Metabolic Profiles of Kona Qualifiers

Alan Couzens, M.S. (Sports Science)

May 8th, 2015

I received an interesting question last week from an LCHF athlete who forwarded me his latest metabolic test data. While, like most LCHF tests I’ve analyzed, it had some pretty impressive max fat oxidation numbers, he asked the question – if it looks this good, and Ironman is a metabolically limited event, why haven’t I achieved my long term goal of Kona qualification?

So, for this athlete, and for the rest of you who may be wrestling with the same qu, I went deep into the database to compare this guy’s results (along with results I have from 4 other LCHF athletes of similar weight) with the average numbers from Kona Qualifiers (of similar age and body mass) that I’ve tested to date. The results are interesting…..

The difference between the mean metabolic profile of the LCHF athletes and that of the Kona Qualifiers is shown below (35-44yo male, body mass 75+/- 2kg)…

The difference between the 2 curves is one of height vs breadth. While the LCHF athletes clearly had higher maximal fat oxidation rates – approaching an average of 10kcal/min, they also had a limited breadth of fat oxidation, with fat burning becoming worse than the Kona qualifiers at ~265W and shutting down completely at ~290W.

The Kona qualifiers, on the other hand, ‘only’ reached a fat oxidation peak of ~5kcal/min but they held fat oxidation rates close to this peak over a much broader range.

Still, considering a competitive age group Ironman takes place smack bang in the sweetspot of max fat ox, this all begs the question why doesn’t the LCHF athlete absolutely crush the average Kona Qualifiers at this intensity? Certainly the data indicates a significant metabolic strength for the LCHFer's in this range. In the absence of pre-race muscle biopsies, I can only offer an educated guess, but here is what I would suggest…

In order to get your fat oxidation up to 10kcal/min you will need to severely restrict CHO. When you severely restrict CHO, muscle glycogen stores will never be full to capacity. A competitive Ironman output for an average size age-grouper is an ~15kcal/min proposition. Meaning, even with 10kcal/min coming from fat oxidation, our prospective qualifier is still going to need ~3000kcal coming from CHO over the course of their 9 and a bit hour day. This presents a problem for the athlete who has been religiously shunning CHO!

LCHF presents 2 problems for Ironman athletes: When ‘out of practice’, in dealing with CHO, LCHF athletes will tend to have both lower overall glycogen stores and their bodies will be less effective in the oxidation of exogenous intake (something I talk about here). In my experience, (and the experience of the guy who inspired this post) this leaves the LCHFer coming up just a little short on output over a competitive Ironman. They can roll 10kcal/min for days (literally!) but start pushing up just a few kcal/min to the 13/14 range and they find themselves lacking that little bit of ‘punch’.

This is not to discount the importance of metabolic fitness for Ironman athletes. While the 10kcal/min represent one extreme, keep in mind that the mean max fat ox. of all the athletes that I've tested is 3.2kcal/min. The bulk of athletes with competitive Ironman aspirations still need to give metabolic fitness, both in terms of training and nutrition, significant consideration.

Bringing this all together, the take home message for the serious Ironman is simple – shoot for optimal rather than maximal fat oxidation! Give just as much attention to the breadth of your fat ox curve as to the height.

I offer some tips on how to facilitate this nutritionally in this post. From a training perspective, while emphasizing aerobic development, regularly check in on your top end just to make sure it’s still there! Obviously, the most effective means of this 'check-in' is via metabolic testing, where you can compare the development of your own numbers to the norms given above.

Bottom line, though, as an athlete, it’s important that the nutrition always supports good quality training specific to the goals of your event.

Train (& eat) smart,



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