Well, the tendency to gain and retain fat is strongly influenced by genetic factors, as well as eating patterns in childhood. There is also a proportion of the population who just don't respond very well to exercise.
However, there are a lot of people who write themselves off as genetic anomalies, or non-responders, who in reality just aren't doing the right things, or at least who haven't yet discovered what works well for them.
One key exercise might be an honest appraisal of your calorie intake. Recently, in the UK, there's been a TV programme called Secret Eaters. The key message seems to be that lots of people who apparently can't shed pounds - despite healthy diets - are radically underestimating the amount of calories they consume. They aren't liars - they've just got into grazing habits of which they're unaware.
This may not be true in your case, but it's worth thinking about as some were underestimating their calorific intake by about 50%.
Having said all of that, I totally agree with offroad that severely restricted diets can flip you into starvation mode, where your body reduces metabolism and desperately tries to hang on to what fat it has.
230 strict press @ 220; bodyweight+187 X 4 dips @ 180; 403 front squat @ 210; 10 000 push-ups.
Ignoring irrelevant credentials since I was 17.