Body weight is controlled mostly by the hypothalamus, a structure at the center of the brain that fine-tunes metabolism to a level that no conscious calorie-counter could match.
The two are really part of the same problem, as installation costs depend to some extent on how good the supporting structure has to be to support the weight of the cells.
These appendages may be well intentioned, but their sheer weight is effectively killing the bridge with love, weakening its structure to such an extent that Paris City Hall is urging tourists to stop the practice.
This relates to the weight gain disadvantage, as the engineers must attempt to compensate for the loss of structure (the roof) by reinforcing the lower parts of the body.