Marty,
Thanks for your reply. I would be very interested to know more about
your sources for the changes in the amount of gluconeogenesis in non
obese subjects. Why I am interested is that they seem to be at odds
with some other reports of studies of the urinary N excreted
during fasting. In these studies although urinary N excretion
decreases it does so in direct proportion to decreases in BMR. This
leads those investigators to conclude that there is no
change in the proportion of fat and protein used i.e.
no increased use of ketone bodies by the CNS. From the figures you
quote:
>Gluconeogenesis (the process of converting noncarbohydrate
>material to glucose) starts to increase about four hours after the
>last meal and it peaks at about 10 grams of glucose produced per hour
>about 2-3 days after the last meal is consumed. Gluconeogenesis then
>decreases to about 6 grams of glucose produced per hour until about 12
>days after the last meal at which time it increases very slowly upto
>40 days (the longest time period that I have) where it's producing
>about 8 grams of glucose per hour.
it would appear that a 40% decrease in glucose production from
gluconeogenesis is not just a reflection of a lowered BMR (this would
not decrease by 40% in 12 days) but does, on the face of it, appear to represent
protein sparing. However could it be that the energy requirement of the CNS is markedly decreased during starvation and that there is not a switch in fuels (glucose to Ketone body) but rather but rather an overall decrease in metabolic rate of the CNS as suggested by henry (1984) ? How is the rate of gluconeogenesis estimated in your references /
data ? and are there any other estoimates of protein catabolism included such as the urinary N ?
If you could send me the names of the references I'd be
grateful
Yours
-- steve collins
