There are a number of potential problems in the food supply.
All foods contain non-nutrient molecules that can cause dysfunction and disease.
Some of our food plants are marginally safe to eat and must be consumed only in small quantities as herbs, spices and condiments. Many foods require proper cooking and other processing before they are safe to eat. We add numerous complications to native toxins on the farm and in the storage, preparation and retailing of food. The problem is that we seldom know what role contaminants play in causing illness and we have no easy technology to find out. The neglect of imponderable factors in our food supply is surely one of the contributors to ignorance about, and denial of ill-defined illnesses.