chrisw77's Journal, 24 Dec 18

Thank you for sharing this Chris. I found the discussion on different types of carbs interesting. There was something I found misleading in the write-up. The author says "The downside of the liver’s demand for glycogen is that when it runs out of glycogen it takes alanine, and the other substrates, from the muscles in order to make more (it can’t actually take the glycogen because once it is manufactured in the muscle it can’t be removed – it must be used for energy). The result is muscle atrophy (i.e. shrinkage)." I find this misleading because alanine is a natural product of the Cori cycle so the liver is just using something the muscle couldn't use. I don't see why that would mean one was at risk of muscle atrophy. Here is a quote from a book describing the process. "These interchanges, known as the Cori cycle (Section 16.4.2), shift part of the metabolic burden of muscle to the liver. In addition, a large amount of alanine is formed in active muscle by the transamination of pyruvate. Alanine, like lactate, can be converted into glucose by the liver. Why does the muscle release alanine? Muscle can absorb and transaminate branched-chain amino acids; however, it cannot form urea. Consequently, the nitrogen is released into the blood as alanine. The liver absorbs the alanine, removes the nitrogen for disposal as urea, and processes the pyruvate to glucose or fatty acids. The metabolic pattern of resting muscle is quite different. In resting muscle, fatty acids are the major fuel, meeting 85% of the energy needs." What do you think? Have I misunderstood something?