Keeping track of everything we eat would be a great idea, and I'm sure we'd learn all kinds of things we don't really want to know about our diet and overall health. Until now it's been a major hassle to do this, but tiny digestible RFID tags could automate the entire process for every single piece of food that we consume.
RFID tags are antennas that don't need batteries or complicated circuitry. When brought near an RFID reader, they passively transmit a simple code that can be used as an identifier. The tags are simple and cheap to make (you can just print them out), and they can be made small enough such that if you eat one, your stomach acid will naturally break it down into a tiny amount of silver that's less than what you'd find in tap water.
NutriSmart is a concept for a food tracking system that uses RFID tags embedded in food along with a special plate that scans everything you eat, for the purposes of tracking nutrition and food allergies as well as to provide a little extra information on just what exactly it is that you're scarfing down:
A RFID-reading plate is definitely one way to go, but it may also be possible to embed a reader into, say, a necklace, where it could scan everything that you swallow even when you're not at home. All those data could then be sent to your smartphone, which might subtly remind you that this is in fact the fifth Krispy Kreme that you've eaten today and maybe you should take it easy before sugary glaze starts flowing out of your eyeballs.