When you eat a lot of carbs, your body produces glucose, which is then used to burn energy. (nutrition-food.info)
When the liver doesn't respond to insulin signals telling it to stop producing glucose, that extra sugar in the blood is stored as fat. (sciencedaily.com)
Therefore, proteins from various body tissues are broken down into amino acids and used by the liver to produce glucose for the brain and muscle. (strengthtrainingendeavors.com)