Who is a heavy soft drink?

There is no such thing as a "heavy soft drink." The phrase doesn't have a meaning in the context of beverages.

Perhaps you're looking for something like:

* A sugary soft drink: This refers to a soft drink with a high sugar content. Examples include Coca-Cola, Pepsi, and Sprite.

* A dense soft drink: This could refer to a soft drink with a thick consistency, but it's not a common term.

* A heavy-feeling soft drink: This is a subjective term, as some people may feel heavier after consuming a sugary soft drink.

If you could clarify what you mean by "heavy soft drink," I can help you better.