There are some definite possible advantages to HIIT. If you are careful to monitor your heart rate to keep a good level overall, then I think it has good potential. I used to run track when I was young (400 and 1500 meters) and we always trained this way.
Honestly, if you are training every day and being relatively careful with your diet, then you will pretty easily get down to a weight that the average North American would call "skinny". The main problems I've seen with people are not understanding what they are eating (Google tells me a single blueberry muffin is 377 calories -- that's practically a meal in itself!!!) or people who are fooling themselves about their exercise (unless you are a competitive athlete, the 5-600 calories per hour is about right -- if you are lifting weights, you can divide that by a fair amount).
HIIT goes against the advise above (low intensity, longer duration to burn fat) but it does work for some