This conversion onf the pyruvate produced in the citosol occurs in the mitochondrion, as so occurs the Citric Acidd Cycle.

To see the possisble fates of the Acetyl-CoA, click on the molecule.
One possible fate is the fatty acids synthesis. This way, a high carbohydrate diet can lead to the formation of lipids. It's becausde this step is irreversible that the animals can not do the opposite: convert lipids into carbohydrate.