Asklemmy

Correct. However, there are many ways to get glucose into the brain that are not dependent on eating glucose directly. For example, starch and cellulose are both big long chains of glucose molecules linked together, although no multicellular organisms have the necessary enzymes to break down cellulose into glucose (at least none of which I'm aware, anyway).

For the most part, getting your glucose by breaking down starch is healthier than eating it directly, because it slows down the introduction of starch into the bloodstream which keeps your blood sugar levels more stable, since the enzymes that break down starch (α and β amylase, IIRC) don't do it instantly. Plus, other simple sugars can easily be converted by the buddy into glucose by a variety of enzymes find naturally in the body.

But even without eating any carbohydrates, the human body had the ability to create its own glucose via a process called gluconeogenesis, which occurs mainly in the liver. So, it's not generally advisable to eat too much sugar directly, as there are plenty of other avenues through which the body can get its glucose, and eating the glucose directly leads to a much higher chance of developing diabetes later in life, even if you remain at a healthy weight.

Source: I'm a chemist who teaches college-level biochemistry and nutrition. If you want a source with more details, LMK your educational background and I'd be happy to provide some reading material.