Changes

* While I could run the marathon distance without fueling, running longer distances required some source of calories. I discovered I could still 'crash' on the Ketogenic Diet, though it is a softer, slower crash than a typical blood glucose/Glycogen depletion crash (AKA "hitting the wall"). My suspicion is that I ran out of available fat to use a fuel, even though obviously I had plenty of body fat left. One issue might have been the depletion of intramuscular triglycerides. On a high carbohydrate diet, intramuscular triglycerides provide about the same amount of fat calories as plasma fatty acids (I've not seen any data on their contribution while on a KD.) However, the other issue might be the rate of lipolysis, which is the breakdown of body fat to make it available for the metabolism. It's possible that I was burning fat faster than I was freeing it up.

* I found that I could put on upper body muscle using weight training at least as easily as I could on a high carbohydrate diet. However, my leg muscle mass was reduced on the Ketogenic Diet.

* I had two runs on the Ketogenic Diet where I experienced a strong feeling of euphoria. The first time the euphoria occurred from mile 16 to 26 of a normal training run. The second time was a shorter 10 mile run with sore legs, where I noted a strange combination of fatigue, soreness and euphoria. I never worked out what caused this euphoria or found a way of reproducing it. Note that while I had a sense of euphoria and strength, my actual pace was not much better than normal. I had one other run where I noted "running 28 miles should not be this easy", and would have run much further had time allowed.

=Ketogenic Ultramarathons=

* It takes more oxygen to burn fat than carbohydrate. This simple bit of chemistry is critical for understanding the Ketogenic Diet. If you want to run at a given pace, it will be harder if you're burning fat than if you're burning carbohydrates.

* I believe the human body is amazingly well designed, and it carefully optimizes the use of carbohydrates and fats, switching gradually from fat to carbohydrate as exercise intensity increases. If there were a simple way of burning fat as efficiently as carbohydrate, humans would make use of this all the time. Instead, it seems that Ketones are a way of surviving famines, something that is quite wonderful.

{{KetoSeeAlso}}