If you don't like watching videos (I hear you, friend), the basic is this: sugar releases dopamine in the brain. That's why it feels so good. We also get dopamine released when we eat a healthy, balanced meal, but that dopamine is dependent on novelty. If we're eating the same healthy food, the dopamine levels fade over time. Sugar, on the other hand, remains constant. So we never get sick of it. Wooooo! Delicious poison.
Oh, and if you're wondering, "umami" is savoury. I may have had to look that up.