I am unable to find any evidence supporting this, but have found evidence refuting it.: The Triathlete’s Training Bible, pg 274 under diet and performance.
“One of the downsides resulting from eating a high carbohydrate, low fat diet is a greater production of lactic acid by the muscles during excercise, and even at rest. This is probably the result of the body using carbohydrate preferentially for fuel when it is abundantly available, while not burning as much fat. Carbohydrate seems to “turn off” the body’s fat-utilization process.”
Before anybody flames me, here is another quote from the sidebar of the same book, same chapter: “Sports Nutrition is an Evolving Science.”
Now on the subject of fatty acid oxidation, the process of burning fat instead of glycogen for energy, I was taught in my personal trainer certification course that this process begins only after an hour or so of low-key strictly aerobic excercise. This means going long and keeping the heart rate down. For me this is about 55min of running at the 150 to 155 bpm range. At this point your body switches over to burning fat for energy. For those of us that race longer distances, or are presently building base miles, this is a crucial step in training because it also encourages our cells to produce more mitachondria. The mitachondria in our cells are the mechanism by which our boddies convert fatty acids into ATP which is the energy that our muscles use. So the more you build base, the more mitachondria your cells will have, the easier it is for your body to utilize your fat for energy, and save the glycogen for the sprint at the end.
I did not mean to go on so long, sorry. Feel free to disagree, I love to be wrong because it means I have learned something. I have a thought on fatty acid oxidation but I will give it it’s own thread.
Jim