How does one go about becoming fat adapted as a marathon runner? Maybe more importantly, what is it like for an older marathon runner who attempts to make a transition from being a glycogen fuelled runner to a fat-adapted runner? I decided to run a 6-week experiment in order to do just that. The process is rather simple and the underlying questions must be asked:
1. Why would someone wish to do this?
2. Does it help or hurt ones marathon running?
In this post, I will go through my personal experience and give you my conclusions.
Why Transition to Becoming Fat Adapted?
I had two objectives for this 6-week experiment. The first reason for the transition from being glycogen fuelled to being fuelled by fat was to attempt to relieve some arthritis pain in my hands. I’m 57 years old and the arthritis has set in making it hard to do certain tasks due to the pain in my hands. It is widepy reported by the Keto community that removing, or greatly reducing carbohydrates from the diet is an extremely effective method for relieving all inflamation built up in the body, and this includes arthritis.
The second reason for becoming fat adapted is to try to drop some weight before my next marathon training block began. I’ve been saying for a while now that I’d like to begin my marathon training as close to race weight as possible. This would allow me to focus more on the training sessions and fuelling my runs and recovery more effectively. I endeavoured to maintain a calorie deficit over these 6 weeks and hit an average of 1800 kcalories per day and see where I could land on the scales at the end.
For many runners though, there are reasons more specific to performance. Many ultra endurance athletes become fat adapted because it is simply far easier to fuel long distance events using fat, rather than carbohydrates. The human body stores glycogen in muscle tissue and to a lesser extent in the liver. In total, this is generally somewhere in the region of 1500 – 3000 kilocalories worth of energy. The upper limits are for those athletes that have been training for a longer amount of time and have adapted to super compensate their muscle tissue to store more.
On the other hand, an athlete can store massive amounts of body fat in order to fuel their endurance sports. This doesn’t mean that the athlete needs to be “fat”. Someone carrying only 5kg of stored body fat has about 40,000 kilocalories to work with.
Think of it like this, an endurance athlete fuelling with carbs has a small tank of fuel, and it burns fast, but performs faster and more efficiently. On the other hand an endurance athlete fuelling with fat has an enormous tank of fuel and can go longer, but it burns slower and less efficiently.
So Why Don't We All Want to Be Fat Adapted?
As with everything in life, just because we can carry more fuel it’s not always best to do so. The reason is that it is less efficient. There is more cost to the human body to burn fat than there is for burning glycogen. It costs more in oxygen consumption and effort to carry us around a marathon course. We can run faster using less oxygen when we burn our glycogen stores and over the course of a marathon, we can top up our stores with on-course nutrition relatively easily. This means that we are less likely to run out of our more-efficient fuel over the course of a 42km race than we would on a 100km ultra. This is precisely why it is less common for marathon runners and more common for ultra marathon athletes to train their body to burn fat for fuel.
My 6-Week Experiment of Becoming Fat Adapted
I did manage to become pretty well fat adapted over the course of this 6-week experiment. It took time, but I think I was well on my way by the time it ended. Over the course of the 6 weeks, I recorded the following data:
Daily Protein: 122g (28%)
Daily Fat: 124g (64%)
Daily Carbs: 37g (8%)
Daily KCalories: 1756
Daily Water: 4.510 Litres
Avg. Weekly Mileage: 27 miles (43km)
Total Weight Loss: 12.4 pounts (5.5kg)
Some interesting findings from my 6-week experiement of becoming fat adapted.
Running:
Running while in the process of becoming fat adapted was very hard in the first 3-4 weeks. It took all I had to just get started and move as my legs felt like lead. In weeks 5 and 6 things started to feel a lot better. By the time the 6th week began, I was able to do back-to-back days without a problem, but it did take more time to get warmed up. Pace only just started to become easier, but still nowhere near the pace I would have found to be steady or even an easy pace only 7 or 8 weeks before I started this.
The biggest challenge was without a doubt the recovery process. It seemed like after any run over 6 miles (10k), my legs just felt tired and my body exhausted for the remainder of the day. Even the following day it would take more time to get started than would be normal. This is strange for a runner who wouldn’t think twice of going out for a 20 miler (32k) run on any given weekend.
Eating:
The diet itself was very easy to do. The foods are readily available and considering the satiating effect of a high fat, high protein diet, it wasn’t nearly as expensive as one would think. Over the course of this 6 week span I probably ate close to 300 eggs, tons of beef mince and burgers, chicken thighs and more butter than most people would consume in 6-months.
I would regularly have about 800-900 kcalories for breakfast and then never even think about eating until dinner time. Even at that point, it was more a matter of habit to eat rather than out of hunger. It’s not that I felt full, rather, I just never felt empty. This was my favourite thing about eating in this manner. Imagine how much easier life is without ever being hangry!
Arthritis Pain:
The objective of relieving some arthritis pain in my hands did not get fulfilled. However, I must be clear that from the anecdotal evidence, this particular effect normally takes about 3-4 months to be actualised. Therefore, I didn’t give it enough time to produce the effects I was looking for. I knew this going in, but I was hoping to get some sort of shift in the pain. Unfortunately, my hands have had no noticeable benefit from this low carb diet.
Clarity of Mind:
One of the benefits that a great many people talk about when eating this type of diet is a clarity of mind that comes. I have to say that I did not experience this effect. Therefore, I can’t speak to that, but because so many people claim to experience it, I feel there must be something to it.
Conclusion: Would I Recommend Changing to Becoming Fat Adapted
Overall, I enjoyed the experiment of becoming fat adapted as a marathon runner. I like to challenge myself and to see what my body can do under different situations and circumstances. However, I feel like I will perform better and be able to train harder on a traditional diet and consuming carbs to keep a fully replenished glycogen store in my muscles and liver. I feel like recovery is faster and performance is better. It takes less time for me to get warmed up and I’m better able to train on back-to-back days.
The big caveat is this: I only did 6 weeks. I know if I gave it more time my body would have made the relevant adaptations to enable me to do and perform the way I did on the more traditional nutrition regime. For me, right now, I don’t wish to take the time for this to happen. It took me 15 years to get my body to be able to store so much energy in the form of glycogen and burning that as fuel is more efficient, at least in the short term.
I do think it was interesting to see the change in how my body felt, performed and dealt with the calorie deficit. This was the most surprising outcome. I feel it’s a very easy way to live and what the long term health benefits or risks are is beyond this 6 week experiment. Am I glad I did it? Yes. Will I do it again? Quite possibly, but as my training block for my next marathon begins today, not for another 16 weeks at the very least.