As you might know, I'm the oldest dog on the Precision Fuel & Hydration team so a question I'm always asking myself is can this old dog learn new tricks? And of course the answer is always yes.

If you read my earlier training blogs, you'll know I took on the ÖTILLÖ Isles of Scilly Swimrun alongside Andy back in June. It was a completely new adventure for me, my very first Swimrun race, with 30km of trail running (in a wetsuit) and 8 km of open water swimming (in running shoes).

What I also did during that race was implement a nutrition strategy that I had never tried before. My calorie expenditure for the event was 4,700 kcal but I only took in about 500 kcal of carbs during the whole event.

Basically, I was 'Running on Empty'. I should have bonked.

How did I manage it? I used exogenous ketones to fuel my 5 hour 15 minute race.

Now before we go too much further with this story, some housekeeping. I'm not a nutritionist, and I don't pretend to be one on the internet. Also, I undertook this exercise as an N=1 experiment. I was racing to win a pair of socks, in other words the outcome was of zero importance. Please bear in mind both of these important facts if you decide to try something similar.

Ketogenic diets, exogenous ketones, they seem to be all the rage. In fact if you head over to Google Trends you'll see that over the past five years the search term 'ketogenic diet' has shot up like a hockey stick.

So, what is a 'ketogenic diet'?

People who follow a ketogenic diet eat lots of fats, a modest amount of protein, and very few carbs (usually a ratio around 75%/20%/5%).

This forces the body to become “fat-adapted” and then it preferentially burns fat instead of carbs, which in turn is converted into ketones, which are used by the body as a primary fuel in stead of glycogen.

I'm not going to spend too much time going into the intricacies of ketogenesis. If you're interested in learning more, I recommend the excellent book by two pioneers in the field, Jeff S. Volek PhD and Stephen D. Phinney MD PhD, 'The Art and Science of Low Carbohydrate Performance'.

I read this book back in 2013 and it prompted me to look further into the subject. Since then I've followed the topic with interest as further research has emerged.

Personally, I've never been in a state of ketogenesis, but I do consume a high proportion of healthy fats in my diet and my ratio is closer to 50%/20%/30%. I also do a 24 hour fast about once every two weeks. I'm quite happy going out on a 10km run or 2 hour Z2 bike ride in the morning having had no food since the night before. I am fairly well fat-adapted.

Bear with me a little longer as we get a little more technical. To initiate ketosis, a common practice is to engage in a 72 hour fast. During this period your body will consume all available glycogen reserves and you'll get incredibly cranky, but eventually your body will look for an alternate food source — fat — which we all have in abundance and start the process of ketosis (and most importantly you'll start to mellow out!).

Ketones in the blood steam are measured in mmol/L and Volek and Phinney suggest in their book that ‘light nutritional ketosis’ is between 0.5mmol/L and 1.0mmol/L and ‘optimal ketosis’ is between 1.0mmol/L and 3.0mmol/L.” After a 72 hour fast the average person will be happily burning fat as their primary fuel source, they'll be in ketosis.

Is there a faster, less painful way to get into a state of ketosis?!

A 72 hour fast is a tough way to get into this state and it isn't desirable or practical for a lot of people. What if there was a faster way to achieve this state?

As you can imagine, quite a few people are interested in this and one notable group is the US Department of Defense. They initiated some research (through DARPA, the same people that brought us the Internet) into developing a method of speeding up this process of ketosis using exogenous ketones (i.e. ketones produced outside the body).

One of the groups that carried out this research was led by Dr. Kieran Clarke, a professor of physiological biochemistry at the University of Oxford. They developed the world's first ketone ester and this in turn was recently commercialised by a company in the Bay Area, called HVMN.

One of Dr. Kieran Clarke's research assistants on the project was Dr. Brianna Stubbs, who has now moved across to San Francisco as the Head Scientist at HVMN. She also happens to be a two-time Team GB world Gold medalist rower, who recently qualified for the 70.3 Age Group World Championships in South Africa later this year. If you want to learn more about Brianna, exogenous ketones, HVMN and many other things check her out on the STEM-Talk podcast.

I know we've gone down a few rabbit holes with this story so far, so if you're still with me, thanks. We're getting close.

Having followed this space with great interest over the past few years, when HVMN announced the commercialisation of the ketone ester I jumped straight on it and ordered some product from the first batch ever produced.

Then, much to my surprise, Brianna reached out to me in an e-mail asking about Precision Fuel & Hydration. Back and forth we went and it turns out that Brianna grew up just down the road from where Andy currently lives in Christchurch and that Andy had even paddled regularly with Brianna's dad. Whoa!

Andy and I were on a West Coast road trip back in May and we dropped in to see HVMN while we were in San Francisco. In that meeting I learned more about the performance potential for exogenous ketones and I decided that I would give it a go and use them in my upcoming ÖTILLÖ race.

On the morning of the race, about 2 hours out, I had a typical breakfast for me which involves absurd amounts of coffee and some kind of nut/berry/oatmeal and full fat yoghurt combo.

Then I kitted up and, about an hour before the race was due to start, I consumed the exogenous ketones — I knew from an earlier test that within 30 minutes this was going to bump my blood ketone level up to 3 mmol/l.

Now an obvious question here is why? Why did I choose to use exogenous ketones for this event. Well, the profile of a swimrun race lends itself to their use perfectly. It's impossible to eat during the swim (and for half the race you're in the water) and, for me, consuming anything while running has always been difficult, I invariably get some form of gastric distress.

So a nutritional solution that allowed me to use my extensive fat reserves and operate more like a diesel engine was ideal.

Another key factor was that this was going to be a 5 hour+ event, so I was going to be operating very much in Zone 2, no sprinting, no big efforts and definitely nothing anaerobic.

Having said that, remember I was racing with Andy Blow. For the last 10K run he decided we were going into hunting mode to track down a few teams up the road. Prior to this effort, I did grab a can of Coke at a feed station because I knew that a rapid hit of sugar was going to be very useful...

Overall, from a nutritional standpoint, it was a fantastic day. Absolutely no gastric distress and I never once felt like I was out of energy, or going to bonk. On paper I used all my glycogen reserves and on past experience would not have been able to go that long without a significant carb top up.

For me it's something I will most definitely use again. If you're thinking of trying these yourself then I would suggest a more conservative approach than the one I took and to test them in training first!

By the way, I did top up my depleted glycogen reserves later that evening with a significant amount of Scilly Isles beer...