There is no set rule that says you cannot use it PWO...

However I for one would much rather use a complex carb when trying to loose body fat... I feel that your body can utilise complex carbs better when your carb intake is generally going to be lower...

TBH tho everything comes down to an energy balance and what you do within that evenergy balance will probably make little difference so long as the balance is where you need it to be to loose BF....