Two metal blocks on the counter of any fast food restaurant which the customer must place his fingers/hands on to check the body fat percentage. If BMI is over 25 or fat percentage is XX, a 50% tax is added which is earmarked solely for health care. Laws would be necessary to require it and drive-throughs would be a bitch but overall it's a sound idea. No restaurant can make a sale without its use.

This doesn't necessarily have to be limited to fast food restaurants. It could be placed in all food service establishments. Maybe even at supermarkets for all junk food.

Of course there are ways around it but there are ways around everything else already. It's the perfect thing for the nanny state!