From owner-metabolic-reg@net.bio.net Sun Aug 11 23:00:00 1996 Path: biosci!rutgers!uwm.edu!news-res.gsl.net!news.gsl.net!usenet.eel.ufl.edu!arclight.uoregon.edu!dispatch.news.demon.net!demon!mail2news.demon.co.uk!concern1.demon.co.uk From: steve collins Newsgroups: bionet.metabolic-reg,sci.med.nutrition Subject: Re: metabolic adaptations during prolonged fasting / starvation Date: Mon, 12 Aug 1996 09:39:52 GMT Organization: None Lines: 30 Message-ID: <326963586wnr@concern1.demon.co.uk> References: <1996Aug7.104658@vms.ocom.okstate.edu> <96123183wnr@concern1.demon.co.uk> Reply-To: steve@concern1.demon.co.uk X-NNTP-Posting-Host: concern1.demon.co.uk X-Broken-Date: Monday, Aug 12, 1996 09.39.52 X-Newsreader: Newswin Alpha 0.7 X-Mail2News-Path: relay-4.mail.demon.net!post.demon.co.uk!concern1.demon.co.uk Xref: biosci bionet.metabolic-reg:810 sci.med.nutrition:48562 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 .