Processed foods are a huge part of toxins in the body. They are developed to make your brain think you are happy and satisfied when eating them, but that is the primary problem. A food designed to make you feel good generally means you'll eat more of it, and with low-grade nutrition and potentially toxic contents it makes perfect sense people are less healthy than they were years ago.
Authority Nutrition recently had a great article that further explains the problems with processed foods and fats. https://authoritynutrition.com/9-ways-that-processed-foods-are-killing-people/
They refer to the "Western Diet" and how after indulging in processed foods people become unhealthy or sick. It's common here in the U.S., and although diets may have you thinking it's strictly sugars, carbs, or fats that are the problem, unprocessed and in moderation ALL of those things are good for you n the end.
*Image used from linked article