Make the right choice – HIIT and/or LSD
There has always been a lot of debate over the efficacy of short duration, HIIT sessions versus long, slow duration/distance (LSD), lower intensity, steady state cardio for fat and weight loss and improved fitness.
High-intensity sessions over short durations will take your heart rate through a wider range of heart rate zones, which is beneficial for your general fitness levels. It is also the most effective way to blast as many calories as possible in a short period of time, which makes it an effective way to lose weight.
Longer duration, lower intensity cardio at a steady state will preferentially ‘tap’ into fat stores for fuel, which assists with fat loss (not necessarily weight loss). However, the shift from glycogen to stored fat as a source of fuel generally only happens after 20 minutes (depending on your stored glycogen levels in relation to your diet and activity levels). You can overcome this by doing your cardio after a weight training workout, which will deplete glycogen stores. However, it is not as effective at improving fitness levels.
As such, if you are looking to obtain all of these benefits from your training a combination is best. If you have limited time to train then HIIT is a better option than steady state cardio on all fronts.