A provocative quote: "Processing food is basically what your body does to food - and you know what comes out". Not the most pleasant way to put it but when you look into the intensive treatment food gets to look nicer and last longer, it's a wonder it is digestable at all.

Kitchen processing. When you chop your vegetables, freshness starts to see out. Same when you make orange juice. The reason is of course that you are opening up more space for the cells to come into contact with the environment and will oxidise ('rust', in a sense) and decay.

Industrial food processing needs to take into consideration the fact that you are not sitting right outside the factory waiting to dine on their product.

Food additives are needed to help maintain the taste, appearance and nutritional quality of processed food and keep it safe...
faia.org.uk

The simple rule of thumb is this: the less fresh, the less healthy. This goes for food that's been sitting on your counter all night and feed that's been treated to last the duration.

Processed foods are to blame for the sharp rise in obesity levels and chronic disease around the globe, according to the World Health Organization.
bbc.co.uk

It's likely you eat a lot of industrially processed food:

The average American eats approximately his/her body weight in food additives each year. This statistic is roughly the same for most English speaking countries.
chekinstitute.com

One way of changing the composition of the food to make it last longer is hydrogenation: Hydrogenated fats - a form of food processing - and it's bad for you. It's that simple. Hyrdogenation can be described as the process of turning non edible oils into badly edible oils that last long and have a high temperature tolerance. It has become illegal in restaurants in Chicago.