Q.1 why sugar is called a source of empty calories?

Answer 1

when sugars are broken down, they provide energy and make wast. While that is not realy empty, the typical fat person doesn't need that much energy and stores this as fat.

When ever you sacrifice calorie consumption you should try to get some nutrients with it (full calories)

Some energy is needed but all empty calories will kill you.

Answer 2

Scarlet Manuka is dead on as far as he goes.
(I gave him a thumbs up.) But to answer your question:
Sugar does provide energy and nothing else, and does get a bad rap, not because it's intrinsically bad, but because we tend to eat too much of it.
Too live, we also need protein, minerals, vitamins, and trace elements which we don't get from sugar.
Sugar will satisfy energy needs and depress hunger, so one doesn't eat enough other food to get the other necessities.
One should eat a well balanced diet, but if your energy is depleted, sugar can give you a quick temporary boost.
Just don't misuse it.

Answer 3

Because it doesn't contain any of the nutrients we need for general health. Sugars are burned directly for energy and are converted completely into water and carbon dioxide, so effectively they have calories but nothing else.