Exercise, diet and weight loss - why is it so hard!

I used to be fit and healthy and felt great. When I started putting on the weight and stopped exercising I felt awful. Why does this not motivate me enough to eat well and exercise to feel the benifits I know will happen if only I cut out the bad stuff and put in more of the good stuff?

Its a common problem – what is it that stops you (and others) from doing what is prooven to be good for us?