The high carb diet group got much less of their energy from fat.

The leg fatty acid (FA) uptake (183 +/- 37 vs. 105 +/- 28 micromol min(-1)) and very low density lipoprotein-triacylglycerol (VLDL-TG) uptake (132 +/- 26 vs. 16 +/- 21 micromol min(-1)) were both higher (each P < 0.05) in the subjects consuming the fat-rich diet.

Not only was the fatty acid uptake higher in the high fat group the fat oxidation was greater.

Whole-body plasma FA oxidation (determined by comparison of (13)CO(2) production and blood palmitate labelling) was 55-65 % of total lipid oxidation, and was higher after the fat-rich diet than after the carbohydrate-rich diet (13.5 +/- 1.2 vs. 8.9 +/- 1.1 micromol min(-1) kg(-1); P < 0.05).

Burning higher fat rates reduces the amount of muscle glycogen which is used.

Muscle glycogen breakdown was significantly lower in the subjects taking the fat-rich diet than those taking the carbohydrate-rich diet (2.6 +/- 0.5 vs. 4.8 +/- 0.5 mmol (kg dry weight)(-1) min(-1), respectively; P < 0.05), whereas leg glucose uptake was similar (1.07 +/- 0.13 vs. 1.15 +/- 0.13 mmol min(-1)). 4.

The study conclude that

…plasma VLDL-TG appears to be an important substrate source during aerobic exercise, and in combination with the higher plasma FA uptake it accounts for the increased fat oxidation observed during exercise after fat diet adaptation.

If fat is available as fuel the body will use the fat in preference to the glucose. If insufficient fat is available the body will use glucose.

The decreased carbohydrate oxidation was apparently due to muscle glycogen sparing and not to diminished plasma glucose uptake.


Increasing Fat Oxidation Rates in Exercise

Fat Oxidation rates can be increased through training. This was demonstrated in this study (Hetlelid KJ, Plews DJ, Herold E, Paul B Laursen, Stephen Seiler. Rethinking the role of fat oxidation: substrate utilisation during high-intensity interval training in well-trained and recreationally trained runners.  BMJ Open Sport & Exercise Medicine 2015.). The study compared well trained (WT) to recreationally trained (WT) athletes on the same HIIT test. Both groups had similar carbohydrate oxidation rates but the WT athletes oxidized substantially more fat than the RT athletes.

Fat oxidation (0.64±0.13 vs 0.22±0.16 g/min for WT and RT, respectively) accounted for 33±6% of the total energy expenditure in WT vs 16±6% in RT most likely very large difference in fat oxidation (ES 90% CL=1.74±0.83) runners.

Despite similar RPE, blood lactate and carbohydrate oxidation rates, the better performance by the WT group was explained by their nearly threefold higher rates of fat oxidation at high intensity.

Note that this was not comparing Low Carb to High Carb athletes but it does offer the possibility that increased fat oxidation can lead to an increase in performance.

2018-07-08 Update: Found this interview with one of the study authors (Paul Laursen, PhD, and Dr. Phil Maffetone: Rethinking The Role of Fat Oxidation At High Intensities, Plus Practical Diet and Training Applications To Yield Results and More).

I don’t think this study invalidates anything related to RER and the VO2max testing. The FASTER study curves shows that some athletes (low carb ones in particular) are better at burning fat at higher intensities.

This does reinforce the value of training to increase fat oxidation rates. Increased volume is only possible through longer training which is done at a lower heart rate.


Using Body Fat for Energy

Since I got back my Bod Pod number of 7.5% body fat I’ve been concerned about having sufficient energy for exercise. Due to the Low Carb diet, the only fuel source I have is dietary and body fat. I have always noticed that my performance during CrossFit is low compared to other athletes, and the little bit of carbohydrates I eat are being used to make glucose for my brain and those other cells which require glucose.

From this study (Journal of applied physiology (Bethesda, Md. : 1985). 88. 1707-14. Substrate metabolism during different exercise intensities in endurance- trained women. Romijn, Johannes & Coyle, Edward & Sidossis, Labros & Rosenblatt, J & Wolfe, R.R. 2000.):

Our laboratory has previously shown that changes in the percent body fat result in altered lipolytic sensitivity that makes individuals with low body fat better able to mobilize fatty acids than might be anticipated otherwise. Thus lipolytic responsiveness is enhanced in subjects with low body fat and decreased in obese subjects.

This may also affect the Alpert study numbers (Hypophagia – How much fat can I lose in a day?).

Lower Performance When Fat Fueled (and Higher Heart Rate)

This one goes against the Low Carb/High Fat diet for athletic performance (J Physiol. 1996 Apr 1; 492(Pt 1): 293–306. Interaction of training and diet on metabolism and endurance during exercise in man. J W Helge, E A Richter, and B Kiens).

Ten untrained young men ingested a carbohydrate-rich diet (65 energy percent (E%) carbohydrate, T-CHO) and ten similar subjects a fat-rich diet (62 E% fat, T-FAT) while endurance training was performed 3-4 times a week for 7 weeks. For another 8th week of training both groups ingested the carbohydrate-rich diet (T-CHO and T-FAT/CHO). 2. Maximal oxygen uptake increased by 11% (P < 0.05) in both groups after 7 and 8 weeks. Time to exhaustion at 81% of pre-training maximal oxygen uptake increased significantly from a mean (+/- S.E.M.) of 35 +/- 4 min to 102 +/- 5 and 65 +/- 7 min in T-CHO and T-FAT, respectively, after 7 weeks (P < 0.05, T-CHO vs. T-FAT).

Evidence that the High Fat group was using fat as their fuel:

During exercise after 7 weeks, the respiratory exchange ratio (RER) was unchanged in T-CHO (0.88 +/- 0.01) compared with pre-training but decreased (P < 0.05) to 0.82 +/- 0.02 in T-FAT.

Heart rate is of particular interest to me:

During exercise, plasma noradrenaline concentration and heart rate were higher in T-FAT than in T-CHO both at 7 and at 8 weeks.

This matches my own experiences with exercise where I see high heart rates.

Heart rate increased progressively in both groups during exercise
to 191 +/- 6 beats/min in T-FAT and 181 +/- 6 beats/min
in T-CHO at exhaustion.


Heart Rate Training (HRT) – Part 14

Part 1 of this series.

I convinced an athlete friend to do the Five Mile MAF baseline test. This is the same athlete friend who did the protein test with me (Blood Sugar Responses Compared).  He is a trained runner. Here are his MAF test results. He is 35 so his MAF HR is 145. He was able to keep an average heart rate of 144. His average pace at that heart rate was 7:58.

He currently eats a mixed diet but does Low Carb some portion of the time.


Heart Rate Training (HRT) – Part 13

Part 1 of this series.

Last month I was not following the Maffetone method. I was getting up in the morning and running as fast as I could. I captured the data from one run around my neighborhood. This is the map of the 1.4 mile loop I ran around my neighborhood.

Elevation Data

That run has a pretty decent uphill (and downhill is even steeper) which makes the heart rate challenge even more difficult.

My Heart Rate Data

During my run, I also recorded my heart rate data. My average heart rate was 157 bpm and my max heart rate was 173 bpm. The average includes the warm-up section at the start. The average after warm-up was more – somewhere around 162 bpm. This is my max heart rate from the 220 minus age method. At 173 bpm I was over the 220 minus age method value. Probably not a great thing to do.

How does this correlate to my VO2max numbers? What was I burning when I was running? My chart from the last post was:

HR RER %Fat %Carbs
120 0.70 99% 1%
125 0.74 88% 12%
130 0.77 77% 23%
135 0.80 66% 34%
140 0.84 55% 45%
145 0.87 44% 56%
150 0.90 33% 67%
155 0.94 21% 79%
160 0.97 10% 90%
165 1.00 0% 100%

This shows nearly all of my run was fueled from carbs and almost none of the run was fueled from fat.

What’s Wrong with Burning Carbs?

This level of heart rate is not sustainable for very long when on a Low Carb diet. Running burns about 100 calories a mile. That is a significant portion of the body’s store glycogen store. Additionally, the body is glucose sparing when on Low Carb so it resists the additional glucose that is in circulation.

My Pace

My pace wasn’t all that great either. The app shows the average pace of 9:38.

Since I was at my heart rate max without training my heart rate to be lower my performance gains would have been hard fought.

Why Heart Rate Train?

Heart rate training offers the opportunity to improve performance within the fat burning zone. The promise is that speed will increase at the same heart rate as cardiac health improves.


Heart Rate Training (HRT) – Part 12

Part 1 of this series.

Second MAF Test

I did a five mile walk on a track tonight. It was an attempt to get a better MAF baseline. Here is the Strava (with my Samsung phone).

Here is my heart rate from my Samsung Gear Sport watch.

I did a good job of keeping my heart rate in the 112-122 range. I would have liked it to be a bit higher and still in the range but I am pleased with the results. Here’s my splits graphically (from the phone).

The splits show a good drop starting at the third mile. This is as expected. Also, I didn’t do a legitimate warmup, I just started into walking so it took about a half mile for my heart rate to get to the range. Next time I do one of these I will do a warmup and then start recording data when at the correct heart rate.

Here’s the happy walker after the 1-1/2 hours were completed.

If the MAF method works for me and I put in the training effort I should see those split times decline. Also, I should be able to start slow running soon.


Heart Rate Training (HRT) – Part 11

Part 1 of this series.

One last look at Ben Greenfield’s 3+ hour endurance tests might give additional insights into what I am thinking here. The original article and data is here (Rewriting The Fat Burning Textbook – Part 2: Why You’ve Been Lied To About Carbs And How To Turn Yourself Into A Fat Burning Machine.).

Throughout this entire 3 hour workout Ben kept his VO2/kg at around 35-37. That resulted in RER numbers from 0.73 to 0.76 which corresponds to between 76 and 90% of his energy coming from body fat stores. That’s exactly what I am referring to. The researchers deliberately kept the intensity at an amount that was appropriate for fat burning. Remember, Ben had a VO2max value of 61.1. So for this test, he was running at around 60% of his VO2max value.

It is interesting that the researchers chose the point that they selected. They chose to work Ben at a higher rate than his optimal point of fat burning. My guess is that they wanted to make his performance look better. Truthfully, he wasn’t completely fat burning for this. The optimal point would have been at 30.5 (or so) VO2/kg or close to 45% of VO2max. Not sure why they didn’t exercise him at that point?

But how did the VO2max test numbers compare to Ben’s endurance numbers? After all, that is the goal here. When Ben was at about 35 VO2/kg in his VO2max test that correlated to an RER of about 0.78. Ben performed slightly better during the endurance test because his RER at about the same VO2/kg was 0.73-0.76.

The consistency in the data shows it is possible to hold a rate of 60% of VO2max for a very long time. This, again, is due to being fat and not carb fueled. Ben could have probably gone on longer had he exercised at 45% of his VO2max (the test ended for time).

This data tends to validate Phil Mafetone’s methodology. What I can’t figure out was Ben’s heart rate. The chart shows RR BPM but the numbers are like 20-30.