I didn't express myself clearly enough. I was thinking more in terms of what it takes to get at the fat, i.e. energy expended to digest food containing dietary fat vs an enzyme cleaving fatty acid chains off a triglyceride molecule. Disregarding for the moment the energy it took to synthesize the triglyceride molecules at home while putting on weight, what is overall most efficient, energy-wise, on the trail, which is where it really counts?
PJ, Roger, et al,
For some of us pushing our limits is part of the enjoyment.
It's one major reason people race, at least at the "less than world class level". For me, personally, competition became secondary after a while and racing against the clock to see just how fast I could go on various types of terrain, in various weather conditions, was the primary motivating factor. And, I found I enjoyed the iterative process immensely. Sort of the kinetic equivalent of a gearhead, I guess. Or maybe a software writer, back in the old days when memory and CPU cycles mattered, iteratively polishing some arcane sub-routine to optimize memory and CPU usage. As for backpacking, the clock doesn't matter, but optimizing gear AND food in an attempt ease the strain on the body, be able to stay out longer, and go further/higher does very much matter to me, not to mention knowing I have enough in reserve to put the petal to the metal in an emergency. Bottom line, we spend a lot of time in these forums discussing ways to shave grams off our base weight, but relatively little trying to shave grams off the food we carry. Last time I looked, a gram of food weighs the same as a gram of gear and if, by a combination of training and careful balancing of food content and pace, we can shave grams(ounces? pounds?) off our total load, I would suggest it's an area well worth exploring.