How to turn yourself into a Fat-Burner

Part 2: A Case Study...

Alan Couzens, M.Sc. (Sports Science)

Orig. published: June 7, 2008 Updated: Jan 14 2019

As promised, the topic of this week’s post is a follow up to my last post on the science of improving fat oxidation. In this post, I want to get down to the practical nitty gritty of how to go about turning yourself into a fat-burner. I figured the best way to do that is to present a real-life case study of one of the athletes that I've witnessed the greatest improvement in fat oxidation thus far and I will highlight some of the practical nutritional and training methods that we used to get him to that point.

I'd been coaching this athlete for a little over a year at the time I wrote this. He came to me as a relative ‘newbie’ to the sport (2yrs), with a background in rowing but limited experience over long-course triathlon and, , if we compare his best single sport efforts with his best longer duration tri efforts, a fairly marked performance drop off with increased duration. Incidentally, this profile describes the vast majority of male age-group athletes coming to me to prepare for Ironman (especially those of average to large size).

When we look at this athlete's first substrate profile, it is not hard to see why many athletes who have a 'big engine' and do really well over short duration efforts, have a hard time fuelling the longer events, e.g the Ironman.

As many of you know, my rule of thumb for best case Ironman (and day to day) pacing for an intermediate triathlete is ~10kcal of CHO/min. This is based on the simple math of average glycogen stores going into the event plus the maximum rate of glycogen sparing if the athlete fuels appropriately. Based on this athlete's first test, even at his slowest pace (~11:00/mi) he was already expending more than 10kcal/min of his CHO stores (gray on the chart) and only burning 3kcal/min of fat(in black). If he raced at this level of fitness, clearly he would be in for a very long day with a best case scenario of an ~5hr walk/jog marathon!

With very respectable ‘top end’ performances of 18:15 for a 5K and sub 60min for a 40K TT, clearly aerobic fitness isn't the limiter here! No, the engine is already plenty powerful(!), it's the fuel economy we have to work on so that we have enough 'gas in the tank' to go the full distance. The only way to preserve the gas in the tank is to improve our access to another (almost unlimited) fuel source, i.e. improve fat oxidation.



Our 2 goals for this athlete were (A) an improvement in fat oxidation at all intensities (B) a reduction in bodyweight. In order to accomplish these goals, I put this athlete on a diet of 400g of CHO/200g of (lean) Protein and 100g of (good) Fat. This represents 3300kcal/day and 48%/24%/28% macronutrient breakdown. Irrespective of whether the diet is eucaloric or not, I have found these ~percentages to be an ideal balance point for most serious athletes to make positive metabolic inroads while still fueling an appropriate workload in base training.

The importance of nutrition to fat oxidation in athletes has been strongly supported in the literature (e.g. this great recent review by Maunder, Plews and Kilding). While not ignoring the strong relationship between diet & max fat oxidation, it is important to also remember the lesson from the research of last week - that at higher (race specific) levels of intensity, the overall aerobic fitness of the athlete, i.e. the ability to hold power at low lactate, becomes more and more important. This brings us to..


To support our objectives of developing basic aerobic fitness, training volume was quite high (20-25hrs/wk) but initially of a very low intensity (with most sessions capped at the aerobic threshold, in this case, ~50 beats below max!!). Incidentally, this is the sort of training that a very successful German pro triathlete advocated when I was fortunate enough to chat with him about how he reached the pinnacle of the sport. It is what Dan Empfield called in an article about how the Germans trained “ridiculously slow”.

Our key sessions each week were long: a 4-6hr long flat bike (often a trainer session or trainer/MTB mix due to weather constraints) followed the day after by a long, relatively flat hike/snow-shoe of 3-4 hours. Other sessions during the week were an aerobic maintenance brick, a strength maintenance session, several short jogs and a few easy technique focused swims.

A couple of important caveats to the athlete looking to undertake such a program:

  1. The athlete was a graduate student with limited commitments and therefore had ample time to devote to such a program without losing sleep.
  2. The athlete was one of the most focused and compliant athletes in my stable. The above program is for the athlete intent on improving performance whatever it takes. This is not for everyone.
  3. This athlete had one of the widest gaps between his ‘top end’ performance and his ‘all day’ performance. Most of the programs for my other athletes, while similar in overall emphasis are more ‘balanced’ across the intensity spectrum.

So, what results did 9 months on the above program yield…….

Simply, the highest rate of fat oxidation that I'd seen to that point (elites included) and, the first athlete to achieve the golden number that Professor Tim Noakes hypothesized that Mark Allen must have averaged to support his Kona performances, i.e 10 kcal of fat burned per minute!! In some ways to us, that barrier was like the 4 minute mile, something that sounded theoretically possible but something that we wouldn’t really buy into until we witnessed it first hand. Well, we witnessed it and it was glorious!! :-)

Additionally, we moved that critical 10kcal CHO/min mark from ~11:00/mi (60% VO2max) to ~7:30/mi (80% VO2max)

This is not to say that I’m expecting this guy to be challenging Macca for the Kona win anytime soon. If you look at the charts you will see that while his overall economy is dramatically improving, he is still a big guy that chews up a good amount of O2 to hold a given pace. However, having a physiological quality that very few people on earth possess (if our sample is anything close to representative) is a great starting point!!

With the sort of base that this athlete has patiently and deliberately taken the time to establish, I will be expecting big things from him in the coming years.

Train (and eat!) smart.



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