I have never heard of pyruvate until yesterday. It seems to be sort of a universal element that is mid-way between being a carbohydrate, fat and protein.
First, glucose (C6H12O6), through the process of carbohydrate catabolism, breaks down into carbon dioxide and water. [C6H12O6 + 6O2 → 6CO2 + 6H2O]. It can also be converted, through the process of glycolysis, to pyruvate. [C6H12O6 → 2CH3COCOO− + 6H+]. Pyruvate, through the process of gluconeogenesis, can be converted back into glucose. Pyruvate can also be converted into acetyl coenzyme-A (ACOA) through the process of pyruvate decarboxylation.
Fats are ingested as triglycerides. Triglycerides are made up of one molecule of glycerol and 3 fatty acid molecules. They are broken up through a process of lipolysis. Fatty acids can be converted into acetyl coenzyme-A (ACOA), through the process of beta oxidation. ACOA can then be used as energy, in a process called ketogenesis, producing ketone bodies. ACOA can also be converted into fat through the process of lipogenesis.
Proteins (meat) are catabolized into amino acids. Amino acids can be catabolized to pyruvate. Pyruvate can be converted into the amino acid alanine.