The only problem w/ HIIT is that it's a stressful modality in itself. With the kind of calories you're taking it, I'd limit it to once a week, if that, for the time being. HIIT is not something to just haphazardly throw into a program w/o consideration. With weight training 3x/week as well, I'd monitor the volume for sure.
In your case I've found extensive tempo runs to be a good compromise of intensity and volume of work, w/o over-taxing a calorie-deprived system.
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