Not so fast brudda. Nutrition is important, but the relationship between nutrition and training is more important. A 20 min cardio session will put you in a deficit if you are expending more than total kcal intake, but if you are relying primarily on anaerobic glycolisis during that 20 min, then your muscles will just suck up glycogen at the next feeding. Low intensity cardio (45 to 60 min) done over a period of time will actually cause mitochondrial density to increase. The end result is you will be able to burn more fat ALL DAY AND NIGHT. Not just during your WO. High intensity cardio doesn't have that effect.