In your book you mention that the brain only uses glucose. What are your thoughts on this statement: During metabolic stress, ketones serve as an alternative energy source to maintain normal brain cell metabolism. In fact, BHB (a major ketone) may be an even more efficient fuel than glucose, providing more energy per unit oxygen used.
– Canny in Canning Town
I agree with your statement completely. I don’t think it’s debatable.
When I wrote that the brain only uses glucose, I suppose I only meant that within the context of the two main energy sources for typical modern humans: glucose and fat. In fact, some cells in the brain do also use fat for energy. But overall, most of the brain’s energy typically comes from glucose.
And the brain can certainly use alternative energy sources like ketones. It would be very risky not to have backup plans to deal with a glucose shortage.
(Though you seem to be alluding to the potentially higher efficiency of ketones as a good thing. Perhaps it is from a wear and tear and waste perspective. But most people are looking to burn extra calories, so efficiency is not necessarily desirable).
More generally though, I would say the lack of discussion of ketones in the book is a major omission (though it wasn’t necessarily so at the time, since I wrote it before the current keto craze). Of course, people have been trying keto diets for quite a long time. But the idea that a typical person would consider an extreme, long-term, low-carb diet is a fairly recent development.
I think the idea of using an alternative metabolic regime is fascinating — and potentially risky.
We know that it is possible to live a long, healthy life on, for example, a Mediterranean-style diet. (Whether or not it is possible to actually adhere to such a diet in the modern world is a separate issue).
We don’t know what the long-term effects are for a typical person who is raised on carbs and then cuts them out in midlife. The effects may indeed be positive. But they may also be negative. We don’t yet know because we don’t have the results of large, well-designed clinical trials to inform us.
I’m optimistic because the animal studies are pretty compelling and some of the theory behind the keto diet makes sense. But it wouldn’t be the first time that predictions based on theory and animal studies were wrong. You can read a recent — and rather pessimistic — view of some of the existing clinical evidence here.
But if I was struggling to stay healthy on carb-inclusive diets, would I try a keto diet?
Yeah, I probably would.
But before making a dramatic change in what I eat, I would see how far I could get by changing when I eat (e.g. I would try something like one-meal-a-day or the 5:2 diet first). With those approaches I would get some of the potential keto-style benefits during the fasting periods, but I also wouldn’t be shocking my body with wholesale change.