Bile
The substance produced when the body breaks down fat for energy is called ketones. These ketones can be used by the body's cells as an alternative source of energy when carbohydrates are not available.
Ammonia is a toxic byproduct produced when the body breaks down proteins and lipids. It is converted to urea in the liver and excreted in urine.
acetaldehyde, more toxic than alcohol itself...
Bile is produced by the liver that helps it break down fats.
I believe you're referring to the hormone glucagon produced by the alpha cells in the pancreas which causes the liver to break down glycogen. There are no nutrients stored in the liver, the liver stores bile as well as lipase, neither of which are considered "nutrients"
Liver
liver
Bile, which is produced by the liver and stored in the gallbladder, breaks up fat particles in the digestive system. The bile salts in bile act as emulsifiers to break down fats into smaller droplets, making it easier for enzymes to further break them down for digestion.
peroxisome
Enzyme that break down fatty acids are called lipases. Bile is a substance made in our liver which contains salts that breaks down fat into smaller droplets. The pancreas also contains a substance called pancreatic juice which contains numerous enzymes that work to break down things such as fat, protein and starch.
It breaks down fats and is made in the liver
Proteins are broken down by proteases, bilirubin is broken down by the liver, and iron is broken down by macrophages in the liver and spleen.