The overall process of glucose metabolism liberates energy through the conversion of reduced carbon in carbohydrate and oxidized oxygen in O2 to oxidized carbon and reduced oxygen in carbon dioxide and water. We will have a great deal more to discuss about this in our discussions of metabolism, so let's leave it for now with a question: Why was carbohydrate selected by evolution for 'everyday cellular energy' instead of triglyceride?. After all, carbohydrate only provides 4 kcal/gram while fats provide 9 kcal/gram through metabolism. The answer is water solubility.