what is reward behavior?

There is evidence that sugar is particularly harmful for the adolescent brain, which is especially responsive to rewarding behaviors. Unsurprisingly, eating tasty foods high in sugar, salt or fat is hard to resist. But research has shown that male rats that drank sugar water during adolescence showed less motivation and pursued rewards as adults, behaviors that signify depression and other mood disorders.

What does rewarding behavior mean here?

Solution 1:

Rewarding behavior means that young people are often given sugar or sweets as a reward for good behavior.

It is not recommended, as during an experiment, rats were seen to be less motivated after consuming sugar.
So the person's body could also be less motivated to continue such behavior in the future.