I learned in Nutrition class that there are standard serving sizes for various types of food. I think it probable that the FDA requires companies to use those standard serving sizes, and forbids them from choosing arbitrarily small sizes like you fear.
For example, one serving of meat is about the size of a deck of cards. If a company sells a meat product the size of two decks of cards, the FDA probably requires that the product be labeled as containing two servings.
Hmm.. That is interesting and comforting to know actually. I always figured there was some lower bound that a company would get called out on somewhere along the process if it was too egregious, but it's nice that there's at least some semblance of a standard.
For example, one serving of meat is about the size of a deck of cards. If a company sells a meat product the size of two decks of cards, the FDA probably requires that the product be labeled as containing two servings.