Of course being a hypnotist myself, I am going to say yes it can (NOT will).
The reason is quite straightforward. Weight loss begins in the mind, and if your thinking is conditioned to eat sensibly and be active, then logically physical changes will take place.
Of course it is not always that simple. One reason for this is that food nowadays is so messed up with, and there is so much misinformation, for example, we are told to consume vegetable oils to prevent heart disease, and yet heart disease has increased over the last 20 years.
Of course some hypnotherapists are better than others, and sadly many are a bit "new age" to be taken seriously. Yes it is not a quick fix, for me a customer must be focussed on doing 3 sessions with the option of a follow up between 3-6 months.
What I can definately say is that with hypnosis you are not going to get worse, you either stay the same, or get better, and I am pleased to say from my experience working with people, is that it is usually successful.
I should also point out that the weight loss gained is NOT my success, it is the success of the person wishing to lose weight. It is a bit like a driving instructor. They don't "make" you drive, you are the one in charge of the car, but with the right guidance AND with the student doing the work, then though not guaranteed, the learner has a greater chance of success.....hypnotherapy follows the same principle.
Plus it is very relaxing.
http://psychology.about.com/od/statesofcon
sciousness/a/hypnosis.htm