A relatively inexpensive modification at supermarket checkouts could give scientists all the information they need to know about the effect of different food products on our physiology.
Simply have a device at checkouts that weighs the shopper and measures their height. The information that the supermarket already knows about what is in the shopper's basket could be teamed up with the BMI of the shopper and we could finally tell if a low fat high carb diet is more effective than a low carb high fat one.
Do shoppers with more bread in their basket have a bigger "bread-basket"?
Sounds like a scheme to me!