Something that took me a while to realise is that you don't necessarily need to be eating rubbish food to gain weight, just too much. I think there's this stereotype of the guy chugging down sugary drinks all day with his greasy burgers in between handfuls of sweets, but that's not the case for most people.

What was a big help for me was getting a food scale, and working out what size portions I should be eating - particularly for carby things like rice and pasta I found I was way off on my estimates of what a decent serving should be.