Well yes...it is correct that, per gram of fat or carbohydrate, fats are able to yield ultimately more ATP than carbohydrates can. However, the amount of energy that comes out in the end is not necessarily the determinant of efficiency, and doesn't even begin to take in the other consequences on the metabolism that are involved.

Carbohydrates are ultimately far more efficient for creating energy than fats are and we can create energy using carbohydrates far faster than we can using fats, which is why high intensity exercise becomes very tough on a low carb regime.

The other things to take into account here are the effects of one or the other on the rest of our biology - Fats, especially when they of the polyunsaturated variety, will over time reduce our ability to use carbohydrates for energy. The use of fat for energy will tend to raise cortisol and other stress hormones in order to maintain sufficient sugar for brain function, and of course fats do not stimulate thyroid function in the same way that carbohydrates do, as well as producing far less carbon dioxide which is needed to use oxygen.

I did A LOT of low carbing, fasting, and calorie restriction for many years, and I totally resonate with you. My understanding is that, at least at first, low carb diets can leave you feeling awake, alive, and extremely productive, especially as they tend to lower gut bacteria and thus levels of our main endogenous inflammatory mediator, endotoxin.

However, over time I slowly began to get cold, especially my hands and feet, my sex drive slowly disspeared, and I got increasingly edgy, anxious, and depressed whilst my insomnia just got worse. This is because of (mainly) cortisol and adrenaline, which in the short term can leave you feeling alive and awesome, but long term will be slowly breaking you down and causing hypothyroidism.

This is a hard one - and I completely resonate with the misunderstandings propagated around topics such as diabetes and metabolic syndrome. M understanding is that diabetes is not caused by sugar, but rather stress, polyunsaturated fats, metabolic disruptors in the environment, and low levels of essential nutrients.

Once stress has caused enough damage to the cells, they become unable to uptake and properly use glucose which, combined with a poorly functioning liver, thyroid, and gut, means that glucose becomes a challenge to our system. The mainstream way of dealing with this is to just say "sugar did it", and find means of controlling sugar from that point on, whereas the metabolic approach would be to look at your current environment, search for foods that actually support, rather than damage, the mitochondria, and use potentially large doses of some supplements and vitamins including thiamine, biotin, niacinamide, thyroid, and others as a means of regenerating and restoring the cells ability to use and process glucose again.

Some doctors worth checking out are people like Dr. Walter Kempner, who in the 1930's was actually curing people of diabetes by putting them on very low fat diets and feeding them nothing but white sugar, white rice, and fruit juice....that shouldn't have been possible under the current mainstream viewpoint.