Does a low carb high fat diet work for runners?

On a quest to improve my running, I’ve been trying out a low carb high fat (lchf) diet.

I’ve read a number of different blogs and forum posts singing the praises of low carb high fat in relation to running performance, especially for endurance running, and I’ll tell you what, it sounds like a real no-brainer. As we all know your body needs fuel when running, and when your muscles are primed with a ready supply of glycogen (from carbs) this is used a your main source of fuel (along with some fat). The problem is that your muscles can only hold a limited supply of glycogen, and when it runs out you’ll know about it. “Hitting the Wall”, “Bonking”, whatever you want to call it, running out of fuel is no fun!

But what if we didn’t need to rely on this limited supply of glycogen and we could turn our fuel needs on their head? What if we could use our fat supplies as the main fuel along with just a little bit of glycogen? Even the leanest runner has thousands of calories worth of fat available to them, so if we could do this we’d never need to “hit the wall”. It sounds too good to be true, but from what I’ve read a number of runners have used this method with great results so I’m going to give it a go.

Carbs, Carbs, Everywhere

To get your body to adjust to burning fat it should be as simple as reducing the carbohydrates you eat and replacing those calories with fats.

Now, being a big fan of bread, pasta and anything sweet or sugary this was not going to be easy. It isn’t until you start looking at the nutritional information on the packet that you notice how many carbs some foods contain. Some aren’t to surprising – biscuits, cakes, etc are all big scorers, but rice, carrots, apples and bananas? These are all high up on the list too!

Getting Started

After consulting a number of different sources I decided on between 100g – 150g of carbs per day. This isn’t as low as the serious low-carbers, but was within a range where my body should adapt to burning fat rather than glycogen. Keeping track of everything I ate was essential to start with, but once I got a grip on what I could eat within my carbohydrate limit it became much easier. Bread and cakes out, Avocados and spinach in!

Apparently it’s normal to experience a period of low energy when swapping from one fuel to another, also known as becoming fat adapted, and I definitely experienced this. My running was slower and harder than it had been for quite some time and I struggled to maintain pace. I reduced my speed work for a couple of weeks to allow myself time to adjust and then re-introduced it back in but I still struggled.

I had no problem when churning out long slow miles but anything else was draining. Even two days after a speedwork session my legs would still be exhausted and it was an effort just climbing the stairs. Something wasn’t right.

After giving the lchf diet 5 weeks I decided it wasn’t working for me, at least not in it’s current form. Maybe this wasn’t long enough to get the full effects, I don’t know, however it’s definitely not been a pointless exercise. It’s got me eating a much more balanced diet, with much less sugar and lots more fruit and vegetables, and more importantly it’s got me thinking about what I’m eating.

What Now…

I’m going to try keeping a low(er) carbohydrate diet around my easier running sessions, but introduce a carb and protein hit as soon as possible after hard sessions to refill those muscle reserves. The fasted long slow runs were working well for me so I’ll keep those too. Let’s see how that works and then I’ll review again.

From this experience I can see that lchf could work for someone who has a level of fitness allowing them to run at their desired pace fairly easily, but I’m just not sure that fat works as a good fuel for more intense running, especially speedwork, at least not for me.

Do you have a different experience of lchf or did you come to the same conclusion? I’d love to hear your experiences. Give me a shout on any of the usual social media or in the comments below.

Remember: I’m definitely not an expert in nutrition and I’m just giving an account of my personal experience. You should definitely go and talk to a doctor or professional nutritionist before making any changes to your diet.

Photo by notyourstandard

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