Friday, 26 December 2014

Low Carb High Fat - How fast can we go?

You may remember from several posts this year that the big question on my mind has been "How far can we go on LCHF?"  And at the Beachy Head marathon I went a reasonable way towards discovering the answer to this question for myself. Last week I heard from a local runner who has done a lot more; and here is an account from Luke Ashton who ran up and down a nasty hill 40 times covering a distance of 116 miles in 27 hours and 20 minutes. Luke uses nuts, cheese, olives,  avocado and olive oil as his principle ultra-running  fuels (he adopts an interesting no sugar no grain diet) and has run for up to 8 hours with no fuel but water; although he does have a ‘trickle’ of sugar on longer runs which is not surprising as we do indeed need some glycogen in the tank when moving at pace (as I described here: . Luke’s achievement is all the more impressive when you consider that it was early December and very cold on that hill.

I am hoping to go a little further than before (perhaps 5-6 hours) at some point next year, but for now my attention has switched to the opposite end of the low-carb debate. “How fast can we go?”.  

It is a long-held belief that fat-adapted runners can’t go fast; apparently you need to be burning glycogen in order to train hard and race.  Right from the outset I have been rather skeptical about this suggestion. The science behind this is partly based around The Crossover Point Hypothesis which was developed by George Brooks at UC Berkeley; this describes the point at which we cross over from burning fat to carbohydrates. This investigation established that athletes, depending upon level of aerobic training, “crossover” between 35-65% of their VO2Max. Now I have already established that with the complete absence of carbohydrates to fuel on I can work for normal periods of training at much higher than 65%. The established science (from Venables; “Determinants of fat oxidation during exercise in healthy men and women: a cross-sectional study”) states the absolute maximum amount of fat an athlete can burn is about 1.0 grams/minute. For normal athletes (including myself) this is not enough to train at high intensity.  One important thing to note from this study is that it was performed upon normal healthy people, not on fat-adapted runners. The body is not a chemistry set where all things remain equal, in the absence of carbs we  adapt to use fat more efficiently. Regardless of this the conventional wisdom has relied upon this kind of science to convince us that fat is only a fuel for gentle endurance and that we will burn-out if we speed up. Our fear of failure, or perhaps out fear of looking odd has prevented us from testing this wisdom for too many years - my ‘Fuelled by Fat’ running shirt certainly seems to mark me out as a bit of a weirdo amongst serious runners, until I run past them that is! 

Thankfully the science is being tested again. A recent "FASTER Study" by Jeff Volek (read this report by ultra runner Zack Bitter) appears to suggest that the 1 gram per minute limit is not correct at all and almost twice as much fat burn can be achieved, leading to the possibility that much more energy for hard work can be derived from fat that was previously thought possible. This study is not yet complete but an initial review of the data available so far is here:

Last January when I set out on LCHF I was not particularly fit. My recent average mileage was about 20 miles per week but I had been doing a little speed training and had notched up a couple of local Strava segment records in December.  I had been expecting the first few weeks on LCHF to be hard work but perhaps luckily for me they were not. I ran 21 times in the first 4 weeks, including both distance on hills and hard speed sessions.  In week 5 I was getting into what I would regard as 'hard' training. I then had a couple of non-running injuries that put me out of action for several months but I was left with the impression that after the initial period of adaptation I had been able to train and race just as hard as ever. 

For the record by ‘hard’ I mean sessions like 4*1 mile reps at 5K PB speed or 3*1K hill reps at PB minus 30 seconds pace. This is as almost as hard as I have ever trained.  Since then I have been aiming at distance running, but I have always had the feeling that I could push a lot harder if necessary and I’ve still notched up another fistful of Strava records without any speed training.

It’s important to have this understanding of what constitutes hard training, because what I am hoping to do in 2 months time is to break my 5K PB. I am no longer a sprinter and have not raced for less than a mile in 10 years and so there would be no direct comparison to be made by running a fast 400 meters; but I set a 5K PB of 18:57 at Hove ParkRun 2 years ago on the back of several months of hard training and so that sets a carb-loaded benchmark that feels like an appropriate target.

I have done no speed training at all since January and have only just started with steady half mile reps in the last week. So I think that this situation represents a fair test of what can be achieved on LCHF. I aim to follow my normal plan of 1 speed, 1 tempo, 1 longish and perhaps one fartlek run each week for the next 8 weeks; and all being well I will have a pop at my PB at ParkRun in February.

By the way, I am in no way suggesting that running on fat is better for performance than running on carbs. I am simply trying to help remove the barriers that have been put in our way and enable people to make a better informed choice about what they eat, rather than follow the received wisdom. I do believe that eating LCHF is a better public health choice than eating HCLF as we have been instructed to do for the last 30 years.

It is no coincidence that this challenge is timed to happen at about the same time as the Premier of the new Cereal Killers movie – “Run on Fat” ( My wife and I contributed a tidy chunk of money to help make this film and we will be holding a public screening of it in Hassocks when the film premiers. One of the suggestions in this film will be that, like any other form of training, fat-adaption is a steady process of change and the longer we spend adapting the more efficient we can get; this leads to the possibility that we can adapt to the point where we can run fast as well as long. Now I have no problem in believing this as I feel that I have experienced it already; but it would be fun to put this one to the PB test.

So, call it vanity or perhaps even science, but I’d like to have some evidence of my own to help support this myth-busting production.

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