I have never exactly been a junk-food junkie but I have certainly eaten my share of pizzas and "things in packets". What has finally prodded me into serious care about my diet has been that I keep hearing "oh noes the doc told me I had diabetes" from my mates and contemporaries. It's one thing reading that in the news but quite something else from people you know and who are maybe younger than you.
After a lot of reading and crap-filtering I came to the conclusion that actually caring about what you eat is the key rather than trying to make sense of conflicting research studies. Incidentally I have come to distrust any food statements from "nutritionists" (anyone can award themselves that title) unlike "dietician" who have serious clinical qualifications.
No matter how much you might identify yourself as a permanent jaffa cake snacker you know in your heart what it is doing to you. Just switch your common sense on and if this is difficult picture yourself having treatment somewhere for your overloaded pancreas.
Finally, do some exercise and if you're not hungry don't eat (sounds obvious but isn't).