I'm fully convinced that large intakes of sugar is more detrimental to one's health than fatty foods and salty foods. Although the 3 of those characteristics certainly contribute to an unhealthy lifestyle when combined, the one that stands out among the other 2 is definitely sugar.
Two years ago, I reduced my intake of sugar significantly and not only did I lose a lot of weight, but I suddenly had more energy than I ever had before. I'm no health nut so I started small, taking away most of my unnecessary sugar intake such as sodas, most candy, and processed foods. If you glance at the nutrition facts on a soda or a packaged drink, you'd be surprised how much sugar is in there. Even those "All-Natural" ones. It's kind of insane.
There's so much to say about this, but if you want to get started, I recommend this book which sort of changed my perspective on how I see and eat foods.