Many scientists and medical personnel think you can only run your brain on glucose. They’re incorrect.
This is another of the misconceptions that I accepted until new information and experience changed my perspective. When I first read Gary Taubes’ book “Why We Get Fat,” he made reference to keto-adaptation, a term coined by Steve Phinney. In “The Art and Science of Low Carbohydrate Performance” Jeff Volek and Steve Phinney claimed the body and brain could adapt to using ketone bodies for most metabolism in place of glucose. I was unconvinced, but after reading more detailed discussion in “The Art and Science of Low Carbohydrate Living,” and observing the changes in other endurance athletes and myself, I came around.
As discussed elsewhere on this site, when you go to a high fat, low carb nutrition regime, there’s an adaptation period of about two weeks. You dump several pounds of water weight as your body stops storing glycogen and shifts to ketone body metabolism. Glycogen is a bunch of glucose molecules bound together. Quite a bit of water binds to the glycogen.
After the adaptation period, your organ systems, muscles, and brain shift to using ketone bodies, which are made in the liver from fatty acids (fats). The two ketone molecules created are “beta-hydroybutyrate” (BOHB) and “acetoacetate” (AcAc). They are similar, consisting of 4 carbon atoms, 3 oxygen atoms, with some hydrogen atoms here and there. Unlike fats, ketones are small and water soluble. That means they can circulate in the blood and get taken up by cells instead of having to be packaged up in the lipoprotein particles that transport full-sized fat molecules in your bloodstream.
The ketone bodies can go the same places glucose molecules do and get used the same way. Since even a thin person has pounds of fat, it’s easy and quick to make new ketones as your body needs them. This seems to be why the endurance runners I speak about in Applied Biology have better endurance and recovery after becoming ketone adapted.
There seem to be a couple of places where you do need a few glucose molecules. Your body makes the few it needs from fats and proteins using a process called “gluconeogenesis.” That’s why even on a low carb diet, people still have blood glucose level in the normal range. Dr. Maratos-Flier’s lab at Beth Israel Deaconess Medical Center is studying the mechanisms of ketone adaptation in mice. She tells me it’s somewhat different in people, but hasn’t been well studied. I contacted her because I’m looking for a lab that wants to study what’s going on in people.