HIIT, which stands for High Intensity Interval Training is by far the absolute best way to lose fat with out losing muscle tissue. HIIT differs from regular “interval” training in that with interval training there is a generally a period of rest after an intense bout of exercise. With HIIT, you are generally hitting the accelerator and keeping it down for 15 to 20 minutes straight. There are ways to perform HIIT training from beginners all the way to elite athletes. All are based on your current fitness level. For example, I perform a HIIT workout a few times a month. I will generally last about 20 minutes. I will run for about 5 minutes to warm up and then I will sprint for as long as I possibly can. Then I will run for 1 minute and then sprint again. I will repeat this process until I am physically exhausted. This is a more advanced workout but HIIT can still be done at the beginner level by using walk/run as a method. There single greatest concern with HIIT training is the possibility of injury. You are only working out for a short period of time however, you are working out at such a high intensity that your body may not be able to cope with the added stress loads you are placing on it. I would recommend starting off nice and slow and as your fitness level increases, so can your HIIT workouts.