The FastDay Forum

[carorees]

This study indicates that the GH response to fasting depends on the level of obesity: http://www.ncbi.nlm.nih.gov/pubmed/11477509

Short-term fasting does not increase GH secretion in obesity... Short-term fasting in obesity has attenuated effects on insulin and IGFBP-1 secretion while it normally increases free fatty acids in spite of any change in GH secretion.

Having done a couple of 23 hour ultra-type events (including the Bob Graham round of the Lake District) without managing to eat anywhere near requirements I assumed I was going slowly because I was burning fat - not muscle tissue. I'm sure I have seen elsewhere (Peter Attia probably) that glycogen and fat are both used during prolonged medium-pace exercise, bonking is what happens when the glycogen tanks are emptied. Eating muscles makes no sense while fat is still available, surely?

[carorees]

Thus study shows the increase in GH in normal weight people: http://www.ncbi.nlm.nih.gov/pubmed/23220077

It's still not clear whether being used to fasting reduces the blunted GH response to fasting seen in obese people. I suspect that the decreases in insulin would be accompanied by an increase in GH and lead to the preservation of FFM.

glycogen and fat are both used during prolonged medium-pace exercise

that's the case with marathon runners, the goal is to be so well trained that you use plenty of fat and decrease your glycogen reserves at a slow rate.

http://ajpendo.physiology.org/content/2 ... 8.full.pdf shows the protein oxidation to be small, at least for 90 minutes of exercise.

It's still not clear whether being used to fasting reduces the blunted GH response to fasting seen in obese people. I suspect that the decreases in insulin would be accompanied by an increase in GH and lead to the preservation of FFM.

Well Krista Varady's study showed the preservation of FFM, so your suspicion about increase in GH seems logical to me.