Many experts believe that up to 90% of the money we spend on food is for convenient processed foods. Processed foods are not usually balanced and generally do not contain adequate fiber and other nutrients. The also usually contain preservatives, artificial coloring and flavoring agents, and various other ingredients the body was not designed to deal with.
Natural foods are real food and carry their original life-supporting vitamins, minerals, enzymes, antioxidants and many other phytonutrients that can be lost in processing.
As best you can, it is best to buy fresh foods. While that is not always possible, in general it is better to go for frozen fruits and vegetables than canned, when you cannot purchase fresh or grow your own.