How to turn yourself into a Fat-Burning Machine

Part 1: What Science Says...

Alan Couzens, M.Sc. (Sports Science)

Orig. published: May 25, 2008 Updated: Jan 9 2019

Pictured: Inaki, clearly in 'fat burning machine' mode! Regular metabolic testing is a big part of improving your fat-burning ability over the long term.

This post is going to be a little different to my previous posts on the merits and methods of getting your fat burning tested. Hopefully by now, you’re as convinced as I am that the ability to utilize fat as a substrate is an important, distinguishing factor between those who excel at Ironman and those who, despite impressive short course results, are unable to put it together for ‘the big one’.

No, this post isn’t for the fence sitters waiting for academia to catch up before making a decision as to whether to devote their time toward improving this physiological variable. This post is for those athletes who have gone through the testing, identified that fat oxidation is a limiter and who are ready to roll up their sleeves and get to work on turning yourself into a fat burning machine!

So, this first post is going to give you a little background reading on what science says about means and methods to improve your ability to utilize fat as a fuel. My next post will be entitled “Fat Oxidation: A Case Study” and will provide more details on the practical methods I've employed with athletes I've worked with to improve fat burning, along with the magnitude of changes you can expect (Spoiler alert: They're significant!)

But first….

One of my favorite papers on fat oxidation is "Determinants of the variability in respiratory exchange ratio at rest and during exercise in trained athletes." Julia Goedecke and her colleagues at the Sports Science Institute of South Africa conducted this landmark study in 2000 that looked at individual differences in fat oxidation across a range of exercise intensities (rest, 25%, 50% and 70% VO2max).

The reason that I find this study especially interesting is because it looked at how fat burning changed with intensity for the same subjects and, just as importantly, what factors were most important for each. More specifically - how important were the key nutritional factors (FFA availability, dietary intake etc) vs the training factors (training mileage, blood lactate at each intensity etc)

Let's start by looking at the large range of fat burning that Julia and colleagues found at each intensity level..

She came to a number of conclusions that have very practical implications for ultra-endurance athletes:

#1. There is a wide variation in the amount of fat that is oxidized at rest.

If you look at the dark blue line (resting fat oxidation), you can see that, while the average fat oxidation at rest was ~75% of total calories burned, some of the athletes were deriving almost 100% of their resting energy from fat, while others were only deriving 25%. This has HUGE implications on both recovery and body composition. If you are currently in the 'carb burner' camp, by increasing your rate of fat oxidation at rest, you could potentially burn body fat 4x faster than you currently are!!! Not to mention preserving your precious glycogen stores for your next training session!

#2. Those subjects who burned more fat at rest also tended to burn more fat at ALL EXERCISE INTENSITIES (see chart)

While the distributions get a bit narrower as intensity goes up, there was still a fairly wide (& important) range in fat-burning ability. Even at 70% VO2max (elite Ironman race output), while most were down to ~10% fat oxidation at that point (and others had ZERO fat oxidation), some of the subjects who were 100% fat burners at rest were still deriving 40% of their energy from fat! In race performance terms, this has HUGE implications, as Ironman is, fundamentally, a metabolically limited event, i.e. the race is won by those who don't run out of gas!

So, what were the distinguishing factors between the gas-guzzling ‘corvette’ athletes vs the uber-economical ‘prius’ athletes? Interestingly the factors changed somewhat with increasing exercise intensity.

a) The concentration of Free Fatty Acids within the blood

This is THE pre-requisite for fat burning at rest and all exercise intensities. In other words, if your blood is full of glucose as opposed to FFA’s, you will not be providing the muscles with any stimulus to ‘learn’ to use fat as a fuel. High FFA levels (and low-moderate blood glucose levels) are a pre-requisite for fat burning. This has LARGE nutritional implications. If you keep your blood sugar levels perpetually elevated, you will never become a fat burner. Period.

b) The concentration of fat-burning enzymes within the muscle.

While short chain and medium chain FFA’s can diffuse into the mitochondria freely, long chain FFA’s must ‘hitch a ride’ with the enzyme carnitine palmitoyl-transferase in order to make it to the mitochondria. A shortage of this enzyme will mean that even if you have sufficient FFA’s within the blood, the long chain ones will be left by the side of the road with their thumb in the air waiting to hitch a ride. This enzyme is inhibited in the post absorptive state when blood glucose is elevated.

c) Mitochondrial content within the muscle.

Of course, in order for FFA’s to be ‘burned’ and used for fuel we need a sufficient number of ‘engines’ to burn them. In this sense, the number of mitochondria within the muscle will ultimately limit the rates of fat oxidation, especially as intensity increases. The researchers found that as exercise intensity goes up, these training related factors become more important to fat-burning (& were most important at ~70% VO2max). In fact, *the* most predictive factor of fat burning at 70% VO2max was how low the athlete's lactate level was at this intensity. Clearly, this is a function of aerobic fitness, which in turn is a function of the number of contractions performed by each muscle fiber, or put another way, as my buddy Chuckie V is fond of saying, miles make champions.

Summing up, the paper suggests that if you want to be a fat-burning machine both at rest and during exercise, you need: A high level of FFA availability, an abundance of fat-burning enzymes that come with challenging your body to create energy from fat..and...a whole lot of 'energy factories' within the muscle that only come about from a whole bunch of low intensity miles.

So, there you have it – 2 simple ways to turn yourself into a fat-burning machine:

1. Cut sugar from your diet (and moderate total CHO intake)

2. Train MORE in your aerobic zones (cut out the hard stuff until after you have a strong 'Metabolic Base' established).

Not exactly earth-shattering revelations, but based on what we are seeing in the lab these 2 principles are not being applied by most athletes. You can beat a large portion of the field by making these simple (though not easy) changes.

I’ll get down to some more specifics of just what a 'moderate CHO intake' diet looks like along with some details of how to train to establish a 'strong metabolic base' in the next post. Until then...

Train (and eat!) smart.

AC.

Update:

Benzing asks:


“I have been tested and my suspicions confirmed that I am about as inefficient as possible. Is there any data on how long it takes a 44 old female body to retrain itself when practicing the prescribed training and change in diet?”

There has been a good amount of research on the physiological effects of low and moderate carbohydrate diets (e.g. Ravussin et al, 1985, Weinsier et al, 1992). Generally speaking, individuals who adopt a low-moderate CHO diet can expect a change in their resting RQ of ~.05 within 12-16 weeks. This translates to an increase in resting fat oxidation of ~20%.

The extent to which this carries over to performance during exercise is dependent on your overall fitness, or how many ‘engines’ you have to process your new found fuel line. This is the reason that studies looking at the impact of training on fat oxidation have returned mixed results. Keep in mind however, that even for the relatively unfit, burning more fat at rest is still a good thing!!

The vice versa argument also applies, as we found while driving the Sportsmobile back across the country from the Triple T. You can have the largest capacity tanks and the biggest engine around, but until you pay the lady at the gas station and she turns the fuel pumps on, the number of miles that you’re going to be able to drive is severely inhibited. :-)

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