Question

varying current without much loss of energy can be possible in variable resistor

Answer 1

According to Ohm’s law, voltage current is directly proportional to resistance.

Thus, current variation is possible in case of the variable resistor.

Also, there will be not much loss of energy. Science always states any fact with due proof and observance.

Thus, you may expect to rely on the same without any doubt.

Answer 2

Variable resistor allows you to build a circuit with some control over the current. That's why variable resistors have the ability to control the current loss in a better way.  

In a variable resistor, you can simply adjust the flow of current with a knob on it. The current will flow through a certain length of the metal strip without any much loss in it. The loss of current depends on where you turn the knob.

Current variation is possible but as I said, it depends on where you turn the knob.