I was an ectomorph. After a coupe of years of weightlifting I have gained some muscle as well as body fat. Now I am planning to lose body fat without sacrificing muscle. Is HIIT suitable for my goal?
HIIT isn't really the factor here, I would say your diet is. You need to calculate your TDEE and find out a deficit including the calories burned from HIIT training(which is a lot).
I'm an amateur boxer and do HIIT workouts 4 times a week, 2-hour sessions each. One 2-hour session easily burns 1500 calories if not more. Hard sparring is included in these. In periods where I need to maintain weight, I calculate my TDEE and try to land a break-even on calories on the days I work out(to have energy for it, also), and eat less the days I don't work out(which isn't many.. in fact..) The "puzzle" has to go together on a weekly basis for me, though. In periods where I cut, i have a calorie deficit of around 400 calories per day.
So to conclude - you need to plan your diet after your workout intensity and frequency, and go on a daily calorie deficit that is not too big(because then you WILL lose muscle). Consistency and steady progress is the key.
I think it depends. If you train in the morning without breakfast it's not a good idea to do HIIT. If you train in the evening with a good dinner before it then you can burn many kcals in short time.
Even if you are low in body fat percentage then HIIT is not the right choice because in low bodyfat ranges your body is more likely to burn muscle in hard cardio sessions. Some say you can save your gains by eating a large amount of protein but I don't think that helps a lot.