Running on Fat

running on fat - fat-adapted - keto - ketosis - jogging
Feeling happy stretching after my first fully fat-adapted run.

Becoming fat adapted happens in stages. The first phase is what people generally talk about when they speak of fat adaption but switching from burning carbs to burning fat (ketones) doesn’t necessarily mean you are instantly an efficient fat burner in terms of being able to use fat as energy during exercise.

The first phase of fat adaptation can happen quite quickly if you keep your carb count low on a ketogenic diet. We’re talking anything from a couple of days – especially if you also deplete your glycogen stores by working out – to a couple of weeks. This is the phase where people often get symptoms known as ‘keto flu.’ Really, it’s just the body detoxing from its carb overload and if you watch your fluid intake + electrolytes, you shouldn’t suffer many (if any) symptoms at all.

The only ‘keto flu’ symptoms I noticed myself back in January were being a bit more tired than usual and finding it difficult to focus because the brain is quick to use sugar as fuel when it is available but actually runs better on ketones. The brain function seemed to improve gradually to normal levels over the first two to three weeks, but I was still struggling to find energy for my cardio workouts.

Yoga and resistance training seemed to work fine but actually running even as the slow plodder I normally am felt like trying to drag two logs around the track. This stage lasted not for days… or weeks… but months.

Today, Easter Sunday, is my first properly fat adapted run ever, so I thought I’d better blog this exciting news – Well, it’s exciting to me anyway…

How Can You Tell You Are Properly Fat Adapted?

Trust me, you will know. Not only will you be able to do any form of cardio exercise just as well as you did when you used to carb load, you’ll have way more stamina!

I came back after this morning run, fuelled only by bulletproof coffee, with tons of energy and keen to get back out there to walk the dogs.

Because of my slight carb blip the other day, I wanted to make extra sure I was definitely in ketosis when I came back from my run feeling so great… and yup, my blood ketones were 1.2 – Up another 0.6 from the morning before, which was the morning after my slip-up.

Perhaps doing a bit of carb cycling is not a bad idea. It also seems to be what most running sites recommend for people on a keto diet.

How Long Does It Take to Get Fat Adapted for Exercise?

In theory it should take about 6-8 weeks according to many of the online source I have checked out but for me it took three months, so cut yourself some slack if it isn’t happening as quickly as it ‘ought to.’

It is possible that my asthma had something to do with it. Inflammation levels were quite high when I started on the keto diet and my muscle cells might have struggled with getting enough oxygen because of that. At the time of writing this, I’m virtually asymptomatic with my asthma. Win-win!

If you are interested in learning more about a high fat, low carb diet for running, you may wish to check this article out.

Love and Light,


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