You've heard it a million times before. You've probably even said it yourself. I have to admit, I'm one of those people who tend to romanticize the past, and I've always thought that food used to be purer. There is a definite tendency to think that before the horrible Twentieth Century, food was pure, unadulterated 100% Natural Stuff
. Nobody dyed the produce, nobody used unnatural preservatives
, etcetera etcetera.
Preservatives have been in use for thousands of years, and they were never exactly a healthy thing. Salting and smoking, both processes that introduce impurities and exotic chemicals into the meat, were probably discovered by the earliest humans. Heavy spices like mustard and pepper were used as early as 3500 BCE to disguise the flavour of spoiled food.
Adulterated food, or food made of other, not neccessarily nice, things, has been around since the Middle Ages at least. In the 14th Century, there were city officials whose job it was to find and punish food-service professionals who had adulterated the food they sold to the poor. The word piecemeal comes from the 14th Century, and may be a reference to adulterated bread. 18th-century literature refers to London bread made of "a deleterious paste, mixed up with chalk, alum, and bone-ashes, insipid to the taste, and destructive to the constitution. The good people are not ignorant of this adulteration; but they prefer it to wholesome bread, because it is whiter than the meal of corn (wheat)..."
In 1820, the English chemist Fredrick Accum wrote an expose of these adulterations, called "A Treatise of Adulterations of Food, and Culinary Poisons, Exhibiting the Fraudulent Sophistications of Bread, Beer, Wine, Spirituous Liquors, Tea, Coffee, Cream, Confectionary, Vinegar, Mustard, Pepper, Cheese, Olive Oil, Pickles, and Other Articles Employed in Domestic Economy, and Methods of Detecting Them" (hell of a catchy title, if you ask me). As a result of this study, which was confirmed by a group of physicians, the first English "Pure Food Laws" were passed in the 1860s. The United States only followed suit forty years later.
The hard truth is that today, with government oversight, modern science, and more efficient canning and refrigeration, we may be eating healthier food than ever. At least we don't get chalk in our bread, and most of our meat isn't spoiled by the time it gets to our kitchen.
Main source: "On Food and Cooking", Harold McGee, 1984. The quote is from "The Expedition of Humphry Clinker", by Matthew Bramble, 1771, as quoted in OFOC.