The occasional foodborne illness outbreak or errant glass shard notwithstanding, Americans generally trust that the food they eat is safe. The Food and Drug Administration is responsible for regulating what ingredients can and cannot be added to foods, but prior to the FDA it was more or less a free-for-all. As this video from Great Big Story explains, before the early 1900s food could legally contain all sorts of undesirable substances like formaldehyde and Borax (which were used to maintain the appearance of freshness).
Thankfully, a chemist named Dr. Harvey W. Wiley decided these ingredients probably had no place in food and decided to put them to the test. For six months, he fed a team of brave volunteers meals that were laced with various substances; with menu items like rice pudding and roast beef, the dinners actually looked fairly delicious apart from the presence of say, copper sulfate. Unfortunately, said meals also caused things like diarrhea, vomiting, and kidney damage — but they led to the passage of the nation's first food regulations.