I would not recommend anyone START with HIIT. You need to be in VERY good shape to do proper HIIT - the stronger you are, the greater your heart stroke and work capacity, the harder you can hammer when you do these sudden bursts. And the harder you go, the more catecholamine and microtrauma and depletion you will promote. Do this with a good strength base AND a good endurance base - ie start with ss cardio and hills training, build up your mitochodrial and capillary density, get strong... and as your cut progresses, gradually cut back on the hunger-inducing steady-state component and concentrate on the intense, interval-based modalities such as sprints, complexes and bicycle sprints.