Fatty acids cannot be used to make glucose because:

Fatty acid can not be used to make glucose because once glucose is converted to aceltyl coA it can not be converted back to glucose again. The pyruvate dehydrogenase reaction that converts pyruvate to aceyl CoA is an irreversible reaction. Lipid metabolism produced acetyl CoA through beta oxidation, because of this pyruvate and oxaloacetate can not be converted to glucose through gluconeogenesis. Besides, the two carbon atoms in acetyl CoA molecule are lost upon entering the citric acid cycle, thus the acetyl CoA is used for energy.