The brain cannot use long-chain fatty acids for energy because they are completely albumin-bound and cannot cross the blood-brain barrier. So that is a big negative if they make up a large part of the diet.

it's probably best to stick with longer-chain fats as your default, just because they are presumably closer to our evolutionary experience. But this is no guarantee, of course, because just as there are historically "paleo" foods that are bad for you, there are "non-paleo" foods that are good for you. See Kurt Harris here, on one of our big coconut threads. (Another piece of relevant information is that the fat in breast milk is about 10% MCFAs -- but infants are usually in ketosis more than adults (more on ketosis below).)

The long answer is this. I have read that MCFAs can in fact make it into the brain (here, p. 507), though what you will usually read is that only glucose and ketones can make it in. I am not sure about the amount of MCFAs that are being used as fuel directly by the brain; I would guess it is not very much, given that most authors don't talk about it. But here I'm out of my depth.

Yet there is another way to understand what Dr. K meant. MCFAs are associated with ketone production, and ketones are the fuel that your brain is going to be using more and more of when there is less glucose around. MCFAs are associated with ketones not because they are the only thing your liver can use to make ketones; your liver can also make ketones out of other fats, and certain amino acids (the "ketogenic" ones!). MCFAs are associated with ketone production because when you eat them they go more quickly to the liver. Because of this you can use them to more easily "flood" the liver with fatty acids, which will lead to increased ketone production. (This part is kind of complicated.)

Practically speaking, this tells us a few things. One is that you can maintain ketosis with a higher degree of carbohydrate if you are also consuming a lot of MCFAs. Another is that MCFAs might be a good thing to consume when you are fasting (or "fat fasting"), to make things easier on your body; presumably your body will need to convert less protein into glucose if you have a ready source for ketones. (If your brain needs either one or the other, glucose or ketones, then if you increase the amount of ketones you can decrease the amount of glucose.) Both of these points and others are made by the Jaminets in their book, Perfect Health Diet (see pp. 84-91).



"Would this behoove the cerebrally-concious person to stick to MCTs exclusively?"

My understanding is that if you like your gallbladder, you don't want to stick with too-easily-assimilated fats all the time. What I've read on it in mainstream sites is that it releases bile no matter what the fat is but I would imagine it's working a bit harder with longer fatty acid chains that have to be broken down. Don't quote me on that, I may be wrong, but just in case, don't give up on the LCFAs yet. I did see a piece on gallbladders indicating that they have found insulin-producing cells in the gallbladder--not enough to stave off type 1, obviously, but still more useful than we had traditionally held gallbladders to be. Anything you can do to keep yours happy would be a good thing. Gallstones form from too little activity. If they are more active with LCFAs then going exclusively MCT would slow them down.

This article explains more about the different fatty acids and where we get them from.

I have not heard any recommendations about ratio. I can say that I haven't heard anything about the brain using fatty acids for fuel. I have heard that fats are important in maintenance of the nervous system but that's a structural issue, not an energy issue.

If it were me I'd just eat whatever saturated fat I felt like eating. If you feel short on energy then hit the MCTs. But try to get the LCFAs at least once a day

MCTs and SCTs are digested by active diffusion and require no bile so I'm ubder the assumption they digest a decent amount faster.  How fast tho I do not know, it should be noted though that you can't really store MCTs or SCTs which could be a good or bad thing depending on your goals.