High intensity interval training is a quick way to ramp up your body’s ability to use fat as a fuel.  You can burn about 36% more fat doing intervals than a steady cardio session.  Speed bursts in interval training spark a 20% increase in the amount of mitochondria in the exerciser’s muscle cells, making it easier to metabolize fat for fuel rather than carbs.

Every workout you do gives you a metabolism boost, not just during it but also afterward.  You get the biggest boost by doing sets of strength training with cardio bursts between sets.  For example, a 50 minute weight training session gives you an additional afterburn of 14 calories.  A 20 minute weight training session using interval cardio bursts between each exercise gives you an additional afterburn of 25 calories.  Or, for a 30 minute jog, the afterburn is 35 calories, as opposed to 75 calories for 10 one-minute sprints with two minute rests in between.