I learned that fat, salt and sugar are engineered into everything we eat by reading The End of Overeating: Taking Control of the Insatiable American Appetite. Actually I had a pretty good idea that was the case long before as I haven't had my head buried in the sand. Although this book does go into details just how engineered our food, or rather food like substances, are these days. The book was an entertaining read and it goes without saying that the best way to eat healthy is to stick to the food that are not packaged into colourful boxes.
For other good books on food I recommend:
1) The Omnivores Diet by Michael Pollan
2) In Defense of Food by Michael Pollan
3) Fast Food Nation by Eric Schlosser