I have done a decent job at exercising for 4-5 years now. A couple of years ago I really focused on what I eat - not so much changing what I eat but just portion control and limiting sweets. I lost about 25 pounds in 3 months and was feeling great. Then work got busy and I slacked off on my disciplined eating and I'm almost back to where I started even though I still exercise pretty regularly.
It's not rocket science. To lose weight, exercise regularly and control how much you eat. You don't really have to change what you eat but just limit your intake. Do that and you will lose weight.
It's simple but not easy.