Saturday, 24 October 2015

A Big LCHF PB in the Beachy Head Marathon

Fuelled by FAT

Nearly two years ago I made a big change to my life. I adopted a diet that had me fuelling my life and my running with fat, not carbohydrates. The low carb high fat diet is hugely beneficial for treating type 2 diabetes but it also has benefits for the distance runner.

There have been positives and negatives along the way but the positives, particularly with regard to my health have now made the diet a permanent change.

There was a big challenge too. Could I prove that it is possible to run just as fast fuelled by fat as I could when fuelled by carbs?

I thought I had reached a peak in performance a few years back. I ran a 3:06 flat marathon, I ran a sub 4-hour 3 Peaks and I ran the Beachy Head Marathon in 3:36:30  5 years ago. That last race was amazing, I was on top form and I came 24th. I was very proud of that achievement and I thought at the time that I would never better it.

But I’d heard a lot about how the low-carb high-fat diet can enable you to perform better and better the longer you stick with it. The science here is simple enough, we adapt to oxidize fat as a fuel source more efficiently over time, to the point where we can perform at perhaps 80% of our VO2 Max burning mostly fat. I knew that If I could do that then perhaps I could still get close to that Beachy Head time.

Well today I did just that. I’ve had an almost injury-free year that has enabled me to prepare perfectly for today. I ran a PB in a tough 20 miler a fortnight ago. I had a scare a week ago when I couldn’t run at all because of an odd knee problem but I rested up and this morning I felt great. The weather was perfect and so were the conditions.

I won’t bore you with a big description of the race, I wrote a long post about it last year. But for the record, today I knocked 6 minutes off my unbeatable PB!  I came 21st in 3:30:39.

Tomorrow I will be 50 years old and I am entering my fifties knowing that I am fitter and faster than ever before. 


  1. Hi Malcolm. I've just switched to the LCHF diet as well. I went for a six mile run today which was hard work. I had a back problem which lasted over two months so my fitness levels dropped drastically so I'm trying to build them back up. At the end of my six miler I was really flagging. A few hours later I felt extremely tired and sick. I'm guessing this was due to my body be starved of carbs. How long did it take you before your body adapted to running on no carbs? Thanks Wayne

    1. Hi Wayne.
      It typically takes between 2 and 4 weeks for your body to adapt to fueling on fat. Even if you are not running this can be a time of short breath and dizziness for some. After than things generally improve rapidly. We have many runners in our local group what have experienced than and all have started to feel more energetic again soon. Having said that, if you were already back to a low level of fitness then perhaps you would expect to feel tired after a 6 miler if you hadn't run for a while, and the change of diet will only compound this.
      I hope things start to improve for you soon.

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