TLDR;

• As people get older, their brain connections start to break down faster in midlife (around 40–60 years) because brain cells don’t use sugar as well. • Giving the brain a different fuel called ketones can help keep those connections strong during this middle‐age window. • This suggests that helping the brain get fuel in midlife could keep it healthier and slow down memory problems later on.

You can ingest ketones on their own (generally expensive supplements), but this article is more interesting in that a ketogenic diet (very low carbs) may have similar benefits.