I'm a bit confused here about your reasoning, Poisonivy. One gram of carbohydrate when metabolized completely produces 4 Calories (kcal) of energy, which is equivalent to 16.7 kJ (kilojoules). One gram of fat produces 9 Calories (37.7 kJ). [A food "Calorie" is equivalent to 1000 energy calories, or one kilocalorie. A calorie is the amount of energy required to raise the temperature of one gram of water by one degree Celsius. 1 kcal is equivalent to 4.187 kilojoules.]

Nine grams of fat contains 9 x 9 Calories (81 kcal) which is equivalent to 339 kJ.

[Kilocalories and kilojoules measure the same thing, just in different scales. Like Fahrenheit and Celsius temperatures. Measure the same thing but have different scales. It doesn't matter which one you use, as long as you are consistent.]

I believe you have gotten your reasoning backwards. Which would mean that it takes half as much fat as carbs (not twice as much as you stated) to produce the same amount of energy, whether it be kcal or kJ.

Yes, there is a metabolic advantage from ketogenic diets, but not nearly as much as we would all like. Certainly not a doubling of calorie consumption. We can consume some small number of calories more than people not on low carb diets can and not gain weight, but energy is energy, and extra consumption will be stored.

I hate to burst the bubble of your post, because it was a good post and logically thought out, but I teach biochemistry, and the science you used for your reasoning was wrong to begin with. I'm sorry.

Joan