There is actually a new company, Proteus (http://www.proteus.com/ http://www.proteus.com/), which has addressed a similar problem. Basically, they've developed

There is actually a new company, Proteus (http://www.proteus.com/ http://www.proteus.com/), which has addressed a similar problem. Basically, they've developed a way to make a drug pill "smart" by embedding a tiny disposable transmitter in the pill. It uses stomach acid to create an "in-situ" battery and then transmits a unique ID to a receiver patch worn by the patient. Something like this perhaps could scale in the future if we could "pepper" FOOD with such nanotransmitters (eg a populate a food item with a certain density of transmitters to indicate calories).