Asked in Carbohydrates and Low-Carb Diets
Why do lipids have more energy per gram than carbohydrates?
September 20, 2015 10:01AM
One molecule of glycerol tristearate (a triglyceride with molecular weight 897.53 Daltons) generates 3 molecules of stearic acid (a fatty acid) and 1 molecule of glycerol. Each molecule of stearic acid undergoes beta-oxidation, Krebs cycle and electron transport chain to yield 135 ATP (theoretical efficiency, same below). Glyceol undergoes metabolism and generates 18 ATP. The total ATP yield for this lipid molecule is then 135 * 3 + 18 = 423 ATP or 0.47 mol ATP/gram. Glucose, with a molecular weight of 180.16, generates only 36 ATP, or 0.20 mol ATP/gram. Since polymeric carbohydrates are simply aggregates of simpler subunits, the efficiency of storage does not improve much more than monosaccharides.