Who would own the data? let's say that your body measures and proportions gets linked to your credit card number, this data could be used to target advertising to you in websites where you have used the same credit card.
If you are overweight it could show ads of gyms/treatments/diet-food; not that there is anything wrong with that, BUT think about the new industry that opens up for penis enlargenment spammers.
Living the joke behind, I think is worth to think about the implications if/when something like this gets implemented.