Forgive me for the incomplete reply, but I looked this up last week and one molecule of fatty acid (in this case DHA soecifically) generates 136 molecules of ATP. This makes fat roughly 2x as energetic (from the standpoint of our bodies' metabolism) as the heat measured from burning it (calories) would suggest. Despite this fact, and the fact that I've been eating roughly 3500 calories per day without exercising, switching to a high-fat, low-carbohydrate diet has lead me to lose 10 lbs over the past three weeks. Clearly there's a lot more to metabolism than is even documented in this lengthy article.